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
Anyone have an opinion about this?
On 6/26/2013 6:37 AM, firstname.lastname@example.org wrote:
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
On Wed, 26 Jun 2013 04:17:15 -0700 (PDT), email@example.com
No. It was NOT a short. In most cases it is a loose, intermittenr, or
high resistance connection that causes a fire - not a short.
In order for this to happen there MUST be a load of some sort on the
circuit. A normal breaker will not respond to an "arc fault" of this
type, and nor will a CFCI - an "arc fault detector" breaker is
designed to trip under those conditions. Not sure how effective they
are in real life - or if they are more likely to false trigger.
I can add some comments about your last point from experience over the last
12 years. I've had circuit-breaker AFCIs on several house circuits during
that time and have had maybe 4-6 nuisance trips overall. A couple happened
when we switched ceiling fan speeds using the fan's wall-box control. The
others happened unexpectedly for no obvious reason.
Frankly, I expected more nuisance trips based upon what I had been hearing
and reading when the installation was new since, at that time, I was working
with one of the NEC code panels and there was a lot of discussion about it.
As I understand it, AFCIs react to an electrical arc by sensing the radio
frequencies that the arc generates. But opening/closing a switch can
generate such an arc (usually very small) and the same thing can happen when
an incandescent lamp filament fails or electric motors with brushes or
inertia switches power up.
Or the brushes "bounce" on ANY brush motor. I've heard of problems
running vacuum cleaners, older sewing machines, handheld mixers, and
food processors, among other devices. Anything that can produce
multiple sparks. Even unplugging a lamp while it is turned on - if
you don't pull the plug quickly - can trip an AFCI
All are certainly possibilities. So, there's some way in the AFCI sensing
circuit to adjust the level of RF that trips the AFCI. I wonder if there
are any AFCI products out there where that adjustment can be changed within
a range to maintain a level of protection while minimizing nuisance tripping
on noisy systems.
*About a year ago a customer called me about a circuit breaker that kept
tripping when they used their treadmill exercise machine. The breaker was
an arc fault type and the problem only occurred when the machine was shut
off . Long story short, I found that by using an extension cord to power
the treadmill from the same receptacle and circuit, the problem stopped.
On 06/27/2013 09:38 PM, firstname.lastname@example.org wrote:
To be fair, I would be hard pressed to describe the difference between
an undesirable arc and one caused by a plug being withdrawn slowly under
load, so it is hard to fault the breaker for not being able to determine it.
replace "roosters" with "cox" to reply.
I agree that the "scuttlebutt" was not favorable regarding nuisance trips.
I was thinking about installing them, too, a while back but after all the
bad luck I had with the first CFL's to hit the market, I decided to wait out
being a pioneer for arc fault technology.
That's fascinating. I just learned that the local water authority monitors
the rebar in their 60"+ concrete water mains acoustically. When one of the
reinforcing bars snaps, it sends out a unique sound that is monitored by a
series of microphones throughout the system and they then replace the pipe
The only problem is that the most recent break occurred where there was no
rebar in one of the large joints. Who would have thunk of monitoring the RF
emissions of an arc or the sound of snapping rebar? As for the AFCI, it
makes sense because the wire leading to the arc must act as a fairly
efficient antenna. I always wondered how an AFCI could differentiate
between normal current draw and the creation of a dangerous arc. Does that
mean you can't use an arc welder on an AFCI protected circuit?
I can live with a breaker popping when a light bulb pops. I've had normal
breakers do that. I assume that like GFCIs (Clare used the term CFCI - is
there a difference?) as they get more feedback from users, they tweak the
design to handle those false triggers better. My first GFCI used to trip
like crazy for no reason. The most recently bought ones hardly ever trip.
I got so suspicious I even bought a GFCI plug-in tester to make sure they
were working. (They were.)
Somewhere out there there's information about nuisance trips and whether
they were over-hyped to begin with or whether the earlier units just
couldn't detect them as well as the newer units do. Our resident sparkies
As for AFCI's, my understanding (from way back when) is that they were
recommended for bedrooms and bathrooms where a high current device like a
space heater or a hair dryer could create an arc big enough to start a fire
very quickly. I can attest that a space heater plugged in only partially
can create enough heat to melt plastic. DAMHIKT. (-:
I once took apart a six-outlet extender that was getting warm to discover
the copper cross bars were press-fit and had become loose and were starting
to blacken at the place they were joined. I also noticed that these old
press-fit six way outlet extenders had two copper bladed plugs and were
electrically cross-connected. The one I bought to replace the burned-up one
had only one live plug. The other was plastic and just acted as a
stabilizer. I suppose that's to prevent someone from plugging the extender
into an extension cord and not an outlet. That would make the second plug
electrically live and exposed.
There's really no need I can see to cross-connect the two plugs to the six
outlets. It could be set up so that each plug feeds only three of the six
outlets and then you could plug it into an extension cord without creating
an electrocution hazard. Maybe it was an economy thing. After all, not
putting a second copper plugs has to be cheaper if you're making 10,000 of
these things. The best design would be to use two isolated plugs because
that way something like a remotely switched lamp outlet would still work as
AFCI look for current components that are higher than power line
frequencies. Wires are not antennas. And it is not just the higher
frequencies. AFCIs look for arc "signatures" to separate normal arcs
from "bad" arcs. My guess is they use digital signal processing but I
The inductance of a welder transformer might hide a welding arc.
The NEC originally required AFCIs only for bedrooms. Those AFCIs could
only detect "parallel" arcs - H-N & H-G. Arcs might have to be 60A to be
detected (series arcs would be 15 or 20A max). The idea, I believe, was
largely to detect arcs between wires in extension cords which were
walked on or abused in other ways.
AFCIs now detect arcs at a 5A level. That can detect a series arc (loose
And AFCIs include ground fault detection at about 30mA. If there is a
ground present in a cord an arc is likely to include leakage to ground
soon. Arcing at a receptacle can also wind up with leakage to ground.
I'm confused now. Do the AFCI's use RF at all to detect arcing conditions?
I've been trying to find some descriptions or patents that detail how they
work without much success. One interesting site I found:
said that one user, who thought his AFCI was "nuisance tripping" discovered
that it was actually tripping because of a dangerous condition in his
<<"I read all the available information on the Web running into all manner
of grousing, but I also saw an article explaining what the breaker is and
what it does. Encouraged, I started looking for the culprit. On and off it
took me two weeks to separate the circuits to discover that an improperly
installed GFCI socket in the bathroom (on the bedroom socket circuit)
compressed the hot wire against the grounded socket box," he said.
"Old Romex insulation fractured, crumbled, and allowed arcing to the box. I
do not know how long this condition lasted, but now it is fixed," he added.
"In six months, neither of the two breakers disconnected. I am a convert and
I would encourage retrofitting AFCI breakers, especially in older
Maybe it IS time to switch to AFCIs!
In my limited experience with them, I haven't had any issues. Every
time it's tripped it's been because of a legitimate problem.
Also, the amount of improper wiring that I found in my last house,
combined with simple age and the tendency for old 60C wiring to become
brittle in ceiling light boxes, makes me think that in general they're a
good idea. I lived in my last place for almost a year before going up
in the attic and doing a serious investigation of the wiring, what if
something had happened before I started fixing everything? And since
everything was working, a homeowner less inclined to do it themselves
could have lived there a decade or more unaware of any potential issues
(as I believe to be the case of the previous owners.)
No, they're not a replacement for proper wiring products and methods,
but in a structure where the wiring is apparently in good shape but
known to be old and not up to today's code, it makes sense. For newer
houses where everything's right, it might be overkill, but won't hurt
replace "roosters" with "cox" to reply.
It seems that's the case for many people who have installed them.
You wouldn't believe the things I discovered when I ripped out the poorly
finished basement's walls and ceiling. The additional wiring was done with
equal disrespect. Neutrals pulled from separate circuits, wires nicked by
bad stripping, grounded outlets installed without any grounds, wire nuts
improperly installed, speaker wire instead of Romex, etc.
I have an old house, too, built when WWII was just starting and all sorts of
compromises had to be made because of war shortages (no building paper
between the floors, for example). I can see great benefit in installing
AFCI's to help detect any concealed faults in the wiring system.
I've added a number of new circuits for high-current devices over the years
because I didn't feel comfortable taxing the old, cloth covered wiring with
loads it wasn't designed for, but those circuits are still active. If I
switched them to AFCI's and they started tripping, I would probably just
disconnect them and put in a new circuit with Romex because tracing a fault
through the old wiring would be very hard. The old wiring runs up to the
attic and then down again and everything's behind plaster and lathe walls
In any event, I agree with you that with old wiring, installing AFCI's could
be a lifesaver.
How much work was involved when you checked/rewired the attic, Nate? I
decided that is was far easier, although slightly more expensive, to just
put in new, grounded 20A circuits from the basement up wherever I could to
replace the 15A cloth-covered wires going up in the attic. I found that the
cloth-covered wires were still mostly OK, except around ceiling junction
boxes and switches that had been replaced. Considerably fraying occurred
wherever the wire had been disturbed for any reason.
In my case, not any more than doing it any other way - I didn't have a
good path to the basement and the house was wired the old school way
with the primary wiring paths going from ceiling box to ceiling box so
ripping everything out and starting over was easy. I reused the homerun
to the panel because it was BX and would have been hard to repull. I
did have to pull one run from a wall recep to a ceiling box behind a
plaster (exterior!) wall which if I'd missed it would have required me
to open the wall... but fortunately I didn't mess that one up.
replace "roosters" with "cox" to reply.
I installed arc fault breakers on two legs, which included both bedrooms.
This was old wiring. One leg would trip on occasion. I called that leg the
big mess, because if you saw it, that's what yo would call it. Most if that
has been replaced, so far so good.
An arc fault breaker is not also a ground fault is it. Are there some ?
Yeah, I had a similar circuit in the basement that had been hacked into by
hack amateurs so many times that yanking it was the only thing to do. It
was the circuit that had speaker wire coming out of one junction box and
going into a flourescent shoplite without any strain relief. The wires went
right into a sharp-edged sheet metal hole that had already begun to saw
through the insulation. Yikes!
Good question. I seem to recall reading something about one, but I can't
recall whether it was an actual product or a prediction. I also came across
someone who's promoting a scheme whereby all outlets and all plugs have RFID
chips in them so they can communicate with each other and establish what the
normal current load should be. That would make it easier to detect way
out-of-bounds over-current draws, but the scheme sounds too complicated to
ever be adapted universally. If I find a combo AFCI/GFCI unit, I will let
you know. I suspect if it's available, it would only be in an outlet
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