On Mon, 03 Oct 2011 16:05:07 -0500, Ignoramus19762
wrote:

On 2011-10-03, 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.

Scary.

Can this happen with 240v 3 phase?

My building has only 240v. 800 amps service.

i

Fault current in your building will be well in excess of 10,000A.
Ordinary domestic fuses can't interrupt that kind of current. You do
need to treat industrial power with respect, but it's not particularly
scary compared to anything else that can get you. Getting blinded by
vaporized metal is a risk. I don't use cheap meters on anything higher
than 120VAC (and gingerly on that). Electrocution risk is no higher
than working on home 240VAC.