I'm installing AFCI breakers but have one that trips immediately. After
investigating I have found one GFCI outlet that is responsible. However
when I check the outlet with a GFCI tester, it is correctly wired.
Tesing the GFCI trips the AFCI.
Is it still possible to have a common neutral or other fault that trips
the AFCI, while being correctly wired for the GFCI?
Can you determine if there's shared wiring anywhere? If it's only the
one GFCI try changing it out for a new one and see if the problem
persists. Is the AFCI in the breaker box? If so inspect the wiring in
the box to make sure it's done correctly. Especially as regards both
circuits. If you aren't confident in the box hire a pro.
An AFCI combines parallel arc detection with ground fault protection of
equipment for protection against series arcs which often devolve into
arcing ground faults that will generate enough heat to kindle a fire.
The presently available AFCIs are not suitable for use on multiwire
branch circuits so if the circuit you are trying to protect is run in
three wire plus ground wiring method the AFCI will trip because the load
on the neutral will be different from the load on the ungrounded
conductor by more than the thirty milliampere threshold of the AFCI's
circuit. The AFCI will trip on a ground fault of 30 milliamperes or
more. The AFCI injects a detection current into the neutral to detect
ground faults. If it is tripping as soon as you close it there is a
short circuit or a ground fault on the wiring it supplies. Disconnect
both the neutral and the ungrounded current carrying conductor from the
GFCI breaker. If the neutral for that circuit is not connected to the
breaker you have found your problem. Both current carrying conductors
of the circuit must be connected through the AFCI breaker. Test those
two conductors to ground with a continuity tester or a ohm meter. There
should be no connection between those two conductors and ground once
they are disconnected from the AFCI breaker. If you measure the
presence of a connection to ground you must find the fault and clear it.
Well we aren\'t no thin blue heroes and yet we aren\'t no blackguards to.
GFCIs do that and will detect a neutral-ground connection downstream
with no load being drawn (and can't be set with that condition). My
understanding is that AFCIs don't and require an applied load to detect
downstream neutral-ground connections.
I was afraid you were going to ask that - I probably would have asked
the same thing. I need to include source info in the notes I keep.
The answer was originally based on an article from Mike Holt
In the section "Does a GFCI circuit breaker offer equal or greater
performance ...." Holt says UL943 devices include current injeciton and
will detect G-N connections with no load but that UL1053 devices only
detect G-N connecitons with a load applied. I took this to be a
distinction between GFCIs and AFCIs but that apparently isn't what Holt
Holt talks about UL489/943/1699 and UL489/1053/1699 devices. UL943 is
for GFCIs. UL1053 is for "Ground-Fault Sensing and Relaying Equipment".
AFCIs are under UL standard 1699. The statement of scope of 1699 at
the UL web site is the sandard doesn't include GFI functions and they
are covered by other UL standards, presumably 943 or 1053. (UL489 is for
molded case circuit breakers.)
A very interesting technical paper on AFCIs is from the Comsumer Product
Safety Commission (AFCIs resulted from work initiated by the CPSC).
The paper insludes info on why circuit breakers don't reliably detect
arcs and on what AFCIs shouldn't detect.
From page 15 describing the possible addition of GFCI protection to an
AFCI (that is 6 ma trip instead of 30 ma trip) "also the grounded
neutral protection is required per UL 943". I would take that to
indicate that AFCIs don't include current injection and it has to be
added. From the combination of articles I think what I said is right. It
would be easy to test.
Relating to another thread I ran across a paper on grounding with
coupled rods I thought was interesting:
Thank you for your responses.
I think I understand most of what you are saying ... maybe !!
I'll swap out the GFCI and see if that fixes it. Failing that I'll do
my best to look for a common neutral, but that may be difficult because
the wiring is not accessible. If I have no luck with that I'll replace
the AFCI with a regular circuit breaker.
Did I get it right?
All my best and thank you
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