AFCIs include ground fault protection. I believe it is required at 50mA
or less and is provided at 30mA. The cpsc.gov link I posted has
information on ground fault protection and why it is included.
GFCIs will trip with a ground fault of 5mA, so AFCIs don't replace
GFCIs. Another difference is that GFCIs have a couple additional
components that will trip the GFCI whenever there is a downstream N-G
connection, load or no-load. AFCIs will trip with a N-G downstream
connection (as gfretwell wrote) but there has to be a load to produce a
voltage drop on the neutral wire.
I don't think the NEC requires both GFCI and AFCI protection at the same
location. GFCI wire-through receptacles can be used downstream from AFCIs.
OK, I see that the question was already answered... sorry...
I actually had a situation where I was required to use AFCIs and GFCIs
together. In my last house while I was in the process of rewiring the
upstairs, I had half of the floor properly grounded and half still using
the original cloth covered ungrounded NM cable. Unfortunately the PO of
the place had installed grounding type receptacles anyway throughout
even though there was only originally one box with a proper ground.
Strictly reading the code at that point I could not install ungrounded
receps (I did order some but never installed them - my eventual goal was
to rewire the rest of the floor including the original wiring that was
still reasonably acceptable, but we sold the place first) alternately I
could provide GFCI protection. So that is what I did, I installed a
GFCI recep at the first box on the circuit and an AFCI breaker in the
panel (since it was a floor with three bedrooms.)
It seemed like a Mickey Mouse setup, but I never had any trouble with it.
One concern I did have though was what if someone were living in a house
that needed some kind of life support equipment? Could not a nuisance
trim be potentially fatal? I'm guessing people more knowledgeable than
I have already run the numbers on this and have determined that AFCIs
are less of a net risk than not having them.
replace "roosters" with "cox" to reply.
AFCIs include ground fault protection, but it is at about30mA. GFCIs
will trip with a ground fault of 5mA, so AFCIs don't replace GFCIs.
I don't think the NEC requires both GFCI and AFCI protection at the same
location. I haven't seen AFCI+GFCI devices. GFCI wire-through
receptacles can be used downstream from AFCIs.
yes they are but not at the same level as a GFCI. A GFCI intended for
personnel protection will trip at 5 mA of fault current, the ones in an
AFCI breaker are a higher threshold, I think 30 mA? so while they do
pretty much the same thing you cannot rely on the AFCI to provide GFCI
protection where required.
replace "roosters" with "cox" to reply.
Looking at the current in the wire, a "spike" is made up of frequencies
that are much higher than 60 Hz. My guess is AFCIs look at the low end
of RF and what is in the audio frequencies. I would also guess AFCIs
pick up the current signal with a current transformer on the hot wire.
(GFCIs use a current transformer around both the hot and neutral.)
It's interesting that in all my research I've yet to come across a circuit
diagram or anything technically detailed about how AFCIs actually work. I'm
going to bite the bullet and order an AFCI outlet to run some tests with.
They ain't cheap!
(Amazon.com product link shortened)
runs $33 from Amazon. If anyone knows of a cheaper vendor, please advise.
Also, how would one go about creating a deliberate arc for testing purposes?
I've got some carbon rods lying around somewhere that I used to create a
carbon-arc light with. I suppose that should work . . .
I found this quote on a Inspectapedia, home inspection site:
"As of September 2008 we have found no test tool that reliably and complete
ly tests the function of an AFCI. Only the integral test button tests the c
ircuitry of the device as well as the trip mechanism. UL classes these "tes
t" devices not as "testers", but as "indicators".
A problem is that some devices used to "inspect" an AFCI, in trying to prod
uce a simulated arc fault condition, may fail to cause the AFCI device to t
rip even though it is perfectly fine.
Literature from the manufacturer of a popular "test tool" tells the user of
the tool to go to the electric panel and use the test button on the AFCI d
evice to make sure it trips. In other words the inspector cannot rely on th
e separate test tool. For this reason you will see such tools referred to a
s "indicators" rather than "testers": they are not a complete and reliable
test instrument for AFCIs"
So, trust the test button, because there is NO external way to verify the d
evice works? Huh? Does that make sense?
"As of September 2008 we have found no test tool that reliably and
completely tests the function of an AFCI. Only the integral test button
tests the circuitry of the device as well as the trip mechanism. UL classes
these "test" devices not as "testers", but as "indicators".
Funny you should bring that up because the Eaton/CH site I was reading
mentioned using a circuit analyzer *before* installing an AFCI to help scan
for potential problems that would cause a nuisance trip. So I started
looking at circuit analyzers that could tell me if there was a problem with
the in-wall wiring. The cheapest I found was $90 for this:
NEEWER TRMS Voltage GFCI RCD Tester Circuit Analyzer MS5908A but it doesn't
appear to test AFCIs although it does test for Residual Current Devices
which turn out to be like a GFCI, but speak with a British accent <g>. From
Mike Holt's forums:
< RCD is the term normally used in the UK, and the most common trip rating
is 30ma though many other ratings exist. A UK type RCD normaly only protects
against leakage to earth/ground, and does not protect against overload or
short circuit, a fuse or MCB must also be employed to protect against short
circuit or overload. A combined earth leakage and overload protective device
is available, these are known as RCBOs. A UK RCD built into an outlet does
NOT protect downstream outlets. The common 30ma trip current does in
practice give good (but not total) protection against shock, especialy as
they normally trip at about 20/25ma, and are faster acting than USA GFCIs.>
The other tester they just got pricier from there: Amprobe INSP-3 Wiring
Inspector Circuit Tester Was almost $300 and folks on Amazon had some
complaints about it.
The Ideal Industries 61-165 SureTest Circuit Analyzer weighed in at over
$330 but deals with both AF and GF CI's but users complained that it was
"short" some necessary adapters.
So it looks, at first glance, like a circuit analyzer that can "test" AFCI's
will set me back the cost of at least 6 AFCI breakers. The question now is
will testing all the circuits reveal the same sorts of problems that
nuisance tripping of AFCIs would also "detect?" Is money better spent on
the AFCI's themselves or on a tool that can reveal potential hazards?
even though it is
Gives you that "warm, fuzzy" feeling about their overall effectiveness,
doesn't it? That's precisely why I've been thinking of buying a single OBC
outlet AFCI unit and testing it under real world arcing conditions that I
create - the kind of testing that drives SWMBO mad. (-:
of the tool to go
sure it trips.
this reason you will
not a complete and
Great. This AFCI investigation is rapidly spreading out into a murky
Only in Bizzaro land. (-: What bothers me most about the lack of testers
that can actually TEST and not just INDICATE is that I would always be
suspicious that the AFCI's might not react to a real arc. There's something
just not scientific about not being able to create a reliable, repeatable
tester for a device intended to save your life. Sometimes, when
manufacturers have problems like nuisance trips, their first corrective
attempts overshoot the mark.
I guess I had just better order a single AFCI and start testing while I try
to decide whether a $300 circuit tester would be a good investment.
I dug into my archive of downloads. Of particular interest is
why have AFCIs
available fault current on a branch circuit
AFCI detection - block diagram
"bad" arcs and normal arcs
30mA ground fault detection
It might answer some of your questions.
Details of detection, as gfretwell wrote, are probably proprietary.
Likely of less interest is:
includes info on 5A trip
Note that "branch/feeder AFCIs" were the original ones that did not
detect series arcs and are no longer available.
Prices likely will decline like GFCI prices did. But AFCIs are more
You can also use mechanical pencil leads wired in series with a load
that runs at higher than 5A. Pencil leads give a pretty smooth arc. Is
it a "bad" arc or a "normal" arc?
Check the cpsc.gov link for some info on good and normal arcs.
I would just assume that if the test button works the AFCI is OK.
There is a page at UL that says about what TimR got from inspectapedia.
I do not find it surprising that testers are not available.
I wonder if it's really fair to call them nuisance trips if there's a real,
underlying electrical fault causing the breaker to open? (-: The more case
studies I read, the more I am convinced that installing AFCI's is a good
thing if only because there almost always *is* a problem of some sort that
they've revealed if they do seem to start tripping for no reason. While
that may not have always been the case - I believe that the first AFCI's did
trip too easily from what I am reading - it seems that now when people
install them and they trip with regularity there's a good reason.
Now the question is - who makes the best AFCIs and do they make them in a
format I can use (dual skinnies)? I can replace the bedroom breakers, which
are mostly single, with full-sized AFCI breakers, but I'd like to protect
other circuits that can carry northward of 10A regularly to be protected as
More Googling required. (It's hard to remember a time when if you wanted to
look something up, you had to go to the library!)
A ground fault on the neutral will not open the overcurrent device but
it will trip anything with ground fault protection. A common suspect
is that big kludge of white wires under a wirenut in a ceiling box.
That is a common cause of the "fan"problem. The fan vibrates the box
and a bare ground bumps into an exposed part of a white wire.
This is a case where taping up a wirenut may be a good idea.
The size of the AFCI precludes them being in a skinny format ... so
Yes, many sites I've scanned talk about vibration loosening connections in
junction boxes. When a wire pops out of a wire nut it can really create
It looks like my options are not good for replacing all the current breakers
with AFCI's. They're expensive, too, at least the list prices I've seen
are. In most of the new lines I've run, I know where the first outlet in
the circuit is located and I can replace it with a AFCI outlet instead of a
breaker except that most of those outlet boxes are occupied by GFCI's. )-:
I am not fond of using outlet protection devices because it means you have
to go all over the house when a GFCI/AFCI outlet "pops" - been there, done
that. That reminds me to annotate the breaker box legend with the location
of all the GFCI outlets . . .
Besides, it's not the new circuits I am worried about. It's the old,
cloth-covered wire circuits that I am most concerned about. I'll have to
review the circuit panel and decide which ones regularly carry more than 5A
and will consider replacing those regular breakers with AFCI units. From
what Bud has said, an AFCI requires at least that much current to trip.
I have a post that covers receptacle-type AFCIs, including that you can
install them adjacent to the panel and use them to protect the circuit
downstream (about the same as an AFCI circuit breaker). For new
circuits, the NEC is particular about the wiring method from panel to
AFCIs will be most useful when the new circuits they are installed on
become old circuits.
I'm not sure I understand the last sentence. Do you mean that the AFCI's
don't use the powerline to transmit the "noise" created by an arc to the
detector/signal processor in the AFCI? From what I've been reading at least
some part of the detection process is based on detecting the RF noise from
an arc. I also read that detecting an arc is difficult because it may not
be drawing detectibly larger amounts of current than a normal device might.
One of my CCTV cameras is badly shielded an acts as an arc detector.
Whenever I run a motor with brushes near it, the image starts to show random
blips across the screen. It's really noticeable when an old power drill is
operated anywhere near the camera. I've been assuming that noise is one
part of what an AFCI "looks" for in trying to determine if arcing is
I'm asking because I've got three different items that appear to use the
home powerline as "antennas" although perhaps that's not the right term.
Each devices uses the powerlines in a slightly different way. X10 home
automation controllers inject a 120kHz RF signal onto the powerlines to
communicate commands. My Netgear Ethernet adapter sends networking signals
over the home powerlines with plug-in adapters (sometimes - it's not very
I've seen numerous discussion refer to the HomePlug technology as
"transmitting" ethernet signals over the powerline. Is the powerline acting
as an antenna in those cases or is their a better terminology for what's
I would also guess that the AFCI's are looking for several parameters to
determine if there's an arc fault. I would suspect that sort of detection
has improved greatly since the first units hit the market.
This site (from 1999!) claims:
<<Enormous progress has been made recently by manufacturers of AFCIs and
engineers/scientists developing the standard in understanding the variety of
conditions an AFCI must respond to in order to be effective. A reflection of
that understanding is in the variety of tests and conditions under the three
categories of the draft standard. These address the majority of arcing
conditions known to lead to fire.>>
Haven't been able to find information about how AFCIs and arc welders
interact but it seems most run off 240VAC and would have their own circuit,
probably without an AFCI.
This site talks about the original bedroom requirements and says it's
because that's where many home electrical fires start:
<<Why do the 1999, 2002, and 2005 versions of the NEC require AFCI
protection for only bedroom circuits?
NFPA fire statistics show that a high percentage of electrical fires occur
in bedrooms. There are many appliance cords in bedrooms, for example,
radios, clocks, blankets, air conditioners, heaters, TVs, vacuums, as well
as, lamp cords. All of these cords can be trapped/abused leading to arcing
faults. Further, there are long runs of installed wiring (M-B, "Romex")
between the loadcenter and the bedroom outlets. The wiring can be abused
during installation (e.g. stapling) and after installation (driving nails
into the wall etc.) Therefore, the most logical room to start with would be
the bedroom. >>
The same site also implies that arc welders do not generate nuisance trips
with the newer AFCIs.
The same site has a good roundup of arc fault types and possible causes:
What is an arcing fault?
According to UL 1699, Standard for Arc Fault Circuit Interrupters, an arcing
fault is an unintentional arcing condition in a circuit. Arcing is defined
as a luminous discharge of electricity across an insulating medium, usually
accompanied by the partial volatilization of electrodes.
There are 3 basic types of arcing faults: line-to-neutral, line-to-ground,
and series arcing.
What causes an arc fault?
Arc faults may occur anywhere in the electrical system and may be a result
of the following:
a.. worn electrical insulation or damaged wire
b.. misapplied or damaged plug in appliance cords and equipment
c.. loose electrical connections
d.. drill bits, nails, or screws driven into the wire
e.. wire staples driven too deep
f.. furniture pressing against electrical cords
g.. broken wires
h.. frayed wires
More reading is in order before I bite the bullet and begin replacing the
rather new <sigh> breakers I installed in the panel just recently. Does
anyone reading this know if AFCI's come in "dual skinny" formats? One of
the site above talks about how AFCI's run warmer than normal breakers
because of the built-in power supply for the electronics. I wonder if they
can squeeze all the required electronics into the dual space-saving
Thanks for your input, Bud!
RF from the arc is not picked up by circuit conductors acting as antennas.
AFCIs look at the current on the conductor. The arc "signal" is created
by current variations through the arc.
That is the current variations created by the arc.
A "series" arc (loose connection) is limited by the normal load that is
on the circuit. The AFCIs that are used now may detect a 5A or larger arc.
Parallel arcs (H-N and H-G) can be a lot larger. The current can be up
to the available short circuit current at the point of the arc. If I
remember right, an investigation found that is very likely over 60A out
to 6 ft of line cord in a house.
The signal from the camera isn't very large so a small noise can be
AFCIs need a 5A or larger "noise" on power wiring that runs at much
higher voltage and current than the camera.
60A through a 14GA cord is going to do some damage. I remember when I was a
kid an electrician working on the circuit panel with a screw driver shorted
it out inside the box with a huge spark that spattered molten metal inside
the circuit panel. I still have that screw driver around somewhere. He
just tossed it in the trash because the tip was cratered but I retrieved it
because I thought it made a great souvenir and reminder to be careful.
It's clear now from what you've said and what I've read that it's not a
"radio" process but a monitoring of the instantaneous current draw that
detects the arc. I wonder if the radio telegraphs used in the Marconi era
would work today with all the background RFI that exists today?
The camera is only of use in detecting things like motors with brushes that
need replacing. It even detects when a gasoline-powered leaf blower is
I've noticed that almost all the AFCI breakers I've been looking at have
pigtails attached. Those are going to make for a very messy looking
installation in my cramped box, IMHO. I see that one of the newer circuit
panels has accommodations for the AFCI pigtails but now we're talking
serious expense and time to replace my old panel with an AFCI compatible
One of the sites I browsed made an interesting comment:
<<The new arc fault breakers cost about $25 - $50 each depending upon
manufacturer, but it is a very small price to pay for peace of mind. An
experienced electrician can install a new arc fault breaker in a matter of
minutes. It actually takes longer to remove and replace the cover to the
circuit breaker panel than it does to switch out the breaker>>
The breakers, to my surprise, all seem to be more expensive on the whole
than a OBC (Outlet Branch Circuit) outlet-format protector. So $50 x 20
breakers is $1,000. The real problem is that now I know that the AFCI's
require pigtails and full breaker slots, it means I would feel compelled to
pull the old box, replace any cloth-wired circuits coming into back to their
source (that's the long pole in the tent) and put in a new box designed for
AFCI's and then probably have to heavy-up the service to the pole. So the
math isn't quite as clean as $50 by 20. I'd think that's a multi $K job for
a licensed electrician and at least $2K for a homeowner DIY'er if everything
listed is done.
What do electricians charge to run a new branch circuit in old plaster/lathe
construction? I've always done it myself so I confess, I have no idea.
The question now is how much is piece of mind worth? Is the money better
spent on a panel full of GFCIs or on smoke, heat, CO detectors or other
safety technology? AFCI's, once perfected, could just as easily ride the
main breaker, couldn't they? The arcing "information/signature" should be
detectable at the service entrance, shouldn't it? Admittedly nuisance trips
that bring the whole home "grid" down aren't going to be pleasant, but I
know that the new home industry would rather not have to add over $1000 in
AFCI costs to new homes if there's a cheaper way to do it.
One site said that there are at least 111 arc-fault based fires in the US
each year. Statistically, that's really not a light. Can't vouch for the
accuracy of the number. Seems like it should be higher. Could be CRS or
the webmaster took a WAG. (-:
Is it time to switch out the old breakers or will there be combo AFCI/GFCI
breakers sometime down the line? I see that some of the AFCI's incorporate
a form of GFCI, but the trigger appears to be 30mA and GFCI's appear to
operate at a more life-saving 5mA level.
I did notice that more than one site (Leviton and Eaton/CH, I think) took
pains to point out that they are continuously improving their arc detection
capabilities. Cynical people might take that as an acknowledgment that they
feel they are "not quite there yet" in terms of 100% reliability.
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