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# 100 amp sub-panel

#1
01-21-16, 12:26 PM
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100 amp sub-panel

Hello all - this is probably a very basic question but it's something I'm curious about. We had a 100-amp sub-panel put it as we're in the process of finishing our basement and needed more circuits. The sub-panel has room for about 15-20 additional circuits. My question is, what does the "100-amp" refer to? Does that mean I can only have 5 20-amp circuits or 6 15-amp circuits in the box? Or does that just mean the most it can handle is 100-amps all at one time (that would be a lot, right)? Thanks!

#2
01-21-16, 12:58 PM
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If fed by a 100 amp breaker you could run up to 100 amps at 240 volts or 200 amps at 120 volts. Many houses run on less than 100 amps.

#3
01-21-16, 12:58 PM
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Adding the breaker handles is meaningless .

#4
01-21-16, 01:11 PM
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Thanks. What are breaker handles? Are those the individual circuit breakers?

#5
01-21-16, 02:00 PM
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The amp ratings printed or stamped on the handles of the breakers (e.g. 15, 20, 30). In other words, a 100A breaker panel can support many more than 5 20A breakers due to the fact that branch circuits do not operate at 100% capacity for extended periods of time. The electrical code provides a formula called a "demand load calculation" to figure out what the realistic capacity of a panel is.

#6
01-21-16, 02:22 PM
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And of course the breaker supplying the panel can be less than 100 amps. It isn't uncommon to use a 100 amp panel on a 60 amp breaker just so you have enough space for all the breakers. All the 100 amp designation means is that is the maximum amperage it is rated for.

#7
01-21-16, 06:59 PM
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All the 100 amp designation means is that is the maximum amperage it is rated for.

we're in the process of finishing our basement and needed more circuits.
In all probabilty you'll never add more than 20 to 30 amps maximum in a typical basement finish. Like you already said, you just needed more circuits.

#8
01-21-16, 07:07 PM
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I have a 200 ampere service. Between the service panel and two sub-panels I have at least 900 amperes worth of circuit breakers. I doubt that I have ever pulled as much as 100 amperes through the main CB.

#9
01-22-16, 03:33 AM
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Thank you all for your help - I appreciate it!