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I have a junction box with two switches. One switch runs a light and the other runs a light and an exhaust fan (separate fixtures). The box has 4 cables entering each with black, white, and ground wires. I was surprised to see two of the black wires are pigtailed together with two other black wires before continuing to the switches. The other terminal of the switches are connected to the black wires of the other two cables. All 4 white wires are pigtailed together and all 6 ground wires are pigtailed together (4 from the wires and 2 from the switches). Is it common for two branches of a circuit to be bonded in this way? All cables are protected by one breaker.

Another surprising (to me) aspect of this circuit is that it is protected by a double breaker (not a tandem breaker). It was my understanding that double breakers were used to create 240V circuits for large appliances. The breaker in question is 15A on each arm and labeled "Hall lights" (which seems roughly correct). Why would a double breaker be used for such a circuit?

Finally, given that there appears to be two hot cables coming into the box and two load cables exiting the box, is it fair to assume that the two loads that are controlled by the second switch are wired together in parallel somewhere inside the walls?

My locale is Pennsylvania, US.

Here's a diagram of the wiring in the box:wiring diagram

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  • Just to be clear when you say "pigtail" what you mean is those wires are bonded by a wire nut? Sep 23 at 22:05
  • Yes, would there be a better way to phrase that? Maybe just like you said "bonded by a wire nut"? Sep 23 at 22:53
  • Yep. Most folks gather the meaning but a pigtail is usually just a short length of wire. Sep 24 at 23:41
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This is a common confusion for the novice. The part of the circuit you are interested in, is not the only part of the circuit.

Obviously what you expect is 1 supply cable (always-hot and neutral) then fanning out into two lamp cables (always-hot and switched-hot). You do have that. But you also have hints of other stuff going on in the circuit.

First, you have another always-hot/neutral cable carrying supply hot off to another switch box somewhere. That tells us this is not the last stop on the circuit.

But you also have a handle-tied supply breaker. That tells us this is not the first stop in the circuit, and that upline (toward the panel) this circuit gets 120V from a multi-wire branch circuit.

All of which is not your problem, as long as you leave it alone.

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There's a good chance that there's only one hot coming into the box. It's wire nutted to a black wire that goes somewhere else as a hot,along with a neutral and ground, maybe to another room. The other two blacks in this group make both switches hot. In this case , all neutrals, white wires, would be connected together.

Double breakers are normally used for 240 Volt appliances but I've seen many used to control two separate circuits serving separate rooms. The installer might have had a double and no singles so he used it. Problem is, when it trips, you lose both loads. It could also be a multi wired branch circuit.

Yes, the second switch controlling the light and exhaust fan have those loads connected in parallel. The wire would connect to one fixture and continue on to the next one.

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    So if there's only one hot wire coming in and one of the wires continues on to another room then that connection would be happening in that junction box just because that's a convenient place for the connection to be made? Is there a reasonable way to test that theory given that I already strongly suspect there are other rooms protected by the same breaker? Sep 23 at 23:00
  • Turn off the breaker and then check each outlet to see if it has power.. keep a record. do this through your whole house. This knowledge will always come it handy. In some instances, I've used those colored dots and color coded the outlets and the breakers.
    – JACK
    Sep 24 at 0:02

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