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how is two-pole breaker rated on main?


Peanut
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I was over to the neighbor's house and he is renovating an older home. He says that the service panel has a double pole breaker and each breaker is 70 amps. Doesn't that mean that the house is supplied with 70 amps and not 140?

I'm still new to the electrical thing and haven't yet completed all my learning on that.

How exactly is a house rated on the amount of amps coming in? If it is one breaker and says "100" I understand it is no more than 100 amps. But if it had a double pole and each breaker said "100"?

If his new house had only 70 amps coming in, would the power company even turn on the power? That's very outdated.

Thanks for any help understanding this.

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Alex, keep in mind that it's a 120/240 volt service. If everything below the 70 amp main was single pole 120 voltage, you could say that the panel is capable of feeding 140 amps total. If everything below was double pole 240 then the total would be 70. Of course we normally have a mix but, no matter what that mix is, the amount of available power or watts actually remains the same (watts = volts x amps). It is a little confusing, and I'm not so sure about three-phase, but for single phase panels the industry standard for sizing nomenclature is the amount of amps per pole or leg, not the total. In other words, a double pole 70-amp main breaker is considered a 70-amp service.

On your last question, I don't think the utility company cares about the the total capacity, but the city inspector/permit guys might if it's a total remodel.

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Now see? That's what I thought. I told him that if more than 70 goes through that breaker, it will trip because they are connected. He seems to think that he will have 140 amps. He thinks he is going to add central heat and air to that house without upgrading the service!

I say he is in for $2500 or more just for the electrical upgrade. Oh, I found out the house was built in

What I don't get is why are some main breakers just one, and some are two? What determines that?

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"What I don't get is why are some main breakers just one, and some are two? What determines that?"

The "single" main breakers are actually two single pole breakers, just in an integrated case with internal linkage. An overload on one leg will trip that side which will then mechanically trip the other. They are really no different than a "double" with an external handle tie. You will also occasionally see a quad main breaker with a handle tie across all four. In the case of a 200=amp quad, what you actually have is 4 100-amp singles, a pair to each leg. The handle will normally state the service amperage.

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You know, I'm not sure about that. Obviously, in the case of a double-pole breaker with a single toggle, the linkage is internal (although I assume it's still "mechanical"). I thought that those with 2 toggles were basically just two separate breakers "glued together" and the handle tie was the tripping mechanism for the other pole. I could be wrong there.

BTW...I believe the term "internal trip" means that a breaker will trip even if the handle is held in the on position, and doesn't refer to tripping of the second pole.

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Originally posted by Peanut

I was over to the neighbor's house and he is renovating an older home. He says that the service panel has a double pole breaker and each breaker is 70 amps. Doesn't that mean that the house is supplied with 70 amps and not 140?

I'm still new to the electrical thing and haven't yet completed all my learning on that.

We call it a 70-amp service.

How exactly is a house rated on the amount of amps coming in? If it is one breaker and says "100" I understand it is no more than 100 amps. But if it had a double pole and each breaker said "100"?

Still 100 amps. Think of the service as a large 240-volt circuit.

If his new house had only 70 amps coming in, would the power company even turn on the power? That's very outdated.

Yes, it is. I would expect that, if he were doing any kind of serious remodeling, the local AHJ would require him to update the service. The modern minimum service is 100 amps. However, they'd probably make him calculate how much power the house requires. A 200-amp service costs little more than a 100-amp service.

- Jim Katen

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Originally posted by homnspector

"An overload on one leg will trip that side which will then mechanically trip the other."

I may be mistaken and it may be splitting hairs, but I think most 220 breakers are "internal trip" and will trip both legs with or without the handle tie, or am I wrong about that?

You're correct. A two-pole breaker that you buy as a set has an internal common trip bar that you can't see.

You can also join two single-pole breakers together with a handle tie. In this case, there is no internal common trip, but there is a common disconnect.

For most two-pole applications, there's supposed to be a two-pole breaker with a common trip.

For some applications, merely having a common disconnect is fine. (For instance, multi-wire branch circuits that terminate on the same yoke.)

- Jim Katen, Oregon

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