Three-way switch tripping breaker
I have a three-way switch controlling a couple of lights. Power enters the first switch box, from there 12/3 goes to the second switch, where the feeds to the lights also are. As far as I can tell everything is wired correctly (I’ve been using the same wiring diagram for these for about 10 years). When the circuit is hot, the second switch will turn the lights on and off, but the first switch throws the breaker.
There’s a bit of complexity to this whole thing. The first switch is in one building and the second is in another, with UF and j-boxes connecting the two. All metal boxes. The main service is in one building and a subpanel is in the other… etc. Not easy to describe all of the circumstances but I’m wondering if this sounds like an easy one to to any of you electro-magicians.
Replies
History? Did it ever work, or is this newly wired?
It's the last bit of electrical hookup for my new shop. The wire has been in place a year or so but I just added the fixtures and switches.
It sounds like you miswired somehow, but I can't quite envision how you might have done it.
One thing to be wary of is assuming that the switches work "as expected". The common terminal should be a different color -- it's not always obvious from the terminal placement which is common.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
The switches are identical. One terminal is brown, and it's generally across from the ground terminal. That's the common AFAIK. There are two more, on opposite sides, that are brass.
I do wonder if one could be faulty. Rarely if ever had that...
Edited 12/6/2008 9:23 pm by davidmeiland
A faulty switch won't trip the breaker, the common is hot, and the travelers are hot, there is a short somewhere.
You sure you didn't get the wrong wire on the ground terminal? Could it be that wires are touching?
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Ohm out the fixtures, maybe there is a short in them, wire pinched etc.
In your case, the white wire should not be on any of the switch terminals. It should run continuously (wire nutted in the boxes) to the lights.
Is that what you did??
Are you positive your switches are indeed 3-way switches not plain vanilla switches? Sounds to me like sw #1 might be wired so that one of the hot travelers is accidentally connected to ground.
If there was a short in one of the fixtures, wouldn’t it trip the breaker right away. It is possible to turn the lights on and off with the second switch, as long as the first switch is in the position that does not trip the breaker.
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The ground terminals only have ground wires connected. No mistake there.
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The neutral runs to the fixtures only. No white connected to either switch.
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The switches are definitely three ways. Four terminals on each… one red wire, two black wires, one ground.
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I don’t think it matters, power gets to the first switch after first feeding a plug and another light that’s on a single pole switch.
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I’m not as sure about the fact that there are two buildings and two panels. The main panel provides the power for this switching setup. Once in the second building there is no connection at all between this switching setup and any of the other wiring in the second building. No other circuits or wires in the same box, etc.
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Tomorrow AM I will get out my tester and make sure there are no shorts. It seems like that’s what it must be. I’ve had a few situations with metal boxes where a conductor is shorted to the box and therefore to ground. Stuff like that doesn’t show up in plastic boxes.
Well, if it works like that, I think one of the travelers is shorted.
I'm thinkin' one shorted traveller as well.
When the second switch is powered by the good traveller it works fine - when the first switch tries to change traveller feed to the second , it shorts.
Think I'd shut down power, disconnect travellers, and check continuity to ground and neutral.
It could be that you have an out-of-the-box defect, either a bad switch or a short in the cable.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
As DanH and MHole said, your problem is most likely a short in one of the travelers. From your description of the wiring, the problem may be in one of the junction boxes.
Pull the first switch out of the box and check which traveler is hot when it is in the "good" position. Then you know that the other traveler is the shorted one. Check that one out at the j-boxes to see if there is an obvious problem. If connections are good, try disconnecting that traveler connection at the first j-box and then see if the first switch trips the breaker. If not, re-connect the traveler and disconnect at the second splice point and see if it shorts then. If it does, the problem is in the wire segment you just re-connected. If not, it's in the last segment.
It's all fixed, and I got off REAL easy on this one. There are three pieces of romex that make up the run between the switches. There is a 7' piece of 12/3 that goes from the first switch to a j-box directly under the floor. Then, there is a 75' piece of 12/3 UF that goes from that j-box underground and surfaces in another j-box in a utility area of the other building. From there, another 25' of 12/3 runs thru the walls to the second switch.
Only the 7' piece of romex was accessible and easily replaceable. That's the one that had a problem. I removed both switches and both splices and found out that the black wire in that short piece was shorted to ground, somewhere in its length. A little later I will do an autopsy on it and see if there's an obvious manufacturing defect. I very much doubt I crimped it with a staple or a romex clamp, since all of the jacket is intact and looks good.
If it had been the UF piece I actually have a BACKUP piece of 12/2 UF that I could have pressed into service. If it had been the 25' piece of romex I woulda been screwed and glued because it's insulated, rocked, painted, and trimmed out.
Thanks to all.
Odds are fairly good that when you open it up you'll find a manufacturing splice in the black wire. The section was supposed to be cut out on the manufacturing line, but it was missed for some reason.
Let us know what you find.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
I took off the entire jacket and could not find anything on any of the conductors. I didn't snip any of the wire off while demo'ing it so I was able to look at my original stripped ends and everything in between. Nothing. It remains a mystery. I want to stress that I completely removed the switches and splices and pulled all of the conductors out of the boxes, so there was absolutely minimal chance of any conductor somehow touching the box.
Look carefully at the black insulation for a "skinned" area or split. Flex the wire every few inches to make a split more obvious.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
Does the second switch work no matter which way the first switch is set, or does the circuit blow every time the first switch is in, say, the down position?
If so, get out the ohm meter and test your 3-conductor to make sure you don't have a grounded leg. For example, you may have pinched one of the hots with the box clamp, grounding it and producing a short when that leg is used.
Mike Hennessy
Pittsburgh, PA
Edit: After I posted, I saw you already fixed it. Never mind.
Edited 12/8/2008 7:54 am ET by MikeHennessy