I finally got a chance to try pulling the wires out of one of the bad runs,
but no dice - I couldn't budge them.

I made sure they were free to move at the other end, wrapped them tight
around a dowel and put my back and legs into it. Tried pulling both together
and each singly. Tried steady pulls and jerks. Nothing doing.

This should have been the easy run - two #12 solid in what looks like
half-inch RMC, 15 feet box-to-box and two 90s. So either I just don't have
the strength (could it be that hard?) or the wires are pinched somewhere in
the conduit. If they are pinched that's probably the cause of the resistive
short.

We're coming up on a remodel soon and I'll have the electrical guy see what
he can do. Meanwhile I've bypassed the run with WireMold.

Anyway, thanks to everyone for all the helpful advice.

Steve

wrote in message
...
On Fri, 11 Aug 2006 01:17:38 -0700, "SteveR" wrote:

Anybody ever run into this? I'm trying to figure out what's causing it.

I've got a 40-year old house in which much of the outlet wiring is in
steel
conduit under the slab (or in it, for all I know). The wires are
individual
#12, with alternate phases sometimes sharing a neutral.

In the first incident I suddenly lost one branch circuit completely. The
wire had no continuity from the panel to where it comes out of the slab.
Two
other branch circuits in the same conduit started tripping their breakers
intermittently. I discovered that randomly the hot wires would have low
and
variable resistance to neutral. (And yes, I measured with the breaker off
and absolutely nothing connected to the problem runs.)

I sort of shrugged off the first incident, but now it's happened again.
This
time another run of conduit carrying just one branch circuit developed the
same intermittent low resistance to neutral problem, causing breaker
trips.

The resistance measurements are particularly puzzling. Sometimes the
meter
shows a few hundred ohms, gradually creeping up over minutes as if some
large capacitance is being charged. And then suddenly the resistance will
drop to 20 or 30 ohms or jump up to a few thousand ohms.

I've worked out fixes for both problems, but I'd really like to hear if
anyone has any idea what's going on. Could it be the slab settling on the
conduit? The floors are flat and level and I see no foundation cracks.


I can only see one of two things happening.
1. The conduit separated at a fitting and the wires got pinched.
2. The conduit rusted out from moisture and the wires had bare spots
that shorted to the pipe or moist soil.

Can you pull any of them out? You will be able to see many things,
such as are the wires wet, so they look pinched, corroded, etc. ???

You might not be able to replace these wires if the conduit is
damaged, or for that matter you might not be able to remove them if
the pipes are bad.

If however you can remove a wire, maybe you should attach a stell
fishline (tool to fish wire thru conduit) and see if you can pull the
fish line out the other side. If you have a moisture problem, you can
maybe pull some UF cable thru to replace the old wire.

If you cant replace them, and you are on a slab with no basement, you
might have to run your wires up the wall, across thru the attic, and
back down. Otherside you may be opening walls.

Mark