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#13627 - 09/08/02 11:16 AM AFCIs and series arcing faults  
electric-ed  Offline
Joined: Jul 2002
Posts: 175
Here are a few items of information that I hope will help balance the discussion with regard to the effectiveness of the AFCI. Some of you are already aware of this information, but there may be some who are not.

It has been stated that AFCIs do not protect against series arcing. This is not 100% true. There is protection against arcing faults that begin as series arcs and progress into line-to-ground or line-to-line (parallel) arcing faults.

Quote from General Electric Advertisement-

"GE AFCI breakers deliver 5 kinds of protection
1. Parallel Protection– direct contact of two wires with opposite polarity
(example: damaged extension cords)
2. Ground Protection – arc between a single conductor and ground
(example: improperly installed wall receptacles)
3. Series Protection – arc across the break in a single conductor, that
progresses to a ground or parallel arc (example: cable pierced by a nail
from a wall hanger)
4. Overload Protection
5. Short Circuit Protection"

It has also been stated that AFCIs do not protect against any arcing faults of less than 75 amps. This is not 100% true either. Some of the “carbonized path” arcing situations were tested with simulated load currents.(5 amps, 10 amps, and 150% of load)
The two Tables below are from a UL document titled “Arc Fault Testing and Arc Fault Scenarios - January 28, 2002”

Table 1 shows some details of the tests conducted. (X indicates which test was conducted)
(Combination AFCI – This is the (common breaker type) AFCI which complies with the requirements for both branch/feeder and outlet circuit AFCIs. It is intended to protect downstream branch circuit wiring, cord sets and power-supply cords.)

[Linked Image]

Table 2 shows which type of device provides protection under various conditions. Here again, “Series Arcing Protection” is assumed to mean - protection against arcing across a break in a single conductor, which progresses to a ground or parallel arcing scenario.

[Linked Image]


Work Gear for Electricians and the Trades

#13628 - 09/08/02 08:22 PM Re: AFCIs and series arcing faults  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
nice Ed.....

add 2 slices of stone ground wheat , and what kind of sandwich does this thread make??

[Linked Image]

#13629 - 09/08/02 08:45 PM Re: AFCIs and series arcing faults  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
The NEC does not require the use of "combination type" AFCIs. The code only requires "branch circuit" protection. Also the AFCI manufacturers tell us that a "glowing connection" or high resistance connection is not an arc of any type and the AFCI circuit itself won't respond to these types of faults. The GFP part of the AFCI breaker will respond to these types of faults after they become a ground fault. So will a GFCI. It is my opinion that this type of heating is the cause of most dwelling unit fires.
I still find it very strange that the AFCI requirement was put into code without any statements saying how many fires these devices would be expected to prevent. Where is the cost benefit study? We will never have the technology to make our electrical systems safe and even if it was physically possible to make them 100% safe, it would not be economically possible.
I have worked up some fire data numbers using information from "Fire in the United States, 12th Edition".
This is 1998 data. The numbers in this report are based on NFIRS (national fire incident reporting system) data. The NFIRS data accounts for 39% of all fires that occur in the US. I have adjusted the numbers by this factor to account for all fires. This data shows that there were 401,695 residential unit fires in the US in 1998. The point of origin for 12.9% of these fires was the sleeping room. Of the fires that originated in the sleeping room, 19.9% were reported to have been caused by the electrical distribution system and 11.6% by appliances. Applying these percentages to the total number of residential unit fires shows that 51,819 fires originated in the sleeping room. Of these 51,819 fires, 31.5% were caused by the electrical distribution system or appliances. This would mean that 16,323 dwelling unit fires may have been electrical in origin.
Mr. Robert Clarey of Cutler-Hammer made the statement that AFCIs could be expected to prevent 40% of these fires. This statement was made in comment 2-68 in the '98 ROC. This means that if every dwelling unit bedroom branch circuit in both new and existing dwelling units had AFCI protection, we would prevent 6529 fires per year. We now have to look at the total number of dwelling units existing in the US and the number that are added each year. US Census data shows that there were 115,253,000 housing units in 1999. 1,640,900 new housing units were built in 2000. If you divide the 6529 dwelling unit fires that would be prevented if all dwelling units had AFCIs and then multiply that result by the number of new housing units being built, we can expect that 93 dwelling unit fires would be prevented the first year of full compliance with the AFCI rule. This number is likely somewhat high as fires do not occur nearly as often in new buildings. The fire data used to get the AFCIs into the code showed that 85% of the electrical fires originated in dwelling units over 10 years old. (This brings up the question of whether the AFCI breaker will still be functional, when it its needed, over 10 years after its installation. The GFCI data and new GFCI standard seems to indicate that they won't be function at that time)
If we assume an installed cost of only $50 per new dwelling unit, that means that we would be spending $82,045,000 to prevent 93 fires. That would allow for a loss of over $820,000 per fire. Yes, I know that in some cases these fires result in a loss of life and that we can't put a dollar value on that, but corporate America does just that every day. Does the AFCI requirement meet any reasonable cost benefit analysis?


#13630 - 09/08/02 09:01 PM Re: AFCIs and series arcing faults  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
an excellent example of the old 'statistics ' addage, unfortunatly lost to CMP-2

#13631 - 09/08/02 09:30 PM Re: AFCIs and series arcing faults  
electric-ed  Offline
Joined: Jul 2002
Posts: 175
I must admit I haven't been doing very well solving Steve's riddles up to this point, but I am curious about the sandwich one.
Tell us, what kind of sandwich? [Linked Image]


#13632 - 09/09/02 02:04 AM Re: AFCIs and series arcing faults  
Joule-E  Offline
Joined: Aug 2002
Posts: 25
Eventually they will come up with little micro-robots that run up and down the cables to check what sort of electrical connection is occuring, it will then run back to the breaker and tell it to trip, or stay contacted.

#13633 - 09/09/02 06:49 AM Re: AFCIs and series arcing faults  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA

A wish sandwich?

#13634 - 09/09/02 07:03 AM Re: AFCIs and series arcing faults  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
the riddle is UL1699 Ed, however we as consumers & contractors bear the brunt of the joke.....

more fat for the fire here......

from feb/mar 00' necdigest:

Eaton Corporation funded a UL Special Services Investigation that determined such hazards could be mitigated by an AFCI circuit breaker providing both arcing and ground fault protection. The "glowing contact" has the potential to eventually melt the wire insulation and the receptacle itself. Typically a line-to-neutral arcing fault or a line-to-ground or neutral-to-ground ground fault will develop. An AFCI circuit breaker employing both arc and ground fault interrupters will respond to these conditions by tripping and deenergize the branch circuit feeding the receptacle.

Q for extra credit...

Are we implying a combo device here only?

#13635 - 09/09/02 07:49 AM Re: AFCIs and series arcing faults  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA

Joe Tedesco, NEC Consultant

#13636 - 09/09/02 08:07 AM Re: AFCIs and series arcing faults  
donles  Offline
Joined: Apr 2001
Posts: 83

Good thought provoking post.


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