On Sun, 30 Oct 2011 08:30:16 -0700, "Bruce L. Bergman (munged human
readable)" wrote:

On Sun, 30 Oct 2011 04:48:03 -0700, Gunner Asch
wrote:

Ive gotten stab slot burns..badly smoking the base of the breakers and
often breaking the shells of the breakers around the stab slots. The
stabs themselves are eroded and rough with pits and burns.

And the breakers have never tripped..so its not a result of an overload.

The only thing I can think of..is salt air..but its a couple miles
inland from the Pacific and nothing else shows any signs of salt
corrosion.

These breakers are only 20 amp, 3ph and are carrying about 8 amps under
load..with less than 18 amps on startup..everything is running under
VFDs.

And Im ****ed off as I cant figure out why this is happening. And its
only happening with the new Murray panels. Nothing at all with the old
SquareDs and other old weird brands that Ive not swapped out yet.

Gunner

I'm betting a big part of this is from the VFD's - they might be
"officially" drawing 18A startup and 8A run, but the chopper effect of
the drives throws a ton of harmonics that your regular clamp-amp can't
see on the power lines and the neutral buss.

The other half of the problem is the tin-plated aluminum busses in
the Murray panel - "When they are good they are very very good, but
when they are bad they are rotten."

Once the tin coating is compromised the aluminum underneath starts
corroding, and it'll run the whole length but you can't see it easily
under the tin. Till it gets peeled off, then.... Eew.

I have a Two Strikes policy - When you go there the first time and
have to shut off power, pull all the breakers, inspect and clean all
the stabs with Noalox and abandon one or two as hopelessly burnt, you
warn them that next time the panel has to get changed.

If it happens again, you have to stand firm or soon it will get so bad
they'll have you back weekly, and worse they'll claim you are
incompetent - pull the panel and put in a fresh one.

Even if the customer claims poverty and insist you "patch it again" -
don't offer the choice if it's really bad. Their just being a cheap
ass, some Millionaires do that as a reflex thinking they're saving
money when they really aren't. And I don't want to keep dicking with
the same damn problem a dozen times.

Effects of high Q-factor harmonics are very visible if you do a
thermal scan of the panels at any large office building - computer
power supplies are switching style also, and the Q Factor (Inductive
reactance) from all those harmonics means they have to put in special
panels with a way oversized Neutral Bar and conductor back to the
transformer.

And the step-down 480-120 transformers for computer-heavy office
buildings have to be specially built ("Q-13" or higher markings) to
damp the harmonics too, or they start glowing at the Neutral
connections.

This shop might need the same rework to address that many VFD's
concentrated on one panel. That, and check into adding power factor
capacitors and filter inductors in front of each machine to try and
stop the crap at the source.

Last time I dealt with this was a bank that burned up the neutral buss
in a 125A sub-panel - I put in a new 200A neutral buss to get them
running again, and warned them they need to buy a better class of
computers and/or get an Electrical Engineer involved.

-- Bruce --

Good advise saved and noted!!

Thanks Bruce!

Gunner

One could not be a successful Leftwinger without realizing that,
in contrast to the popular conception supported by newspapers
and mothers of Leftwingers, a goodly number of Leftwingers are
not only narrow-minded and dull, but also just stupid.
Gunner Asch