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Posted by dpb on June 28, 2007, 10:49 am
daokfella wrote:
> I've been in my home almost 10 years and all of a sudden, a single
> circuit in my home started to flicker and intermittently power on and
> off (the breaker never tripped). I've done electrical work in the past
> when I finished my basement. The first thing I thought of was to
> replace the breaker. It's a Cutler Hammer twin (slimline) 15A breaker.
>
> After replacing it, the problem still occurred (so it was unlikely it
> was the breaker). After some diagnosising, I noticed that there was
> some arching ocurring in one of the terminals on the neutral buss bar.
> I tapped on the panel, and a small spark shot from the terminal. I
> turned off the circuit in question, and the arching and spark ceased.
> I then knew that the arching neutral belonged to the circuit in
> question.
>
> I found it odd that there are one or two ground wires on the neutral
> buss bar. However, the neutral buss bar is right on top of the ground
> buss bar. Don't they go to the same place anyway? Is this odd or OK? I
> know I've seen some panels where the ground buss is totally separated
> from the neutral buss.
>
> This neutral wire is sharing the same screw terminal on the buss bar
> with a ground wire from another circuit. I shut off the main breaker
> and screwed down the terminal firmly which fixed the problem. However,
> 5 days later, it started happening again. No sparks fly when I tap on
> the panel, but there is slight arching in that same termAinal.
>
> Just eyeballing it, it looks like my neutral is a 14 gauge whilst the
> ground in the same terminal might be a 12 gauge which would explain
> why the neutral is not secured enough by the screw terminal. I am
> going to to shut off the main breaker do some housekeeping on the
> terminals making sure the same gauge wire is shared by neutrals in the
> same terminal.
>
> 1. Does it look like I've diagnosed the problem and I'm taking the
> correct measures to fix it?
>
> 2. Why would this happen all of sudden after 10 years of living in the
> home? The terminal screw didn't seem all that loose when I tightened
> it the first time. I barely got 1/16 to 1/8 of a turn on it.
>
> 3. Is it OK for neutrals and grounds to share the same terminal on the
> neutral buss bar? Of different or same circuits?
>
> 4. Any other comments to add on what I've described?
What Doug said plus...
2. Time is the key along w/ load cycling and relaxation/compression of
the conductors. Things gradually tend to loosen some over time.
Particularly, if a small amount of corrosion begins, that acts as a
small heater and then it is a progressive thing w/ a positive
feedback--more heat leads to more thermal expansion/contraction and
corrosion which causes more loosening and so on. Very slow initially,
but eventually troubles become apparent.
4. As Doug says, depends a lot on whether this is copper or aluminum
wiring.
Either way, my recommendation would be to also turn power off and take
the affected circuit(s) neutrals free from the bar and check carefully
for signs of oxidation/corrosion on both the wire end(s) and the
connections and the screw. Shine 'em up a little can't hurt.
If it's Al, connections need to be made w/ anti-oxidant lube--I'm
assuming probably aren't or would have been mentioned, but if are,
that's critical as Doug says.
I would also do a routine check for tightness of all connections in the
box at the same time -- you might find a couple of others that aren't as
tight as they might be.
And, of course, examine all wire ends for any signs of excessive heat
just as a precaution since you're in there anyway...
--
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