How to locate a disconnect in electrical wiring?

Question

Disclaimer: grasping for straws here, fully aware that an easy solution is unlikely and I may end up having to retrace the wires which will involve opening walls.

We recently moved into a house built in mid-70's, did moderate renovation on the upper floor: replaced carpet with hardwood, replaced doors and trim. I hired a contractor to do the painting, since it would be too much to handle myself (doors, trim, closet doors, walls, ceilings...) in 4 bedrooms and a staircase. When the crew finished a week later, there is no power in one corner of the house (includes master bedroom, the adjacent bathroom, and a walk-in closet). There was power when they started and for several days into the job.

Flipping circuit breakers did not help.

Now for the details. There were some ceiling lights that were removed by the contractors. Nothing looks wrong there, just the three wires: black, white, and ground. There used to be a fold-out wall mounted ironing board built into the wall, which had a built-in electrical outlet in it for connecting the iron. This was removed by me, leaving approximately 1' by 4' hole in the wall, studs exposed. I pulled the wire back through the hole drilled in the stud, terminated the exposed ends, and packed it neatly behind the stud. Part of the job spec for the contractor was to drywall the opening, sand and paint. When they started last week, there was still power. The switches were operational, and the lights would come on. I recall having to go upstairs to turn the light off every night after they finished work. They would just leave the lights on. Last time I remember having to do that was Friday. Then things get a bit fuzzy. On Monday or Tuesday they removed the ceiling light in master bedroom and patched the opening in the wall around the same time. The bathroom was off limits because it was in the sealed-off area adjacent to master bedroom, so I could not test there, and the light fixture in MB was gone, so obviously no light there. They also fixed water damaged corner in the ceiling of the walk-in closet around the same time, another area where wires could be disturbed.

Later last night, after I did the walk-thru and paid the remaining balance, I noticed there was no power in that corner of the house. I contacted the contractor, who was understanding, but said none of his guys could remember doing anything that would cause this.

I am weighing my options. I tested electrical outlets and switches and confirmed there is no voltage there. The working hypothesis is that a cable is disconnected or severed somewhere. The trick is to find this spot. I do have the original blueprint for the house which should include the circuit diagram. But I am certain that it does not reflect the more recent changes introduced as a result of patchwork of remodeling jobs over the years.

It is tempting to open the drywalled area to see if the problem is there. But if I am wrong in my suspicion, I get a hole in the wall and one potential spot eliminated, with tens of linear feet of wire still hidden. Intuitively, the solution should be to retrace the cable, find the last spot with voltage before the problem area, and look there. At least some of the cables run in the ceiling, which can be accessed through the attic, if I were to dig up layers of insulation to expose them (not something I am looking forward to doing). Another idea is to use an in-wall wire tracer to avoid excavating fiberglass insulation in the attic. What other things could I try before I hack that wall open?

Update 1

Later that day, after work. Double checked two lights in other bedrooms that I had previously installed and found everything to be in order. Started testing outlets and switches with a tester (I have a fancy Hioki one, measures everything), confirmed no voltage (nothing new here). Then started testing for shorts. The second outlet I measured had a short! The outlet was right under the spot that was drywalled before. I unscrewed it and pulled it out, still a short. I removed the receptacle and checked it - no short. I checked the cables - still a short. There was a juncture of 3 cables. One that used to power the iron (that I left in the wall, it was marked with a piece of masking tape that had 'IRON' written on it). And two more cables, thick round black 4-wire one, and a 3-wire 14 or 12 gauge flat white cable. The whites and blacks were connected, three each. There was a short. I disconnected all and found that the flat white cable (but not the one that was labelled 'IRON') still had a short between white and black. I marked the ends with pieces of electrical tape. That's when I decided to open the wall. I thought, it must be there. I don't know what I was expecting to see there, maybe a screw put through a cable. Maybe damaged insulation... When I opened the wall everything looked normal. I pulled out and got rid of the piece of cable labelled 'IRON' (it was not connected to anything by then). I re-tested the wires that had a short and found the short was no longer there! Mind you, I checked and re-checked many times. I concluded that was an intermittent short activated by moving the cable. I went downstairs and flipped the circuit breaker to ON. That's another strange thing - the circuit breaker never tripped. I was expecting to measure 120V in one of the two remaining cables, the flat white one or the round black. Nothing. I thought, maybe the cable is damaged in such a way as to have a short while also having internal disconnect. I cut about 2' of it from the outlet (that part seemed to have some scuffs on the insulation) and opened it with drywall knife. No damage. Black, white, paper-wrapped copper ground... Everything looks intact, no hint of damage.

Here's what does not add up:

• The short should have caused the breaker to trip. This did not happen.
• There is no short now. Flipping the breaker does nothing. Still no power.

Some unlikely hypotheses, however crazy:

• Is it possible that part of the circuit is not plugged through the breaker?
• Is it possible that current through the short melted 12-gauge copper wire, turning it into a fuse, so now there is a true disconnect?
• Is it possible that there is another circuit breaker or a fuse box unknown to me?

Is it time to get that wire tracer and climb the attic?

Update 2

Two days later. I might be onto something! Found a GFCI outlet hidden behind a cabinet under the sink, in close proximity to the area where I opened the wall. I had no idea there was one. I measure 125V on the terminals, but pushing R or T buttons does nothing (I am used to GFCI outlets making a "click" and and shutting off power, but this may be an older/malfunctioning one). It is partially covered by plywood, which I am going to cut out, so I can get better access to it. The presence of GFCI outlet might explain why the breaker did not trip.

Update 3, post mortem

The root cause was faulty GFCI outlet, which was discovered much later in the process than I would have preferred. Apparently, the painters shorted the circuit while removing ceiling lights from a live wire, which caused the GFCI outlet to trip, which in turn happened to be malfunctioning. Additionally, the GFCI outlet was mis-wired: the entire bedroom and walk-in closet were wired into the "load" circuit. Since there is no reason to have GFCI protection on outlets and fixtures with no conceivable access to water, I rewired them straight into the "line" circuit (a circuit breaker is sufficient to guard against shorts there).

I ended up with an open wall which will require some work to close, but I am happy I ended up opening it for two reasons:

• This allowed me to remove live wire that I left in the wall due to negligence and inexperience.
• The painters did an extremely poor job closing the wall. They just put some kind of adhesive tape over the seams and spackled over it. This produced a very uneven and conspicuous finish. Not to mention, it lacked rigidity. Sorry, I am going on a tangent, but when I do walls myself, I fill gaps with mud, tape over, wait to dry, spackle again, sand, paint. Then it's solid. The use of adhesive tape inside a wall seems plain wrong, unless it is a new painter's trick that I missed.

I extended the wire that I cut while troubleshooting (on suspicion of having a short in it), using a device they sell at Home Depot that is advertised as electrical box removal kit. Picture attached. I feel comfortable leaving that in the wall (assume they would not be selling it otherwise).

Answer 1

In my experience, it's more likely that a problem is in a connection somewhere than an outright severed wire.

Start by identifying which outlets have power or not. A simple plug-in tester is an easy way to do this (as well as identify some common ways to miswire).

Next, take the covers off (but don't remove the outlets) and use a non-contact voltage meter to check if there is any power to the wires.

I'm actually hesitant to post this picture, but I couldn't find one without an idiot holding a live outlet in their hand. Don't do this. This person is one tiny mistake away from electrocuting themselves.

Hopefully what you'll find is that power eventually comes into one but isn't connected correctly, and that it continues on from there.

Check light switches and fixtures as well.

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Also worth nothing: if your non-contact tester beeps, but your plugin tester doesn't show power, this is a good indication there is a problem with the neutral.

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After this, if you can't identify any power in a non-working outlet, you can check working ones. You're looking specifically for a disconnect in a wire that is feeding the rest of the circuit, so logically the ones nearest the dead circuits are most likely to be doing that.

It's also possible the connections are done using pigtails, and there can still be a bad or miswired connection so it's worth checking this too:

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After you've exhausted all of this, it's time to start thinking about hidden junctions and broken wires. If you know of a hidden junction, that's not only illegal but highly likely to have a problem.

You probably will have a good idea now of which wires go where, so if you can identify power on one receptacle that is likely feeding to a broken one, then you can start trying to trace the wire through the wall (and this is when you'll start opening drywall or climbing through the attic).

Your non-contact tester (especially if you have one with a sensitivity adjustment) MAY be able to trace through the wall, but it's actually quite difficult in my experience. Likewise stud detectors often have voltage detection, and this might be able to trace the wire, but again it's just not that accurate.

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One thing that might also help to identify a broken wire is to check for continuity. Turn the power off, and use a multimeter in continuity (Ω) mode. Test between receptacles: neutral to neutral, ground to ground and hot to hot. If you get continuity on one or two of them, it will at least tell you that there is a partial connection and you're looking for a bad connection or broken wire. Tip: use an extension cord plugged in to one receptacle to test two that are farther apart than your multimeter leads.

Since in your case you said it was working and there were no changes that should cause it to stop, I'm not sure this will really provide you any useful information, but thought it's worth putting out there.

Answer 2

If you are certain it is a severed wire (versus a disconnected one), a capacitance meter could tell you where the break is. They used to be pricey, but now can be had for under $10.

Measure the capacitance of a measured length of the same wire as is in the walls. Then measure the capacitance of your in-wall wiring. The proportion between the two tells you how long the in-wall wire is.

Be absolutely certain that power is off when you do this! 120 VAC will destroy your capacitance meter!