Jules wrote:
On Tue, 13 Oct 2009 19:51:24 -0700, Don Kelly wrote:
Other
hazards such as arcing at switches or poor contacts, worse with DC, were
ignored.

I recall the breakers at one site I was working at fed compressed air
through the breaker upon opening, just to extinguish any arc that may have
formed (that was a 400V DC setup) - I think that's typical on higher power
DC stuff. The breakers were about the size of a lunchbox.


Hi voltage AC breakers still do use compressed air in some. The 'blast'
is aimed between the arcing contacts to literally blow out the arc.

Lower voltage DC (up to 350VDC) that we used on submarines just used
blow-out coils to create a magnetic field that 'pushed' the
arc-conducting gases up into chutes lined with alternating metal and
insulating plates that would cool and stretch the arc.

But I've seen enough stuff that I know I haven't seen everything :-)

daestrom