Circuit breaker basics

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  #1  
Old 05-22-06, 11:07 AM
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Circuit breaker basics

My service panel has three different ways of providing the 120v circuits (in addition to the 220's) - single pole breakers, the two-circuit piggyback type single-pole breakers, and some double-pole breakers (single breaker switch)where each pole goes to a different 120v circuit.

Question: Is there some reason why a double-pole breaker (single switch) would be used to power 2-120v circuits vice simply using 2single pole breakers? Takes up the same amount of space and provides the same protection, so why do it? Or am I missing something.

Came across this while planning the circuits to connect for a generator switch box. In two cases I have 120v circuits that I will want to power from the transfer switch where they are one of the two 120v circuits run off the same double-pole (single switch) breaker (albeit on a different terminal). I'm thinking I can't do that because wouldn't I get a backfeed of power?
 
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Old 05-22-06, 11:20 AM
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I have a situation whereby one 120v electronic device should not operate unless a second device (a pump) is running. So, if someone kills the pump by tripping the breaker both devices turn off... that is one reason.
 
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Old 05-22-06, 11:25 AM
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There are three reasons that I can think of (off the top of my head) that someone would use a 240 volt breaker instead of two single 120 volt breakers.

They have a 240 volt breaker and for whatever reason donít want to go buy single breakers, perhaps because they are hard to find or expensive. The issue here is that an overload or problem will take out both circuits, possibly making it harder to find.

They have a single junction box containing two different circuits and they want to make sure that power is cut to both circuits if there is a need to work on either circuit. Again, the issue here is that an overload or problem will take out both circuits, possibly making it harder to find.

They have a multi wire circuit and they either want both halves of the circuit to trip or it is required for both halves to trip at the same time.

In either of the first two cases the breaker could be replaced with two single pole breaker. In the third case it may be permissible to replace the breaker, or it may not. You would have to investigate each and every junction box on the multi wire circuit.

To figure out whether you can move any of these to your generator transfer switch will require you to determine why the 240 volt breaker is used.
 
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Old 05-22-06, 11:33 AM
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Originally Posted by the_tow_guy

Question: Is there some reason why a double-pole breaker (single switch) would be used to power 2-120v circuits vice simply using 2single pole breakers? Takes up the same amount of space and provides the same protection, so why do it? Or am I missing something.
Yes, this maybe a multiwire circuit. ( 2 hots and one nuetral)

If both "hots" terminate on the same yoke of a device, a 2p breaker is commonly used as a disconnect, as per the NEC.
 
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Old 05-22-06, 11:36 AM
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Well, you pretty much hit the thoughts going through my head. Additional info:

Here are the circuits involved:

15a breaker - one pole has two black wires and is for "master bedroom". Presumeably one circuit is lights and one is outlets, although I haven't varified that. This is the side I want to power through the gen transfer switch. Other pole has single red wire and is "master bath".

20a breaker - one pole has single red wire and is "refrig". This is the side of this one I want to power. Other pole has single black wire and is "kitrec" (kitchen receptacles). Not planning on powering this circuit, but might change my mind since I'm pretty sure that will be the microwave (I can eat cold sandwiches in a blackout, but gotta keep the beer cold).

If necessary I can work around it. The master br circuit is not a big deal and I could power some other circuit that is on a single-pole, but the refrigerator circuit would be nice to have "hot". Fortunately our deep freeze is already on a single-pole, so we would still have refrigerating capacity. (refreigerator works better for beer, tho).
 
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Old 05-22-06, 11:39 AM
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Tow Guy, you're not planning on backfeeding a breaker to provide back up power are you?

Tell me I'm reading something wrong pls...


(never mind, I see the "transfer switch" post now)
 
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Old 05-22-06, 11:44 AM
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Sorry, thought I was more clear on that. Yes, it is a UL approved transfer switch panel.
 
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Old 05-22-06, 11:55 AM
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Originally Posted by the_tow_guy
but gotta keep the beer cold.
LOL
 
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Old 05-22-06, 12:05 PM
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The fact that there are red wires on these breakers says that there are multi wire circuits involved. The second black wire on one side of the 15 amp breaker suggests that a circuit was added later and someone did not know how to add a new breaker or could not add one. You might be able to split off the extra black wire from the 15 amp breaker, if all you want to power are the circuits from the separate cable only.

The multi wire circuits will have to be transferred completely to the transfer panel.
 
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Old 05-22-06, 12:15 PM
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I'll probably just leave that one alone (the 15a br circuit) and power a different circuit. Trying to figure out the routing in my head for the 20a, which is the refrig I would like to power. So - the 20a has a red for the refrig circuit on one pole and a black for the receptacles on the second pole. Proper way would be to route the red through the transfer panel and back to the breaker and then route the black through a second circuit on the transfer panel and back to the other pole on the breaker? I assuming twisting those two together and routing them through a single circuit on the transfer panel (it has a total of six; 4-15's and 2-20's) would be a no-no.
 
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Old 05-22-06, 12:23 PM
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You need to completely understand the wiring of the entire circuit. If it is wired a certain way then you cannot use anything except a 20 amp 240 volt breaker in the transfer switch. You may be able to use two individual breakers in the panel, but even if this would be legal, I discourage it. The chance you make a mistake is too great.
 
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Old 05-22-06, 12:31 PM
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Got it. Going to stick to circuits that don't make my brain hurt trying to figure out. Just have to keep the beer on ice.

Thanks for all the assistance. Now all we need is a good hurricane to knock out power for a couple of days so I can appreciate the time and $ spent getting ready.
 
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Old 05-23-06, 11:05 AM
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What brand is your panel?

There are transfer interlocks made for many recently manufactured panels. The transfer interlocks allow you to transfer the entire panel to the generator as long as you only use loads that the generator can carry. In that way you can pick and choose any set of loads in your home that are within the generators rating.
 
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