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I have installed multi port exhaust fan in the attic to serve 3 separate bathrooms. How can I wire the fan so that the fan can operate independently from a switch in any of the bathrooms?

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    Have you already run a cable from the service panel to the fan? Or do you intend to run the fan from the power already present in the bathrooms? – A. I. Breveleri Jan 12 at 23:08
  • Are all the bathrooms on the same circuit, or on different circuits? – ThreePhaseEel Jan 12 at 23:13
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    @larry To amplify ThreePhaseEel's question is all the bathrooms' electricity being paid for on the same bill ie. through the same meter? – Duckisaduckisaduck Jan 13 at 1:11
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The answer to your question depends on many exact details of your existing circumstances. Are you building anew, or are you modifying an existing construction? If modifying, do you have access to run new cables? Is power supplied at the fan location or must you draw power from one of the bathrooms?

The following diagram assumes power supplied at the fan location. In general, the wiring for such a shared fan should look something like this:

generic multiple switch loops for one load

The idea is to distribute the always-hot from the service panel to all the switches, then collect the switched-hots and connect them to the hot side of the load. The neutral side of the load is connected to the neutral from the service panel.

The name for this kind of circuit is "multiple parallel switch loops".

If power is to be take from one of the switch locations, the circuit becomes slightly more complicated:

multiple switch loops power at a switch

But the principle is the same -- always-hot to all the switches, switched-hots in parallel to the load, neutral to the load.

In any case, in most places, your electric code now requires neutral to be distributed to all switch locations.

  • As OP has not yet responded to amplifying questions, this answer is intended more for the general reader than for him. If larry provides more details, I'll provide more diagrams. – A. I. Breveleri Jan 13 at 4:46
  • Where are the neutrals in these switch loops? – Harper Jan 13 at 8:41
  • @Harper: Presumably in the "other switches and appliances". Per my second paragraph, this diagram is for the case where the switches are to be added to existing junction boxes. Per my final paragraph, if the switches are alone in their boxes, additional wires will be required. - Waiting for larry to tell us if that is the case. – A. I. Breveleri Jan 13 at 16:17
  • Wait?? What???? You can't just not run neutral in a switch loop and tell people to grab neutral off another circuit. You don't seriously think that, do you? And it's a bathroom, there's gonna be GFCIs, so neutral imbalance is super not ok. Not that it's normally ok. The neutral must be provisioned in the same cable as the hot and switched hot that the smart switch will be powered by/acting on. – Harper Jan 13 at 18:47
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    @Harper: I am compelled to agree with you. I was beginning to think along those lines, as the design principle of "least surprise" would dictate that everything belonging to the switch loops should be independent of anything already in the switch boxes. - I will change my answer. – A. I. Breveleri Jan 13 at 22:48

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