On 06/26/2013 09:39 PM, micky wrote:
On Wed, 26 Jun 2013 17:41:18 -0400, RBM wrote:
On 6/26/2013 6:01 PM, bud-- wrote:
On 6/26/2013 8:47 AM, wrote:
On Wed, 26 Jun 2013 10:12:30 -0400, "John Grabowski"
wrote:
My neighbor just suffered a serious fire. His house had an
enclosed
porch at the rear, with an open, roofed desk connected to the porch
rear. He had several GFI breakers out there, including one on the
rear porch wall. Around one AM, when he and family were asleep,
a fire started at that GFI switch (according to Fire Marshall), and
got going pretty good before their dog started barking. That saved
their lives for sure. Almost killed their dog and cat, though.
The
fire badly burned the rear half of the house and sent black soot
throughout the rest of the house. The house is pretty well
totaled.
That's what happened. I have to wonder how a GFI could do that!
I heard the Fire Marshall actually say that what happened was
the GFI
wires arced, but that was not a 'short' to the GFI. Hence it didn't
trip. So, the GFI presented no protection did it! The arcing just
continued until it started the fire!
All this makes me think that my GFIs are not providing me the
protection I always thought they did. I'm not sleeping as well
these
days.
Anyone have an opinion about this?
Thanks
me
GFCI devices don't provide short circuit protection. They provide
ground
fault protection. The device that would have, should have
prevented this
is the circuit breaker, or better still, an arc fault circuit
breaker
Right, the usual GFCI does not against electrical arcs. The National
Electrical Code now requires arc fault circuit interrupters (AFCI) in
certain rooms of homes to reduce such fires. Wikipedia has a good
summary
of what GFCIs can and cannot do at:
http://en.wikipedia.org/wiki/Arc-fau...it_interrupter Arcing
that
results from loose connection at outlets and switches or broken
wires are
a
major cause of house fires.
Tomsic
So it seems like the ground fault is especially useful near water
faucets and wet places.
But the arc fault seems especiallly useful everywhere, not just
bedrooms. Does that mean every circuit breaker should be arc fault?
*Article 210.12 in the 2011 National Electrical Code requires them for
almost every circuit in a home.
That's great for new houses. But my house was built back in 1998.
me
You can likely add them one way or another. If circuits are multiwire
branch circuits with a common neutral that is a problem.
I don't advise trying to use current technology on older wiring systems.
Aside from Edison circuits,
Even after looking it up last year, I never did understand what an
Edison circuit is or how it's different from any other circuit.
It's basically a 120/240 two-phase circuit with two hots and a neutral.
The advantage of using it is that it requires two less wires to be
pulled than two separate 120VAC circuits, because only one neutral and
one ground is required rather than two of each. The reason that you can
get away with it is that if you are only using 120VAC loads, but they
are evenly split between the two hot legs, the current in the neutral
will actually be zero! This is because the two 120VAC hots are 180
degrees out of phase (they add to a potential of 240VAC) it's very
similar to the way a three phase system works with 480VAC/277VAC if you
are familiar with that but with only two "phases."
Apparently this was devised by Edison as a means to provide two DC
circuits with only three wires (I guess the two "phases" in that case
would have been one wire at the positive nominal voltage relative to
ground and the other would be at negative nominal voltage relative to
ground) and someone appropriated the terminology to include the
analogous AC configuration... which makes sense as we all know that
Edison was a proponent of DC not AC. (Tesla and Westinghouse were the AC
guys...)
The problem with using an AFCI on an Edison circuit is that you would
need a two pole breaker, which do exist but are unsurprisingly more
expensive than a single pole unit (or even two single pole units!) An
alternative would be two single pole breakers, but the manufacturer
would have to list them as being acceptable to use with a handle tie and
I haven't researched it enough to determine if there are any like that
or not.
https://www.platt.com/platt-electric...px?zpid=473677
you find anomalies caused by mixed neutrals
and the like. You certainly could test each circuit with an AFCI, and if
it holds, you're good to go
I know approximately what a mixed neutral is. I don't think my home
described below is likely to have the anomalies you speak of.
My house is from 1979, has quite a bit of empty space in the breaker
box, and there has only been one change, one added circuit, to the
attic to power the attic ceiling light (with receptacle), the roof
fan, and the outdooor floodlight. Along the way it goes by the far
wall of the laundry room where it powers a ceiling light and 5 double
receptacles (no more than 2 sockets are used at any one time, a lamp
and one power tool or another.) The circuit breaker has never
tripped.
Do you think it's likely I'll have problems changing to AFCI?
I'm assuming what he means by a "mixed neutral" is one where neutrals
from one circuit are cross-connected to another circuit. That would be
a code violation and has been for ages - when neutrals from different
circuits are connected together you can no longer assure that the
currents in a cable sum to zero which has been a requirement for a very
long time.
So... you shouldn't have that situation, and if you do, might as well
find out about it now and fix it (should not require opening any walls
unless you have hidden splices which would be another violation...)
nate
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