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Discussion Starter #1
I'm hoping someone can help me out with this. I'm doing a remodel for a lower income family and I'm trying to replace a bathroom vent fan. The fan has a timer switch. The old fan had two "sets" of wires running into it. Two separate cables with a black, white, and ground apiece. When I took the old one out I had to snip all the wires so I never got a chance to look at how they were hooked up.

My question is: Why are there two cables? There are no lights in either the old or new fan vent. The new one only has the hook ups for one cable.
 

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Flashman said:
I'm hoping someone can help me out with this. I'm doing a remodel for a lower income family and I'm trying to replace a bathroom vent fan. The fan has a timer switch. The old fan had two "sets" of wires running into it. Two separate cables with black, white, and ground apiece. When I took the old one out I had to snip all the wires so I never got a chance to look at how they were hooked up.

My question is: Why are there two cables? There are no lights in either the old or new fan vent. The new one only has the hook ups for one cable.
Is the old unit a combination fan/heater unit? Why don't you trace where both wires go? Do they connect to switches/timers? Consider bringing in a licensed electrician to properly wire the fan and handle all the electrical for the bathroom remodel.
 

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Master Electrician
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2 cables running into the fan housing? One may be power, the other the switch leg to the switch.
 

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Fan unit in ceiling 'plugs in' to an outlet usually so it can be unplugged and replaced when necessary. It would require only 1 pair of wires. If the tin housing in the joists for the fan was multi purpose as in fan/light, it could have been pre wired, just in case. A good electrician would have used a 3 conductor wiring, usually black/red/white. That assumes switch or switches in wall were designed to be from same location. There would be 2 outlets to plug into in the housing, a fan and a light. If it was more logical to have a light be turned on when entering the room from a different location, it could have its own switch somewhere else. It is much more difficult to add wires later, after construction. Having more is actually much preferred so you are better off. Just figure out (trace) where they start/finish. One pair may not be needed if light only.
 

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Discussion Starter #7
Thanks for replies guys

I tried to trace the wires and they just go into a wall that is not getting remodeled so I have no idea where they go. Also it is very uncomfortable in the attic crawlspace, about 2 feet of crawling room between the joists and roof with a lot of insulation. As I said there is no other need for a wire, only the fan, no light or heater.

WHat do you mean the other switch leg Kyle? I'm not familiar with that term. Also how would I go about wiring it?

Today I hooked up just one of the wires hoping it would work and instead it just ran constantly without turning off so I had to unhook it again.
 

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Ahh…Sounds like you hooked it up directly to the source cable. I’d bet the other wire is the switch leg then.

A switch leg is where you have power enter a lighting box in the ceiling for example, then (pre-2011 code) you run a 2 wire cable (plus ground) from the ceiling box to the light switch, allowing a switch to be hooked up to control the fixture. There’s a proper way to do it, wire color wise, so if you don’t know, just ask us.
 

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Thanks for reply Kyle

Yes if you could explain how the wires should go together that would be great. I've tried to research it and understand but I'm not completely confident in it. The way I understand it is (1). There is a hot 3 wire cable running to the fan. (2). There is another 3 wire cable going to the switch, and this is how the switch operates. (3) So from the hot wire, I hook the white directly to the fan, then I hook the black from the leg wire to the fan (colors matching the fan wires on both) then I hook the black from the hot wire to the white from the leg wire and ground both wires. Is this even close?
 

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Yep that’s it.
When you say 3 wire cable, I think you mean 2 wire with ground? Black, white, ground.

Source white directly to fan white,
sw leg black to fan black,
re-color the sw leg white at both ends (a sharpie works well for this)
source black to re-colored white.
both grnd wires together and to fan housing…may have to make a small jumper for this connection
At the switch, black to the sw, re-colored white to sw (doesn’t matter which terminal)
ground wire to sw,
 
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