Electrician Testing- A guide for all Electricians

Journeyman electrician license?

2011-11-07T08:05:00.001-08:00

Q. Journeyman electrician license? Is the Texas statewide journeyman electrician exam an open-book test?

A. Yes the Texas statewide journeyman electrician exam is an open book test. You are allowed to take your 2008 NEC Code book. You are allowed to have permanent tabs and highlighted areas but no writing or marks of any sort or loose leaf papers tucked in. For more info or any other questions you may have visit our website. electriciantesting.com
Good luck with your exam!
Mitch Tolbert
Electrician Testing
www.ElectricianTesting.com

Daily Practice Questions:

2011-10-31T14:58:00.001-07:00

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electrical License exam.

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Houston- Electrical Exam Prep

2011-10-31T11:17:00.001-07:00

Pass the TDLR electrician exam the first time. Our powerful weekend seminar will teach you a system that will help you understand the way the PSI expects to see an answer. It’s like having your personal exam cheat sheet. We sell highlighted and tabbed 2011 NEC Codebooks for your convenience and other reference material to help you study for the exam that no one else has! Our seminars are on the weekends with an intimate setting to focus on you as an individual.

Our instruction for the exam is more of a 'system' than anything else. You WILL pass your exam. We will walk you through, step by step and help you understand not only the types of questions, but even the way that the PSI expects to see an answer.
If you want to feel confident on test questions, calculations, cheat sheets, or formulas: this is the place to go. So easy it's almost cheating. See you there!

Check out our quickie sneak preview on YouTube|| http://www.youtube.com/watch?v=Lk_60xVFnZI
Visit our website for class dates, location information and our reference materials for sale. www.ElectricianTesting.Com
Journeyman Electrician Prep Seminar $249
Master Electrician Prep Seminar $299
Sign up today, classes fill fast!

www.ElectricianTesting.com

Contact@ElectricianTesting.com

(888) 473-1826

Ask us about our Tabbed and Highlighted 2008 & 2011 National Electrical Code book, Study at Home Kits, Index Cheats, MI Stickers, Pass Tabs, Crash Course Books, and 4 hours One on One Tutoring session with our Master Electrician and Instructor Mitchell Tolbert.

Check out our Featured Products on YouTube|| http://www.youtube.com/watch?v=uPhzs_H35Yw&feature=related

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What do you call an electrician with a hammer?

2011-10-31T11:12:00.001-07:00

Q: What do you call an electrician with a hammer?
A: Thief

Had to share this one. This is a type of joke that is funny because ‘it’s true’.

Found the joke on http://forums.jlconline.com/forums/showthread.php?t=37859

Have a great day!

Texas Electricians: A note from TDLR

2011-09-07T15:34:00.000-07:00

Note from TDLR:

"The National Electric Code (NEC) 2011 was recently adopted by TDLR. Many of you will be purchasing the new code book and we would like to remind you that loose leaf NEC code books such as spiral-bound or ring-bound books will NOT be allowed in the PSI test centers. Furthermore, candidates are not permitted to bring in any additional papers (loose or attached) with their approved reference. For more detailed information about taking examinations at PSI please download the Electrician Candidate Information Bulletin (CIB) on the TDLR web site."http://www.blogger.com/img/blank.gif

You can also visit us at http://electriciantesting.com/Texas-License-Types.php for PSI and TDLR links.

Important Texas PSI articles of the 2008 NEC book Chapter 2 to know.

2011-05-11T13:48:00.001-07:00

This is a sneak preview of one of our Texas PSI Exam Prep Seminar.

Important Texas PSI articles of the 2008 NEC book to know. Instruction led by Mitchell Tolbert at Electrician Testing. 1(888) 473-1826, www.ElectricianTesting.com.
Get to know chapter 2:
Here are the most important Articles:
*210...Branch Circuit Rules & Requirements.
*215...Feeders.
*220...Calculations.
*225...Outside Circuits and Feeders.
*230...Services.
*240...OCPD (Breakers/Fuses).
*250...Grounding.
This is a sneak peek of our Texas PSI Journeyman and Master Exam Prep Seminars. If you'd like to know more about our seminars contact us today. contact@electriciantesting.com
1(888) 473-1826
www.ElectricianTesting.com

We love great reviews!

2011-05-03T10:11:00.001-07:00

Who doesn’t love a great review? Well we love them and we want to boast about the latest one from Luis Olivares. Copied and pasted directly from his e-mail he wrote:

Hello Mitchell,
My name is Luis Olivares, you had spoken with my wife a few times via email regarding my Journeyman's examination. I wanted to take this opportunity to thank you for the study materials you sent for me. It was extremely helpful, and I believe it helped me pass my exam. I only wish I had known about your company sooner, I would have taken your classes I wanted a class like what you offer but had a difficult time finding one. It wasn't until I was looking to purchase a code book that my wife found your company. Please know that I will pass your information on to my co-workers who are trying to get their license, as well as the company I work for. I will also plan on using your services when I prepare to take my Masters exam.
Again, thank you for your help,
Luis Olivares

Thanks Luis for making our day

2011 NEC TOP CODE CHANGES

2011-04-29T08:11:00.000-07:00

GFCI devices must be installed in a readily accessible location (This impacts ceiling garage door opener devices).

The tables in 310.15 & 16 have been rearranged. Now you have your Ambient Temperature Adjustments separated into their very own table.

Transformers now require disconnects on the primary side. Now transformers fall under very similar rules that we see for other equipment.

Tamper-resistant receptacles are now required in guest rooms and in child care facilities. This increases the TR rules in most areas now.

Neutral conductors will be required at switch points, though there are a couple of exceptions, including where conduit is the wiring method.

No Grandfathering: where replacing a receptacle that would have to be AFCI, tamper-resistant, or weather-resistant, according to the 2011 code, those types of receptacles must be used in the replacement.

Ampacity and Conduit Fill Calculation Considerations (Dangers of Annex “C”)

2011-04-29T06:49:00.001-07:00

Wire Ampacity and Conduit Fill Calculation

This week I want to take a minute to review our wire ampacity and conduit fill (wire fill) calculation.

There seems to be a lot of common confusion out there when it comes to wire fill. Annex "C" in the back of the 2008 NEC © is a good tool, but it can be very dangerous to use it without considering the impact of de-rating factors found in Chapter 3.

Annex C is only concerned with the protection of the wire during installation. It does NOT take the ampacity of the wire into consideration!

When de-rating wire, we begin with table 310.16 (page 147, 2008 NEC ©) and de-rate for our ambient temperature AS WELL AS the number of current carrying conductors. The de-rating table T310.15(b)(2)(a) on page 145 shows us:

"Adjustment Factors for more than Three Current carrying conductors in a Raceway or Cable"

Number of Current Carrying Conductors

% of 310.16 Values

4-6 Conductors	80%
7-9 Conductors	70%
10-20 Conductors	50%
21-30 Conductors	45%
31-40 Conductors	40%
41+ Conductors	35%

You can quickly see that in our earlier example, if we put 16, #12 THHN conductors in that 3/4" conduit, we would have to drop the circuit breaker to a 15 ampere size!

Now seriously, how many electricians in the field really do that? You understand now how dangerous the casual use of Annex "C" can be.

For all practical purposes, only 9 current carrying conductors could be placed in that conduit without having to drop the OCPD (circuit breaker) size: [T310.16 value for #12 THHW=25 Amps. 25 Amps X 70% (the de-rating for 7-9 conductors) would equal 17.5 Amps, and due to 240.3(B) we are allowed to round up to a 20A breaker.] The Cut Off point is the 10-20 conductor line that HALVES our breaker/fuse sizing.

Neutrals CAN count as Current Carrying Conductors:

The grounded conductor (neutral) can also cause confusion sometimes. It counts as a "current carrying conductor" in some cases, but not in others. If it is shared between two different phases in a multi-wire circuit, it usually does not count as a current carrier , as it only carries the unbalanced load in the circuit. [For example, a "full boat with circuits #3, #5, #7 in a 30 panel, would not usually have their neutral counted.]

Where non-linear loads are supplied however the neutrals DO count. If you have electronic fluorescent ballasts or heavy computer loads (etc...) on a shared branch circuit neutral, it will have harmonic distortions that will disrupt the cancellation of loads between phases and can actually cause larger loads on a neutral that are found on any single ungrounded phase conductor in the circuit.

Two other common issues with Annex C are considerations for different sized EGC/GEC conductors, and differences between Annex C values and manual fill calculations using Chapter 9, tables 4 and 5.

The value of Annex C is a "stuff it full" value. Therefore you would have to keep in mind your additional ground wire, which is usually a smaller size than that of the phase conductors. The only way to use Annex C in this case is to always consider your EGC or GEC as a full size conductor count. A manual calculation is more accurate than Annex C and it has been this author's observation that Annex C values sometimes vary quite a bit from a manually calculated fill based on Chapter 9 tables.

All of that considered, going back to our 3/4" raceway, we could put 3 "full boats" in this raceway (3 neutrals not counted, 9 phase conductors, and 1 equipment ground) for a total of 13 conductors. This results in 3 less than our "fill amount" according to our Annex C tables. Thus, our advice is to always carefully consider your ampacity de-rating factors as required by 310.15.

(Author's Note: As evidenced by the above, an electrician would have to refer to several different tables in order to correctly and safely calculate the correct fill and ampacity values for watch and every pipe run. we are excited to provide and industry first for all our members. Electrician Testing has painstakingly prepared a custom table; available only through us, that considers ALL required factors. Everything is brought together in one quick and easy to follow chart. Contact us today to get yours, and look for our upcoming publication that will include this chart along with many, many more custom time saving tables!)

Mitchell Tolbert

Master Electrician

Mistakes Made in the 2011 NEC Code Book

2011-04-28T08:10:00.000-07:00

Here is a list of the Errata Sheet (errors) made in the first printing. If you purchased your 2011 NEC Code book within the first 4 months of release, you probably have a first edition.

This is a list of errata to the first printing of the 2011 NEC®. A first printing is indicated by the numeral 1

as the last digit in the line of number appearing at the bottom of the first page.

1. Page 70-36 110.14(C)(1): Revise 310.15(B)(6) to 310.15(B)(7)

2. Page 70-78

3. Page 70-86

Figure 230.1: Revise ‘‘Source’’ to ‘‘Serving Utility’’ and 230.49 to 230.32

230.90 Exception No. 5: Revise 310.15(B)(6) to 310.15(B)(7)

4. Page 70-102 Table 250.3: Revise 300.50(B) to 300.50(C)

5. Page 70-116 250.68(C)(2)(b): Revise to read : ‘‘By bonding the structural metal frame to one or

more of the grounding electrodes, as specified in 250.52(A)(5) or (A)(7) that comply

with 250.53(A)(2).’’

6. Page 70-129 250.180: Revise 250.190 to 250.191

7. Page 70-139 300.5(C) Exception No. 2: Revise 330.10(11) to 330.10(A)(11)

8. Page 70-148 310.10(E) Exception No. 2 (d): Revise Table 310.13(D) to Table 310.104(D)

9. Page 70-148 310.10(F): Remove deletion bullet and add second paragraph to read : ‘‘Cables rated

above 2000 volts shall be shielded.’’

10. Page 70-154 Table 310.15(B)(16): Add double asterisk to 18 AWG and 16 AWG copper

11. Page 70-178 314.16(C)(1): Revise 314.16(C)(2) to 314.16(C)(3)

12. Page 70-240 392.18(E): Revise 392.10(D) to 392.18(D)

Three Bulbs in One: GE’s Hybrid Halogen-CFL with an Incandescent Shape

2011-04-27T08:07:00.001-07:00

Instantly bright halogen capsule sits inside an energy-saving and long-lasting compact fluorescent swirl that’s contained in an incandescent-shaped glass bulb.

“It looks like an incandescent in size and shape but it’s really three bulbs in one,” observes Kristin Gibbs, general manager of consumer marketing, GE Lighting.

“The instant brightness factor makes our new hybrid halogen-CFL more versatile than other CFLs.

It’s an optimal choice for use in hallways, stairways, kitchens, bathrooms and anywhere immediate brightness is essential. Simply flip that light switch and it’s at your service—immediately.”

These new GE CFLs offer eight times the life of incandescent bulbs (8,000 hours vs. 1,000 hours). The new products — 15- and 20-watt GE Energy Smart® Soft White (2700 Kelvin) and Reveal® (2500 Kelvin) CFLs with exceptionally low levels of mercury that can replace standard 60- and 75-watt incandescent bulbs or other CFLs that don’t offer a satisfactory quality of light or instant brightness.

http://www.genewscenter.com/Press-Releases/Three-Bulbs-in-One-GE-s-Hybrid-Halogen-CFL-with-Incandescent-Shape-Arrives-in-April-2f9c.aspx

Handy Calculators

2011-04-13T13:01:00.001-07:00

I was doing some research and found some great calculators online that you can use for the field.

Concrete Materials Calculators
http://www.concrete.com/calculators/concrete-materials-calculators

and

Cubic Inches to Cubic Yards converter

ENJOY!

Journeyman and Master Electrician PSI Exam Prep Seminar - Classified Ad

2011-03-16T11:15:00.000-07:00

Journeyman and Master Electrician PSI Exam Prep Seminar - Classified Ad

Electrical Questions I’ve Been Asked

2011-03-16T10:15:00.001-07:00

How do I become a Master/Journeyman Electrician?

Q. I'm looking at getting an apprenticeship with this local company. After I'm done with my apprenticeship, what do I have to do to become a Master or Journeyman Electrician? How long would it take? Do I need to go to college? If so, what do I need to major in?

A. Hey there, depending on your state you may have to enroll in approved courses or take certain exams. But for you to get a general idea, I am posting links to previously asked questions that will hopefully have the answer you are looking for.
Best of luck and please contact me if you have specific questions!
-Mitch Tolbert

Light switches operate plugs. How can I make outlets hot and use the switch to operate a ceiling light?

Q. My house was built in the 40's and there are no ceiling lights in any room. All the wall plugs are run by the light switches. I would like to rewire the switches so that the outlets are always 'hot' and the switch can then be used to operate a ceiling light, once it's installed. I would like to do this without an electrician.

A. The good news is that half of your problem is a very easy fix. The bad news is that you are in for some considerable work to accomplish the other half.
Making your outlets constantly hot is the easy part. You simply need to open your light switch outlet boxes. You will find two wires attached to each switch (assuming none of them are 3-way switches). If you have a few other wires stuck in the back of the box that are joined together (taped or wire nutted etc...) you are in business. Those other wires are the so called 'neutrals' and you will need them in order for your new lighting to work. Once you've completed this part of the discovery, you can then plan out the installation. If there are no neutrals inside the lighting boxes, then you will have to provide one at the lighting outlet. You will also need to get wires down to your light switch, from the lighting outlet. The number and task of these wires will depend on whether you find neutrals in your existing installation or if you have to run new circuits to your new lighting outlets.
Try to do some discovery, and then email us directly. I will draw you a schematic of the wiring that you'll need to do, as it's really too complicated to try and type out. I'll scan and email it to you if you'd like. Good luck with this and let us know if we can be of further assistance!
-Mitch Tolbert

How can I tell my girlfriend's parents about electrical code violations without offending them?

Q. I'm 16, and I'm starting to see a girl who's in a few of my classes at school. I went to her house for dinner with her family yesterday. It was the first time I've been inside her house. I noticed a bunch of electrical code violations, especially in the basement. There are no GFI's in the kitchen nor the bathrooms. There were a few extension cords being used as permanent wiring, when an outlet should be installed instead. I saw a lot of jury-rigged wiring in the basement with a lot of unnecessary junction boxes. The circuit breaker panel is in a room cluttered with a lot of junk and hard to get to.
I didn't want to say anything because I didn't want to offend anyone. But, as an electrician, those things really bother me when I see them in people's houses. Electrical is the very first thing I notice when I visit someone at their home. Is there a way I could bring this up without offending anyone or risking any chances of starting a relationship with the girl?

A. Kuddos to you, young man. It is great to see someone young, sharp, and passionate about our trade. It is also admirable that you feel compelled to address and attempt to remedy severe code violations.
Actually though, it sounds to me like you could turn this into a positive advantage for yourself. Talk to the dad and explain your love of electrical work. Volunteer to "put on your tools" for a weekend's worth of DIY upgrades. An offer to spend a Saturday, helping the father around the house, should be the LAST thing that 'offends' them!
Regardless of the outcome, if you're truly so committed and concerned with these glaring safety issues, you owe it to yourself AND them to say or do something. It should not be a consideration for you to be concerned with how they'll feel about you after it's finished. At the very least you'll have attempted to keep their most valuable things - their lives and their home - SAFE!
-Mitch Tolbert

2 Day Seminar Coming to Austin

2011-01-08T21:14:00.001-08:00

Join other electricians to learn how you can increase your exam score, pass the exam with time to spare and familiarize yourself with the latest version of the NEC book.

Electrician Testing will walk you though, step by step and help you understand not only the types of questions, but even the way that PSI expects to see an answers.

The Seminar will show you:
General Electrical Theory and Math Review
Wiring Methods, Materials, Installations
Branch Circuits
Motors and Generators
AC and Refrigeration Loads
Transformers
Services and Feeders
Grounding and Bonding
Special Occupancies
Test taking tips and information
Visit our website for more
http://electriciantesting.com/Seminars.php

Location: Hampton Inn, Austin TX
When: January 29 and January 30, 2011
Time: 8 am to 5 pm

Register online at:

http://electriciantesting.com/Seminars.php
or call 1-888-473-1826 ext 1

Significant 2011 NEC Code Changes Part II

2010-12-30T12:49:00.001-08:00

Significant 2011 NEC Code Changes Part II

Chapter 2, 2011 NEC

"Article 200.1, Scope,"

Informational Note Changed:

"Grounding Conductor" has been changed to "Equipment Grounding Conductor (the EGC) and "Grounding Electrode conductor (the GEC)" was added. This more accurately reflects Article 100's defined terms.

"Article 200.2 "General,"

Wording/Section Changed:

Previously there were 10 specific code sections listed for systems that prohibited or exempted the installation of grounded (neutral) conductors. Now the wording is changed to "systems SPECIFICALLY exempted or prohibited by OTHER SECTIONS of this Code."

"Article 200.2(B), Continuity,"

Informational Note Added:

Section B was a 2008 NEC edition code change that prohibited using a metal enclosure as a connection pathway for the continuity of the grounded conductor (neutral). For the 2011 edition, an informational note was added, linking this section to the device rule in Article 300.13(B), "Device Removal." That article prohibits the use of a device or lampholder as a continuity pathway for the grounded conductor in a multiwire branch circuit (the "pigtail" rule).

"Article 200.4, Neutral Conductors,"

New Section Added:

Wording has been added that restricts the sharing of a neutral conductor by more than one set of feeders or one multiwire branch circuit. It does allow an exception if another are of the Code specifically allows for neutral sharing as is the case in Article 215.4(A) "Feeders With Common Neutral Conductor."

"Article 200.6(A) Means of Identifying Grounded Conductors, Sized 6 AWG or Smaller,"

Section is Changed:

The new outline greatly simplifies and makes this section easier to read. Essentially the basic rules are no longer in their former paragraph format. They are now bulleted into the existing numbered list, increasing the previous edition's list from 4 items to 8 items.

"Article 200.6(D) Grounded Conductors of Different Systems,"

New Paragraph Added:

A new directive has been added that now requires a placard or some sort of permanent type documentation to be installed at the origination point (panel) where different grounded conductors from various services are installed. This documentation shall list the color/identification scheme employed in the installation. An example of this was shown as an Exhibit (200.3) in the 2008 NEC Handbook, and is now a requirement. This helps the technician readily and easily trace different system's neutrals safely and quickly. Note that there was already and existing requirement for the Phase Coloring Scheme in 210.5(C).

"Article 200.7(C), (the so-called "Neutral as a Switch Leg" rule)

Article is Changed:

Wording has been added that clarifies and specifically allows the use of colored tape when re-identifying a white or grey colored insulation for the use as an ungrounded (hot) conductor.

Paragraph #(2) has been deleted and it's intent has become the formerly numbered section (3). It formerly contained the rule that allows for the use of the white colored conductor in a cable assembly (such as in a "romex" cable) as a switch leg in single, 3-way, or 4-way switching. This wording is now deleted. In it's place is the rule allowing the use of the white or grey conductor in a flexible cord (such as an SO or Appliance cord) as an ungrounded (hot) conductor.

"Article 210.4(B) Multiwire Branch Circuits, Disconnecting Means,"

Informational Note Added:

The new informational note adds a reference to Article 240.15(B) "Circuit Breaker as an Overcurrent Device" to tie the two articles together. 210.4(B) requires a simultaneous disconnecting means for all ungrounded conductors. 240.15(B)(1) allows the use of an OCPD for multiwire branch circuits; with identified handle-ties in order to operate ALL poles of the circuit simultaneously.

"Article 210.4(D) Grouping"

Article is Changed:

New wording extends the grouping rule that was new for the 2008 Code. Previously a wire tie (or similar means) was required in panels to show the 'grouping' of multiwire branch conductors. The new rule is to extend this requirement out to each junction box or anywhere that splices or connections are made in the entire circuit. Note that the rule excluding cable assemblies (such as MC Cable or NMC, "Romex") and individual dedicated conduits has not been changed.

Significant 2011 NEC Code Changes Part II

2010-12-30T12:17:00.001-08:00

Significant 2011 NEC Code Changes Part II

Chapter 2, 2011 NEC

"Article 200.1, Scope,"

Informational Note Changed:

"Grounding Conductor" has been changed to "Equipment Grounding Conductor (the EGC) and "Grounding Electrode conductor (the GEC)" was added. This more accurately reflects Article 100's defined terms.

"Article 200.2 "General,"

Wording/Section Changed:

"Article 200.2(B), Continuity,"

Informational Note Added:

"Article 200.4, Neutral Conductors,"

New Section Added:

"Article 200.6(A) Means of Identifying Grounded Conductors, Sized 6 AWG or Smaller,"

Section is Changed:

"Article 200.6(D) Grounded Conductors of Different Systems,"

New Paragraph Added:

"Article 200.7(C), (the so-called "Neutral as a Switch Leg" rule)

Article is Changed:

Wording has been added that clarifies and specifically allows the use of colored tape when re-identifying a white or grey colored insulation for the use as an ungrounded (hot) conductor.

"Article 210.4(B) Multiwire Branch Circuits, Disconnecting Means,"

Informational Note Added:

"Article 210.4(D) Grouping"

Article is Changed:

Significant Changes in the 2011 NEC Part I Continued

2010-12-30T11:44:00.001-08:00

Part I Continued:

Chapter 1, Article 100, "Definitions:"

Definition Changed:

"Non-automatic"

Essentially the same type of wording change as is seen with the definition of "automatic," where the wording has been simplified to "requiring human intervention..."

Informational Note Changed:

"Non-linear Load"

Electronic and inductive ballasts and LED drivers have been added to the list of common types of non-linear loads. This is an important distinction as non-linear loads are one of the 4 rules for allowing the counting of "current carrying conductors" for the purposes of correctly sizing conductors for ampacity.

Re-labeled and Moved Definition:

"Overcurrent Protective Device, Branch-Circuit"

Changed from "Branch-Circuit Overcurrent Device." No wording within the actual definition was changed. It now corresponds with the common acronym "OCPD."

Re-labeled and Moved Definition:

"Overcurrent Protective Device, Supplementary"

Changed from "Supplementary Overcurrent Protective Device," and moved. No wording was changed within the definition itself.

Definition Added:

"Service Conductors, Overhead"

Definition added to describe the actual conductors within the "Service-Entrance Conductors, Overhead System" definition. Specifies the portion of conductors from the service point and to the "first point of connection to the service entrance conductors at the building etc... sic..."

Definition Added:

"Service Conductors, Underground"

Definition added to describe the actual conductors within the "Service-Entrance Conductors, Underground System" definition, (ROP 4-206).

Definition Changed:

"Service Drop"

Wording has been simplified from "from the last pole or other aerial support...connecting...at the building," to a more broad and encompassing description: "The overhead conductors between the utility distribution system and the service point."

Definition Changed:

"Service Lateral"

Wording simplified to "The underground conductors between the utility distribution system and the service point." A lot of the previous definition's wording was moved into the new definitions of "Service Conductors, Underground" .

Informational Note Added:

"Service Point"

Adds a simplified description of "where the serving utility ends and the premises wiring begins."

Definition Added:

"Uninterruptible Power Supply"

Defines UPS's as a backup emergency power supply and also systems that may offer voltage regulation as well. A UPS may be a single unit type piece of equipment or be the sum of various pieces of a whole systems.

END OF CHAPTER 100, DEFINITIONS

BEGINNING OF CHAPTER 1

"Article 110.10"

In this article, the title was amended to include "short-circuit current ratings." The word "equipment" was added in front of "grounding conductor" to more accurately reflect the change to the term EGC and its associated definition. A reference to Article 250.118 was added.

"Article 110.14(A)"

Added a note instructing the manufacturers to identify terminals for the use of "fine stranded" conductors and cable terminations. A new table in Chapter 9; Table 10, has been added to correspond with Class B and Class C stranded conductors.

"Article 110.16"

Title is changed to "Arc-Flash Hazard Warning." Also the word "units" was substituted for "occupancies," to more closely correlate with the term "dwelling units" and its associated definition. It should be noted that this article only addresses a requirement for Hazard "labeling" but does not specify requirements for the attenuation or mitigation OF flash protection. Those types of requirements are provide by the NFPA 70E the "Standard for Electrical Safety in the Workplace."

"Article 90.5(C)"

Article Has Changed:

All FPN's (formerly known as Fine Print Notes) have now been relabeled and changed to "Informational Notes." All FPN references in the entire Code have now been deleted and replaced with this new labeling.}

Final installment of Part 1

"Article 110.24 (A) and (B) and Exception, "

NEW ARTICLE ADDED

This article has been added to address an new requirement for field marking of Service Equipment. This article now requires a durable label with that contains the available fault current and the installation date, to be provided in addition to the manufacturer's labeling as is required in 110.16 "Arc-Flash Hazard Warning," 110.21 "Marking," and other code sections. This label shall also be modified if and when changes are made to the service equipment. The exception allows for the exclusion of equipment in industrial applications and where conditions ensure that only qualified persons service the equipment. This entire article and section helps to maintain compliance and knowledge of the proper AIC interrupting ratings of the equipment as is required in 110.9 "Interrupting Rating."

"Article 110.26(A)(3)"

Article is Changed:

The 2008 NEC simply referenced "Article 110.26(E)'s" requirements for working height. The new wording improves the clarity and intent of both articles. Moving the 2008's reference also places ALL electrical equipment under the so called "6 1/2 foot" rule. The "headroom" reference was deleted to eliminate the confusion of what it consisted of or to what equipment it should have been applied. This eliminated section (E) and 2008's section (F) was changed to the 2011's section (E).

Exception No. 1:

Was amended to eliminate the "headroom" wording and replaced with: "the height of the working space."

Exception No. 2: ADDED

This exception covers utility meters and trans-socket (meter can) enclosures. It allows for the glass meter itself to extend past the 6" limitation specified in 110.26(A)(3) . However, the socket enclosure itself must follow all working space rules in 110.26(D) .

"Article 110.26(D) "Illumination"

Article is Changed:

Former wording in this article section required that the illumination in electrical equipment rooms, NOT be controlled by automatic means ONLY. New wording eliminated "electrical equipment rooms" and placed the automatic lighting control restriction in the upper part of the paragraph. This now serves to increase the scope of the rule to include many more equipment areas and spaces.

"Article 110.28 "Enclosure Types"

Article is Changed and Moved

Previously numbers as Article 110.20 along with its corresponding table, labeled Table 110.20 "Enclosure Selection," they are now 110.28 and Table 110.28 respectively.

The new wording adds eleven additional types of equipment to the previous list of items included under the rules of this article. In essence this now requires most all types of enclosures to have their type (enclosure number, such as a "3R" etc....) marked on them.

"Article 110.31(A)" "Electrical Vaults"

Article is Changed:

This article has been drastically expanded and now includes 5 separate sub-sections that did not previously exist. 2008's 110.31(A) was labeled "Fire Resistance of Electrical Vaults." The new sections include further rules on such as "Doors," "Locks," and other items. Two new Informational Notes were added to clarify and reference fire rating standards and levels.

"Article 100.74" "Conductor Installation"

Article is Changed:

Applicable to manhole installations, this article has, for the most part, the same wording. It has been broken out and numbered into separate paragraphs to facilitate easier understanding of the section.

END OF CHAPTER 1

Significant Changes in the 2011 NEC: Part I

2010-12-30T11:40:00.001-08:00

Thank you for taking the time to review our blog for changes that are significant to all of us in the electrical industry. While these changes may take some time to gradually work their way into rules to abide by and follow, it's a mark of your superior desire to better yourself in your awareness of these code changes. I hope that they are clear and useful for you and urge you to take a few moments each week to review these as they are posted. You will get postings of every single change in the 2011 NEC over the course of the next few months, right here, and free of charge! Please pass the word to others so that they may also benefit from this. Look for our new publication that will contain all of these changes, along with diagrams and clarifying pictures and charts to be published in January. Again, I thank each of you for spending some of your valuable time reading my work.

Significant Changes in the 2011 NEC

PART I.

Article 90 "Introduction

Article 90.2(C), wording has changed:

New wording in this section clarifies more specifically when "special permission" may be granted for the exclusion of service conductors and/or equipment from the Code's jurisdiction. Previous editions simply specified that such installations "terminate inside a building wall." Now it specifies "within service equipment... inside nearest point of entrance of the service conductors." This broadens the language and allows for better independent judgment calls by the Inspector or other Authority Having Jurisdiction (AHJ).

Article 90.5(D), New Section Added:

This new paragraph now specifies the Annexes as solely "informative annexes," and as such are thus non-mandatory. We have previously excluded all Annexes as solely informative, but this wording now makes it clear and official. The information provided in them has been provided simply as a further assistance, but are not meant to be used as official Code material.

Article 100 "Definitions"

Definition Added:

"Arc-Fault Circuit Interrupter (AFCI)"

As AFCI's are becoming more prevalent and are mentioned in many sections of the Code, wording that clarifies and describes the devices has been added.

Definition Added:

"Automatic"

The previous wording was lengthy and attempted to cover all aspects of mechanical and automatic types of forces that devices or equipment might use. The new wording greatly simplifies the definition of "automatic," as being simply the "Performing a function without the necessity of human intervention." This is a more simple manner to cover all aspects of automatic devices and the actual function of operation without a person to oversee or initiate them.

Definition Changed:

"Bathroom"

This definition has been expanded to now include more types of plumbing fixtures such as , urinal, showers, bidets, and foot baths. This closes loopholes in what might have previously fallen outside the scope, and thus the requirements and restrictions of electrical installations in bathrooms.

Definition Added:

"Bonding Jumper, Supply Side (SSBJ)"

A fourth bonding jumper definition is added to describe and quantify the bonding on the so called "Line Side" or 'supply' side of a service. The acronym SSBJ has now been officially adopted to describe the grounding Bonding Jumper on the service side of separately derived systems and services.

Definition Changed:

"Building"

A more specific definition that describes in detail what structures now qualify as buildings. This expansion of the definition of what comprises a building may have a significant impact on many electrical installations. A prime example is Article 230.3 which limits the installation of service conductors where they might pass through a building different to that which they supply. Often times feeders will pass through joining apartment/condo units or tenant spaces, however, with the clarification and tightening of the term "building" some of these installations may have to be re-routed in order to fall into compliance with Code rules and statutes.

Definition Added:

"Ground Fault"

This definition describes ground faults specifically as an "unintentional...connection between an ungrounded conductor...and the normally non-current-carrying...equipment, or earth." This helps to clearly differentiate ground faults from short circuits and phase to phase shorts.

Definition Changed

"Grounding Electrode Conductor (GEC)"

This change added the commonly utilized acronym "GEC." It also expanded the language to include other systems such as communications, network, and antenna equipment that may be connected via the GEC.

ICC Exam Part II

2010-09-17T07:35:00.001-07:00

SCORING SYSTEM & TEST SCORE IMPACTS

The ICC does NOT score the same as any other exam. There is no one "unit" value for each question. In other words, in a 100 question test, each question has its own different value. Some are worth MORE and some are worth LESS than one point. For example, you may see an easy code question that is worth only 1/2 a point, yet a motor calculation question may carry a value of 1 & 3/4 points. No one outside of the ICC organization knows exactly what each question type is worth. We have seen evidence, however, that proves the "weighted score" method.

Because of this type of scoring system, it becomes important to attempt to answer EVERY question. If you run out of time and leave 15 questions (as a random example) unanswered, you may actually be losing as much as possibly 20 points off your score.

Experience shows us that most electricians initially answer code questions as a hunch or from experience. Many then continue to verify their answers by referencing their code book. Often times they'll then try to "talk themselves out" of their initial answer. Unfortunately for them, 90% of the time, their initial answers were the CORRECT ones!

STRATEGY FOR YOUR EXAM

These two reasons, the scoring system and "gut reaction" answers; led us to create the following strategy that has been one of our greatest triumphs in our teaching method which sees a 95% first time passing rate success!

Your test strategy:
Upon first sitting and beginning your exam; leave your code book CLOSED!!! Do NOT touch it. Begin with question #1 and go through EVERY SINGLE question without STOPPING! Use the following "answering methodology:"

There are three ways to answer a question and 5 steps to complete on an ICC Electrical Test:

1) Answers that you KNOW for a fact are correct simply get answered and you then move on to the next question.
2) Answer the questions that you THINK you know (the so called "gut creations," but mark the (flagged) for later review.
3) Questions that stump you or that you have NO IDEA how to answer get left BLANK and flagged for later review.
4) AFTER completing your initial answering/review session, go back and begin answering ONLY THE QUESTIONS that you skipped and that have NO answer at all. You will find that your biggest block of time will then be spent on these questions.
5) After those have been answered, go back and begin reviewing & code verifying your "gut reaction" question block.

This method will allow for three things. First it will assure that you've read and answered EVERY question. Next, it helps you devote your time to only those questions that need it the most. Finally, you'll be surprised at how many questions that you'll inadvertently "stumble" across the answers to, during your steps 4 and 5. At the very least, you'll be armed with the complete knowledge of ALL the questions contained on your electrical exam version.

(Part III coming up)

"Secrets of the ICC Electrical Exams"

2010-09-16T10:33:00.001-07:00

"What you don't know about HOW to take these exams CAN cost you 15 to 20 points off of your potential score."

There are many states that offer the ICC Master Electrician's Exam as well as the Journeyman Electrician's Exams. Our firm has tracked and sat for many of these exams throughout the years. We have a better understanding of the author's questions and intentions, than the author probably has himself.

Many electricians sit and cram for the weeks leading up to their exam and our experience has been that they average around only a 25% first time passing rate, when studying unassisted. This is NOT a call for alarm, rather it's simply to drive home a point: Getting back ground information on HOW to pass the ICC Electrical exam can be almost as important as KNOWING what information will be on the exam! Just knowing a few key items and understanding WHAT the authors are looking for in an answer can add 10 to 20 points to a final score. That can make a major difference in passing or having to continue to re-exam. We've seen electricians take the same exam 5, 6, even 7 or 8 times, and never really understand WHY they keep failing. We know exactly why, and that is what this blog is about.

Half the battle of passing your exam is knowing the strategy and reasoning BEHIND the ICC's questions. We have seen many an experienced, knowledgeable master electrician fail their exam just because they don't know the mine fields to the ICC author's mindset. Even the way you should attack the questions during your first initial 15 to 45 minutes of your exam can have a critical and dramatic impact in your overall score.

To give you a list of every detailed strategy, would take an entire book's worth of blogs. So we will look at just a few major issues and how to address them in this edition.

First, know how and when to apply Code "Exceptions" in formulating your answers.

Next, because of the weighted "scoring system" employed by the ICC exam makers, understand the importance of your initial review/answering strategy.

Finally, watch out for questions within questions - be aware of "context" installation clues.

CODE EXCEPTIONS

NEC Articles are full of exceptions. There are exceptions to almost 50% of the most important sections in the code book. The use or disregarding of an exception can completely change an answer to an exam question. Motor overcurrent protection is a prime example. Article T430.52 is the table employed when sizing fuses or breakers to protect a motor installation. In fact, because there are TWO separate exceptions to this table, there will be THREE different answers to a circuit protection question. Alone, ignoring exceptions, T430.52 is a NOT TO EXCEED table of values. In other words, you would round DOWN in that instance. The use of exception #1 allows for the sizing UP to the next larger protective device size. Exception #2's use would allow for even larger calculable values but then they would require a DOWN sizing after all calculations have been performed. You now have 3 separate answers to the SAME exact motor installation. Now, do you choose to IGNORE the exception, employ exception #1, or implement the values in exception #2? You can see now why it is CRITICAL to understand how and when to apply exceptions.

Stay tuned for Part II coming this weekend! We'll get you up to speed for your exam and passed the first time!

Small Branch Circuit Rules: Part II (cont'd from last week)

2010-09-11T22:03:00.001-07:00

We've reviewed the initial two items in our small branch circuit rules review blog, last week. In it, we looked at "fastened in place" and continuous load considerations. Next we will examine the types of connections and "Appliance" issues, to see how these impact our installation of an "Insta-Hot (tankless water heater).

CORD & CAP VS. HARD WIRING

In a 15 or 20 Amp branch circuit, we would be allowed to use a cord cap and receptacle as our connection means. Staying mindful of our disconnect rules for appliances, we often use cord caps as both connecting and disconnecting means. Article 422.30 and 422.31(B) require us to provide a means to disconnect for ANY appliance that is over 300 VA or 1/8th HP (roughly anything over 2.5 Amps at 120V). In addition, Art. 422.33(A) allows us to utilize a "separable connector or an attachment plug..." as our disconnect method.
On a 30 Amp branch circuit, the rules are similar to the 15 to 20 Amp's, EXCEPT with one item. IF a cord and plug connection is used, our 80% restriction is back in place. Therefore, a "hard-wired" 30 Amp circuit may serve loads up to and including 30 Amps, but a cord connected 30 Amp circuit is only rated for a maximum of 24 Amps. The "catch-22" trade off here, is that you would then have to provide a separate means of disconnect, other than a cord cap, to size the load from 25 Amps up to 30 Amps. There are no "fastened in place" restrictions explicitly mentioned for 30 Amp circuits, but it is implied from the cord cap restriction of 80%.

Finally our focus turns to Article 422; "Appliances." Article 422 covers ALL occupancy types and appliances, even ones that are motor operated, and hermetically enclosed motors (such as compressor motors). It requires the rating of an "individual branch circuit" to be not less than the marked rating of the appliance, see 422.10(A).

The specific section that deals with our tankless water heater is 422.10(E). The "Single-Non-motor-Operated Appliance" article gives three ways to comply.
1), Not to exceed that which is marked on the appliance.
2), Maximum size is 20 Amps if the appliance is 13.3 Amps or smaller.
3), Maximum size is 150% of the amperage of the appliance, where it is larger than 13.3 Amps AND where the maximum size is not already marked.
(Note: next standard size breaker is allowed under item 3, i.e. size UP when calculating your breaker size).

One final word of caution, the location of the installation may require GFCI protection. If you utilize a receptacle and attachment plug connection method in bathrooms, garages, and some kitchen/utility areas, you must provide GFCI protection.
To sum up this installation, a tankless water heater, rated at 20 Amps (2.4 KW) shall be allowed on a 20 Amp branch circuit. It would be fastened in place (most likely), thus either an attachment plug or direct wire connection would be allowed. Direct wiring of the appliance would however, require a separate disconnect and would likely add more expense and bother than a simple cord cap connection does. A 30 Amp tankless heater could be placed on a 30 Amp circuit, if it is direct wired with a separate disconnect, or a 40 Amp circuit if an attachment cord is utilized.

Don’t forget to check our blog next week.

-Mitch Tolbert

"Small Branch Circuit Rules"

2010-09-09T11:45:00.001-07:00

"How do you correctly size a 20 Amp tankless water heater (Insta-Hot)? shouldn't you have to follow the "80%" rule and place it on a 30 Amp circuit with a #10 wire?"

Several code questions arose this week about an insta-hot water heater installation. They are becoming a much more common installations these days. In order to answer the question, we must look at what the requirements are for small branch circuit sizing. This device itself is also considered an "Appliance," so we must also include considerations for appliances. Our main issues here are, what are the percentages of permissible loads on the circuit, continuous load or non-continuous load classification, plug and cap connections, permanent wiring and disconnecting means, and ultimately, "Appliance" considerations.

PERMISSIBLE LOAD SIZING 15A - 20A

We use the 80% rule quite frequently in the field to size branch circuits. It has become a 'rule of thumb.' However, there is some confusion in its application. There is no "blanket" rule that requires EVERY 15A and 20A circuit to be restricted to 80%. Article 210.23 under 'permissible loads,' states that we may supply ANY load for that which it is rated. This article in one of our key controlling sections.
There are three critical main installation specifics used to navigate and correctly apply Article 210.23. (1), The first is whether or not the equipment is "fixed in place." Is the equipment readily mobile? Does it have coaster wheels or the like, or is it small enough to be easily repositioned? (2), Next we examine what loads are supplied by that branch circuit. Is it a dedicated circuit, feeding that piece of equipment alone? Are there other loads, such as lighting or general purpose outlets, on the same circuit? (3), Finally, is the equipment connection anticipated to be a cord and plug type or will it be "hard wired?"

Rule #1: A cord and cap connected piece of equipment that is not "fastened in place" is restricted to 80% of the maximum branch circuit rating.

That rule applies no matter what else the circuit feeds. Whether it is a dedicated branch circuit is not a consideration.

Rule #2: If the equipment IS fastened in place AND if the circuit ALSO supplies lighting and/or other cord & plug connected equipment that is not fastened in place, the load is restricted to 50% of the branch circuit rating. For example, a room air conditioner, placed on a 20A branch circuit, would NOT be allowed to exceed 50% - or 10 Amps. Waste disposal (in sink garbage disposal) and dishwasher (non-mobile) would be two other good examples.

continuous & NON continuous LOAD CLASSIFICATIONS

       As you can see, the rules are specific and narrow. If the equipment IS 'fastened in place,' and the circuit supplies nothing else, then there is NOT any de-rating or percentage restriction required. This does, however, raise the next major issue of "continuous Load and Non-continuous Load" classification.
      The statement above ignores continuous load considerations. Equipment that operates, or can be anticipated to operate, for 3 hours or more, shall be classified as a continuous load. Further, Article 422.13 specifically classifies storage type water heaters as continuous loads. Any tank type water heater that is 120 gallons or smaller, MUST be considered a continuous load. (NOTE: this excludes "tankless water heaters.")
      Article 210.20(A) clarifies that continuous loads must be calculated at 125% of their rating. This 125% is the sister reciprocal of our 80% branch circuit restriction. 80% deals with our branch circuit size (ie. a 20A breaker is DIVIDED by 80% = 16 Amps). 125% deals with the load size itself, which comes from the opposite direction than our breaker sizing step. A load, sized at 16 Amps MULTIPLIED (multiplication is the reciprocal operation of division) by 125% = 20 Amps! In other words, 80% is a divider, 125% is a multiplier. If you know the branch circuit size, divide by 80%. If you know the equipment size, multiply by 125%.
      Thus a 20 Amp tank type water heater would result in a 25 Amp breaker size, along with #10 AWG (CU) conductors. 20A X 1.25 = 25 Amps. Sized at a 25 A breaker per 210.3 as an "individual branch circuit," and 240.6(A), "Standard Ampere Ratings," and 240.4(D)(7) - the so called "Small Conductor Rule."

We will examine the rest of the rules in Part II. Look for it this Saturday!

-Mitch Tolbert

Visit www.ElectricianTesting.com for study prep materials. ICC and PSI exams.

Part III "Circuit Considerations for Calculating Wire Sizes."

2010-08-22T21:33:00.001-07:00

**** Earlier this week I received the following code question. I will post this, and the very first person who can respond with the correct answer, including ALL code references, will get a FREE laminated wallet card. This wallet card is a special tri-fold sheet with a unique way of cramming a lot of commonly utilized field calculations into one simple card.

"When or would it be allowable to use a plastic [or similar non-conductive material] old-work box with MC cable installations?"

***Remember, the answer MUST be complete and ALL code references should be cited. I will take the first complete and correct answer or the best answer of all responses, whichever is first. The winner will be announced the next day! Good Luck!

Part III "Circuit Considerations for Calculating Wire Sizes."

The past few weeks we have examined several of the 6 'rules' for circuit sizing. The final three, Sizing for economic considerations, Sizing for voltage drop considerations, and Sizing for "copper losses," are our final ones. We will look at these last three issues briefly. None of these are code considerations, but they are all three important for a complete and efficient system. Always remember that, even though the "Code" may be considered the "electrician's bible," it is STRICTLY concerned with safety ONLY! There are many other items outside its scope that are still very important to consider.

Rule "C" says that "It should be sized for economic considerations so as not to exceed those limitations." The simple meaning of that is, be wary of the expense when making calculations (or rather, when NOT making them....) Most often, technicians will make "seat of their pants" decisions and simply 'up size' an installation rather than trouble themselves with the calculations necessary to ascertain the correct minimum sizing. While this method is overlooked in small branch circuit sizing on a limited scale, it can have HUGE impacts over a span of time. If the same electrician did this here and there over the course of his career, he could ultimately cost his employer and/or clients tens of thousands of dollars in wasted material and the additional labor units it costs to install them. In addition, on larger runs, (for example,) calculations over a 200' fun of 250 KC MIL of copper feeders can add up higher costs extremely quickly. You would not want to guess at up sizing these feeders to a 300 KC MIL as the cost difference could be well over $2,000.00! The bottom line is that 15 minutes of the technicians careful planning and calculations may save hundreds of dollars.

Voltage drop considerations have been exhaustingly examined in earlier blogs. As such, I only wish to remind you that they are a very crucial consideration and I invite you to go back and review those postings.

The final consideration is for "copper losses." This has also been covered in earlier blogs. It is a caution to remind you, the installer, that where high amperage loads are encountered, a smaller wire size will have a higher resistance. This resistance will cause heating in the conductor. In the same way that a small heat strip will spin your utility meter's dial, it will cost money in heat losses over the entire time the conductor is in use! Of course, the cost of the next higher size conductor may outweigh the losses over five to ten years, so BOTH should be considered. There is a formula to utilize for this calculation, however, due to its complexity, we will cover it in a future edition.

Okay everyone, that's all for the 5 rules (plus the bonus rule!) of wire sizing for circuit conductors. Let me have some feedback and questions if you have them! Have a great week!~

Part II

2010-08-17T08:39:00.001-07:00

Last week we discussed the first few rules of calculations, when sizing wire for circuit considerations. In Part II we will cover rule "B," which states that wire sizing shall be of sufficient mechanical tensile strength in order to withstand the stresses incurred within a normal and expected installation. Within the scope of this, we'd be concerned over the complete raceway sizing, pathways, and fill rates.

All electrical wires MUST be physically protected against damage during the installation. To that end we carefully safeguard against using too many degree's worth of bends between pull points. This rule is exhibited in individual raceway articles, such as 358.26 "Bends - Number in One Run," which states that no more than 360 degrees shall be allowed. This keeps the amount of force, required to pull the conductors through the points, below that of an amount that could cause irreversible damage due to strain or stretching of the actual copper or aluminum of the wire. In this Author's opinion, there should also be a maximum footage rule between pull points for the branch circuits. As the length of the circuit increases, so to does the sheer weight of the wire itself. A #10 AWG Copper conductor, for example, weighs about a pound per every 31 feet. Thus a 200' run would add almost 7 pounds of drag to the pull, not even considering the additional amount of side wall friction that the 200' of wire adds. Hence, our suggested rule of thumb would be no more than 100' of raceway between pull points, in addition to the 360 degree rule.

An installer would also need to be wary and mindful of always reaming out all cuts of raceway, to minimize sharp edges that could cause damages to the insulation of the conductor. As well as provide bushings where Articles 300.4(G), 342.46, 344.46, and 352.46 requires. Thus ANY raceway containing #4 AWG or larger wire MUST have bushings, and where the raceway is of IMC type, Rigid type, or PVC type.

Our installation should also comply with the maximum fill percentages of 53% for a single conductor, 31% for 2 conductors, or 40% for 3 or more (applies to all runs over 24"). We find these table values and rules in Chapter 9, Tables 1, 4, and 5. Actual conduit fill applications and calculations are outside of the scope of this blog. However, do keep in mind that these are MAXIMUM values, and in order to mitigate the adverse effects of longer conduit run lengths, severe bends, or complicated and difficult pulls, and to facilitate the ease of conductor installations, the electrical technician should consider applying smaller percentage fill values, or increasing the size of the raceway itself.

Finally, FPN No. 2 in Table 1 of Chapter 9, warns against what is called a "Jam" ratio, higher than 3.2%. This is a seldom considered issue that usually occurs only with 3 conductor installations. Essentially what happens is that a raceway may not be completely "round" at a bend. When the conductors enter the bend, the middle one may slip between the two outer ones, and when they exit the bend, it may cause a jam. The Jam ratio is simply the Inner Diameter of the raceway (found in Table 4) divided by the Outer Diameter of the conductor (found in Table 5). {Hint: this value will ALWAYS be greater than 1, so ALWAYS divide the Biggest # by the Smallest #.}

All of these cautions, when used together, insure a mechanically safe installation of electrical wire. Don't forget that ALL conductors count - grounds etc... when calculating conduit fill! More next week, have a safe week everybody!

Don’t forget to check out our website at www.ElectricianTesting.com for your test preparation material. Check back often since we give away helpful stuff for use on the field and the test room!

Circuit Calculations (The 5 Major Considerations)

2010-08-11T14:25:00.001-07:00

This week I'd like to take a quick look at the "Big 5" considerations when calculating a branch circuit. Often times in our rush to complete a project, we will over look one or more of the following items. However, each single item is a very important part of a successful, economical, intelligent, and efficient installation.

There are actually five separate and distinct considerations (rules) when sizing wire for an electrical installation. These 5 rules are:

A) (Insulation Rating and Ampacity Sizing)
The insulation must be able to withstand the heat generated by the current flow without damage or risk of fire.

B) (Conduit Fill and Physical Strength)
It shall be of sufficient mechanical tensil strength in order to withstand the stresses incurred within a normal and expected (reasonable) installation.

C) (Cost per Sizing)
It should be sized per economic considerations so as not to exceed those limitations.

D) (Voltage Drops)
It should be sized large enough to accommodate losses due to voltage drop considerations.

E) (Energy/Heat Losses)
It should be sized so that the cost of the Current (squared) Resistance energy (I2R) losses would not be excessive.

There is a further consideration for "future expansion or load requirements." This is not a "Code" requirement by any definition. It is also something that the average "low bidder" does NOT want to have to bear the burden of cost, as it is an upfront investment for the owner of the property. However, a good design, upfront with potential and foreseeable future loads, having been taken into consideration, ultimately gives the end user a tremendous value in their property's ability to expand easily. It also can potentially eliminate situations whereby future installers would be tempted to "overstress" the current system due to the cost and expense of having to completely replace an existing electrical installation. Therefore, even though code calculations would allow for an 80% lighting load on a single 20A circuit (for example), it might be more prudent to limit the installation loads to only a 50% capacity. That would allow for a much more flexible system for easy additional lighting to be moved, added, or taken out. This additional expense upfront is negligible, however it would be a considerable expense for a later technician to rip it all out and install larger provisional circuits in the future. So one can easily see how some common sense and minimum expense upfront may make a enormous positive difference to the client's property.

Rule A) is where our Tables in 310.15 and 310.16 come into effect. This is a major reason why we instruct our students to rely on their table 310.16 on page 147 of the 2008 NEC from "Temperature Rating of CONDUCTOR" to "Temperature Rating of INSULATION." It makes the application of this table more sensible and easier to grasp it's correct usage. I have gone over Ampacity rating of conductors in previous blogs, so I won't re-visit it in this edition. It is one of the more commonly recognized and applied rules of the 5 above rules.

Next week we will take a longer look at the other 4 major rules. I will take you step by step through them so that you'll be able to see the reasons behind each of the rules, and why they not only make sense, but they're MUSTS in creating a good, safe, and usable electrical installation.

Grounding & Bonding, Part III

2010-08-01T20:35:00.001-07:00

This week we finish our Grounding and Bonding installation for the Gym remodel project. In previous blogs we discussed two separated services that enter the building, supplying two separate panels, each with its own set of feeders.

Our initial grounding choice might be the "Metal Underground Water Pipe" as is specified in 250.52(A)(1). I hesitate to utilize this method however, due to the fact that it can be very difficult to verify the "minimum 10' of direct earth contact" rule. There is simply no easy method to verify that the cold water service doesn't change over to PVC, two feet or so after it goes underground. Therefore, we might bond it regardless, but we would not want to consider it our primary grounding electrode.

Thus, we're left with a Rod, Pipe, or Plate electrode type. Ground rods are the most commonly installed, and we'll most likely use these in this application. The only draw back to this, is that we MUST then perform a final resistance to ground test, when the installations are completed, in order to comply with 250.56's rule of 25 ohms or less.

We would size our Grounding Electrode Conductor (GEC) from table 250.66, ignoring the maximum rule of 250.53(E). That rule allows us a maximum of a #6 AWG, but it only applies when the ground rod is a supplementary electrode -- not the sole electrode as is true in this application.

T250.66 sizes the GEC based on the "Largest Ungrounded Service Conductor." I found 2/0 CU feeders in each panel, thus we would be in the "2/0 to 3/0" row and find a #4 AWG CU would be required. We would encase it to protect against physical damage in accordance with 250.64(B).

Because there are two separate services, each would receive its own identically sized GEC installation based on the service conductors present in each panel. We would not be allowed to tap the two together. Article 250.28(D)(2) instructs us to supply a main bonding jumper to each service disconnect. We bond each panel per 250.24(A)(1).

One final note, if we use a metal conduit to encase the #4 GEC, we MUST bond EACH end of the conduit with a grounding type clamp or fitting, attached to the same size bonding jumper as we used for the GEC. This prevents dangerous "choking" potential during high voltage discharge releases, such as found in lightening strikes etc...

Voltage Drop Formulas

2010-07-25T12:43:00.000-07:00

This week we will take a break from Grounding and Bonding to talk about Voltage Drop formulas. Voltage Drop calculations are arguably the most complicated, yet one of the most important items an individual electrician must perform. Total impedances and resistances of conductors may cause a substantial variation of voltages between the service supply and the voltages present at the point of utilization. Overly excessive VD's can severely impair starting and the operational running of equipment. Voltages that are too small for their nominal ratings cause substantially high inefficiencies in equipments, lighting, and heating. Even a small drop of only 10% of the rated voltage causes decreases of 15% for fluorescent lighting, and as much as 30% for incandescent lighting! Motors will run with less torque and operate at higher temperatures. Given the same 10% VD, the Full Load Amperage increases by 11%, the operating temperature rises by 12%, and the torque produced would DROP by 19%!

These figures showcase the field electrician's ability to help (or harm) the overall efficiency of an electrical system's installation. In today's climate, conserving energy is now a MAJOR consideration. Many electricians hate math and granted, voltage drop formulas seem only a step down from an engineer's level of calculation. Few, maybe as small as 10% of us, even remember the formulas off hand, much less apply them on a daily basis. However, the electrical engineer isn't present during an installation, YOU are! The EE has no way of knowing the actual routing or footage a particular circuit conductor may take. Thus the installer MUST be the person responsible for these calculations!

There are essentially five types of voltage drop formulas. These are,

(1):Direct Current VD (the most commonly used and the simplest one) that uses a "constant value" for "k" (specific resistivity),

(2): Direct Current VD that use individual resistance values from Chapter 9, Table 8 of the NEC,

(3): A/C resistance VD using an 85% Power Factor and multiplying factors from Chapter 9, Table 9,

(4): A/C resistance VD using the "Neher-McGrath" method for specific Power Factors other than 85% (the single most difficult formula to use), and finally,

(5): The "Mid-Point" calculation, used for multiple loads over a distance but on a single circuit. Here are the formulas written out:

(1) VD = 2*(K)*I*D

-----------

CM

(2) VD = 2*D*R*I

----------

1000

(3) VD (line to neutral) = Table Value * D * I

--------------------

1000' (Multiply times 2 for 2 pole circuits such as 240V etc...)

(4) Zc = (Rx * cos0) + (XL * sin0)

(5) Includes steps from 1 and 2 with averages (more about this formula next week)...

While none of these are NEC code requirements, they are listed as FPN's in 210.19(A)(1) FPN(4), and 215.2(A)(2) FPN(2). VD calculations are simply good and smart practices to include in your day to day work. The use of any of these formulas will give, in most cases, fairly close values, therefore, many use the simplist of them for ease of daily use. Formula 1 has, for the most part, become the "de facto" one to use in the field. All you must remember is that "k" is a constant value of 12.9 for copper and 21.2 for aluminum. The circular mils value is a quick reference in Table 8 and you're all set. (The 12.9 ohms value is derived by using the ohms per 1,000' of a given stranded wire, divided by 1000 to get the per foot values, then multiplied by the circular mils of the wire size. Interestingly, solid wire has a smaller "k" value of 12.6 ohms. However, use of the 12.9 value will give you the more conservative value.)

One final note to always consider is that all of these formulas and values are based on a temperature rating of 75 degrees C (167 degrees F). Any higher temperature would greatly increase the VD percentages. Temperature increases would use R1 [1 + .00323 (T2 - 75)], where T2 is your higher temp value in degrees and R1 would be the ohms value from Chapter 9, Table 8. (Use this formula for copper only).

All of this being said, VD calculations can be quite the time consuming, confusing, pain in the rear for the field electrician. Electrician Testing has created some very unique and very useful/helpful charts for VD. These charts virtually eliminate the need to remember any of the above formulas, values, and math! Contact us, via email, for a copy of them. Next week we should be back to grounding and bonding! Hope you have a great week, and let us know, as usual, if you have any specific questions....

Grounding and Bonding Part II

2010-07-19T07:50:00.000-07:00

PART II

Last week we discussed a discovery where two panels, in a service for a newly converted gym, were not properly grounded. Article 250 is normally considered to cover two specific topics, Grounding and Bonding. However, it really covers three distinctly separate issues, and those are Grounding, "Earthing," and Bonding. Many in the industry are beginning to separate and treat the "Earthing" component as a majorly separate area. This helps to distinguish between grounding WITHIN a system FROM the grounding OF the system. Our issue here is more of an Earthing concern, where we must insure that stray currents and our "intentionally" grounded conductors have a safe and unfettered path to earth.

The initial 2008 NEC section to confer is Art. 250.52. This article explains what your accepted and physical grounding electrodes must be. Under "Electrodes Permitted for Grounding," there are 8 classes of Grounding Electrodes (GE) and 2 that are specifically prohibited. In most retro-fit remodel jobs, we would use two of these classes the most. These are our "Water Pipe" rule and "Ground Rods." We find the first of these two in section 250.52(A)(1) and the rods under 250.52(A)(5) "Rod and Pipe Electrodes."

There are a couple of installations rules to follow with these two types. The biggest of these is the so called "5-foot" rule. A water pipe that is FURTHER than 5 feet from the ENTRANCE of the building CANNOT be used as an acceptable GE. (Note, there is an exception to this; however, very FEW remodel jobs would ever meet the qualifications for this exception). We must also ensure that a minimum of 10' of continuously bonded metal pipe and casings exist that make DIRECT contact with earth for the entire minimum length. Water meters and the like must be jumpered over with a bonding conductor. Under Article 250.53 we also find a combining rule that REQUIRES an additional supplemental GE be used when we utilize the water piping system as a GE. Thus we see that we're required to use a ground rod or something similar in conjunction with our water pipe.

Ground rods must be at least 8' in length, and according to 250.53, 8' of that length MUST be in contact with soil. Most ground rods are manufactured in 10' lengths so that the bonding connector would not have to be buried in soil. Clamps that are buried must be listed for direct burial. The rod must be driven vertically, unless rock bottom is encountered. (In the Austin area, that is an extremely common situation. In that case, a 45 degree drive/burial angle is allowed or it may be completely buried laying flat, under a minimum of 30" of soil. DO NOT bend your ground rod into a 90 degree "stub up" configuration, where the top portion is above ground and the remainder is horizontally flat. This is a poor practice that is not only a code violation but is also a functionality liability! A situation that I've see and run across too many times beforehand)

There are two final rules to consider. The first is that you are not required to use a bonding jumper for the supplemental GE rod that is larger than a #6 AWG CU conductor. The second is that your resistance reading between the rod and earth shall be 25 ohms or less. The use of special grounding meters should be utilized to determine this value. Where it is greater than 25 ohms, additional rods should be installed at a distance NOT LESS than 6 feet apart. (See Art. 250.56).

Next week we will talk about how to apply Table 250.66 and review more installations rules and requirements. If you have specific questions about any grounding or bonding issues, we encourage you to send us an email. We will respond promptly and your question may even be featured on our web site!

Grounding and Bonding

2010-07-14T15:06:00.000-07:00

Grounding and bonding are two words that cause a lot of electricians to flinch or roll their eyes. One can hardly blame that kind of reaction due to the complex nature of the extensive rules for "earthing," "grounding," and "bonding." In fact, Article 250, "Grounding and Bonding" in the 2008 NEC is the single most largest section in the entire code book! There were 40 significant code changes from the 2005 NEC edition, making it also one of the most changed articles as well. With 81 separate sub-sections, there is a tremendous amount of material to absorb and understand. It is a foregone conclusion that anyone preparing for ANY type of electrician's exam must study and know Article 250 fluently. There have been many books, articles, and studies published on this subject. There is an entire industry in and of itself surrounding this subject alone. So don't feel bad if you are a little shaky on this subject. Over the next few weeks you will find several blogs on our site dealing with various parts of Article 250.

Last week I visited a job site where an older residential home was being converted into a commercial type workout gym. One of the electricians on the site had made himself a pretty ingenious device to trip circuit breakers. It was a single pole toggle switch mounted in a single gang bell box with a cord cap attached to about 36" of SO cord. He'd simply plug it in and flip the toggle switch, thus causing a purposeful direct short. (he must have had the equipment grounding conductor on one side of the toggle and the ungrounded conductor on the other side) He had also left one end of the bell box unplugged to allow the arc flash or heat to have a convenient path for discharge.

In this building, he mentioned to me that every time he employed his shorting device, he'd noticed a much louder and larger arcing inside his device. I immediately had a suspicion that the system may have a poor grounding system, thereby creating a much larger potential resistance to ground to overcome, "forcing" the circuit breaker to function. There were two separate 100 amp panels in the basement. Each panel had its own service conductors feeding it from an outside utility transformer. (a very rare and odd set up) After removing the dead fronts, I discovered that there was NO grounding electrode conductor what-so-ever! I was extremely surprised and I would have chalked it up to simply being a case of an old service that had not ever been brought up to code. BUT, these were obviously newer panels and it was very apparent that at least one panel was less than two or three years old. I have to assume that it must have just escaped notice, however, this was a serious safety over-site by those technicians in the past!

One panel had a neutral/ground bond, the other did not. The two grounding bars between the panels had been bonded together with a #8 AWG copper conductor. We must treat these two panels as two separate services. Our controlling Articles would be: Art. 250.52, 250.53, 250.56, 250.64, and finally Table 250.66. Next week we'll go into detail on how these specific articles apply to this installation.

Part II

2010-07-09T19:32:00.000-07:00

Last week we looked at the proliferate use of service cords in the electrical industry. We left off after looking at our ampacity rating tables. Our 30 A load ultimately needed a size 8/4 service cord (SC). According to T400.5(A), in the 2008 NEC we find an 8/4 rated at 35 amperes as its maximum rated ampacity. SC installations must also follow other de-rating factors for; numbers of current carrying conductors, ambient temperature corrections, as well as other installations restrictions.

In a similar method to how we treat other wire types, we must also de-rate anytime an installation of SC's contains either: more than three (3) current carrying conductors (CCC) or where our ambient temperature rises above 86 degrees F. First begin by obtaining your "Core Ampacity" (as in the case above it was 35A for an 8/4, according to table values). The next step (step II) is to de-rate where there are 4 or more CCC's. SC's come in many different conductor counts, but they usually range from 2 to 6 conductors. Our rule for grounded conductors ("the neutral") follows us from 310.15(B)(4), see 400.5(B). If the "neutral" only carries the imbalance load from different phased conductors (ie 'shared neutrals'), we do NOT have to count it as a current carrying conductor. Where it is the "load side" of a 120V circuit (as an example, or in any other single phase voltage branch circuit) you MUST count it as a full current carrying conductor. T400.5 adjusts by a percentage of our core ampacity value. It is the same exact table as you see in T310.15(B)(2)(a). Ambient temperature factors would be used from T310.16 under the temperature column that corresponds to the temperature rating of the Service Cord. (*Note SC temperature ratings are NOT shown in T400.4 and should be taken from the printed or scribes ratings on the outer jacket of the cable). Portable power cables, types G, PPE, and W, and Flexible stage and lighting cables, types SC, SCT, and SCE; follow their own pre-calculated temp rating/de-rating in T400.5(B).

I have also noticed SC's installed in commercial buildings as substitutes for permanent wiring. One contractor used it for branch circuit wiring to feed under-cabinet lights. His installer had fished it into several wall cavities. He explained that he couldn't get the bend radius neccessary to conceal it using MC Cable. Unfortunately for him, he had to remove it. 400.8 specifies 7 specific uses that are NOT permitted when installing SC's. Essentially the rules are: 1) Not used as fixed wiring of a structure; 2) Not run through walls, doors, windows etc; 3) Not concealed by walls, floors, or suspended ceilings; 4) Not installed in raceways, and finally 5) Not where subject to physical damage. If you are ever tempted to run a SC inside a conduit or raceway, DON'T do it! Not only does that suggest a more "fixed type wiring" scenario, but you are not permitted to encase an SC in a raceway (unless specifically permitted to do so under any other section of the NEC or where in an industrial application, under certain restrictions, a maximum of 50' of raceway may be used as a means to protect a SC; see Art. 400.14).

In our earlier scenario where we had a 3 phase, 480V, 50HP motor, our first step is to find the FLA of the motor in T430.250. Under the 460V, 50 HP column we see that to be 65 amperes. Referring back to T400.5(A), our SC Ampacity chart, we find that to achieve this per code, we'd need a size #2 service cable. That is substantially larger than what was currently installed. The #6 being utilized is only rated for 45 amps, a 20 Ampere Deficit!

Finally, to recap, Service Cords are NOT "ordinary wiring." They follow specific rules and MUST be treated in a different manner. The ampacity ratings are much less than typical wiring. The installation restrictions are numerous. It's even interesting to note that you may not install a NEW SC service that has ANY splices or taps. You may repair an existing usage, but you may NOT reutilize it with the splice remaining. Strain relief to keep tension off of joints and terminations must be employed. The voltage rating on many of them is only a maximum of 300V so be cautious that you match the proper insulation voltage rating with the voltage supplied by the service. For example, a Junior Service Cord, type SJO etc... could NOT be used for a 480V, 3 phase motor application. They cannot be encased in raceways, above suspended drop ceilings, or be used inside walls. I urge you to re-read the entire Article 400 to re-familiarize yourself with the SC installation requirements. As always, be safe and remember your responsibility is to keep others safe from your work!

The Ampacity and Proper Application of Service Cords (SO, SJO, etc...) (Flexible Cords and Cables)

2010-06-27T13:35:00.001-07:00

I have seen dozens and dozens of uses for service cords (SC) in the field that are very improper. The use and installations of SC's appear to be a weak point in many technician's training. It seems like the industry has simply adopted their use as a catchall "extension cord" to be used as a multipurpose, fits anything type of cable. However, there are some specific restrictions to SC's and their ampacity ranges are MUCH different than other types of cables and conductors.

Recently I ran across the following scenario. Take a quick minute to test yourself and see if YOU know what the proper size cord would be needed for the following installation:

a 3 phase, 480V, 15 HP, Squirrel Cage motor, operating at approximately 300' away from its supply. I found a 4 conductor SOOW cord, sized at #6 being used. We'll look at the answer next week in Part II of this Blog.

We find that Article 400 "Flexible Cords and Cables" to be our main ruling statute for SC cords. Table 400.4 lists their types, sizes, and usage, among other important data. Three critical tables, but the most often overlooked ones, deal with SC's. These tables, 400.5(A), 400.5(B), and 400.5 are our ampacity and adjustment tables that must be utilized when installing SC's. Lets look closely at table 400.5(A). We find two important columns, A & B. column A is for cords that will have (3) current carrying conductors. So in essence, ALL three phase installations would fall under that first column. Column B is for (2) current carrying conductors. Thus MOST single phase (such as 120V or 240V type installations) would fall under this column. Take a quick moment to write "3 Phase" under Column A and "1 Phase" over Column B in your 2008 NEC Code Book for your future ease of reference.

So a three phase, 208V, 30 Amp load would require an 8/4 service cord! That is a pretty substantial difference from what a normal #10 THWN conductor, encased in a flexible conduit installation would be. The 6/4 SOOW I mentions earlier would have a MAXIMUM ampacity of only 45 Amps.

In Part II we will cover adjustment factors, voltage drops, and installation restrictions. We will also determine the answer to our question posed earlier. Because of the nature of SC's vs other cables, I have created a custom table for technician's easy field reference. Get a FREE copy, by simply emailing a request "Free Ampacity Table" to our web site. Stay tuned for Part II.!

Breaker Sizing According to Art. 210.3

2010-06-20T21:44:00.000-07:00

Recently in the field I have run across a few panelboards that utilized 25 Amp breakers (over Current Protective Devices - OCPD) for lighting circuits. It struck me as odd because you normally don't find anything other than 15A or 20A OCPD's for lighting. I suspected that whomever installed it was attempting to fit extra luminaries on the circuit for some reason. However - this is not an allowable installation per the NEC Article 210.3. We'll cover why this is so in a minute.

After removing the deadfront, I was at least pleased to see #10 wire being utilized for the branch circuit conductors. According to 310.16, a #10's rating is from 30 to 40 Amps, depending on insulation type and other de-rating factors. Granted, a #12 THWN or THHN would be rated 25 to 30 Amp according to the 75* & 90* columns (T310.16), but due to the so called "small conductor rule," a #12 is still restricted to a maximum of 20 Amps in ampacity. Even if if you could get around that ruled, you'd most likely hit a derating factor of 80% or more if you placed more than 3 current carrying conductors in the same raceway.

Understanding the rule in 210.3 takes a bit of referencing definitions and cross referencing a few other articles. The rule in 210.3 states "The rating for other than Individual Branch Circuits shall be 15, 20, 30, 40, and 50 amperes." <Looking at Article 100 under "Branch Circuit, Individual," we see that defines it as a BC having a SINGLE piece of utilization equipment, i.e. a single motor etc... Under "Branch Circuit, General Purpose," we find that to include most lighting and receptacle loads. There-in lies the problem with the application I talked about earlier. A 25A OCPD shall be used only for a specifically designated and designed for a SINGLE piece of equipment, NOT for a general lighting load. The same principle applies for 35A and 45A OCPD sizes as well (note Article 240.6(A))

There are of course, exceptions to this rule, but those fall outside the scope of this blog. this article in 210.3 is an oft overlooked, albeit important rule. It also lends to uniformity and conformity in field installations, whereby a technician can immediately identify a 25A or 35A OCPD as having it as a supply for a specific piece of equipment. In any case, always remember to size your circuit by the size of the OCPD FIRST, then size BC wiring to match that, keeping in mind any aspects of voltage drop or de-rating factor considerations. Finally, insure that your OCPD size conforms to the rule in 210.3.

Proper wire Ampacity

2010-03-10T13:10:00.000-08:00

Proper wire Ampacity, and choosing the correct wire size for a particular installation seems to be an area many of us get rusty on. calculating correct wire Ampacity is a critical step in order to protect and provide for proper branch circuit loads and feeder requirements.
Table 310.16 is too confusing! I hear this a lot. As an electrical instructor for Texas Electrician Exams, I teach many journeymen, masters, even city inspectors hot to study for, and successfully pass their Texas electrical PSI provided test. It is my opinion that wire sizing for correct amperage is the single largest areas of confusion. to be fair, the 2008 National Electrical Code added an additional step to the Ampacity de-rating requirements. I have even seen recent nationally publishes articles that have incorrectly applied these new de-rating factors. So don’t feel bad if you have some confusion, you’ve got lost of company!
There is some hope with the new edition of the 2011 NEC in it’s proposed format. A new layout for T310.16 is probably going to happen, and hopefully this new layout will make it an easier table to utilize.
I always instruct my students to mark step I through Step IV in their code books. Step I is the top chart on page 147. We begin (always) with what I like to call our “core” Ampacity. For example, a 350 THHN cu conductor under the 75 degree column is 310 Amperes. This is the core value that we will perform all subsequent steps on.
The biggest question I get, by far, is “What is the 90 degree column for, and how/when can I use it?” Well, it’s simple really, you must have three (3) separate items (rules) in order to utilize that column as your beginning core value AND your final calculation must answer TRUE to one additional item. The 3 caveats are:

Rule I. There must be de-rating factors to consider.
Rule II. The insulation of the conductor must be rated for the 90 degree column (and not limited by any specific code article to a lower temperature).
Rule III. The installation must be a dry or damp location for the conductors.

True or false: The final adjusted must NOT be larger than that Ampacity value under the 75 column.

Under Rule I, we must have an ambient temperature adjustment, roof-top temperature adjustment, or a number of current carrying conductor adjustment. If none of those apply then the 90 degree is off limit. Any one of these adjustments factors alone or together with others, would be enough to allow for the 90 degree as a starting point.
Under Rule II, this initially seems to be a given, however, a closer look at certain insulation ratings in their various respective sections in Chapter 3, and T310.13, restrict certain type and certain installations to a lower temperature rating. (Examples: 336.26 (NMS) restricts the cable assembly to the 60 degree column- even though it requires the individual conductors to be rated at 90 degrees; Types XHHW, XHH, THHW, and RHH(among others) are all limited by T310.13 to 75 degrees column when installed in a WET location.)
Under Rule III, we acknowledge the previous examples and use caution when installing in a wet location. Most 90 degrees rated insulation types are restricted to 75 degrees in wet locations. Further, new code rules for 2008 classify ALL interiors of raceways, where directly exposed to weather or buried below grade, are classified as wet locations.
Finally, our calculated core Ampacity-after adjustments for any applicable de-rating factors-must not exceed the value for the same size wire under the 75 degree column. So to answer the 90 degree column question: hardly ever used.
Back to our 350 kcmil cu conductor Ampacity calculation. Step I we found the core Ampacity to be 310A under the 75 degree column (let’s assume a roof top installation: therefore a “wet location”). Next we examine our two ambient temperature steps. Under the main amperage chart on page 147, we see C degrees and F degrees de-rating factors. Notice 26-30 degree C and 78-86 degree F are equal to 1.00 or (100%). This is because the table is based on 86 degrees F initially. Temperatures greater (hotter) than 86 degrees F or (30 degrees C) must be de-rated. (Heat causes resistance-resistance in turn causes more heat, with a potential of a thermal run-away effect). These values are multipliers. A 106 degrees F installation would have a factor of .82 (or 82%). Thus our 310 Amps would be de-rated at 310AX.82=254.2 Amps. Flipping back one page (146) we see the new rooftop temperature adder table. If exposed to sun-light on a roof top, we have to increase our ambient temperatures PRIOR to choosing our multiplier.
The table in listed by heights (in inches) above the roof top surface. (The closer to the surface- greater convection of heat transfer occurs due to the reflected heat). At 3” above we would increase our 106 degree F by an amount of 30 degree F. Therefore we actually have a 136 degree F installation. That ambient temperature has a factor of .58 (or 58%). Thus our 310A core Ampacity is=310AX.58=179.8A (or 180 Amps) A very significant Ampacity de-rating!
Finally we must count our current carrying conductors under T310.15(b)(2)(a) for more than 3 current carrying conductors. Always keep in mind that neutrals can sometimes be considered a C.C.C. and might push a 3 phase service into this de-rating table.
That’s it. Pretty simple-yes? If anyone has further questions, comments, suggestions, or wants more practice, contact us via email and we will be glad to help.

Thanks for Reading,

Mitchell S Tolbert
1-888-473-1826
Contact@ElectricianTesting.com
www.ElectricianTesting.com

Wire Ampacity and Conduit Fill Calculation

2009-12-29T21:49:00.001-08:00

Wire Ampacity and Conduit Fill Calculation

This week I want to take a minute to review our wire ampacity and conduit fill (wire fill) calculation.

There seems to be a lot of common confusion out there when it comes to wire fill. Annex "C" in the back of the 2208 NEC © is a good tool, but it can be very dangerous to use it without considering the impact of de-rating factors found in Chapter 3.

We normally use a 20 amp circuit breaker to protect #12 AWG cu wire. Annex C tables show that we can safely place a total of 16 of this size (Type THHN, THWN, or THWN-2) in a 3/4" EMT conduit. this is only for the protection of the wire from a physical stand point. Annex C is only concerned with the protection of the wire during installation. It does NOT take the ampacity of the wire into consideration!

"Adjustment Factors for more than Three Current carrying conductors in a Raceway or Cable"

Number of C.C.C.	% of 310.16 Values
4-6 Conductors	80%
7-9 Conductors	70%
10-20 Conductors	50%
21-30 Conductors	45%
31-40 Conductors	40%
41+ Conductors	35%

You can quickly see that in our earlier example, if we put 16, #12 THHN conductors in that 3/4" conduit, we would have to drop the circuit breaker to a 15 ampere size! Now seriously, how many electricians in the field really do that? You understand now how dangerous the casual use of Annex "C" can be.

If the (neutral) grounded conductor is NOT shared between phases, i.e. a single 120V single phase branch circuit, such as a general purpose receptacle outlet circuit conductor, it counts as a current carrying conductor. In this installation it carries the full load on it back to the distribution point. Two other common issues with Annex C are considerations for different sized EGC/GEC conductors, and differences between Annex C values and manual fill calculations using Chapter 9, tables 4 and 5.

The value of Annex C is a "staff it full" value. Therefore you would have to keep in mind your additional ground wire, which is usually a smaller size than that of the phase conductors. The only way to use Annex C in this case is to always consider your EGC or GEC as a full size conductor count. A manual calculation is more accurate than Annex C and it has been this author's observation that Annex C values sometimes vary quite a bit from a manually calculated fill based on Chapter 9 tables.