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Old 11-25-2008, 12:51 PM   #1
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GFCI and dimmable halogen ceiling fan light


Hi guys,

I've got a problem and was looking for any insight...

I've got a ceiling fan with a dimmable halogen light fixture in it. It seems to work fine. Because the circuit that it's on is old 2 wire stuff, I decided to hook up a GFCI outlet as the first thing in the circuit, thereby protecting the rest of the circuit as well. This also seems to work fine, except that when I turn on the light, the GFCI immediately trips. The fan works fine on all settings, and the light worked fine before I installed the GFCI. The fixture is not even connected to a ground, so I don't see how there could be a ground fault in the fixture itself. It's remote controlled, so a person being the ground path doesn't seem possible either.

Are there any known issues with GFCI and this kind of light, or do you think the fixture is faulty? If you think it's the fixture, can you explain how there could be a ground fault with no ground connected? Anything I can do to make this work?

TIA

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Old 11-25-2008, 03:33 PM   #2
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GFCI and dimmable halogen ceiling fan light


The dimmer might have less than 30 kΩ, or more than .09F, to ground. The second case is somewhat harder to test.

Or, most of the 4 mA GFCI "budget" is used up by whatever else is on the line, and this dimmer is just the icing on the cake.

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Old 11-25-2008, 06:43 PM   #3
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GFCI and dimmable halogen ceiling fan light


If there is leakage to ground from the dimmer, and there is no ground in the circuit, why would this cause the GFCI to trip? I may be wrong on this, but I would think there has to be a path to earth (bypassing the neutral) for the GFCI to trip.

Dimmers have been known to cause RFI, and some GFCI may be sensitive to this. You might try installing an RFI line filter in the wall box with the dimmer, or maybe it's the halogen fixture that's causing RFI, so the filter may be more effictive up there.
You should be able to buy a suitable one from Digikey (www.digikey.com) or possibly Radio Shack (but most of their stores don't sell too many parts anymore). The ones I am familiar with are made by Corcom.

I just remembered that Digikey has a $25 minimum order, and I don't think the line filter will cost more than about $5, so try Mouser, www.mouser.com instead. No minimum there the last I looked.
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Old 11-25-2008, 09:05 PM   #4
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GFCI and dimmable halogen ceiling fan light


Quote:
Originally Posted by KE2KB View Post
If there is leakage to ground from the dimmer, and there is no ground in the circuit, why would this cause the GFCI to trip? I may be wrong on this, but I would think there has to be a path to earth (bypassing the neutral) for the GFCI to trip.
You're right. With no grounds, there's no capacitance or resistance to ground (I guess).

The RFI idea might be a good guess. They do mention noise immunity on page 6 of this link.
http://www.national.com/ds/LM/LM1851.pdf
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