I was on the truck company one evening. The engine went on an electrical short and
came back to the station around a half hour later. Another half hour later
and the tones went off again… this time for a structure fire at the same
address as the previous electrical short. Uh oh. Luckily when we got
there, there was no fire. The engine had pulled the two fuses in the house
on their previous visit, but the conduit was still very hot to the touch.
Burn your fingers hot.
This particular house has 120 volt service only, controlled by a whole two
15 amp fuses for the house. (~800 sf.) The affected area of the house has
metal flex conduit running throughout possible because it wasn’t originally
drywalled. The main service to the house came in on the second floor
through a piece of conduit, not a weatherhead. The service then ran down
through a wall, under a deck, out the wall of the first floor and into the
meter. It was uncontrolled that whole way.
I had my guys pop a couple of small holes in the drywall in the garage and
adjoining bedroom to ensure that there was no fire. Meanwhile the chief
showed up with the thermal imager, so we used that to further confirm that
there was no actual fire. Now we’re some hour and a half to two hours after
the first call and the conduit is still hot to the touch. The little voice
in my head says “Dude, something ain’t right here. Let’s just hang until
the electric guys get here.” And that’s what we did.
Eventually a private electrician showed up. He offered to pull the meter
for me to ensure that power was off. He did that with no problems.
However, when I got close to the fuse box I could still hear an ominous
humming. The conduit was still hot. Uh oh. Finally, Gas and
Electric showed up. We decided to cut the drip loop, which of course I had
the electricians do. There was quite an arc upon cutting the loop. The
conduit cooled off immediately.
We figured out that what happened was that the main service rubbed against
the conduit coming into the structure and shorted against it. It
electrified the metal conduit running throughout the structure. The only
thing that kept one of my guys or myself from getting zapped was that the
conduit was grounded better than us. I usually carry a cheap electrical
proximity tester in my turnouts, but it was at home due to some extensive
remodelling on my house. Ooops.