A friend was hanging a new light fixture (replacing an existing one) and
accidentally drilled into the romex behind the wall. He found out because when
he flipped the switch, the breaker tripped. He removed the new fixture and the
screws holding in the metal box, flipped the switch, and the other two lights
on the switch came on just fine.
Question. How concerned should he be about the cut romex that is in the wall?
Most likely, the wire is not cut, just had some of the insulation scrapped off.
In fact, by his best guess (by measuring the resistance) the screw cut into
the black wire and not the white. To get access to the romex would be a real
Something isn't right here. If he was replacing a fixture, what was he
If the fault is caused by drilling into the romex, why would removing the
new fixture relieve the short?
Between what points was the resistance measured?
Sorry, should have given more info.
The reason for replacing the light fixture was not because there was a problem.
The old one looked like crap for years of weather exposure! The fault
happened after the new installation.
The existing plastic box had stripped threads where you secure the bracket for
the light fixture. He decided to replace the box and all that was available at
Home Depot was a metal box with a different mounting hole pattern to secure it
to the wall.
His thought is that the short was caused by the new screw that held the box in
place, since the box was metal (the old one was plastic) and was grounded to
the bare copper wire of the romex.
Removing the screw and the metal box ceased the short.
Before he removed the box, he measured the resistance between the box and the
wires. He got about 5 ohms between the box and the white wire and 0.0 from the
box to the black wire. There are two other lights controlled by the same
switch on that circuit, so the 5 ohms makes sense. The fixture itself is about
10 or 12 ohms, so putting two of them in parallel would result in about 5 or 6
Does that make sense?
Assuming that the insulation was scraped off of the black wire, how can he fix
I was changing a bunch of outlets to one of the decora style outlets.
In one box I discovered that one of the wires was wrapped with
electrical tape. I took it off and saw that there was a small nick in
the insulation. I re-wrapped it with new tape. Any problems with
that repair or do I have to pigtail it with an extension and wire nut
which seemed like over kill to me.
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