Something’s wrong.

“Hey, we’ve got two outlets that are out. I checked the fusebox, opened them up for loose cords or wires and everything seems legit. Any thoughts on what could knock them out?”

That’s funny.  Receptacles are supposed to work.  It’s amazing how often they just work, flawlessly.

The timing was weird because it was just after a rainstorm, so I thought maybe water had gotten into one of the junction boxes.  There had to be some kind of short or break somewhere.  If it was one, I’d figure it was a broken receptacle.  It had to be something fixable; if I couldn’t fix it, then what the hell was going on?

Tools on.  First, a circuit tester to see what’s loose, what’s wired…

We've got hot and ground ... and neutral mixed?
This isn’t a listed error.

Well, that’s just not right.  Red lights up only when hot is mixed with ground or neutral, and all three shouldn’t be lit for any reason.

This calls for more precision.  Let’s see what’s going on numerically.

At least three of these numbers are wrong.
At least three of these numbers are wrong.

LL is 95V, which isn’t within the right parameters.  BC Hydro will give you 120V, give or take a couple of percent, under as many circumstances as they can think of.  95V means that something’s in-line and consuming power.  How?  This got weird when the NG voltage was about 22V, and LG was 120V.

I called an electrician I know, Mike at Groove Electric, to see if he had any thoughts.  I figured it was water or critter ingress, somehow shorting juuust enough that the breaker wasn’t responding.  (It happens, that’s why the new code requires arc flash and ground fault protection.)  We thought along the same lines, hot touching something else, and some high-resistance thing doing the touching.

I checked in the air space, sort of like an attic but on the side, and saw an unlidded junction box, pointed up.  Case solved, so I went to Home Depot, picked up a lidded plastic enclosure, and went back the next day.  I also replaced the older receptacles with newer TR versions and plastic plates.  (I never trusted the metal ones.)

Now, I’m a bit of an arachnophobe, so I don’t like going into spaces full of spiders, but hey, I can deal with it, and house fires and kids without heat are worse than me dealing with some spiderwebs.  I crawled in, and found that the box I’d mentally convicted was dry as a bone.  A couple of cobwebs, but that wasn’t the culprit.  I found the junction box powering the receptacles, and this had to be the problem.

This is behind a chimney. So many insect nests and so many well fed spiders.
This is behind a chimney. So many insect nests and so many well fed spiders.

The top right is the source, which then feeds the round box.  The top right box splits to the bedroom receptacles.  The round orange box splits to the kitchen fan and lights.  (I thought the orange box was the source based on the cable age.)  So, disco on all the stuff going in, power up, and measure the voltage on the hot wires.  (Don’t try this at home; I am a professional.)  It read 120V, so whatever I disconnected was causing the problem.

It was the fan.  It was old, wired in backwards, and vented into the attic.  When the circuit was energized without the fan attached, everything was back to normal.  The solution was to just coil it back and leave the fan in place.  (Otherwise there’s a hole.  I guess I could have installed a ceiling cat, but that seemed a little silly.)

The DMM just had to find a place to rest.
The DMM just had to find a place to rest.

My guess is that the insulation in the fan coils was in rough shape and was slowly shorting out.  The coils would isolate the fault from the circuit, causing the breaker to stay active.  It slowly got worse until the receptacles failed one day.

I wonder how much longer it would have been before the fan caused a fire.  I’ll dissect it when it gets removed.  This afternoon I remember replacing a shaver outlet with a GFCI.  The house owner noticed that it was often warm; when I pulled it out, the insulation had started burning away.

Good times.

Published by



Magnus is a Professional Electrical Engineer from Victoria, BC. He's worked on projects ranging from new code for embedded radios to inspecting [redacted] government systems. He'll relax and unwind by teaching yoga or Cyclefit, or going out for a dive in the cold ocean.

Leave a Reply

Your email address will not be published. Required fields are marked *