On Mon, 03 Oct 2011 10:10:51 -0700, "Bruce L. Bergman (munged human
readable)" wrote:

On Mon, 3 Oct 2011 03:23:42 -0700 (PDT), "
wrote:

On Oct 2, 11:00*pm, Wes wrote:
Ignoramus23561 wrote:
After a short while, I opened up the receptacle. It turned out that it
was full of grinding dust (! -- how did it get inside) -- and,
apparently, the dust shifted and shorted the contacts. It was a short
circuit, but with a lot of resistance from the dust, so it caught
fire, but did not trip a breaker.

I'm glad there wasn't an explosion. *A long time ago, at a company long auctioned off, a
30A 480V twist lock cord fell into a mop bucket. *In addition to the bang that sounded
like a rifle shot (wires slapping in conduit), a marathon splice block that was part of
200 amp run to the panel this cord was attached to exploded along with tripping the 4000A
breaker in the boiler room.

All that from a little 10 ga SO cord and water.

Wes

My friend had a 440 motor or line short right in front of him in an
elevator motor room. He was temporarily blinded for a couple days. He
said it felt like someone poured sand in his eyes.
Karl

Just servicing kitchen and hallway exhaust fans can be a heart-stopper
when it's a high-rise Condo in West Hollywood and the common
"Mushroom" fans on the roof are 1-HP 480V 3Ph.

Renewable fuses in a motor control center, and the only way to find
out if you'd fixed it was to throw the switch and try it - if the
fuses didn't go off like a shotgun blast and the motor started, then
you were done.

And you make DAMN sure they are locked off/tagged off and well and
truly dead before sticking your hands in...

Iggy: Don't screw around with this - take some time, get a Dust
Collector system or a good Shop Vac with a HEPA element and your big
air compressor, use a cross-draft and blow it toward the vacuum hose.
Clean up and out EVERYTHING in the shop area, starting with the
rafters and working down. Take apart the light fixtures, the boxes
for the building wiring, everywhere.

And your last stop is to pick a nice day, have Con Ed (or whoever) pop
the fuses out and kill the power to the Main Service for the day, and
you pull the covers and clean it out too. (Bring in a gas powered
compressor and a generator.) If that sucker burns up, you'll be in a
world of hurt. That grinding dust can be miserable stuff when it gets
inside electrical gear.

-- Bruce --

Ive replaced a surprising number of 3ph and single phase outlets,
connectors and boxes in the 15 yrs Ive been repairing
machinery...replacements necessary because of metallic/conductive dust
in the boxes etc.

Some were quite spectacular...in both initiation and later investigation

Gunner

"In the history of mankind, there have always been men and women who's goal
in life is to take down nations. We have just elected such a man to run our
country." - David Lloyyd (2008)