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487 Posts
That's a good question since not many breakered loads in your panel will be running all the time or at 100% of the breaker value. If you want to be super safe you could add up all your breaker values and stop loading the panel when you got to the mains rated value, but and there always seems to be a butt (like me) Your mains are equally rated breakers. Your case 200A mains = 2 200A breakers for 120 vac. DON'T try to stuff 400 amps of breakers into your 200 amp box; 200 on a side. You are liable to see smoke then. I had an electrician tell me one time that I could figure about an 80% load factor on the mains with all the breakers on and wired. Or in other words you could push the max rating by about +20% of the rating of the mains because not all loads will be on at the full rating of every breaker in your box. The rest of you guys may have a different run on this , but it made sense to me.

· Civil Engineer
5,832 Posts
You can in theory load the panel with as many breakers and as many amps as you can fit, because the main breaker (the 200 amp one) will trip if you exceed 200 amps total draw at 240 volts. Each individual breaker is designed to protect the wiring (not the devices) that are controlled by the breaker. As previously noted, you need to do a demand analysis to determine how many amps you can load onto the panel without creating a risk of tripping the main breaker due to overloading.

Overloading the main breaker will not damage anything, but would be quite annoying if you tripped it frequently.

Many older homes were wired with 60 amp service, and have in some cases 150 amps total potential draw. As long as you keep the total actual draw below 60 amps, they function fine. My house is wired with a 100 A main panel, but my total breaker capacity is about 200 A. Most devices never draw close to their rated capacity, i.e. my cooktop is rated at 50A 240 volts, but to get that I would need to turn on every burner full, never gonna happen. Ditto for the electric oven, 40A theoretical, never gonna happen.

· Banned
17,249 Posts
I have a 200 main feed
I currently have over 800a of breakers connected - not counting the 200a Main
This includes only the main breaker rating for 3 sub panels
It does not include the breakers in the sub panels
Add another 315a of breakers for the sub panels
My load calc comes in at 143a

A load calc is the only way to determine how much power you are using

DON'T try to stuff 400 amps of breakers into your 200 amp box; 200 on a side. You are liable to see smoke then

· Banned
17,249 Posts
Not that it isn't possible to draw smoke :thumbsup:
But the main breaker should shut off 1st

Load calc assumes some things:
AC & Heat will not be on at the same time
Allows 3w per sq foot (lighting?)
1500w for each small kitchen appliance circuit
---even tho these are 2400 watt circuits :huh:
---assumes full wattage of circuits will not be used

I had a 55,000 watt load
It only assumes that the 1st 10,000w will be used at any given time at 100% (83a)
The remaining load is figured at 40%

I'm at 142a Load calc now with
- I replaced some high power lights w/CFL
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