breaker box capacity

Old 03-06-03, 06:05 PM
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Join Date: Jan 2003
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breaker box capacity

i recently bought a house with a square D main load center, model QOC 30MW 225, series L7. the house has 200 amp electrical service. the box was inspected and approved in 1997 by a very rigid town inspector. the owner at the time did everything correctly (afaik!), so i assume that the box is within its legal limits. it ias the following: one 220v 50a, two 220v 60 a (two central a/c compressors and a feed to a sub-panel); 7 half-position 20 amp; 4 single-position 20 amp; 5 half-position 15 amp; 6 single-position 15 amp, and one 20 amp GFCI breaker.
there is one blank position; if i replaced some of the single position 15s or 20s with half-position, i can make space for one more 220v 50 a breaker for a third a/c compressor.
i do not want to rip the panel out, because it is inside a finished closet, and i want to avoid an unnecessary cost.
first question - how do i determine if the box is within its capacity limits? if it is, how do i determine how much more load it can carry? the house has tons of lighting circuits, and the two (soon to be three) a/c systems, but we arent actually USING all of its capacity, and i cannot imagine that we ever would.
tons of thanks to all!
Old 03-06-03, 06:47 PM
Join Date: Jun 2002
Location: Brethren, Mi
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here is a site with a link on it somewhere with a load calculater on it. This can be a complex question at times with several variables. I have a panel with hundreds of ampacity worth of breakers in it but certainly not all run at the same time. If you are running only 2 of the AC's at a time things will probably be alright. Even a load calculation is a generalization and a good test besides that is to get an amp probe and check when demand is at its highest. You might possibly do it from the meter too but it would be complex. The amp probe migh be the best and you may even find you can balance one or two of the circuits if things are getting close. If the incoming wire is sized correctly the breaker will trip if it overloads, also you can put your hand on the main and if it is uncomfortable hot it is too much. I am kind of babblin here and so much just becomes instinct after a while that it can be difficult to explain.
Old 03-06-03, 10:12 PM
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Post number of breakers

Does your panel label list the maximum amount of breakers?Usually a # of full size(1 inch) and a # of mini(1/2 inch)

I believe from the part # that you gave that you are currently using 29 spaces in a 30 circuit panel.If you add another 2pole breaker,you are in violation of the code because of the listing of the panel.

Last edited by texsparky; 03-06-03 at 10:31 PM.

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