Under capacity?

[shocku2]

A customer is questioning my installation of three 2-pole 50 amp breakers in a 100amp single phase residential meter/main panel. These are the only breakers in this panel. This should be under the "80%" capacity rule. ?? Also, where is this in the NEC? Thanks.

 

[jimwalker]

Re: Under capacity?

Need more details.What do they go to and what are the loads exspected.

 

[ryan_618]

Re: Under capacity?

Nothing is benifited by adding up the number of breakers in a panel and comparing it to the rating of the panel, unless these loads will be going full load at the same time, which is probably pretty rare. Think about all of the 42 circuit panels you see with (42) 20 amp breakers. 42*20=840 amps!!! I have installed plenty of 42 circuit panels on 200 or 225 amp breakers, and I have never had a problem.

Ultimately, the load is going to give you the answer you need.

 

[charlie b]

Re: Under capacity?

Originally posted by shocku2: Also, where is this in the NEC?

408.13:

All panelboards shall have a rating not less than the minimum feeder capacity required for the load computed in accordance with Article 220.

Your panelboard is rated for 100 amps. The Article quoted above would require that you not load it beyond 100 amps. That is, if for example each of the loads was calculated to draw 40 amps, so that the total load was 120 amps, then the required feeder capacity for that calculated load would be a feeder with an ampacity of 120 amps. The panel would have to have a rating of at least 120 amps, and your 100 amp panel would not be acceptable.

But putting three 50 amp breakers does not cause the load to become 150 amps. As both Jim and Ryan have pointed out, you know nothing until you know the load.