 |
| |
|
| |
AFCI Update
MIKE HOLT'S POSITION AS
OF OCTOBER 30, 2002
I have pressed the manufacturers of AFCI devices to demonstrate
the superiority of the AFCI circuit breaker (as compared to a
standard circuit breaker) in preventing a fire from loose
terminals and connections. My challenge was specifically directed
to Cutler-Hammer because they disputed some of the comments I
made in my newsletters. Cutler-Hammer had offered many times to
"demonstrate their AFCI technology," but I refused this
invitation. I requested, instead of their demonstration, a
comparison test of AFCI circuit breakers against a standard
circuit breaker, but Cutler-Hammer refused this request. As a
result, I submitted a proposal October 30, 2002 to have the AFCI
requirement removed from the NEC based on the following:
1. UL 1699, the AFCI standard, does not require the AFCI circuit
breaker to protect against fires caused by arcing at loose
connections, at loose wires in wire connectors, or at loose
screws.
2. Many in the industry (including myself) felt that an AFCI
protective device, as required by the NEC, will not significantly
reduce the incidence of fires at loose terminations and
connections and the AFCI protection device (as currently listed)
will not prevent them.
3. The public and the electrical industry have placed their trust
in UL and the National Fire Protection Association to protect
them. The Code process must be a guardian of public safety and it
must put the public interest first. We will fail to maintain
public trust if we do not remove the requirements for AFCI's from
the NEC until this technology is demonstrated to prevent a fire
from loose terminals and connections.
4. If the AFCI protection device is not required to protect
against loose terminals, then what good is it? The data available
today does not support how many residential fires have been
started from loose terminal connections as compared to an arcing
fault. Nor can data support how many fires can be linked to
faults in premise wiring as compared to faults associated with
the plugged-in load.
5. The public and the industry should have the opportunity to see
a demonstration where an AFCI will prevent a fire from loose
terminals, under the same conditions that a standard molded
circuit breaker and fuse could not, or did not. Since the
manufacturers state that this device will prevent a fire from
this condition (their promotion material), they should show us
the proof.
6. What is needed is a comprehensive study on the true causes of
electrical fires by a Task Force of people qualified for this
purpose. This study should provide the details on the causes of
fires, where they occur, and what actions the industry should
take to help reduce them. This study needs to be available for
public input and debate (just like the NEC process). I'm sure
that with the proper study valuable information will be acquired.
We may learn:
MIKE HOLT'S POSITION AS OF NOVEMBER 5, 2002
On October 31, 2002, Cutler-Hammer contacted me and offered to
provide the comparison testing of protective devices as I
requested. This meeting was held on Monday, November 4, 2002 in
Pittsburgh, PA with Dr. Clive Kimblin [Manager of Standards], Mr.
John Wafer [VP and Group Chief Technology Officer], Dr. Joe Engel
[Electronics Engineering Manager], and Mr. Brendan Foley [Product
Manager]. I personally paid all of the costs incurred for this
trip, including transportation and lodging (very expensive when
you make last minute reservations).
After having attended the comparison demonstration, and getting
the chance to have my concerns and questions addressed directly
by those that have the knowledge of this technology, I have
changed my position on the effectiveness of AFCI protection
devices. As a result, I will withdraw my proposal to remove
AFCI's from the NEC.
It is true that AFCI circuit breakers are not required to protect
against loose "glowing" connections, but AFCI circuit
breakers that are dual-listed for AFCI/GFI or AFCI/GFCI should
prevent most fires from high-resistance heating (glowing) at
loose terminals and connections http://www.mikeholt.com/htmlnews/afci/ULreportonterminals.pdf.
The performance tests comparing AFCI/GFI with a standard circuit
breaker demonstrated that AFCI/GFCI circuit breakers will save
lives under the conditions identified by the manufacturers,
including from loose terminals or connections. The comparison
test was simple; there were two outlet boxes each containing a
duplex receptacle with loose terminals. A 1,500W load was applied
to each, and after an hour or so, the receptacles melted and the
AFCI/GFI circuit breaker opened within three to eight half-cycles,
whereas the standard circuit breaker did not trip.
I personally thought that it was the heat (650ºF at the hottest
point) from the loose terminals that caused the fire. What I
discovered was that the heat from the loose terminals melted the
wiring device and the circuit conductors in the box, creating a
line-to-neutral or line-to-ground fault. If the available short-circuit
current of the fault was 100A, it could take between one and five
seconds (120 to 600 half-cycles) or even longer to clear the
fault with a standard inverse-time circuit breaker, whereas an
AFCI/GFI circuit breaker would clear the fault in less than nine
arcing half-cycles from a line-to-neutral fault or two half-cycles
from a ground fault.
NOTE: AFCI circuit breakers are not required by the NEC to be
dual-listed (AFCI/GFI or AFCI/GFCI). Nevertheless, all four U.S.
manufacturers include ground fault circuitry and Cutler-Hammer
has chosen to dual-list their devices. The NEC should make dual-listing
a requirement since there is no cost difference between dual-listing
or not.
I still feel that a comprehensive study on the true causes of
electrical fires by a Task Force is needed to provide accurate
details on the origin of electrical fires, where they occur, and
what actions the industry should take to help reduce them. This
study should be available for public input and debate, just like
the NEC process.
We all play a critical role in improving life safety by becoming
involved in some manner, whether by submitting a proposal,
commenting on a proposal, being a Code panel member, or an "outsider"
like myself trying to keep people on their toes.
I know you must have lots of questions and I hope the following
will answer most of them. I am organizing a meeting in Pittsburgh
at the Cutler-Hammer Technology and Quality Center for December
17th from 9:00 a.m. to 3:00 p.m. to demonstrate how an AFCI
circuit breaker protects against a fire from loose terminals and
connectors, as well as the technology. If you are interested in
attending, please contact me as soon as possible.
As always, please let me know your thoughts and feelings. Mike
Holt
QUESTIONS:
Would it be possible for you to give more information on
how the tests were conducted?
A typical receptacle installed in a metal and
nonmetallic box mounted on wood studs with drywall. The hot wire
just touching the screw on the receptacle, it was move around so
that it began a very small arc when the 1500W heater load was on.
In less than one hour the receptacle and the wiring in the box
would melt. The AFCI opened because of an arc fault (line-to-neutral)
on one case (when the peak current of a half-cycle exceeded 50A,
three times in a row) and it was the Ground Fault Interrupter (GFI
- 30 mA) that opened in the other. In both of these examples, the
arc energy was as low as could be detected.
What are the characteristics of an arc on the electrical
circuit?
I teach an apprenticeship class and I would like to be
able to explain the theory to the class.
What makes the AFCI protection any different from that in
a standard circuit breaker?
AFCI's have the electronics to open the circuit for low-level
line-to-neutral faults when three to eight half-cycles exceed 50A
peak (within .5 second), whereas a standard circuit breaker might
not open for many hundreds of half-cycles.
Why not trip the AFCI in one or two half-cycles, instead
of three to eight half-cycles?
If the AFCI tripped in one half-cycle then, then many
voltage surges could cause the protection device to trip and in
many cases we might not be able to turn on the loads on. A light
bulb sometimes takes two
Half-cycles to burn out, so two is out.
Does a GFCI circuit breaker offer equal or greater
performance than an AFCI circuit breaker, given the same
conditions for which an AFCI breaker was designed?
GFCI circuit breakers are designed to protect against
ground faults of 4 to 6 mA or more, short-circuits, and overloads.
Dual listed AFCI/GFCI circuit breakers are designed to protect
against ground faults of 5 mA or more, short circuits, overloads,
and arcing line-to-neutral faults. Dual listed AFCI/GFI circuit
breakers are designed to protect against ground faults of 30 mA
or more, short circuits, overloads and arcing line-to-neutral
faults. A GFCI does not offer protection against arching line-to-neutral
faults.
It seems to me that the demonstration you witnessed
proved only that 30mA GFCI breakers improve safety, not that AFCI
breakers improve safety. I don't understand why you feel a dual
listed AFCI/GFI breaker is any better than a GFCI breaker.
Because a GFCI circuit breaker with ground fault
protection of 5 mA does not have line-to-neutral arc fault
protection.
What still doesn't make sense to me is that if a GFCI
breaker trips at a lower level than an AFCI - why mandatory AFCI?
Why not an option to use GFCI?
A GFCI protection device offers tremendous line-to-ground
and neutral-to-ground protection (maximum 5 mA), but a GFCI will
not clear a line-to-neutral arcing faults in three to eight half-cycles,
only a AFCI can provide this level of protection.
I don't see the value of an AFCI protection device that
is not GFI or GFCI listed because it only senses a line-to-neutral
fault, and really how often does that happen in branch-circuit
wiring?
I agree with you, the likely hood of a line-to-neutral
fault in branch-circuit wiring causing a fire is very rare. But a
line-to-neutral arc could occur in two wire NM cable or knob-and-tub
wiring (particularly in the outlet boxes). Line-to-neutral faults
are very common inside an outlet box when the conductor
insulation melts because of excessive heat from loose terminals
or connections. Only an AFCI is capable of clearing the fault
within three to eight half-cycles.
I can't imagine any type of fault on a Code compliant
building wiring system that will not develop into a ground fault
which would be protected by a GFCI.
The likely hood of a line-to-neutral fault not evolving
into a ground-fault is not likely in today's NEC compliant wiring
systems consisting of metal boxes, raceways and cables.
Installations consisting of metal enclosures, raceways and cables
should be safe from a fire if GFCI. But a GFCI protection device
cannot be installed on all circuits because of leakage current
from induction loads such as motors and fluorescent fixtures. The
ground-fault setting on an AFCI is no lower than 30 mA, much
higher than the mA setting of a GFCI.
Does an AFCI/GFI provide the same level of ground fault
protection as a GFCI device?
No, AFCI/GFI circuit breakers will de-energize the
circuit when the ground fault exceeds 30 mA, whereas an AFCI/GFCI
circuit breaker opens at 5 mA. However, a AFCI/GFCI circuit
breakers should only be installed on circuits where nuisance
tripping would not be a problem.
There are many homes dating back to the 1920's that still
have knob-and-tube that has outlasted subsequent wiring
technology, such as BX with rubber insulated conductors and early
forms of romex. Do AFCI breakers protect existing knob-and-tube
wiring systems?
An AFCI circuit breaker will trip and clear the circuit
when a line-to-neutral arc occurs (often caused by the melting of
the conductor insulation at loose terminals) within three to
eight half-cycles, whereas a standard circuit breaker might not
open for many hundreds of half-cycles. Note: If the AFCI is dual
listed as a GFCI, the two wire receptacle can be replaced with
three-wire receptacles and no equipment grounding conductor is
required to be run to the receptacles [406.3(D)(3)].
Is it okay to replace a regular circuit breaker with an
AFCI circuit breaker if there are GFCI receptacles on the circuit
in question?
Yes. The GFCI receptacle should not interfere with the
AFCI protection circuitry.
What type of arcs are the most common factors in
electrical fires, and will today's AFCI circuit breakers detect
these faults?
An AFCI is designed to detect and clear a line-to-neutral
fault under conditions where a standard circuit breaker might not
(3 to 8 cycles as compared to 600 half-cycles, depending on the
available fault at the failure). Loose electrical terminations
and connections should generate enough heat to create a line-to-neutral
fault or a line-to-ground fault, which will be detected by the
AFCI or GFI circuitry.
I have heard that the AFCI technology would be improving
in the future. What do you think?
I don't know if the AFCI technology in a circuit breaker
can be made to do more than it does right now. You have to
understand that this technology is not new. The manufacturers
have been working on this for almost 10 years.
I've heard that AFCI devices won't protect against fires
from 2-wire NM cable. Is this true?
False. AFCI's have superior performance protection over
a standard circuit breaker when it comes to low-level line-to-neutral
faults. In an old house I would surely install them, even though
they are not required by the NEC.
Would an AFCI circuit breaker work as a service or feeder
protection device?
No, because they are limited by UL to 15A and 20A, 120V.
Are the electronics in AFCI devices subject to the
damaging effects of high-voltage surges? And if so, do they
continue to energize the circuit giving the false impression that
they are working properly?
Yes and yes. The electronics in AFCI devices are subject
to the damaging effects of high-voltage surges, just like a GFCI
circuit breaker. The instructions supplied with both GFCI's and
AFCI's stress that they should be tested monthly to ensure that
they are operational.
NOTE: The AFCI UL standard was recently revised
to raise the surge voltage test from 4kV/2kA to 6kV/10kA and all
permanently connected AFCI's must meet this requirement by July
15, 2004.
I read there's a nuisance-tripping problem with AFCI
devices. Has this problem been resolved yet?
The major problem is that some installers do not yet
understand how the AFCI circuit protection device operates. If
there is a neutral-to-ground connection on the load side of the
circuit breaker, the breaker will not trip until a load has been
applied, whereas a GFCI, even without load, will not operate
until the neutral-to-ground connection has been removed.
What occurs is that the electrician leaves the property after
installing and turning the devices on, then the homeowner calls
two hours later complaining that there is no power. Trouble-shooting
determines that as soon as a load is applied, the AFCI trips
because of a faulty neutral-to-ground connection on the load side
of the device.
Why does the NEC only require AFCI protection for bedroom
circuits?
This is an area in the home where the disabled, elderly,
and young children spend a great deal of their time. The ratio of
the bedroom space to the total area is relatively large as
compared to the ratio of the number of bedroom circuits to the
total number of circuits. So, basically, you get the most
protection for the cost.
Mike, do you think the data supports the requirement that
AFCI protection devices should be required by the NEC in new
homes?
No, but if the NEC does not require it when the home is
built, then there is no way to require it later when it's really
needed. However, newer homes have fires via electrical origin as
well, just statistically at a lower rate than older homes.
Will you be replacing the breakers in your home with AFCI
breakers?
Well, that's a tough one. They are very expensive (about
$30 each) and if I replaced all of them, it would cost me about $1,500.
I will have an electrical contractor visit my home and check all
terminals for tightness. Since it's a new home, I don't feel the
risk is that great.
Yes, but Mike what's a life worth?
Okay, okay… I will install AFCI breakers for all 15
and 20A general-purpose circuits (before the electrician checks
all terminals, he'll probably find some neutral-to-ground
connections), but not the individual circuits. This should give
me the greatest level of fire protection for the cost.
Should the NEC expand the requirements for AFCI's?
It's easy for me to give opinions because I don't have
all of the facts and it won't cost me anything. Since I have
confidence in the NFPA Code process, I'll leave this tough
decision to the experts that sit on Code Panel No. 2.
What do you do about an older house with fuses? Are you
required to upgrade your panel if you do any modifications within
a bedroom?
AFCIs are not required for existing homes.
Do AFCI breakers work with multiwire circuits?
Yes if it's of the two-pole AFCI type.
I was under the opinion that when any renovation/modification
is done to a bedroom, even adding an outlet, the wiring was
required to be upgraded to the AFCI protection requirement. Is
this the correct assumption?
This is up to the local electrical inspector/building
official.
To the best of my limited knowledge, there is still no
way to test any of these breakers. How can an AHJ approve a
device that may or may not be working properly?
Sure there is http://www.mikeholt.com/news/archive/html/20/AFCI_Tester_08-16-2002.htm I have one!
INDUSTRY COMMENTS
Mike, I am proud of you and Cutler Hammer for going the extra
mile in your efforts. The electrical industry is better today
than it was due to the apparent success of this meeting. Don't
stop asking for better data on how fires start so that
improvements in safety will continue to improve.
Dan Prather, Inspector
Mike, I wish that I could have witnessed the testing. Your
interest in the AFCI has had an extremely positive effect on our
industry. I respect your ability to put in writing that you have
changed your position on a serious issue.
Jim Dollard, IBEW
I'd really like to know exactly what changed your mind. Don't
tell me these devices will work to detect loose connections…and
don't tell me that with better technology we can't detect loose
connection-type arcing either.
Bob Huddleston, Engineer
I read the "AFCI New Thoughts" file. I thought it was
very good and showed integrity and graciousness in changing your
point of view. I do agree with a couple of comments you added at
the end. I too, would have liked to see the test that changed
your mind, and what do you base your statement on that "AFCI
technology is probably about as good as it is going to get?
I would not have expected anything less than you changing your
viewpoint immediately and without hesitation once you have proper
facts. You have always been the first to admit it if you're wrong
or incorrect on anything. That is part of what I mean by
integrity.
Mike Culbreath, Graphic Designer, Mike Holt Enterprises,
Inc.
Click here to view the survey results from this newsletter.
Copyright © 2002 Mike Holt Enterprises,Inc.
1-888-NEC-CODE (1-888-632-2633)
