Two Breaker Issues: Violation? Article Number?

[charlie b]

I am doing an independent review of another person?s design. I found two things I know are ?wrong,? i.e., bad designs, but I cannot find the specific NEC article that would forbid them. I do know that a feeder must have an ampacity no lower than its calculated load ? 215.2(A)(1). In this instance, I wasn?t given the feeder sizes, but I have already written that up, so it is not my present issue. So, are these two items violations?

• A 225 amp MLO panel that has a 116 amp calculated load is protected by a 100 amp upstream feeder breaker.

• A main service panel whose current rating is not shown on the drawings has a calculated load of 875 amps. Its main breaker is rated 800 amps.

 

[david luchini]

So, are these two items violations?

• A 225 amp MLO panel that has a 116 amp calculated load is protected by a 100 amp upstream feeder breaker.

I feel this would be a violation of 215.3.

• A main service panel whose current rating is not shown on the drawings has a calculated load of 875 amps. Its main breaker is rated 800 amps.

I don't think this violates any code section, but I could be missing something. 230.42 would require that the service entrance conductors have sufficient ampacity for the load, but, 230.90(A) only requires that the service OCPD has a rating or setting not higher than the allowable ampacity of the service conductor. So if your service entrance conductors were 3 sets of 350mcm (with an ampacity of 930) the 800A main breaker is "not higher than" the allowable ampacity of the service entrance conductors.

 

[charlie b]

Thanks, David. But I don't think 215.3 is a player. Recall that I do not know any of the feeder (or service conductor) sizes. In the first example, if the 100 amp upstream breaker was feeding a 225 amp rated panel via a 225 amp feeder, then it would only be a matter of the breaker being smaller than the load. I am not sure that is a violation.

 

[david luchini]

Thanks, David. But I don't think 215.3 is a player. Recall that I do not know any of the feeder (or service conductor) sizes. In the first example, if the 100 amp upstream breaker was feeding a 225 amp rated panel via a 225 amp feeder, then it would only be a matter of the breaker being smaller than the load. I am not sure that is a violation.

In my opinion, 215.3 makes that a violation, specifically the second sentence of 215.3. The (unknown) size of the feeder conductors is not relevant to the violation as you have stated it.

215.3. Overcurrent Protection. Feeders shall be protected against overcurrent in accordance with the provisions of Part I of Article 240. Where a feeder supplies continuous loads or any combination of continuous and non continuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

Your 100A c/b is less than the load on the feeder - 116A. This violates (the second sentence of) 215.3.

If the 116A load is completely non-continuous, then the circuit breaker feeding the panel could be no smaller than 125A. If the load is completely continuous, then the c/b feeding the panel could be no smaller than 150A.

 

[don_resqcapt19]

Charlie,
Take a look at 230.79 for the service disconnect.

The service disconnecting means shall have a rating not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).

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[charlie b]

OK, thanks David and Don. I quit looking at 215 when I saw that it was talking about the feeders. I missed its statement about the feeder breaker, and the similar statement in 230. Too early on a Monday morning, and not enough coffee yet. :slaphead: