Switch Wiring for a Bath Exhaust Fan

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How to Wire a Single Switch for a Bathroom Exhaust Fan: Understanding Switch Wiring for a Bathroom Exhaust Fan.

Exhaust Fan Switch

Electrical Question: How can I wire a single switch for a bathroom exhaust fan?

  • I just removed a recessed light from above my shower. It had three sets of wires connected. One coming from breaker, one to switch and I am not sure where the other goes. The wires were all live when I had them apart.
  • I put in a Light and Vent Exhaust Fan Combo. I couldn’t fit all the wires back in so I tried a junction.
  • I connected the original three wires to a new wire. I then ran the new wire to the fan. It was working until I turned off the switch in the bathroom. It sparked and threw the breaker.
  • Now the Breaker trips every time I try to reset it. Do I possibly have too much connected?
  • All I added was the new wire so that I didn’t have to connect them all to the vent fan like they were with the recessed light. The home was built in 1985.

This electrical wiring question came from: James, a Homeowner from California.

Additional Comments: Very Helpful

Dave’s Reply:
Thanks for your Electrical Wiring Question James.

Wiring a Switch for a Bath Exhaust Fan


Application: Wiring a Switch for an Exhaust Fan.
Skill Level: Intermediate to Advanced, best installed by a licensed electrical contractor.
Tools Required: Basic Electricians Pouch Hand Tools and a Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with tools and the  switch wiring.
Precaution: The exhaust fan circuit should be identified, turned OFF and Tagged with a Note before working with the wiring and installing the switch.

Understanding Switch Wiring for a Bathroom Exhaust Fan

James, if you have connected all of the three cable wires color to color, then you have created a dead short at the wall switch for the exhaust fan.

  • From what you have described, this may be the wiring designations for the cables:
    • Cable for Power In – from the circuit breaker.
    • Cable for Power Out – to provide power to other devices on the circuit.
    • Cable for Switch Control – to the wall switch.

How to Wire a Single Switch for a Bathroom Exhaust Fan

  • The key here is to identify the cable that is used for the wall switch, which will basically be a loop from the source power to the switch and then back up to the bath exhaust fan.
  • When a 2-wire cable is used for a switch, the white wire is marked with black electrical tape to indicate that it is not being used as a neutral wire. So this cable is the loop from the source of power, to the switch, then through the switch, then back up where it will be connected to the black wire of the exhaust fan.
  • The white neutral wires of the bath exhaust fan are connected to the white neutral wires of the power source cables.

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