Combo AFCI

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Twenty four hours later, and I am still not able to keep from wondering. . .understand what? :confused:
 
al hildenbrand said:
understand what? :confused:
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Al, I don't get it. Whats the difference between the AFCI breakers the resi guys have been using and the combo type? I read Doug's UL link.
 
My understanding is that the combo types are meant to protect all the way downstream to something small like a cordset.
Their trip threshhold is much lower than a branch circuit AFCI and thus offer more protection (as well as more nuisance tripping?).
 
Doug,

I wonder about nuisance trips, as well.

The old AFCI (Branch Feeder) requires an arcing event that has currents that, at least, reach 50 to 70 Amps before the AFCI circuitry triggers an interrupt.

The new AFCI (Combination) lowers the arcing event threshhold to around 5.0 Amps.

The UL "White Book" Dirctory -General Information for Electrical Equipment doesn't list this lower threshhold current, but does show the outcome. . .that is, the higher impedances at the far end of the circuit, the equipment at the end of a power cord set, will be "visible" to the AFCI circuitry.

To me, this implies that the circuitry of the AFCI actually has to work. . .the question I have is will it truly discriminate between "good" and "bad" electrical arcs accurately enough to allow me to do electrical contracting without bad customer relations.

I can imagine explaining, "The AFCI is required by NEC. The AFCI is sensitive and will shut things off even when there is no problem. . .but you should treat it as if it is a dangerous event until you know that nothing actually happened".

I'm asking my client to prove a negative. If I just installed this AFCI for my client, my warranty has me proving the negative.
 
According to a Sq D engineer (been w/ Sq D over 50 years) the combination type AFCI will detect both series and parallel arc faults.
 
Al,
I'll be honest with you.
I have not had any experience with AFCIs and I am just trying to bring myself up to speed on them so I can talk intelligently about them when dealing with homeowners and inspectors.
 
dezwitinc said:
. . . I am just trying to bring myself up to speed on them so I can talk intelligently about them when dealing with homeowners and inspectors . . . As their contractor.
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Ask us what you think you might be asked.
 
Pretty much, I think this is about all I know about AFCIs, unless there's something (besides history) I missed.

I'm with Larry, I think a "what if" scenario would help us out in helping you. :)
 
Doug,

I tried to say it above, and it bears repeating, in my opinion.

The new combination AFCI has a trip level that is well down into the normal running current on a branch circuit in a dwelling.

Now, admittedly, the current flowing in any given branch circuit is a function of what happens to be turned on. . .so, in a dwelling, the load will be low in a lot of instances. However, around mealtime, and / or, around the hours when folks are home and still active, various AFCI protected circuits will load up to more than 5 Amps (the threshold that is required for a combination AFCI to trip if the electronics determine the activity out on the circuit is "wrong").

The AFCI breaker will see the sum of the current drawn by all the running loads. Let's say there is a cheap incandescent dimmer (think lots of undamped high frequency current and voltage oscillations each half cycle) dimming a 100 Watt lamp, a couple Compact Fluorescent Lamps with Pacific Rim electronic ballasts, a computer, printer, monitor, and TV all with switching power supplies sucking off little square wave pulses of energy from the branch circuit. . . and for "fun", occasionally, an old Hoover vacuum with a brush commutated universal motor.

That imaginary list of loads might be in a bedroom or a family room. These loads will present a lot of high frequency "hash" in the current and voltage waveforms at the AFCI breaker terminals. The nature of the "hash" is going to be highly unpredictable, in my opinion, because nobody can control what Mr. & Mrs. Homeowner will find attractive to purchase and energize. . .after all, this is America! . . .they have a consumer's right to freedom of choice!

To date, the manufacturers, that have participated in discussions about AFCI operation I am aware of, have not responded cogently to direct inquiries about the how an AFCI discriminates between "good" and "bad" arcs.

The normal running current of a moderately loaded 15 Amp 120 Volt branch circuit will cause the new combination AFCI to be continually testing for arcs. The old AFCI needed 50 to 70 Amps in an event, before it would arm, which doesn't easily happen, by comparison, to 5.0 Amps. Only after a 50 to 70 amp "bad" event did the old AFCI arm and then only for eight half cycles. . .then it shut down again.

To date, a testing tool, independent of the AFCI breaker TEST button, that tests the arc detection circuitry of the AFCI does not exist. (There may be laboratory apparatus. . .but there is nothing for the electrician's tool pouch).

As an electrical contractor, I'm going to find out, once the combination AFCIs are installed, if the manufacturer's have made something that will survive in the wilds of Mr. & Mrs. Homeowner's equipment, yet actually Interrupt an Arc Fault.
 
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