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How to wire two switches to control bathroom fan/light combo (only two 12/2 cables in receptacle)?

Home Improvement Asked on March 6, 2021

My bathroom has a light/fan combo fixture. The wall receptacle previously had:

  1. Single pole switch to control the light (on/off)
  2. Single pole switch to control the fan (on/off)
  3. Mechanical timer switch for the fan

There are only two 12/2 cables coming into the box (I assume one for fan, one for light). I removed the old switches because I just wanted to replace with a new rocker switch for the light and a new timer for the fan (no longer 2 switches for fan). I believe the two fan switches before were tied together to you could either leave the fan on/off with one switch or set a timer for it with another. Unfortunately, I didn’t pay close enough attention to how it was wired before and am at a loss for how to wire this correctly.

Here is a picture of the wires in the receptacle:

enter image description here

I want to connect a single pole switch for the light on the right side (has a ground nut and two brass nuts) and an Eaton 9590AW 5-Button Preset Minute Timer for the fan (has a green ground wire, a red wire, and a black wire sticking out of the back). The timer supposedly does not need a neutral wire.

Any input on how I should wire this? When I just try to wire the timer switch to the cable on the left and the light switch to the cable on the right, I get no power to the fixture. When I try combining wires with pigtails, sometimes I can get light to operate but either the fan is always on or the fan has no power. I cannot seem to figure out how to wire the light and the fan separately so that I can use the timer feature for the fan.

One Answer

Each of these cables is a switch loop. In theory, the taped white (red or blue) is the always-hot wire and the black wire is the switched-hot. However, it could be the reverse. There are two easy ways to tell:

  • Open up the fan and light and see which wire is connected to another black (= always hot) and which is connected to the fan or light (= switched hot)
  • With all the wires carefully separated, turn the breaker back on and see which wires show hot with a non-contact tester.

Once you know which wires are always hot and which wires are switched hot:

  • For a standard "both screws are the same, nothing fancy" light switch, connect one insulated wire to one screw, the other insulated wire to the other screw, bare ground to the green screw and done.
  • For the timer:
    • Connect (wire nut) bare ground to green
    • Connect (wire nut) always-hot wire to black
    • Connect (wire nut) switched-hot wire to red

Answered by manassehkatz-Moving 2 Codidact on March 6, 2021

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