DIYbanter - View Single Post - 3 phase electrical receptacle on fire, explosions

J. Clarke[_2_]

In article ,
says...

On Mon, 03 Oct 2011 16:58:34 -0400, Wes
wrote:

Ignoramus19762 wrote:

OSHA has gotten religion on the arc flash issue. The #1 chance
for such that will kill folks is when you close a large
main/sub-main breaker. They can and do explode outward with
enough force to blow apart cabinets, taking out the chump
standing there closing the breaker.

So, why exactly do they explode? Can you explain?

I can't but I stand to the side of control panel boxes when turning on the main
disconnect. One time seeing a Hoffman box open from the arc flash was enough for me. No,
I didn't do the work, I was a by stander.

Wes
================

Hey Wes,

Our "rule" was: Stand off to the side of the disconnect (ie..not "in
front" of the cabinet door), one hand in pocket, other hand on the
lever, face away before throw. I've had three occasions to be happy I
did, although I still get a ringing in my left ear.

Somebody mentioned replaceable link fuses....they are not legal here
in Ontario anymore, but I have a long wonderful (nobody actuall "hurt"
story) about them when 200 amp links were tripled up, and the 575 volt
elevator motor was a dead short. We couldn't find the disconnect at
all or about 4 feet of the bus duct feeding it, but we did find two
ends of the fuses (that's how we knew about the tripling) and it took
out the whole powerhouse because it made every disconnect along the
way go short...sort of a ripple effect. You could hear them popping
every few seconds throughout the building. By the way, it was the
building maintenance electricians that had done the tripling, and they
should definetly have known better...I say that, becuase they get to
work with hot supplies most of the time, versus construction
electricians who really don't work hot as much.

FWIW, I'm reminded of the time I was talking to my boss about something
or other and there was a loud "bang". We both looked around, nobody
seemed excited, no alarms went off, we went back to what we were doing.
Then there were three more. And a few more after that and smoke started
pouring out of a conference room. One of the engineers, Ben, a West
Point graduate, looked in the conference room, dragged a guy out, closed
the door, and pulled the fire alarm. A few minutes later the
administrative assistant to the vice president for our division went
into the conference room and started pulling out furniture. Ben argued
with him for a while and finally punched his lights out. About that
time somebody among the Powers That Be grew a brain and ordered the
building to be evacuated.

Turns out that the guy who Ben pulled out was a phone technician who for
reasons unknown had run a steel fish tape through a live conduit that
was feeding a bank of 500 HP motors, and managed to create a short. Why
that conduit came out in a conference room I have no idea.

Ben ended up getting a commendation.

And for Iggy...I've seen 120 volt hanging cables that were in very
damp conitions shorted, and they arc and catch fire and burn like a
dynamite fuse or like a July 4th hand-held "sparkler"...they don't
blow a fuse for about 5 feet.

A point to note that amazes me some people don't know.... with
electric current, the point of HIGHEST resistance will be the point of
highest heat(ing). Think about it.

Take care.

Brian Lawson.