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#14233 - 09/17/02 07:08 AM AFCIs...my turn  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Well, after sitting on the sidelines with this topic, I now have some thoughts

After reading the thread in the other section of this forum, and learnig about the 75 amp trip requirement, Id like to ask what happens if an arc fault (parallel) occurs that has a high enough impedance to limit the current flow to 10 or so amps. Most of us know that arcs are so hot that a welding machine will melt steel at much less than 75 amps.
I was under the impression that these devices "recognized" the asymmetrical wave form associated with arcing, regardless of the magnitude. So what happens to a high impedance arc that limits the current to about 10 amps? Do we have to wait until a low enough impedance path results, or will they trip at the 10 amp level due to the "noisy" waveform?


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#14234 - 09/17/02 08:07 AM Re: AFCIs...my turn  
electric-ed  Offline
Member
Joined: Jul 2002
Posts: 175
Canada
It has been stated that AFCIs do not protect against any arcing faults of less than 75 amps. This is not 100% true. 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"
http://www.ul.com/regulators/afci/AFCI_scenarios020502.pdf

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]

Ed


#14235 - 09/17/02 08:35 AM Re: AFCIs...my turn  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Maybe I'm stupid, but I can't see where table 2 addresses the level of current at which the device operates. Table 1 shows what type of test and the current level. Table 2 only shows whether or not it operates as an AFCI, but not which scenario it operates under.???


#14236 - 09/17/02 09:09 AM Re: AFCIs...my turn  
ElectricAL  Offline
Member
Joined: Oct 2001
Posts: 597
Minneapolis, MN USA
Redsy,

Your question centers in on one of the black holes in the available information.

To my knowledge, the technical info on the contents of the black box "sophisticated technology" contained within the manufactured branch feeder AFCI units is not available to us, the end installers.

As I look at the UL1699 AFCI Test Scenarios that Ed posts above, I note that the low current (below 75 A) tests rely on enough physical damage occurring as a result of the failure, that a connection with the egc is established.

I presume that the "AFCI" then operates because of the add-on feature of also being built with a 50 mA (or thereabout) GFP. The manufacturers have stated that the AFCI portion ignores events below 75 A magnitude.

The branch feeder AFCI fails the low current tests when the wiring method is ungrounded (knob & tube, 2-wire NM, 2-wire zip cord).

The silence of the manufacturers about the construction of the microprocessor(s) and memory(ies) inside the branch feeder AFCI, and the silence about the progamming executed by the same, really concerns me.

Al


Al Hildenbrand

#14237 - 09/17/02 05:10 PM Re: AFCIs...my turn  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
it has many concerned Al,
and there is no harm in questioning this, or the authority(s) involved......

many simply wish for some straight answers, less double talk , but this will apparently not be so unless there is a strong enough voice from the trade and/or end consumer for it to happen.

people, products, companies, orginizations should be accountable or they simply loose much hard earned credibility...



[This message has been edited by sparky (edited 09-17-2002).]



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