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I have an oil boiler for heat. 14-3 cable runs from the panel to a thermal cutoff above the boiler, then into the boiler's control box, and from there to a Taco controller that manages three zone thermostats and controllers for forced hot water heat.

At the panel, the 14-3 cable is presently double-tapped so that both the black and the red are attached to the same 15-amp breaker.

double-tapped 14-3 cable

I'm in the process of migrating the whole circuit to a subpanel so I can put the boiler on a transfer switch to a generator for backup power. I'm tempted to attach the red and black wires to 2 ganged 15-amp breakers, but I'm afraid because I don't understand the original intent of this wiring.

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    Inside the boiler's control box, does the one of those wires supply power to the boiler's electronics while the other supplies power to the Taco controller? – TDHofstetter Aug 23 '14 at 23:13
  • There may be nothing wrong with this. Check the labeling on the breaker, it may allow two conductors. I think most Square-D breakers allow two copper conductors, not sure about GE. – Tester101 Aug 24 '14 at 11:55
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    Are you sure that both the red and black on that breaker come from the same cable? Usually if you have a red wire in a breaker box it is part of either a 220V circuit or a multiwire branch circuit. In both cases the black and red go to both parts of a double pole breaker. – Brad Gilbert Aug 24 '14 at 15:25
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    Best guess - a previous boiler was 220VAC and actually needed 14-3 to feed it properly. It was replaced with a 110VAC unit, and someone didn't want to waste the red wire, so they used it. – Ecnerwal Aug 24 '14 at 17:47
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If that is the red and black from the same 14/3 cable it is anyone's guess why they did this. In any case they are using the same circuit on both wires, obviously. If there is no problem at this time just splice the two wires to a tail of the same gauge and put that one tail on the breaker. Those GE breakers are NOT made to accept two conductors, but it's also not the end of the world either. Since you are working on it is worth fixing.

IF you do feel that stongly that you want them on separate breakers you MUST use a 2-pole breaker, and NOT a tandem, or twin, breaker.

  • Side note FWIW - I've recently been chastised for using all-caps to indicate emphasis, and asked to make use of bold instead. It's a paradigm shift, but it satisfies the gods. You might be well-advised to do the same. – TDHofstetter Aug 24 '14 at 14:23
  • ( To make it bold just put two asterisks on both sides of the word **bold** ) – Brad Gilbert Aug 24 '14 at 15:27
  • Honestly, WHY does it matter??? I'll leave it as it is. Thanks for the heads up though. – Speedy Petey Aug 24 '14 at 15:59
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In response to TDHofstetter's comment, I opened the thermal cutoff:

Inside thermal cutoff

The 14-3 cable (on the bottom of the picture) is coming from the panel. The black wire terminates all by itself (on the left). The red (coming from the same breaker) runs through the cutoff and to the black wire in the armored cable that proceeds to the boiler controller. The ground and neutral are also nutted straight through to the boiler controller.

I tested the red and black on the 14-3 for continuity just to be sure that they run uninterrupted back to the breaker. They do.

So it appears the black wire is just unused. I reopened the panel and detached the black from the breaker and nutted it, and the heat still seems to work just fine.

I don't know why both wires were connected to the breaker, but I think my problem is solved. I apologize for posting a question prematurely; thanks for the guidance.

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    Not prematurely - you asked, someone suggested looking, you looked, you reported back - it's the point of having some folks (albeit not in person) to bounce questions off - sometimes they make you think of things that would take a long time to think of yourself. Thus, the system is working. Nice clear pictures, BTW. – Ecnerwal Aug 24 '14 at 20:47

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