What could cause conduit to arc where it touches another conduit? How
can this happen without the conduit being charged with 110V?
A few months back, I added two AFCI breakers and a new house ground
wire in a home improvement project. A licensed electrician installed
the breakers and made the box connections. I assume he did it
Heres the problem:
I installed a basement HVAC duct touching an old metal flexible
conduit. A few weeks later, I noticed arcing between the conduit and
HVAC duct where they touched. Neither of the two shocked me when I
touched them, but sure enough an orange arc was making a little
noise. Upon examination, the arcing had welded holes in the HVAC duct
and the conduit.
I snipped & dissected the conduit. The wire sheathing inside were fine
one was a bit darkened. Over a few weeks, I expected much worse. Oh
well, problem solved. Maybe it was HVAC static discharge.
But then yesterday, I heard the same noise inside a kitchen light
fixture on a different circuit. The box was hot to the touch. Upon
dissection, however, nothing in the box was damaged.
HOWEVER that boxs conduit was touching another conduit, and sure
enough a little hole had been welded where they had been touching.
What could be causing this? I am a little spooked.
*My first thoughts are that a neutral wire is touching something or is
broken and the conduit or duct is being used as the return. My other
thought was that maybe there are some grounding (Or lack of) issues and the
conduit or duct is some how energized. However you did mention the
installation of a house ground wire. Was a new ground rod installed? Are
all of the pipes bonded? How old is this house?
When this is happening, put an ammeter on each of the ground wires in the
circuit breaker panel to see if any are carrying a load. Then check the
loads on the neutrals and compare the readings to the respective hot leg for
each. You could also try putting the ammeter around the metal conduit and
see if you get a reading.
You could also use a voltmeter and check the volts by touching one lead to
the metal conduit and the other to a water pipe (Assuming the water pipe is