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Old 06-09-2009, 12:58 PM   #1
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Strobe Lights + AFCI circuit = Bad Combo


So last weekend I found one reason to hate the new AFCI circuit breakers in my new panel. They simply will not allow a strobe light to work (at least not at a very fast rate). I have 2 800watt strobe lights and it doesn't take much for them to trip the 20 amp AFCI circuit. Though I have found they work just fine on the 20 amp bathroom circuit that just has a GFCI outlet and no AFCI protection.

I guess this would be one of those times when the AFCI is unable to determine a bad arc from a good arc...

I don't plan on using my theatrical strobe lights in the house very often, but just something I happened to notice this weekend.

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Old 06-09-2009, 01:08 PM   #2
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Strobe Lights + AFCI circuit = Bad Combo


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Though I have found they work just fine on the 20 amp bathroom circuit [...] just something I happened to notice this weekend.
I hate when I just "happen" to have dance parties in the bathroom. Really disrupts the ol' morning routine.

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Old 06-09-2009, 01:11 PM   #3
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I hate when I just "happen" to have dance parties in the bathroom. Really disrupts the ol' morning routine.
Haha, it was the downstairs bathroom which is right next to the wet bar/family room area and was the only nearby outlet that was not an AFCI protected outlet (there is another in the laundry room for the washer, but that is further away). Most of the wiring in the basement is all new since I did the re-wire recently and code required several of these circuits to be AFCI.

Until last weekend I haven't had any problems with nuisance tripping of the AFCI's and see no need to change them out anytime soon, though I think my wet bar area can be changed to a standard breaker since these outlets are all GFCI's.
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Old 06-09-2009, 01:14 PM   #4
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Strobe Lights + AFCI circuit = Bad Combo


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They simply will not allow a strobe light to work (at least not at a very fast rate). I have 2 800watt strobe lights and it doesn't take much for them to trip the 20 amp AFCI circuit.
I guess this would be one of those times when the AFCI is unable to determine a bad arc from a good arc...
1600/120 = 13A, so it's not an overcurrent condition.

I can't imagine how this is happening, but I don't doubt it is.
The lamps fire from a charged capacitor so I don't think this triggering signal is coming up the cord. Can you post a link to your strobes?
It could be a power factor problem, like you get with switching power supplies. This new AFCI design may be an attempt to fix this problem.
http://www.freepatentsonline.com/6590754.html

And, from a paper on aircraft AFCIs,
"Many standard aircraft loads and
normal operating conditions on aircraft can exhibit seemingly anomalous waveform signatures. These
can include motor start-ups, strobe lights, landing lights, bus transfers, TRU’s, incandescent and
fluorescent lighting loads, and mechanical switches opening and closing. "

Last edited by Yoyizit; 06-09-2009 at 01:25 PM.
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Old 06-09-2009, 01:28 PM   #5
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Strobe Lights + AFCI circuit = Bad Combo


These are the strobes I have, I bought them for a lot less on eBay a while back: http://www.americandj.com/ProductDet...tSearch=strobe

They work ok so long as the strobe speed is set slow, but if I turn up the strobe speed too fast it trips the breaker. Both the wet bar and bath circuits are 20 amps, and both have GFCI outlets, the only difference is the wet bar circuit is protected by an AFCI breaker (and probably doesn't need to be AFCI). There is also a standard full size fridge plugged into the wet bar circuit, but it hasn't been running when trying to use the strobes (and I doubt an 800 watt strobe + fridge would trip a 20 amp circuit because of an overload).

Edit: I originally tried 2 strobes, then when that tripped the breaker I went and tried just one strobe and it still tripped the breaker.

Last edited by theatretch85; 06-09-2009 at 01:31 PM.
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Old 06-09-2009, 02:05 PM   #6
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Strobe Lights + AFCI circuit = Bad Combo


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They work ok so long as the strobe speed is set slow, but if I turn up the strobe speed too fast it trips the breaker.

Edit: I originally tried 2 strobes, then when that tripped the breaker I went and tried just one strobe and it still tripped the breaker.
Seems to me a pulse rate is spec'd in the UL specification for what is a bad arc. Of course I can't find it at the moment.
An arc, being a "fourth state of matter [plasma]" is kinda' hard to pin down, I'd think.
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Old 06-09-2009, 02:09 PM   #7
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Strobe Lights + AFCI circuit = Bad Combo


The way I understand it, AFCI works by sampling the current the same way a digital scope samples a voltage, except much slower (probably khz instead of mhz). What could easily happen is the strobe light is surging lets say 50-60amps of draw every time it turns on. When the frequency of the turn-ons synchronize with the sampling rate of the AFCI, trip.... because the AFCI sees a sustained high current draw over many sample periods.

Eventually the beat patterns synchronize at some frequency multiple.
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Old 06-09-2009, 02:19 PM   #8
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Strobe Lights + AFCI circuit = Bad Combo


Many people use strobes for Halloween & for Christmas displays

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