GFCI gone bad?

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Steelhead

Senior Member
Location
Southeastern Wisconsin
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Industrial Maint/Journeyman
Do you guys see any problems with using a RAB STL200 motion sensor to switch power to the line side of a GFCI dead front? I have two post lights connected to the load side. Lights (incandescent bulbs) were working for a few days or so then stopped. Customer says the GFCI won't reset. Haven't had a chance to look at the problem yet, but was wondering if the motion sensor could cause problems for the GFCI. GFCI was new when installed about a week ago. I suppose the GFCI could of malfunctioned, or there is a legitimate problem with the load side portion of the circuit. Just wanted to make sure my motion sensor wasn't causing problems with the proper function of the GFCI.
 
Can the customer distinguish between a GFCI that has tripped and won't reset vs. one that isn't being powered on the line side? If not then maybe the GFCI is OK but it's not getting power due to an issue with the motion sensor, etc.
 
synchro said:
Can the customer distinguish between a GFCI that has tripped and won't reset vs. one that isn't being powered on the line side? If not then maybe the GFCI is OK but it's not getting power due to an issue with the motion sensor, etc.
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I don't think he would be able to determine if its tripped or there is no line side power. The motion sensor does turn on the porch lights that are on the line side of the GFCI so I know the sensor is working.
 
Steelhead said:
The GFCI is downstream of the sensor because it is protecting buried UF cable supplying power to the two post lights
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retirede said:
Same protection is provided if wired upstream of the sensor.
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Correct, plus protection for the run to the porch lights and whatever else is downstream of the GFCI.

If a motion sensor does not have sufficient hysteresis and/or time delays, it's switching might be intermittent or noisy when it's close to a detection threshold for measuring movement and determining whether to switch or not. I could envision that causing a GFCI to trip if it's powered up with an intermittent line voltage, but I don't have direct experience which confirms that.

At least as a diagnostic measure if not a permanent change, could you do what Larry suggested by putting a GFCI breaker on that branch circuit, and then bypass the dead front GFCI to see if that eliminates the problem? That should be easier to do than relocating the dead front GFCI.
 
retirede said:
Same protection is provided if wired upstream of the sensor.
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Yes, you are correct, but because of the physical location of the dead front it would require a large amount of work ($$) to rewire so it is upstream of the sensor. I initially thought of using a GFCI breaker, as others suggested, but the cost of the dead front was more appealing to the customer. Synchro's comments were interesting and is more along the lines of what I was thinking might be causing the problem. I guess I'll know more when I check things out. I just may end up going the GFCI breaker route. Thanks guys for your help!
 
Newer GFCIs will not reset when there is no power on the line side. Except those for construction use, they will not trip on losing line power, so once they have been reset with the sensor-controlled power on they should continue to hold through later losses and restorals.
But I would not be comfortable with this installation. Among other things, the behavior of the sensor while the GFCI is open is also uncertain.
 
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