AFCI vs. GFCI breakers

rpoet

Member
Join Date
Jun 2008
Location
New York, NY
Posts
536
Hi All,
I have a question regarding AFCI (Arc Fault Circuit Interrupter) circuit breakers. How do they compare to GFCI (Ground Fault Circuit Interrupter) breakers? After a recent fire at a relative's home (no one was hurt, but the smoke and water damage was total. The house will have to be completely renovated) caused by chaffed wiring on a cheap floor lamp, we were told that AFCI protected outlets in the bedrooms might have prevented the fire.

I have installed GFCI breakers and understand how they work; the breaker compares current going to the load with current returning from the load with a current transformer and trips if the imbalance exceeds (typically) 6ma.

What does an AFCI do that a GFCI can't? Wouldn't a GFCI detect an imbalance in current from an arc to earth? I've read up on AFCI's on Wikipedia ( http://en.wikipedia.org/wiki/AFCI ), but I'd still like to know what's going on inside them.

Is it also true that AFCI's may nuisance trip if used to protect motor loads like ceiling fans, as well as some types of compact fluorescents? I've received differing views on this.


Thanks,

rpoet
 
AFCI's are now code required for new installations in living spaces such as bedrooms. They are different from a GFCI in that their purpose is to detect large demands of electrical current and trip with milliseconds with the main purpose being to prevent household fire. The GFCI detects an imbalance between the hot and neutral conductors and shuts down in a similar manner, but the purpose of a GFCI is to prevent electric shock. They both have test buttons and may look similar, but it is important to note that on new installations by code you are not supposed to install AFCI's in bathrooms or kitchens, and vice versa with GFCI's in the living spaces.
 
Read up on these a few years ago so memory just may be a bit vague.
1. "Normal" house breaker does a quick trip at about 100 to 120 amp.
2. This current / power is adequate to set fabrics on fire.
So the AFCB trips at a lower level within the same time frame to keep the power of an arc smaller to prevent fire.

Dan Bentler
 
An AFCI looks at the 'signature' of the current, determining from that if any arcing is taking place. Many also contain the GFCI function.

While in the NEC, that part has been deleted in many places when they adopted the code. Yes, the 'code' is not law until adopted by each state. Many states modify it.

AFCI are pretty good, but there are still utilization loads that can fool it into tripping.

If you would like to see more discussion about AFCI's go to MikeHolt.com and search the forums there. See http://www.mikeholt.com/mojonewsarchive/AFCI-HTML/HTML/AFCI_Questions_and_Answers~20030301.htm for more info.

...by code you are not supposed to install AFCI's in bathrooms or kitchens,...
I don't think so. The code tells where it's required, I don't recall seeing it state where they cannot be used. Can you provide a reference?
 
Here are the NEC references.

210.12 Arc-Fault Circuit-Interrupter Protection.
(A) Definition: Arc-Fault Circuit Interrupter (AFCI).
A
device intended to provide protection from the effects of
arc faults by recognizing characteristics unique to arcing
and by functioning to de-energize the circuit when an arc
fault is detected.

(B) Dwelling Units.
All 120-volt, single phase, 15- and
20-ampere branch circuits supplying outlets installed in
dwelling unit family rooms, dining rooms, living rooms,
parlors, libraries, dens, bedrooms, sunrooms, recreation
rooms, closets, hallways, or similar rooms or areas shall be
protected by a listed arc-fault circuit interrupter,
combination-type, installed to provide protection of the
branch circuit.

FPN No. 1: For information on types of arc-fault circuit
interrupters, see UL 1699-1999,
Standard for Arc-Fault
Circuit Interrupters
.
FPN No. 2: See 11.6.3(5) of
NFPA 72®-2007, National
Fire Alarm Code
®, for information related to secondary
power supply requirements for smoke alarms installed in
dwelling units.
FPN No. 3: See 760.41(B) and 760.121(B) for powersupply
requirements for fire alarm systems.

Exception No. 1: Where RMC, IMC, EMT or steel armored
cable, Type AC, meeting the requirements of 250.118 using
metal outlet and junction boxes is installed for the portion
of the branch circuit between the branch-circuit overcurrent
device and the first outlet, it shall be permitted to
install a combination AFCI at the first outlet to provide
protection for the remaining portion of the branch circuit.
Exception No. 2: Where a branch circuit to a fire alarm
system installed in accordance with 760.41(B) and
760.121(B) is installed in RMC, IMC, EMT, or steel armored
cable, Type AC, meeting the requirements of
250.118, with metal outlet and junction boxes, AFCI protection
shall be permitted to be omitted.

210.8 Ground-Fault Circuit-Interrupter Protection for
Personnel.
FPN: See 215.9 for ground-fault circuit-interrupter protection
for personnel on feeders.
(A) Dwelling Units.
All 125-volt, single-phase, 15- and
20-ampere receptacles installed in the locations specified in
(1) through (8) shall have ground-fault circuit-interrupter
protection for personnel.
(1) Bathrooms
(2) Garages, and also accessory buildings that have a floor
located at or below grade level not intended as habitable
rooms and limited to storage areas, work areas,
and areas of similar use
(3) Outdoors

Exception to (3): Receptacles that are not readily accessible
and are supplied by a dedicated branch circuit for
electric snow-melting or deicing equipment shall be permitted
to be installed in accordance with 426.28.
(4) Crawl spaces — at or below grade level
(5) Unfinished basements — for purposes of this section,
unfinished basements are defined as portions or areas of
the basement not intended as habitable rooms and limited
to storage areas, work areas, and the like
Exception to (5): A receptacle supplying only a permanently
installed fire alarm or burglar alarm system shall
not be required to have ground-fault circuit-interrupter
protection.
FPN: See 760.41(B) and 760.121(B) for power supply
requirements for fire alarm systems.
Receptacles installed under the exception to
210.8(A)(5) shall not be considered as meeting the
requirements of 210.52(G).
(6) Kitchens — where the receptacles are installed to serve
the countertop surfaces
(7) Laundry, utility, and wet bar sinks — where the receptacles
are installed within 1.8 m (6 ft) of the outside
edge of the sink
(8) Boathouses.
 
Here are the NEC references.

...(snip)...

210.12 says where you MUST have an AFCI, 210.8 says where you MUST have a GFCI.

Nothing prevents you from having them in other places or from you putting them in places that are listed in the exceptions.

I can install an AFCI for my garage branch circuit that has hardwired lights or a GFCI in my attic, if I want to.

I can also put a ACFI in the breaker panel that feeds the branch circuit that has required GFCI's at outlets, such as the ones for bathrooms.

I can also put GFCI's on the outlets of a branch circuit that needs a AFCI protecting it. While that would be redundant as most AFCI's also contain GFCI functionality (combination-type AFCI), there is nothing preventing me from doing this.

Of particular note is that where an AFCI is required, it is for an outlet and where an GFCI is required, it is for a receptacle. A
receptacle is one type of outlet. Many people think an outlet is what you insert the plug that is at the end of a cord, into. Not the case. That is a receptacle. See NEC Article 100 for the definition.

 
Arc fault

Here's a video explaining how each type of breaker works...

http://www.youtube.com/watch?v=uqZfuRDNz04

🍻

-Eric
Good video but still having trouble. They trip with drill motors and just about all universal motors that have brush wear or poor com contact. The bedroom is indeed the best place for these breakers. In Canada they are required in reisdential bedrooms.
 

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