ECN Forum Forums General Topics of the Trade General Discussion Area breaker box

does anyonehave some sort of formula on amp calculating in a breaker box? i went to a customers home she is going to add a addition to her home. she had a 40 space breaker box 200 amp . she has about 5 free spaces left but is she already overloaded are they a calculation i can do at the box by looking at the panel box?????

Stan;
well it would be a 'Demand Load Calc', i think...

You are required to comply with the 1999 NEC Article 220, Part B. Feeders and Services.

You may also want to review the examples in Appendix D, they show the procedures for making various calculations.

Sometimes Section 220-3(c) Loads for Additions to Existing Installations can be applied.

The electrical permit process and electrical plan review at the local level by qualified persons will also help to clear up the mystery.

You may want to hire an electrical consultant or electrical contractor who is familiar with the situation you describe.

Stan;
You can do a load check on your own with a clamp-on to give you some idea which way to proceed. I would first check each phase and then check how bad the unbalanced load is on the neutral. I assume this is residential, and with 5 free spaces left in the panel you can surely add a sub-panel to feed the new addition. I have never seen a residence with a 200 amp service yet that was maxed out and drawing anywhere near that, generally they if fully loaded draw about 100 amps with a large load.
A utility company a few years ago did a comprehensive study on load usage in their area and found that the average customer drew about 27 and 1/2 amps which means tthat a 100 amp service is probably 4x larger than what is needed, but the code says 100 amp min.

>I have never seen a residence with a 200 amp service yet that was maxed out and drawing anywhere near that, generally they if fully loaded draw about 100 amps with a large load.
Well, if everything that could be on were running at the same time, including the curling irons and hairdryers, I've seen a lot that could be close and no small number would be over. I will grant that there are seasonal appliances that would not normally operate simultaneously. But does that mean that I should not be able to use a bypass to test the electrical heat in the summer since the a/c might come on?


>which means that a 100 amp service is probably 4x larger than what is needed
on average. But the average is not representative of the peak amps. I think 200 A should be the minimum busbar rating.