# Is my breaker capacity 100 or 200amp

• posted on July 17, 2013, 7:41 am
My main breaker is 100A at 240 volts. I've always been confused about this. Does that mean I can use up to 100amps at 240volts, OR up to 200 amps at 120 volts?
Or does is the limit 100amps at either voltage?
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• posted on July 17, 2013, 8:12 am
On Wednesday, July 17, 2013 3:41:15 AM UTC-4, snipped-for-privacy@theshop.com wrote:

Physically there is never more than 100 amps flowing in the service. However, if the 120V loads are balanced, meaning there is an equal load on both hot legs, then you can have 100 amps flowing through each of those loads, making it appear like it's 200 amps at 120V.
For a simplified version, think of a 240V voltage source connected to two 1.2 ohm resistors that are in series. There is 100 amps flowing in the circuit, with 120V appearing across each resistor. So, each of those resistor loads has 100 amps going through it, with 120V appearing across each.
For you to get 200 amps at 120V out of your service, 100 amps of load must be on each leg. If you put all the 120V load on one leg, you'd only get 100 amps. That 100 amps would be coming in on the one hot and going back on the neutral. If you put say 70 amps on one leg, 50 amps on the other, then you'd have the difference, 20 amps, flowing back in the neutral. But there is never more than 100 amps of total current.
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• posted on July 17, 2013, 11:08 am
On 7/17/2013 3:41 AM, snipped-for-privacy@theshop.com wrote:

You have a 100 amp main breaker. You have a 120/240 volt single phase 3 wire service Your main breaker limits the amperage to 100 for each of the two ungrounded legs This service will allow either a total of 200 amps @ 120 volt or 100 amps @ 240 volt. What you have is considered a 100 amp service
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• posted on July 17, 2013, 11:34 am

Nicely said! I get it.
Tomsic
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• posted on July 17, 2013, 1:09 pm
On Wednesday, July 17, 2013 7:08:34 AM UTC-4, RBM wrote:

I'd add the caveat that it only allows 200 amps @ 120V if the loads are exactly balanced on both legs, ie you have 100 amps of load on one leg, 100 amp on the other. If you had a bunch of large loads all on one leg and tried to pull 110A @ 120V, it would exceed the circuit and breaker capacity.

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• posted on July 17, 2013, 8:59 pm
On 7/17/2013 9:09 AM, snipped-for-privacy@optonline.net wrote:

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• posted on July 17, 2013, 10:45 pm
my neighbor has a 200 amp service and some years ago he was tripping his main during christmas outdoor light season. he was a true grizwald:)
turned out his main was very unbalanced, a few minutes with my clamp on ampmeter fixed his all up......
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• posted on July 18, 2013, 12:14 am
Do you think Griswold was unbalanced?
my neighbor has a 200 amp service and some years ago he was tripping his main during christmas outdoor light season. he was a true grizwald:)
turned out his main was very unbalanced, a few minutes with my clamp on ampmeter fixed his all up......
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• posted on July 18, 2013, 12:39 am
On Wednesday, July 17, 2013 8:14:05 PM UTC-4, Stormin Mormon wrote:

That's who I figured Bob's neighbor must be too. LOL That was a great movie.

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• posted on July 18, 2013, 10:25 am
(Family trudging through the snow.) "Dad! I can't feel my legs...." "That's all part of the experience, Rusty."
http://www.imdb.com/title/tt0097958/
On Wednesday, July 17, 2013 8:14:05 PM UTC-4, Stormin Mormon wrote:

That's who I figured Bob's neighbor must be too. LOL That was a great movie.
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