Troubleshooting a dead AC circuit

solar_dave · June 2014

Late yesterday the Master bedroom circuit died in our house. I did the obligatory thing and looked for a tripped breaker. I cycled every single (120V) breaker in the panel, No such luck.

I was surprised on everything wired on that line, all the bedroom outlets plus ceiling fan and light, 2 patio ceiling fans and lights, 2 dual outdoor flood light fixtures. The flood lights and patio lighting & fans are all on dual switches so that either exit door can fire them up. Seems like a lot of stuff, in 1997 the NEC must have been pretty lax or the inspector missed it.

So I am going to pull the panel cover off first thing this morning now we have some light to work with and make sure that all single (120V) breakers are outputting power.
Assuming they are all OK what would the next steps be? How do you determine the first landing spot for the circuit?
Makes me a bit nervous to think the failure may be in a wall someplace!

Cariboocoot · June 2014

Re: Troubleshooting a dead AC circuit

There's actually a circuit tester for this sort of thing. It consists of a transmitter you plug in to an outlet and a receiver that you test against wires to see which are connected to that outlet. You should get one. http://www.homedepot.ca/product/digital-circuit-breaker-finder/814359

You are in for some no-fun. It sounds like the contractor did a lot of daisy-chain connections, possibly in violation of code considering how many things appear to be on one circuit. You will need to identify the offending breaker (which should have been labeled) and then everything on that circuit. You are then going to have to pull every outlet and look to see where power stops. If it is a neutral wire that is broken you may have a lot of trouble locating the wire in question.

Quite likely the cheapskate who wired it used those lousy push-in wire connectors on the duplexes and one of them has failed. The NEC should have never have allowed that sort of connection; they are crap. Also suspect any GFCI outlets on the line as they are known to fail and prevent series connection to other outlets ganged to their "protection".

Finally you may end up tearing out all the wallboard through the whole house, stripping out all the stupid, wrong wiring, and replacing it as it should have been done to begin with.

Anecdote: one of the strangest wiring mix-ups I ever encountered was a circuit that had been looped back to the main service panel and connected to another breaker on the same line. You had to switch off two breakers to kill the circuit. This also made it dangerous as there could have been 30 Amps pulled on that loop of 14 AWG wire.

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Yeah thanks Coot, I just checked all the breakers and all the neutrals in the main panel, Everything there seems copacetic. All breakers providing 123V and all wires torqued down OK it seems, checked all the neutrals as well. Not really labeled, generic "general lighting & receptacles".

Yes I pulled one outlet, the push-ins are in use

Yeah I found a nasty "splice" in that box, It is also the fan for the gas fireplace blower. I remember when we bought the house new in 1997 they missed wiring that item in. Obviously that is where they tapped for the needed power. I bet they had some clean up boy do that work by the looks of it.

Ugh no drywall rip outs I hope. Every thing should be accessible via the attic, remember these slab houses keep the wiring above except where they run the wall horizontally.

BTW my local home depot has one of those in stock.

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Coot I just picked one of those up at the home depot. Glad I didn't open it as it requires the circuit to be hot to use it.

Got any other ideas to test the circuit? I guess I could just start looking for dead outlets and open them up and the associated switches that seem dead as well.

What I was hoping for was a battery powered transmitter I could back track the line.

Cariboocoot · June 2014

Re: Troubleshooting a dead AC circuit

Hmm. Mine doesn't require a live circuit. Too old and no longer made I guess. Not sure where it is otherwise I'd dig it out and see.

Okay you're down to hard work.
How many outlets/fixtures are dead with everything on?
New test procedure: long extension cord from an active socket that you can check the dead one against for neutral and hot: if dead socket reads Voltage from hot to the extended neutral then it is a neutral wire gone. If dead socket reads Voltage from neutral to the extended hot then it is a hot wire gone. If neither works they're both broken and you've got a BIG problem.

Now the hard part: continuity testing on long wires. You're trying to find a known live outlet that shares hot and neutral with the dead one. Only one conductor is going to be good, as per the test above. Trouble is; all neutrals are in common. If the hot is still good this is easy as you can shut off breakers and test for continuity from hot to hot. If the neutral is still good you have to disconnect neutral at the service panel for each circuit you check; you only want to read neutral from one outlet to another, not from one outlet to the neutral bus bar and every other neutral in the whole house!

Does that make sense?

I didn't say this would be easy, did I?

BB. · June 2014

Re: Troubleshooting a dead AC circuit

I was debugging several dead circuits at a church... Had to take out every outlet/open every box. Eventually found broken copper wire (nicked when stripped 60+ years ago, finally failed--Bad outlets to be replaced, poor connections, etc.).

Lucky all the bad stuff was in boxes accessible without having to cut the building wall up.

-Bill

Thom · June 2014

Re: Troubleshooting a dead AC circuit

I would use a battery powered voltage tester . The kind that beeps if power is present . Check for 120v every place u can. Determine which wire is at fault. The smaller hole in the outlet is the black or hot wire .Check with a multi meter from the black hot wire to ground to see if their is 120v to ground . Re wire all outlets using the screws . The push on holes in the outlets don't work for 12/2 wire so I guess it might b 14/2 wire

Thom

BB. · June 2014

Re: Troubleshooting a dead AC circuit

The simplest method I found... If debugging outlets--Figure out what outlets are on which breaker (turn on 1 breaker, then all outlets on that breaker, etc...). The bad outlets/lights you can now trace back to a single breaker or follow back the failed connections back to the good connection.

Another was to get a filament lamp (10-500 watts). And plug in/screw into the fixture... With power off and all other outlets/fixtures disconnected/removed, start measuring resistance--Frequently you will find that you have two outlets that "see" the lamp load--And you can figure out where the feed is coming for that isolated circuit.

-Bill

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Yeah I knew this was gonna be a bitch, I suspect it is the hot someplace as hot to ground shows nada on the outlet I think is the closest. I think the failure is one box closer to the main and finding it is the bitch.

Well my trusty electrician is only a call away and usually is extremely reasonable.

DanS26 · June 2014

Re: Troubleshooting a dead AC circuit

Dave, you or your electrician will find and correct this problem.

But after the fix you need to identify every single thing on every single circuit. Those little electrician notes in the panel are no good. You need a detailed circuit description attached to your panel. After you do that, there is no more quess work about your circuits. Yes, a little bit of work but it will help if this type of problem ever shows up again.

In your case a loose hot or neutral will probably show up again in another circuit since whoever wired your house probably used the same techniques throughout........and it is a matter of time until another problem shows up again.

zoneblue · June 2014

Re: Troubleshooting a dead AC circuit

9 times out of ten the problem will be at an existing intersection, juntion box, or outlet. And methodical inspection will usually turn something up. For the remainder, a chippy once put a cladding nail through a sub circuit wire and the contractor borrowed a time domain reflectometer to determine how far along the cable the fault lay. They are kinda pricy though.

mike95490 · June 2014

Re: Troubleshooting a dead AC circuit

"Fox & Hound" is a battery powered tester.

You may also have a GFI outlet, and the rest of the circuit is behind the GFI side.

Blackcherry04 · June 2014

Re: Troubleshooting a dead AC circuit

I'll second Mike's post and others, GFI's can be a pain where they are daisy chained. I once had a Refrigerator that was wired into one with a bunch of kitchen outlets , it didn't take long for me to get it off that circuit after I lost my food.

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Thanks guys all good suggestions. I am pretty sure it isn't a GFI issue.

We moved our fridge last year during the remodel, the line we wanted to use was a GFI daisy chain, the electrician that did the work removed the daisy chained outlets and replaced each outlet with its own GFI except for the fridge.

Thanks for the Fox and Hound suggestion.

verdigo · June 2014

Re: Troubleshooting a dead AC circuit

I once had a similar problem that turned out to be a fault on an outlet plug where the hot side of the plug has a little strip between the two plugs had broken and taken out the rest of the circuit. The upper pug on the same outlet was functioning but the lower was not. You could do a quick check of each outlet, upper and lower and maybe get lucky.

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Well I pulled a few more outlets and then called the electrician. He came right out today. There was a #14 wire bundle with 7 wires under a single wire-nut in the back of one switch outlet box, the loose one of course is the hot feed from the breaker panel. He replaced it with a little block where each wire has its own attachment. I asked if that passes code with 7 wires in one wire nut, he said up to 9 wires under that size nut but now eliminated. He had one of those fox & hound battery operated testers.

Thanks for all the feed back guys.

And DanS26, a great recommendation, I will work on a full map of the place.

DanS26 · June 2014

Re: Troubleshooting a dead AC circuit

Dave, here is a template of the circuit description I use. Notice that the the phase of each circuit is identified along with type of protection device.

Hope this helps.

Dan

Attachment not found.

inetdog · June 2014

Re: Troubleshooting a dead AC circuit

solar_dave wrote: »

I asked if that passes code with 7 wires in one wire nut, he said up to 9 wires under that size nut but now eliminated.

He has it right about the listing instructions for a particular size wire nut, but that assumes that you have prefect working conditions to line all 9 wires up exactly matched in length and then pre-twist them before screwing on the wire nut without anything moving out of place.
A permitted solution is not always the best one, nor even a good one.

Cariboocoot · June 2014

Re: Troubleshooting a dead AC circuit

inetdog wrote: »

He has it right about the listing instructions for a particular size wire nut, but that assumes that you have prefect working conditions to line all 9 wires up exactly matched in length and then pre-twist them before screwing on the wire nut without anything moving out of place.
A permitted solution is not always the best one, nor even a good one.

Yup; in the real world there's no wire nut gonna take nine wires.

What's odd is that one section of the NEC, if I recall correctly, limits the number of cables that can be joined in a junction box to four. Perhaps it's "four per inch of box" or something like that. I can't imagine cramming nine into a standard outlet box and getting the duplex in as well. Asking for trouble, that is. Makes you worry about the quality of the rest of the wiring job.

inetdog · June 2014

Re: Troubleshooting a dead AC circuit

Cariboocoot wrote: »

Yup; in the real world there's no wire nut gonna take nine wires.

What's odd is that one section of the NEC, if I recall correctly, limits the number of cables that can be joined in a junction box to four. Perhaps it's "four per inch of box" or something like that.

Actually, the NEC limits the number of wires in a box based on the cubic inch capacity of that box. And deducts volume for any devices (switches, receptacles, etc mounted in the box and even deducts for cable clamps that are on the inside of the box.

However there are some strange exceptions like not counting a wire which begins and ends in the same box (e.g. pigtails) and does not count ground (EGC) wires whether they are bare or insulated.
I don't think you would be allowed 9 wires in a standard depth 2" box though.

And, yes it does call into question the original "craftsman"'s skill and good judgement.

solar_dave · June 2014

Re: Troubleshooting a dead AC circuit

Cariboocoot wrote: »

Yup; in the real world there's no wire nut gonna take nine wires.

What's odd is that one section of the NEC, if I recall correctly, limits the number of cables that can be joined in a junction box to four. Perhaps it's "four per inch of box" or something like that. I can't imagine cramming nine into a standard outlet box and getting the duplex in as well. Asking for trouble, that is. Makes you worry about the quality of the rest of the wiring job.

3 gang switch box.

Troubleshooting a dead AC circuit

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