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?
Wiring – How to wire 3 separate switches to a single exhaust fan
exhaust-fanwiring
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I don't know about code compliance. But, this might work for you:
1 Y-Connector at the outside vent.
2 Backdraft Dampers (one on each leg) at the Y to stop the backflow of noxious gases from one fan(on) to the other (off).
Note that the backdraft dampers will add to the resistance of the duct work. You may wish to move up to the next size of duct.
It is possible that the two black wires (other than that going to the switch) are going separately to the fan and light. If so, the change is easy.
To test this do the following:
- turn off the breaker
- separate the three black wires nutted together
- wirenut the black to the switch with one of the others and insulate the other in a separate wirenut
- turn the breaker back on test the switch. Hopefully, the switch will operate only one of the fan or light.
- turn the breaker back off
- switch the black wires so the other one is connected to the wire to the switch
- turn the breaker back on and test the switch. Hopefully, it will only control the other of the light or fan
- Turn the breaker back off and optionally restore the original wiring
If the test results followed what I marked "hopefully", you are in business. Remove the other wire to the switch and wirenut it to two wires to run to one side of the dual switch (if one side of the switch has a removable bridge, just connect the single wire to that side). Connect the two blacks originally wirenutted together to the other side of the switches (if that side has a removable bridge, remove it).
For the pigtail wires, you should use the same guage wire as the rest. Examine the wires for printing on the insulation (look for an AWG number).
I'd also recommend against using the back push-in connectors. It's better to use the screw terminals.
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Best Answer
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:
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:
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.