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Old 10-29-2012, 06:19 PM   #1
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Generator Circuit Breaker Help

Attached are a couple pics of the circuit breakers on our 7.5 kw onan generator. These are not from the service panel... they are right on the generator. Can someone please tell me why these two circuit breakers are so different? One large, the other small, but both rated at 30 amps... and no common trip. What is up with that? I'm trying to come up with a reason why there isn't a common trip, but I can't figure it out.

The generator outputs 120/240. There must be a couple relays in the junction box where the shore power and generator line converge prior to electricity being sent to the service panel. Obviously, when the generator turns on, there is one relay that disconnects the shore power. Then, depending on whether the shore power is 15amp, 30amp, or 50amp, there is another relay that either runs one leg of 120 down both sides of the service panel (15 or 30 amp) and that runs two separate legs of 120 down each respective side of the service panel (50 amp or generator). IF that control strategy is correct, I still can't see why a common trip breaker at the generator would be bad.

So you're probably wondering why I am so concerned about the common trip thing... Here's what I am doing: I am installing a 4 prong 50 amp rated receptacle next to the generator. This will serve two purposes. 1) so we can plug our house into the rv generator when the power goes out. We have a transfer switch wired to our service panel here in the house, and underground lines run out to the garage for a generator hook-up. 2) I want to be able to offer electrical power to our non-generator-owning friends when we are on the road and have to boondock.

The issue that I see is that the if I am to hook the house up to the generator, it needs to have a common trip breaker since there are a few appliances that will be running off of 240v. You would not want just one leg of a 120/240v appliance to drop - this could fry motors. You need to have a common trip for those appliances/motors.

At this point, I guess I can see why a common trip isn't necessary for the motorhome since everything runs off of 120v anyways... although if you trip one leg, and the relay breaks the remaining leg to both sides of the service panel, the appliance that originally tripped the first breaker will still be energized and you'll trip the second breaker any ways. Doesn't make sense to me. Might as well just have a common trip breaker right on the generator...???

I guess to make a long question short... does anyone see any problem with replacing these two breakers with a set of standard 30 amp common trip breakers?

Sorry that was so long winded... but I really want to understand how all this works.

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Old 10-30-2012, 11:11 AM   #2
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Stupid computer trashed my reply....

If those are both 120volt breakers I see no problem with a standard replacement and no reason for them to be different.

On a 30 amp RV, normally one of those breakers would be 20 amp and feed nothing except an air conditioner,, The rear one if you have 2.

On a 50 amp RV they should both be 30 One for each leg.

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Old 10-30-2012, 04:01 PM   #3
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Thanks very much for confirming my suspicions. I picked up a little 30 amp breaker box today from Home Depot. I should have this all taken care of in an evening or two. Thanks again.

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