I have a customer who's brother is in the filming business. He has a 2000 Watt lamp that he says trips the GFCI every time he powers it up. The filming area is all GFCI protected. The best explanation I can come up is the high inrush from the cold tungsten filament must be causing an imbalance between the line/neutral enough to trip the GFCI. I suggested using a dimmer to bring the lamp up slower.Am I even on the right track?

Is it a gfci breaker or receptacle? What is the rating of the breaker?

It's a GFCI receptacle, 20 amp on a 20 amp ckt with downline receps on it's load side. The light works fine on a non GFCI 20 amp circuit. I thought at first maybe a ground/neutral fault in the fixture, then I thought about the inrush.

Well I know that some reactive circuits trip GFI's but if this is a total resistive circuit it should work fine. Is it a total resistive circuit? 16.6 A is high for that circuit anyway. But if its only on now and then it should be fine.

[This message has been edited by RobbieD (edited 12-05-2004).]

if the light MUST be GFCI protected, and there are nobody else can think of a better idea, then try using a dimmer switch on the light. make sure it has a 2000 watt capacity. with the dimmer you could bring the bulb up to full power slowly, reducing the inrush.

Coming from the one 2000 watt lamp alone you have the 16.6 Amps, With basic ohm's law. let alone what else is on the circuit. It's probably a good chance it is overloaded.

Can you not just use a GFCI class 'B' instead to prevent nuisance tripping in this case?

-Greg

"Coming from the one 2000 watt lamp alone you have the 16.6 Amps, With basic ohm's law. let alone what else is on the circuit. It's probably a good chance it is overloaded."

I thought it was a misconception that a GFCI receptacle will trip on overload. I thought it would only trip on ground fault.

I think I will ask him to let me check out the lamp, just to satisfy my curiosity.

Your right GFCI receptacles do not trip on overcurrent.

Why are GFCI receptacles being used there anyway? This a kitchen show? I'm for using GFI's where required but if you use them everywhere because you are paranoid you are going to have problems like this.

-Hal

I know GFI's are supposed to trip with an imbalance of 5-6 milliamps between the hot and neutral.

But, I was told a GFI will trip on overcurrent. And if it does not trip on overcurrent would anyone like to explain why GFI's come in 15 and 20 amp?

A GFCI breaker will trip on overload. A GFCI receptacle will not. A 15 amp receptacle is the rating of the receptacle this means that if you have only one receptacle on a 20 amp circuit it would have to be rated for 20 amps so you would need to install a 20 amp receptacle. 15 amp rated receptacles can be used on a 20 amp circuit if you have more than one on the circuit. Some equipment is also rated for 20 amp circuits. They cannot be plugged into a 15 amp receptacle. A 20 amp receptacle has the extra sideways slot in the face of it. I have a pvc hot box used for bending pvc conduit. It has a plug with one prong 90 deg. from the other. This prevents you from plugging it into a 15 amp rated receptacle. Although both receptacles are rated for 120 volts they have different amperage ratings and different nema configurations. The only difference between a standard receptacle and a GFCI receptacle is that the GFCI receptacle will trip when there is an imbalance between the hot and neutral. Both types of receptacles come in 15 amp and 20 amp versions.

[This message has been edited by A-Line (edited 12-07-2004).]

[This message has been edited by A-Line (edited 12-07-2004).]

hbiss, it's a studio with a concrete floor. I didn't install the GFCI protection and I'm not going to be the one to recommend bypassing it.

Yet again.......

Class B or 30mA GFCI products are typically used to protect equipment like heaters, cables etc where 5mA would cause nuisance tripping.

-Greg

Does this lamp trip _all_ the GFCIs in the facility _all_ of the time? If so, then I would strongly consider a ground-neutral fault in the lamp.

But if the lamp trips some of the GFCIs or only some of the time, then you might want to replace the 'sensitive' GFCIs.

GFCIs are supposed to trip on current imbalance. However what they really do is trip on the net current as measured by a current transformer which encloses all of the circuit conductors. If the circuit conductors are not both equally coupled to the CT, then even with balanced current in the conductors, current will be present on the output of the CT.

It is entirely plausible that high balanced currents will be registered as an imbalance on some GFCIs, causing nuisance tripping.

-Jon

I am assuming that the 2000 watt lamp is pluged into a duplex receptacle. If that is the case, you are in violation of 210.23(A)(1) which limits the load that can be drawn from a other than single receptacles. the load of a cord and plug connected load is limited to 80 percent to the rating of the branch circuit, in your case, 16 amperes maximum for a duplex GFCI receptacle.

Why dont you run a dedicated circuit for the light? It should have one anyway. You get $$$$ and the customer gets a light.

Yes, an inrush will often trip a sensitive GFCI in such circumstances.

A way around this has already been mentioned, using a dimmer to hold the lamp 'warm' when not required, and bring it up slowly when needed. This will also extend the lamp service life by about 50% as well.

I have come across thi problem on higher-power stage lighting where some of it was not controlled through dimmer-packs.

You are quite right not to recommend disconnecting the GFI; such locations are just the very places they are useful!!

Well he's going to bring the light to me for a look see, and let me mess with it in my shop. It's more of a curiosity than anything for me at this point, I'm not expecting any work out of it, just a friend of a friend sort of thing. You know, one of those things you just have to know the answer to. Some people golf on Sunday, I tinker.