Don't Leave Me Hot and Hanging
November 13, 2011 9:09 PM   Subscribe

How do I wire my new bathroom exhaust fan? The old fan has three functions (fan, light, nightlight) and therefore connects to a triple switch on the wall. It also means that there are two runs of wire to it. The new fan has only two functions (fan, light) and therefore only needs one run of wire. How do I wire this thing up; what do I do with the extra run of wire?

Just some more detail: One of the black wires was connected to the black of the fan connection. The other black wire was connected to the night and nightlight portions. All the white wires were connected together.

My assumption is that the run of wire that went to the fan will only respond to one of the three switch on the wall and the other run of wire will respond to two switches on the wall. So, do I simply:

1) Use the run of wire that was previously connected to the light/nightlight of the old unit to connect everything of the new unit; and
2) Not use the other run of wire at all, and thus "cap it off" by putting wire nuts on the end of it and leave it in the attic? This wire will still be hot as hell once I turn the power back on, so can I actually put nuts on the end of it and leave it in the attic?

Or does it get more complicated than that? Do I need to install a double switch in place of the triple switch and remove a run of wire entirely? I am hoping this last paragraph would be optional and wouldn't be required.
posted by TinWhistle to Home & Garden (9 answers total) 1 user marked this as a favorite
I don't understand how the fan has light + nightlight with only one wire (after one wire goes to the fan portion)? Or is one of the runs of wire a 4-conductor cable (neutral+ground+hot1+hot2)? How many wires came out of the old fan, in total?

If you do end up with a piece of unused wiring, FWIW, you should disconnect and cap it at both ends so that it's not hot.
posted by hattifattener at 9:31 PM on November 13, 2011

Response by poster: Both runs of wire are exactly the same: black, white, ground.

The old fan housing has two holes/inlet for each run of wire: One run of wire went in the top hole and connected to a plug-in that was colored black. The fan motor plugged into this black outlet-looking plug.

The other run of wire went into a hole in the back of the housing. That wire connected to two white outlet-looking plugins. The light fixture plugged into one, and the nightlight plugged into the other.

The switch on the wall has three switches: one each for the light, nightlight, and fan. I assume that one of the runs of wire is connected to two of the switches (what was the night and nightlight, separately), and the other run of wire connected to the switch for the fan.

I already know that I should cap the unused wire at both ends and lable it, but the junction box is a rat's nest as it is, and I don't want to do any work in there if I don't have to.

The house was built in 1939 with updated wiring, but no set of red and blue wires going into the ceiling.
posted by TinWhistle at 9:42 PM on November 13, 2011

Best answer: Can you take pictures? Your vocabulary is a little lacking :)

The safe answer to this question is, of course, stop and call an electrician.
posted by sbutler at 9:48 PM on November 13, 2011

It is not safe to leave a wire exposed in the attic disconnected, even with a cap, although I am unclear from your description exactly how things are arranged. If you are talking about leaving a one of the wire conductors capped within the new fan, that may be OK, but don't quote me on that.

Also, if you have three switches connected to 2 runs of wiring, my guess would be that one run of wires is wired with a hot and neutral, and the other run is either both hot or both neutral. That way you would be able to control 3 separate circuits with 4 wires. This is just a guess, though, and I don't have extensive experience with wiring. From your descriptions, it sounds like you are making guesses which can be potentially fatal, and I would suggest contacting an electrician.
posted by markblasco at 9:56 PM on November 13, 2011

If you don't know, then hire someone who does. Amateur Hour in a case like this can result in dead bodies.
posted by Chocolate Pickle at 10:04 PM on November 13, 2011

That wire connected to two white outlet-looking plugins.

Huh. Each plugin presumably has two connections, for a total of four; how are they connected? I would assume that you (and markblasco) are right and one of the runs is a pair of hots, except that you write “All the white wires were connected together”. Your runs of wire total four conductors (excepting ground), two black and two white; but if all the whites are connected together then they are all neutrals. Your fan needs at least four conductors for all its functions (three switched hots, plus a common neutral) but you only effectively have three. How's that work?

I'm beginning to agree that you should call, if not an electrician, then at least a friend who's familiar with house wiring and can examine things in person, check theories with a meter or tester, etc. Probably you can just rewire the two-hots-in-one-cable run as a conventional switched run, take out one of the switches, and cover the empty slot in the switch box with a blank plate.
posted by hattifattener at 10:44 PM on November 13, 2011

Best answer: Call an electrician and sleep soundly.
posted by kinetic at 3:13 AM on November 14, 2011

Response by poster: For those wondering, I have decided that I am going to just hire this job out after all, mainly due to lack of time. Also, the "handyman" that worked on the house with the previous owner made up his own rules so often that I spend almost every weekend correcting one disaster after another as they come up, so I don't want to guess about his wiring.

posted by TinWhistle at 6:26 AM on November 14, 2011

Basically restating hattifattener: What I think is going on is this: there are four wires going in between the switches and the fan unit. From the switches, there are three hots and a neutral. In the old fan box, each function has two wires coming from it- three black/hot wires, and three white/neutral wires. So the three white wires are connected together with the neutral coming from the switches, and then each black is connected to one of the hots from the switchbox.

And in the switchbox, the power comes in on two wires. The neutral runs right through, up into the fanbox. The hot is split or daisy-chained to one pole of each switch, and the other poles goes to each of the other wires running up to the light.

To me, the right way would be to switch it back to the way it probably was in the beginning: two switches, two hots and two neutrals, running up to the two functions of the fan.
posted by gjc at 6:39 AM on November 14, 2011

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