Saturday, September 11, 2010

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

     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).


     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

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