So last Saturday I decided to test the GFCI outlet in my bathroom, as any good homeowner should at least once a year. For those who don't know, a GFCI (Ground Fault Circuit Interrupter) is an electrical safety device that automatically shuts off power when the circuit is shorted, often via human or water contact. That's why GFCI equipped outlets are typically installed in bathrooms and kitchens. Your typical GFCI outlet has a test button and a reset button. You test it by (gasp!) pressing the test button, which causes a short to trigger the interrupt circuitry. Then you push the reset button to restore power and go on your merry little way, secure in knowing that you can splash around in the bathtub with the hairdryer on all day (note: do not splash around in the bathtub with the hairdryer on all day, or even the tiniest tiny fraction of the day).

So anyway, I pressed the test button and the outlet tripped like it should. However, to my great dismay, the music in the other room also stopped. WTF?? I came to realize that my bathroom GFCI happened to be on the same circuit and upstream of the other bathroom plus half of 2 bedrooms. I'd just killed the computer in the office. The one that isn't on a UPS. When a GFCI is wired into an electrical circuit, it protects not only anything plugged into itself, but also every electrical device downstream in the circuit.

In a perfect world, this house would have no more than one room per circuit, but that's obviously not how it was wired. Phooey! I don't want my computers getting killed just because some bozo was aiming the shower head at the bathroom outlet for kicks (note: do not aim the shower head at the bathroom outlet for kicks, or for any other reason). Both rooms with computers have outlets on different circuits, but in both cases, those are on the opposite sides of the rooms. Do I run trip-hazard extension cord across each room to avoid the GFCI-protected circuit, or do I play bathroom roulette with my computers? Dang.

But that's not really what this post is about. It's about what happened when I pushed the reset button.

For about a half second, power came back on, then poof! Back off again. WTF?? I went outside to check the circuit breaker at the service panel. It was not tripped, so apparently it wasn't a simple short circuit. I flipped it off and back on, just to be sure. Still no power.

I was determined to solve this problem myself, as I have no trouble doing minor electrical work. I have the theoretical background on electricity and circuits from my under-utilized physics degree, and I've carefully studied several books on wiring in the last year and a half. I've done a number of minor projects around the house (fixing outlets, adding a GFCI on another circuit, rewiring special outlets so I could control my Christmas lights remotely via computer this year, etc). An electrician has orders of magnitude more practical experience than I, but I feel confident to do easy wiring jobs. This one shouldn't be a problem!

I bought a bunch of cool testing equipment from Home Depot. After a fairly long process of elimination, I unwired the GFCI outlet and hooked up a plain old simple outlet to the circuit. Everything downstream was disconnected, so it was literally one simple outlet on this circuit. My snazzy new voltmeter showed 120 volts between hot and neutral, with neutral at ground level. My snazzy new outlet tester showed all systems go. My snazzy new line voltage detector showed a voltage on the hot wire. Everything looked good.

So I plugged in a lamp and turned it on. No light. Instead, my stupid voltmeter now showed 0 volts between hot and neutral. My stupid outlet tester went dead. And my stupid line voltage detector didn't beep to me at all, indicating no voltage. Yet my snazzy new voltmeter showed voltage at the service panel was still a perfect 120 volts. WTF?? Back inside, I turned off the lamp. Now my snazzy new voltmeter showed 120 volts at the outlet again, snazzy new outlet tester lit up a perfect score, and snazzy new line voltage detector beeped a song of voltage. Double WTF??

I searched and searched for any explanation. It made no sense based on my physics training. If there's voltage when you apply a resistive load across that voltage, current will flow. No ifs, ands, or buts about it. Instead, the flow of current seemed to suddenly drop voltage to nil, immediately killing that flow. WTF??

(This is one of those many cases where theory falls flat on its rear, in spectacular fashion. Those theoretical physicists may act all smart and intimidating, but the reality is that they know almost nothing about how the real world actually works. Down with theory!)

Time to break out the big guns. I returned to Home Depot and bought myself a super snazzy new tone and probe kit. This is really cool. With the power off, you connect its leads to the hot and neutral wires of the cable you want to trace. You turn it on and it emits an electrical signal across those wires. Then you take the wand and wave it around in the air like a crazy person. When the wand gets within a few feet of the cable, it starts playing back the tone audibly. The closer you get, the louder it gets. You can trace your wire along walls, ceilings, and up to any problem spots. Just what I needed!

Using this, I found that my wire went up the wall and across the ceiling, above the dining room, and finally to the outer wall of the house where it promptly goes down into the service panel. Gotcha! The problem had to be somewhere along this stretch of cable, so up to the attic I went.

Again using the wand from my super snazzy new tone and probe kit, I located the cable in question out of numerous electrical wires strewn about the unfinished attic floor. Followed it across the dining room ceiling (now my floor), through all kinds of insulation, and WHAT? What is that I see?

That's right, a previous homeowner had apparently connected two romex cables using a third, merely twisting hot/neutral/ground wires together, and then bundling it all up in wads of electrical tape! I don't know how many electrical codes this violates, but I'm willing to bet it's more than one! Clearly this was the problem. The GFCI reset had probably drawn enough current to fritz out this horrible, horrible mess of wires, causing it to act all funky afterwards. See that green gunk? It's most likely copper sulfide (same stuff that makes the Statue of Liberty green) all over the copper grounding wires. No wonder the circuit stopped working!

Now that I knew the problem, the solution was simple: remove that abomination of an electrical connection, and replace it with something proper (and up to code). A couple of junction boxes, cable clamps, wire nuts, and a length of romex should do it. Here's the end result:

This is the right way to connect two romex cables. With power turned off at the service panel, clamp the cables into a box, pull back the sheaths a few inches, strip the ends of the hot (black) and neutral (white) wires. Twist together black with black, white with white, and copper (ground) with copper. Put wire nuts on your twisted pairs, and cover the hot and neutral liberally with electrical tape. Push it all back into the box, making sure the box is large enough that it's not too crowded. Secure the box to the framing.

 

When it's all ready, the box should be covered for even more safety!

 

Here's the final installation, using 2 boxes — one at each end. The yellow romex in the middle is new, connecting to the old white cables at either end. Nice, clean, legal, and SAFE!!

 

I even stapled the new cable to the attic joist for more safety.

All in all, this took me about an hour to fix (I spent many more hours diagnosing the problem). The bozo who originally did that atrocious piece of wiring could have spent the same hour and saved everyone a lot of trouble. Not to mention risk of fire!