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Joined: Jan 2005
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I provided a link to the Wiki entry regarding Paschen's Law.
What more "rationale" is needed? When physical laws say something can't exist ... it can't exist.
Clearly the problem is the non-existent "rationale" behind the NEC requirements. For the very first time, UL is listing a product that they simply can NOT test for the promised function.
That is, the units are NEVER asked to detect any sort of arc-let alone interrupt one. They might was well call them "Pixie dust detectors."
New Hampshire is correct. The NEC lobby is wrong on this one. New Hampshire has to answer to it's citizens. The NFPA answers to no one -not even its' members. Nor, for that matter, does UL.
It's time to reign in these self-appointed kings.
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Joined: Oct 2000
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It's time to reign in these self-appointed kings.
That takes education Reno. And education takes time , and i'm glad you've remembered Paschen from Dr Engels dissertation i posted here a while back. I'll be back with more to the story, when i'm told to post it, just for sorts like you ~S~
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Joined: Jul 2008
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OK Guys,
At the risk of displaying my ignorance, I don't get it.
I skimmed over Reno's link and read that the minimum breakdown voltage in air is 327V. But I'm sure that we've all seen arcing on 120V circuits. So what am I missing?
Thanks... Bruce
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Joined: Jan 2005
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Please note the 327 figure is a theoretical minimum voltage for a sustained arc between two copper electrodes.
In practice, a higher voltage would be needed.
A sustained arc is not the same as a simple spark. Think of a spark as an arc that dies at birth.
The value would differ if either of the electrodes are of materials besides copper. A broken wire, or a loose wire at a connection, would create two copper electrodes.
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Here's the rub: UL tests fire extinguishers against "standard" fires. UL tests smoke detectors with real, "standard" smokes. Yet UL performs absolutely no test that asks any AFCI to detect or open any form of arc whatsoever. All the UL tech does is press the test button.
Development of AFCI testing equipment has been stymied by UL allowing the makers to assert "proprietary" arc forms, forms which are withheld from UL.
UL might as well test them using a forked stick.
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Joined: Jul 2004
Posts: 9,931 Likes: 34
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We are confusing arcs with sparks. Anyone who has ever seen a cigarette lighter knows sparks can start a fire if the fuel is easy enough to light. You can also see pretty big sparks from low voltage supplies.
When Harvey Johnson from CH was explaining the AFCI to me in the 90s (before it was really known outside their labs) the example was a pinched lamp cord behind the bed, buried in cotton dust bunnies. That broken or shorted wire could easily create a spark big enough to light the cotton without tripping the O/C device.
Their mission was to design a circuit that would detect that situation and open the circuit.
Whether the ones they came up with actually work as advertised will be borne out by history. We are on something like Version 3.2 tho. I would certainly not have much confidence in the Ver. 1.0 device we were forced to use in 2002.
Greg Fretwell
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We are confusing arcs with sparks. Anyone who has ever seen a cigarette lighter knows sparks can start a fire if the fuel is easy enough to light. You can also see pretty big sparks from low voltage supplies.
When Harvey Johnson from CH was explaining the AFCI to me in the 90s (before it was really known outside their labs) the example was a pinched lamp cord behind the bed, buried in cotton dust bunnies. That broken or shorted wire could easily create a spark big enough to light the cotton without tripping the O/C device.
Their mission was to design a circuit that would detect that situation and open the circuit.
Whether the ones they came up with actually work as advertised will be borne out by history. We are on something like Version 3.2 tho. I would certainly not have much confidence in the Ver. 1.0 device we were forced to use in 2002.
Greg, do us a favor the next BBQ you have with your neighboring manufacturing reps, and ask them specifically what changes in the detection algorithm(s) have had UL1699 amended ~S~
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Joined: Jul 2004
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Alas Harvey has gone off to that construction trailer in the sky so I am not talking to those folks anymore. His son is still working at CH but he doesn't come around here.
I am not trying to sell AFCIs. I just understand the intent. Reno is right that they still have not actually proved that they work. Only time will tell. Trying to compare this with a GFCI is bogus. The GFCI has a very simple standard, the AFCI, not so much.
Greg Fretwell
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Joined: Mar 2004
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I think the proof AFCIs work and the proof they are garbage is the same. In my limited experience, they trip when a light bulb burns out, when a light switch sparks, when a clothes iron cycles, when a heater thermostat switches and when a vacuum is used. I saw an extension cord run into a bedroom to overcome the problems with the AFCI breaker.
The standard excuse for being late for work should be "My AFCI tripped and my alarm didn't go off."
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Joined: Oct 2000
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I am not trying to sell AFCIs. I just understand the intent. Reno is right that they still have not actually proved that they work. Only time will tell. Trying to compare this with a GFCI is bogus. The GFCI has a very simple standard, the AFCI, not so much.
So this begs the Q, how would one 'sell' afci's Greg? Originally Zlan, in conjunction with Thompson Microelectronics forwarded what was no more than conjecture 1998 minutes Unless i've missed a technical piece, the 'LCM" , or microprocessor , this integral sensing element remains somewhat a mystery to this day. Further, the version upgrades do not address this issue any more than informing the market they've simply 'made it better'One would think our trades level of electrical curiosity would be inquiring as to specifics, especially since our end users are going to pitch $1K on average for a panel full of them ~S~
Last edited by sparky; 02/21/15 01:56 PM.
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