Difference between a motor and a light on a 3-way switch? (1 Viewer)

[EricG]

I'm trying to debug a problematic 3-way switch in the addition I'm building. It controls a duct blower for a duct that runs from above the fireplace on the 1st floor, to the bedroom on the 2nd floor.

The setup is such that the power comes into one box, the wires go through the fan, then to the 2nd box. I'm working off this diagram:

How To Install a 3-way Switch Option #3 :: Home Improvement Web

When I first had it set up, the switches would only work if the other switch was in the "on" position - kind of like the switches were wired in series. I figured out that I had the black wires reversed on the switch on the left side of the diagram. I've checked the rest of the wiring at both switches and the load (fan) and it appears to be correct WRT the linked diagram.

Now, I can turn the unit on/off with the left switch, but the right switch trips the breaker when I throw it?!?!

More info - this is on an arc-fault breaker - I'm going to swap it for a regular and see if that matters. And the fan has a largish capacitor in it.

Any ideas?

 

[EricG]

Just swapped out the arcfault for a regular breaker and it's still tripping. Took longer though - I heard the motor start a bit before it tripped.

 

[Toyo FJ40]

Are you using 3 way switches? I ask this because you said the other switch has to be in the on position and 3 way switches have no on position.

Motors shouldn't make any difference

Kevin

 

[EricG]

I think I figured it out. My hot wire coming into the left hand switch has continuity to ground - meaning it's really the neutral and they got swapped somewhere. Time to take apart some outlets - fxxx fxxx fxxx

Wait - no, that can't be right. I've unwired both switches to make sure I had the hot/load/travelers identified correctly. What I checked:

- When I turned the breaker back on, the black wire that was attached to the black screw (common) on left switch had voltage.
Conclusion - hot wire ID'd correctly

- Both travelers were continuous and had no continuity to ground or each other.
Conclusion - Wiring not damaged or screwed up in the fixture. Travelers ID's correctly

- Continuity from wire that was on the black screw on right switch has continuity to ground (ie - through the load).
Conclusion - Load wire ID'd correctly.

So why do I have continuity to ground on the hot wire on the left switch??? That can't be, or the breaker would never set to begin with. Ok, back to look at it again.

 

[EricG]

Are you using 3 way switches? I ask this because you said the other switch has to be in the on position and 3 way switches have no on position.

Kevin

Yes, they are 3-way switches. What I meant was that it only worked if the opposite switch was in the right position.

 

[Toyo FJ40]

Yeah it sounds like a short somewhere. Does it trip when you throw the switch or when you turn on the power?
I would disconnect the fan and see it it still trips.

Kevin

 

[EricG]

Yeah it sounds like a short somewhere. Does it trip when you throw the switch or when you turn on the power?
I would disconnect the fan and see it it still trips.

Kevin

The fan operates when the left switch is thrown.
The breaker trips when the right switch is thrown, and the fan was not already operating.

 

[EricG]

Edit - nevermind about the continuity from hot to ground. Other stuff was plugged into the circuit, so was measuring the resistance of the other loads on the circuit. With everything unplugged, there is no continuity.

 

[Toyo FJ40]

One of you wires from the right switch has to be going to a neutral at the fan. If you using the white wire as one of the switched legs then make sure it's not tied into the neutral at the fan. There should be no neutrals in the right box or coming from the right box at the fan.


Kevin

 

[EricG]

One of you wires from the right switch has to be going to a neutral at the fan. If you using the white wire as one of the switched legs then make sure it's not tied into the neutral at the fan. There should be no neutrals in the right box or coming from the right box at the fan.

Kevin

Absolutely right - I have the romex confused where it goes into the fixture. And I was sure of that because I did it when the walls were open and I could trace the wires.

Thanks - off to fix it.

 

[fledglingme]

it sounds like you've got two problems going at once. as kevin suggested, disconnet the fan motor from the circut. i suspect it's bad. and leave it that way untill you get the switching going correctly. use a voltage meter to check for 110volts at the fan supply. checking contunity will only have you chaseing all over the place. the switches sound like they are wired into the circut incorrectly. on three way switches they'r three connection points-errr 4 if you want to count the ground. but actual current carrying connections....three. two will be the same color, and the traveler a different color.