Home>Discussions>ELECTRICAL & LIGHTING>Romex has 3 wires but new timer switch also has a red wire
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Mr. Bananas
Romex has 3 wires but new timer switch also has a red wire

I bought a timer switch for my bathroom fan.

The romex in the wall has the traditional black, white, and ground wires while the timer switch has one more, a red wire. I tried wiring it by connecting black to black and capping the red but the switch didn't work at all. Then I tried wiring the red to black (in romex) and capping the black - the led lights on the switch worked but the bath fan didn't turn on.


A. Spruce
Re: Romex has 3 wires but new timer switch also has a red wire

You have to identify your "line", the incoming power to the switch, and the "load" the outgoing power to the device. You should NOT be capping a wire, the timer has to be placed "inline" between the power in (line ) and the power out (load ).

Without seeing what you have, both at the switch location and at the light/fan location, it is hard to say exactly how you'll be wiring the timer into the circuit.

Assuming you have incoming power supplied at the switch, then you tie color to color and red to the load (fan ). If the power is at the fan, and a switch leg is run down to the switch, then what you're going to run into is that either the black or the white will be hot at the switch, then the other remaining wire will be the return to the device. In this instance you hook the hot lead to the black timer wire and the carrier lead to the red wire. I would highly recommend you open up the fan connections and describe what is there and what is hot and what is not.

To further confuse things, do you have a light and fan on the same switch, and are you trying to separate these two devices to separate switches?

Re: Romex has 3 wires but new timer switch also has a red wire

It sounds like you have a switch loop on which you are trying to install the timer, it won't work. You need to get a mechanical timer that just replaces the switch.


Re: Romex has 3 wires but new timer switch also has a red wire

I agree with Jack.

It appears that you have what's known as a "switch loop" -- one insulated wire is is the hot supply line, the other is the feed from the switch to the fan. The white wire is not a neutral, and it should be colored with a black marker or electrical tape to indicate that it isn't neutral. Marking is now required; when your home was built it may not have been required, or maybe the electrician was lazy.

Your switch box apparently doesn't have a neutral wire. The timer switch you selected requires a neutral wire to work properly. As Jack said, you will need to use a mechanical timer, or replace the wiring to the switch location so that you have a neutral.

A recent change to the codes (2011 National Electrical Code) now requires a neutral wire in every switch box for this very reason: to support electronic timers & occupancy sensing switches. However, previous wiring is grandfathered, so there is no requirement to retrofit except during remodeling.

Note that all of the above is based only on what you told us and serious speculation on my part. I can't see your exact situation from here, and there may be important information that I'm missing.

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