"Percival P. Cassidy" wrote in message
...
Pulled a switch to replace it and noticed that

(a) the switch brought one black wire with it but left two other wires
(one black solid, the other white stranded -- the bare ends were clearly
visible) in the box;

(b) the temperature in the box seemed high -- decidedly warm;

(c) there was a charred black mess that seemed to be "cooked" insulation
tape with a small area of something red and hard at the end where the
wires went in and the end of a screw sticking out of the other end of this
mess.

As I cut away the insulation tape, it became clear that this was a "fried"
wirenut, and that what had looked like screw threads was the wire spiral
that was gripping (or was supposed the gripping) the conductors.

The first time I ever saw a wirenut, I thought "What kind of a Rube
Goldberg kludge is this?" but I now understand that they are NEC approved.
So what would cause a wirenut to "fry" like this? Note: I had never
noticed any problems with the lights that the switch was controlling, or
with any other circuits fed through the wires being held by that wirenut.

BTW, I think the white stranded wire must have been the ground wire to the
metal "frame" of the switch. The wirenut fell off the ground wires before
I had a chance to take careful note of where the other end of the white
pigtail went.

Perce

If the wirenut is not twisted on tight there will be a high resistant joint
and it will heat up. How hot depends on how much current is being used and
how much resistance is in the joint.

I work as an electrician in a large plant and there are thousands of wire
nut joints. Most work just fine. We very seldom have any problems with
them.
We almost never use any tape on them. Sometimes I will put some tape on the
motor leads or other devices that have some vibration.