Originally posted by stan:
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?????
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.