Arc Fault Situation

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kid993

Member
A single family homeowner complains that every morning when his photocell controlled post light goes off, an arc fault breaker on top floor trips. After much fruitless investigation, photo cell feed was replaced with dedicated circuit. Still trips each morning. When photocell was bypassed, problem disappeared. Can a photo cell turning off somehow simulate an arc? And if so, how could it affect a different circuit?
 

Hendrix

Senior Member
Location
New England
A single family homeowner complains that every morning when his photocell controlled post light goes off, an arc fault breaker on top floor trips. After much fruitless investigation, photo cell feed was replaced with dedicated circuit. Still trips each morning. When photocell was bypassed, problem disappeared. Can a photo cell turning off somehow simulate an arc? And if so, how could it affect a different circuit?
exterior outlets don't need afci protection.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
A single family homeowner complains that every morning when his photocell controlled post light goes off, an arc fault breaker on top floor trips.
So, I assume that this is a standard solid state three wire photoresistor controlled silicon switch that is incandescent only, and it is mounted in the post directly below the controlled light.
After much fruitless investigation, photo cell feed was replaced with dedicated circuit. Still trips each morning.
So . . . Was the post light a new install with GFCI protection on the underground portion, or is this a legacy post light and underground? Is there a switch in the "top floor" that also controls the post light?
When photocell was bypassed, problem disappeared. Can a photo cell turning off somehow simulate an arc?
A generic post light photo cell has no arc in it. What is the lamp . . . CFL by chance?
 

kid993

Member
So, I assume that this is a standard solid state three wire photoresistor controlled silicon switch that is incandescent only, and it is mounted in the post directly below the controlled light. So . . . Was the post light a new install with GFCI protection on the underground portion, or is this a legacy post light and underground? Is there a switch in the "top floor" that also controls the post light? A generic post light photo cell has no arc in it. What is the lamp . . . CFL by chance?

Photocell is Intermatic K4321C Plate mounted 120V 15A. Post light is on separate 15A GFCI protected circuit w/ no switch, lamp is 60W A19. To the best of my knowledge the 2 circuits only meet at the service.
 

ELA

Senior Member
An AFCI (feeding a different circuit) trips when the post light goes off?

What brand of AFCI, if it has diagnostic LEDS does it show it has tripped due to an Arc or a GF?
Is the AFCI breaker located next to the breaker that feeds the post light?

I am not familiar with all Photocells, don't some of them have a relay in them? If so that could simulate an arc when the lamp is shut off, but of course should not normally affect another circuit.

When you say you bypassed the photocell what does that mean (is the light still turning on/off via some other switch?)

Can you make it repeatable by "fooling" the photocell and thus turning it on/off repeatedly?
If so then can you temporarily wire in an alternate brand AFCI as a test to see if that helps (one with diagnostic leds)?
 

ELA

Senior Member
The photocell number you posted is a thermal (bi-metallic) switch.
Could be it creates a lot of noise as it switches.
Might try replacing with an electronic output type.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
The GFCI protection on the underground of the post light rules out a ground fault detection at the AFCI. I agree with ELA about using an electronic version, a lesser photoeye, that is, one that has ~300 VA capability.

One more Q. Is the AFCI the older branch/feeder type or the newer combination type?
 

ceb58

Senior Member
Location
Raeford, NC
Simple fix. Take one piece of black tape 2'' long, place over PC eye. Light will come on and not shut off so AFCI wont trip :D
 

ELA

Senior Member
This situation brings up an interesting question.
Can arc-fault breakers open on an upstream fault ?

That has been brought up here before.

I would like to hear what the manufacturers claim is on that point. I do not believe they are intended to.

In this particular thread we are talking about separate circuits. An upstream arc of a different circuit should not affect the AFCI on another circuit.
I say should not (in theory), however in practice there does seem to be some evidence that this may occur. I think this is an indication that AFCIs are not all that they should be.

With regard to an upstream arc on the same circuit as the AFCI then it might more plausable because the AFCI is sensing current and the series current would be the same upstream and down.
One thing to consider though is that when the upstream arc occurs it causes interruption of the voltage to the breaker itself which does not occur in the same way when it is a downstream arc. Will the AFCI breaker continue to operate normally when it is experiencing an intermittent voltage source?

Sandsnow:

http://forums.mikeholt.com/showthread.php?t=118684&highlight=intelli-arc

I have read about that device but have yet to hear from anybody who has used it. It sounds like it could be usefull in helping you know if the circuit is experiencing a level of arcing or high frequency noise. Beyond that it is not going to fix anything. Seems to me that substituting a "known good" AFCI breaker with indicator LEDS (as a temporary tester) would be more cost effective. Seems like you would have to do a lot of AFCI work to justify buying the Siemens tester.
 

kid993

Member
Now is occuring in a second home. still no closer to finding out why. Separate circuit, different phase, no connections between circuits. Combination type AFCI. WTF?????
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Now is occuring in a second home. still no closer to finding out why. Separate circuit, different phase, no connections between circuits. Combination type AFCI. WTF?????
Interesting.

Help us, please, with some answers to previous questions, and we'll do our best to help with more ideas.

I note, with interest, that the AFCI and the "other circuit" are on different buses at both of your jobs. This is quite curious. The more detail you can give, the better.

At the post light job, did you try replacing the thermal (bi-metallic) photoeye with a solid state switch photoeye? If so, how did the behavior of the AFCI tripping change, if at all.

On the new trouble instance, what is the load (or loads) that are on the AFCI and non-AFCI circuits? New or old install? What is the age of the dwelling? If the install is old, and different from the dwelling's age, how old (ballpark will do)? What is the wiring method (NM, MC, AC, BX, EMT, flex, mixed, etc)?
 
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