Fixing a shorted circuit?

[Wade Lippman]

http://www.diychatroom.com/images/icons/icon1.gif Fixing a shorted circuit?
I moved a year ago, but haven't been able to sell my house. Friday my realtor told me a circuit in the bathroom was out. I went over yesterday assuming it was a GFCI, but it wasn't even that circuit.

One breaker is tripped. Resetting it, it trips immediately. Presumably either the breaker is defective or there is a short. Since the circuit hasn't been used in a year, it is hard to see how it could go bad.

On the circuit there are:


6 outlets in the master bedroom
Two lights and a fan in the bathroom, controlled by three switches in one box
Two outside lights, controlled from three boxes.

It is one side of a multiwire circuit, but I am not sure if that is relevant.

My plan is to disconnect everything, one switch/outlet at a time, and see if/when the short goes away. (unfortunately I have no idea how the circuit runs, which would have made it easier)

Any alternative to that?

Two questions:
1) Could the breaker (a 10 year old duplex 15a) be defective so as to trip even when there is no load? If so, I guess changing breakers is the first thing to do; if not, I won't bother.
2) Since the breaker still trips with all the switches off, does that establish that the short is not in the lights? (seems to me that if the switch is off, a short in the light fixture wouldn't matter as no power gets to it anyhow; which would be nice because the outdoor light would be my primary suspects, and I can't really get at them.)

[Brian Elfert]

I had a brand new breaker that would trip immediately even with no wire hooked up. If you suspect the breaker I would turn it off, disconnect the wire, and then see if it still trips right away.

[Jim Matthews]

You need a "Fox and Hound" rig to trace this sort of thing on your own.

It's better done with help and a walkie-talkie set.
http://www.amazon.com/Triplett-9650-Breaker-Sniff-It-Digital/dp/B0002THPOS/ref=pd_sim_indust_2

I also recommend a plug in outlet tester for home users, it has a set of lights for quick diagnostics.

In my experience, swapping the simplest part (the breaker) would be a starting point.
If the new breaker holds, and the outlets function - you're done.

If not, start investigating to greater depth.
It's really rare for eletrical outlets to spontaneously fail - they typically degrade in contact with moisture, from mechanical insults (think things with teeth, eating insulation) or from drawing too much current and melting.

Like taking a test, answer the easiest questions first.

[Wade Lippman]

I had a brand new breaker that would trip immediately even with no wire hooked up. If you suspect the breaker I would turn it off, disconnect the wire, and then see if it still trips right away.

Why didn't I think of that? Will do.

[George Bokros]

Changing the breaker would be a cost you may not need to expend. You likely cannot take a breaker back once you install it, of course there is no way they would know you installed it, however electrical such as breakers may not be returnable under any circumstances.

I would test the existing breaker by disconnecting the wire from it and see if it still trips. If so replace it and you are done. I would doubt anything that is controlled by a switch would be causing the issue since the light or fan has no power if the switch is turned off. I would start at the switch or outlet closest to the breaker as I would think that is the first stop on the circuit and go from there.

You will likely know more as you open the boxes.

[Dan Hintz]

I can make it even easier for you... disconnect the wire from the breaker and check the continuity of the wire to ground. If it's shorted, you know it's not the breaker.

Keep the circuit disconnected form the breaker and make sure all of the switches are turned off. Take out all of the light bulbs and check there for a short between the line and neutral. If there's no short, you can ignore the wiring for the lights. Do the same with the electrical sockets. Narrow down which branch of the circuit has a short.

[Stephen Cherry]

I can make it even easier for you... disconnect the wire from the breaker and check the continuity of the wire to ground. If it's shorted, you know it's not the breaker.



Good advice, but you need to make sure that there is no inductive load (coil, motor, etc.) hooked up to the circuit. They will look pretty much like shorts.

You may be able to swap the wire to the breaker to go to another breaker, and see if it trips. Usually the 15 amp breakers are in groups, and you temporarily switch it with the next.

Super careful though. If you are the least bit uncomfortable, it's OK to get professional help.

[Dan Hintz]

I should have put the "make sure all switches are off" part at the beginning...

[Stephen Cherry]

I should have put the "make sure all switches are off" part at the beginning...

Dan, I throw that in because I have been professionally faked out by this sort of thing more than once. Also, using a digital volt meter on an ac circuit can be full of surprises. You sometimes get coupled voltages even on parts that are turned off. I guess that's why there are specialized testers for this sort of thing.

[David G Baker]

Check the outside lights and any outside plugs. If they are not sealed from moisture this can cause the short.

[Jim Koepke]

Make sure the power to the breaker box is off when messing around with the wiring.

There are many things I would do to troubleshoot such a case. I am reluctant to try and instruct someone in the methods of electrical trouble shooting without knowing how much they know about electrical systems.

My first order of business would be to turn off power then visually inspect and open all the boxes on the effected circuit. Look for evidence of problems like arcing or burnt smell. You may need to remove the items (plug sockets and switches) from the boxes to fully inspect. Depending on the code when the house was built, you may find a wire nut or other splice that has open up to expose bare wire.

My next step would be to use my ohm meter to see if the lowest point of resistance could be found. This requires a good meter with a low ohms range.

Often a bad breaker will feel different in its action than a good breaker. A weak breaker (bad) feels weak.

Other things to consider is if there was any work done on the home before this happened. Often a screw or nail is driven through a wire and could be the cause of your problem. If work was only done on one part of the house, this could narrow down the problem.

If your lights are properly wired, having the switch in the off position should remove them from the circuit.

You do mention that two lights are controlled from three boxes. If a lamp is controlled from two switches, then there may be power running through the lamp socket box at all times.

jtk

[Jim Koepke]

One more thought... Does the house have a door bell?

Is it working?

It is possible that the door bell is on the circuit and the transformer has gone bad.

jtk

[Mike Cutler]

Wade

Pulling the load side wires off the GFCI will only test 1/2 of the GFCI. Just replace it, they're cheap. If that doesn't do it you're into a troubleshooting exercise.
GFCI's have a notorious mortality rate. I installed one for our Microwave and about three weeks later it did the exact same thing. It wasn't a cheap big box one either. GFCI's fail.

[Lee Schierer]

http://www.diychatroom.com/images/icons/icon1.gif Fixing a shorted circuit?

On the circuit there are:


6 outlets in the master bedroom
Two lights and a fan in the bathroom, controlled by three switches in one box
Two outside lights, controlled from three boxes.

It is one side of a multiwire circuit, but I am not sure if that is relevant.



Is it just me or does this list of things on a single circuit seem to exceed code? I'm not sure what a multiwire circuit is, is but 6 outlets, 2 fans and four lights seems to be an overloaded branch circuit.

If I had to guess, I would say start by checking the two outside lights controlled from three boxes. It is very common for someone to replace a three or four way switch improperly since many people don't understand how the switch circuit is supposed to be wired and don't label the wires when they need to replace a failed switch..

[Kevin Bourque]

Check the outside lights and any outside plugs. If they are not sealed from moisture this can cause the short.

Ditto.

This is where I would start

[Wade Lippman]

I sorta fixed it.

Tested the breaker, it was fine.
I started disconnecting things to see how it affected the short; using a continuity tester.
I disconnected everything and there was still the short. Had to be in the wall. ARRGH
Then I realized there were 2 4way switches and only 1 3way. Has to be another 3way.
I finally found it in the basement. In 20 years, it has never been used; but when I disconnected it the short went away.
I put in another switch and all is well.

I say I sorta fixed it because the switch tests out okay; no shorts in either position. So, I am not really sure why it stopped working after 20 year, and why it works now. All I can think is that the ground was contacting a screw for one of the travelers that was harmless up until now if the position of the unused switch sent current down the other traveler. Someone at an opening house must have flicked it, shorting the circuit to ground. But I didn't see that when I took the cover off.

I was much afraid it was in the outside lights, since that is the likely place, and I don't have a ladder big enough to reach them. But if the short is still there with three switches removed, it can't very well be the light.


Let's hope I sell the house before it reoccurs. Talked to the realtor today, as it is the one year anniversary. She sells 50 houses a year and has never had one last this long; average is 2 weeks. But she says she has trouble believing the price is too high; it seems to be the best bargain in the county. But at least the short is gone.

[Ken Fitzgerald]

Wade,

Switches go bad! Glad you found it.

[David C. Roseman]

Great sleuthing, Wade. Love the convenience of 3-way and 4-way switches. But once everything is closed in, they can be a real challenge to trouble shoot because they can be wired in different ways relative to the loads, all perfectly correct. Even more of a challenge when the installer doesn't bother (or know) to mark any white wires used as hot travelers. :)

David

[Chris Padilla]

An unused switch can short over time. Simply moving it can keep it in working order for a long time. Gunk, dust, etc. can get inside and build up plus heating and cooling of the current flowing through it can cause issue if the switch never moves. Anyway, nice that you found it.

I had an issue in my bathroom and one bedroom. I finally figured out that one of my attic fans shorted because as soon as I unplugged it, all was well. It took some time to even realize the fans were on this circuit. Now I have solar attic fans...only needs the sun. :)

[Steve Baumgartner]

Great sleuthing, Wade. Love the convenience of 3-way and 4-way switches. But once everything is closed in, they can be a real challenge to trouble shoot because they can be wired in different ways relative to the loads, all perfectly correct. Even more of a challenge when the installer doesn't bother (or know) to mark any white wires used as hot travelers. :)

David

An anecdote almost on point: when my parents bought a house a number of years ago, there was one switch that apparently worked nothing. I opened up the box and found that it was a three-way but it was disconnected (wires capped off in the box). Suspecting from its location that it was meant as a second switch for the lights in the living room, I reconnected it. As soon as I threw the switch, the breaker popped! But my meter showed no shorts. To make a long story short (pun intended) after a long search I tracked the problem down to an outlet at which the original installer had crossed the black and white wires entering and leaving the box! They encountered the breaker blow, but couldn't figure out the cause, so they just disconnected the switch! Uncrossed the connections and everything worked!

Steve