Obviously a 5-amp switch can't replace a 20-amp switch. But here's what happened and why I'm stumped.

In my old house, a previous owner's refit of a bathroom involved putting in a fairly high-powered exhaust fan, controlled by a switch that you twist to set how long you want it to run for. It looked very industrial, and on a whim while I was at the hardware store, I picked up a more modern one with push-button controls and installed it.

I hadn't realized I'd taken out a 20-amp switch and replaced it with a 5-amp one. No wonder it didn't work. The fan whined but didn't turn, and after a short time there was an audible electrical POP! And everything shut down. I'd stepped out of the bathroom and didn't hear where the sound came from.

So I turned the breaker off again, figured out what I'd done wrong, went out and bought a 20-amp switch. Now I've installed it; the LED lights on the switch activate and show there's power running through it and the different timer settings all light up properly. But no matter what, the fan does nothing. Not even the sad buzz it made when I tried to run it on the 5-amp switch.

All I can think is that I somehow damaged the motor -- although my amateur's instinct is that'd be hard to do by feeding the motor too little electricity rather than too much.

Any advice? Do I need to change the motor in the fan?

Run a separate cable or extension cord to the fan and direct wire black to black and white to white, does the fan spin? It should because the weak link in your install was the switch, that is what should have cooked. Both switches delivered 120 volts to the fan, just one would be able to carry a heavier load. Test it and come back, can't see how this would cook a fan motor

Haven't tried the above test yet tonight, but there's one detail I left out that might be relevant.

The old 20-amp switch had only two black wires. One connected to a single black wire in the box. The other connected to a pair of black wires. Also in the box were two white wires, connected together but not connected with the switch -- there'd be no way to do it.

The new switch has a black wire, a blue wire, a white wire and a green wire.

I've now got:
1) the black wire connected to the two black wires in the box
2) the blue wire connected to the single black wire,
(my initial install had this configuration reversed and the LEDs didn't come on, so I switched them)

3) following the instruction sheet that came with the switch, the white wire from the switch connected to the two in the box.

There's nothing in the box to connect the green wire to.

Could the white wires be the source of the problem here? As I say, the LEDs on the switch light up, so something's going on in there. But might I have set it up so the electricity runs through the switch and then right away again without heading off to power the fan?

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One connected to a single black wire in the box. The other connected to a pair of black wires.
To me that says that there is 3 black wires


Also in the box were two white wires

If you have 3 black wires you should have 3 white wires.

Yes -- three white wires in all.

Suggest that you eliminate the possibility of a defective switch by connecting all black wires together and connecting all white wires together with wire nuts. Keep track of the black wire that goes to the fan (the single black). If the fan is not damage it should run. If it runs then reinstall the switch. If the fan runs after reinstalling the switch the cause would be a poor connection. If the fan does not run replace the switch.

It would be very useful to us to be able to see the wiring you are speaking of.

Would you be kind enough to take some pics of both the wiring in the switch box and at the fan.

You may have been looking at nothing more than a switch loop configuration (one black wire from the supply in the ceiling to the switch and one black wire back to the fixture.

The new switch has a black wire, a blue wire, a white wire and a green wire.

This is odd. It somewhat suggests tat the switch may require a neutral. Is it an electronic timer of sorts? Model # of the switch?

The way you described the original wiring suggests that power is fed to the box and then the fan.

So the two tests seem resonable:

1. Connect all whites together and all blacks together and see if it works.

2. Use an extension cord to the fan and see if it works.

"The new switch has a black wire, a blue wire, a white wire and a green wire." never seen a switch which had a white and a green. We need serial numbers, brand name to check this out. This is not a standard residential switch from what you tell us. BTW, switches do not have wires, they have screws. What color screws are actually on the switch?

This morning I tried disconnecting the new switch's white wire from the three white wires in the box. The fan still doesn't work and the LEDs in the switch no longer light up. So that was a step backward and all I had time to try.

I'm at work and don't have the switch in front of me, but I believe it's this one: 6215M-I > Timer Switches > Commercial Grade > Lighting Controls (Box Mounted) > All Leviton Products from Leviton Electrical and Electronic Products (http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?item=6533&section=10834&minisite=10026)

I'll take pix but they'll have to wait till the weekend. My son sleeps in the next room and I can't bang around too much in there after getting home.

The whole set-up does appear pretty simple, though, which is why it's all such a pain: two black wires together in the box, one black wire on its own, and three white wires together.

ballengerb1: No screws on the switch itself, other than the ones that hold it to the box when it's working.

Only the wires: the black, blue and white ones emerging from a close group of three holes in the back, and the green one coming from a hole slightly separated from the other three.

The replacement switch, is it rated OK for use with a fan motor?

Try connecting all three black wires together and all three white wires together (keep track of which black wire WAS single). Then cut the power back on. Does the fan run?

The instruction slip specifically lists exhaust fans and attic fans as a suitable purpose for the switch. (Mind you, the slip with the 5-amp switch said the same thing.)

Haven't tried wiring it all up without a switch in the way. That'll have to wait till Saturday morning.

To add to the above good advice, ground is ground, Neutral is for LED's and Electronics(Rectifier built inside). Black is likely line and blue likely load. Jump the connections that go to the switch to verify fan operation, once working, connect black to line and blue to load/fan(verify colors with your instructions).

The switch you linked in post 10 is rated 20 amp

ballengerb1: Yes.

The old original switch, which I didn't bother to check before I bought the first replacement, was rated for 20 amps. I replaced it with a 5-amp, which understandably died but which showed signs of sending (inadequate) current to the fan before it conked out.

Now I'm struggling with a new 20-amp switch whose LEDs light up but that doesn't seem to send power to the fan.

The next step is, as several people have helpfully suggested, to connect the wires in the box without a switch and see whether the fan runs. But just because of my household schedule — when I work and when the 10-month-old sleeps — I can't realistically do that till Saturday.

Unless it is a whole house fan, I doubt the fan itself draws more than 5 amps. You can always check with an amp meter.

ceilingfanrepair: Interesting point. As far as I know, the switch doesn't control anything except the fan there in the bathroom, and clearly the 5-amp switch wasn't up to the job. The fan isn't a whole-house fan but it is pretty powerful. Definitely stronger than other bathroom fans I've ever encountered.

But there is the question of why there are three black wires and three white wires in the box instead of just two of each.

The other electrical applications in the room are an overhead light (on its own switch) and a two-plug outlet, which works regardless of whether the switches are on or off.

Why three cables?

One cable (one black and one white wire) brings power to the switch box. Another cable takes power to the next outlet or device. The third cable takes power (through the switch) to the fan.

I am questioning whether the problem is that the 5 amp switch wasn't up for the job. If it wasn't, it may not have been because of the amperage rating.

New intel: I popped the cover off the fan and plugged it into an extension cord, and the fan doesn't run. The extension cord, to be extra-sure, does power, e.g. the vacuum cleaner I used to suck some of the accumulated dust and gunk off the fan.

There's some blackening on the housing above the motor, too, although to be fair that could have been there for 20 years, since I haven't been in there since we bought the house a couple of years ago. But that's some pretty strong circumstantial evidence that the fan motor is the problem, not the new switch.

So I'm off to the hardware store to invest in a new fan motor. Will advise.

But in the meantime: Any idea how putting in an inadequate switch could have blown the fan motor?

That switch likely had nothing to do with the motor blowing. A 20 amp swiycth delivers the same voltage a 5 amp switch sends. Either way 120 volts got to the fan and it blew, unrelated to the swicth that sent the power. You will probably not find a fan motor at the hardware store. I'd replace the whole unit with a Broan or Nutone and be done with it. They frequently come out of the box with their own switch included. Whatever you eventually buy just make sure the switch, breaker and wire all match and can carry what the fan reuires. A fan/heater/light usually draw near 20 amps and needs #10 wire and a 20 amp breaker, dedicated

If you have about $150, Nutone/Broan make a .3 Sone(Super Quiet) Exhaust fan, can't hear them if vented properly, larger duct.

$60 later and a bit of a struggle with the housing later, I've got a working fan on a working fancy switch.

How the new switch fried the old fan (it still smells faintly of burned plastic or rubber, now that I've taken it out and gotten a close look at it), I guess we'll never know.

A switch with bad contacts introduces a resistance. If it's not enough where the fan creates an inductive reactance which will be much higher than the resistance of the fan, the fan windings could overheat.

If you take the fan apart you may or may not find evednce of that. Increased temp of the winding could result in shorted windings.

Thanks, experts, for all your volunteer help.

But in the meantime: Any idea how putting in an inadequate switch could have blown the fan motor?

Yes, if it was a switch not designed for use with motors.