Fluorescent fixtures on a GFI circuit

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goldstar

goldstar

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New Jersey
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Electrical Contractor
I'm curious to know if anyone has run into this situation before. I replaced (3) 2-lamp, 4' magnetic ballast fixtures in a walk-in closet with (2) electronic ballast, 4', 2-lamp fixtures. Whoever installed the original fixtures ran the circuit from the load side of a GFI receptacle in a nearby bathroom. The original fixtures worked fine. However, the electronic ballast fixtures began tripping the GFI receptacle. I discovered further that as long as there were only a total of (3) bulbs installed in the fixtures they worked fine. As soon as I installed the 4th bulb the GFI tripped.

Can anyone come up with a logical explaination ?

Thanks in advance.

Phil
 
Re: Fluorescent fixtures on a GFI circuit

Phil,

This is a great question. I suspect the complexity of the electronic ballast line current waveform from the ballast's switching power supply. . .but I don't know.

This question has been raised for me as I try to understand the interaction between the electronic fluorescent ballast and a controlling switch like an occupancy sensor. If the sensor uses a silicon controlled switch (not a mechanical relay) there is likely a destructive interaction.

Any one have an understanding about the behaiviour of the fluorescent electronic ballast?
 
Re: Fluorescent fixtures on a GFI circuit

Hmmm never had a flo on a gfci but you made me think whats gonna happen on afci
anyone been there yet.Closet in bedroom might easily end up on that circuit.I mostly been doing remodels in last 2 years so the problems of afci havn't all surfaced yet.
 
Re: Fluorescent fixtures on a GFI circuit

3 points come to mind in this scenario:

1: Higher Cap. Coupled leakage from each Ballast (Electronic Ballast will normally have an output Frequency between 20 kHz and 40 kHz) - this would leak to Grounded Equipment, such as the EGC, and if no EGC is used, something close enough to complete the circuit back to the source,

2: Higher level of Capacitive "Firing" concentration per each Lamp using Hi Hz Ballastry (the field created around the Lamp during initiation draining to the EGC),

3: AC Line Filering &/or TVSS @ Line Input of Hi Hz Ballast - seen a few commonly used Ballasts which have center tapping points of the Capacitors array (on line side of Inductor) driven to the Ballast's case to dump interference to "ground" (typical PI Filters).
Also seen the "Other End" of MOVs bonded to the Ballast's case (this would be the TVSS section).

Scott35
 
Re: Fluorescent fixtures on a GFI circuit

Scott,

What you've posted makes sense. It brings to mind a service call I had recently where the electrician before me didn't ground the fluorescent fixture and the lamp would not ignite. Once I grounded the fixture it worked fine. Seeing as how the ballast requires a solid bond to ground in order to ignite the bulb I would imagine there is some cumulative amount of current leakage to the EGC on a per bulb basis. The insertion of the 4th bulb in my scenario seemed to exceed the limit of the GFI receptacle.
 
Re: Fluorescent fixtures on a GFI circuit

Scott,

Wouldn't the circuit created by high frequency capacitive coupling of the tube to the reference ground have its source at the output of the ballast high freq power supply?

I'm working from the lack of any ballast circuit diagrams, but isn't the basic idea to sample enough energy off the AC branch circuit line to run a DC power supply that drives a high frequency power supply?
 
Re: Fluorescent fixtures on a GFI circuit

I think Scott is on track with points 1 and 3. It's either the "noise" from the electronic ballast getting to the GFI electronics (either back through the supply wiring or radiated through the air) or leakage to ground through power line decoupling in the ballast.

I can't explain why adding that fourth tube in one of two separate fixtures was the straw that broke the camel's back. It would make sense though that it is the "noise" and the fourth tube exceeded some threshold causing the GFI to trip.

...It brings to mind a service call I had recently where the electrician before me didn't ground the fluorescent fixture and the lamp would not ignite.

Fixtures do not have to be connected to an equipment ground to work. Plenty of fixtures around with two wire cordsets. I believe you when you say you think this was the cause but there had to be some other reason.
 
Re: Fluorescent fixtures on a GFI circuit

I have seen where a switching power supply was causing a GFCI to trip. a friend had a bench set up in his garage to repair car radios and when he loaded this B&K 30 amp power supply down it would trip the GFCI there was no leakage to the grounding conductor he put a scope on the circuit and saw that the current harmonics were about 40%
Could these ballest be of a switching type? and causing a harmonic current to unbalance the current between the hot and neutral?
 
Re: Fluorescent fixtures on a GFI circuit

hbiss,

I know it probably sounds wierd but I can tell you first hand that this particular fixture would not light unless it was grounded. Prior to my grounding the fixture I called my supply house and asked if they had seen this problem before. Their response was that it sounded like a grounding problem. It wasn't until I pulled the fixture down from the ceiling that I realized that the EGC was not bonded to the fixture. Once I connected the EGC the fixture worked fine.

I'm not saying that ALL fluorescent fixtures have to be grounded in order to work but the fact is that ALL FIXTURES SHOULD BE GROUNDED VIA THE EGC.

Perhaps if anyone out there works for a ballast manufacturer they might verify that this is possible.


hurk,

Could these ballest be of a switching type? and causing a harmonic current to unbalance the current between the hot and neutral?
Click to expand...
I don't know that much about ballasts. All I can tell you is that I plugged in one bulb at a time and waited a few minutes between each one. As soon as I plugged in the 4th bulb (no matter which position or fixture) it tripped the GFI receptacle. No matter how many times I tried to reset the receptacle with the switch in the on position it would trip. So all I can guess is that somehow with the fixtures on the load side of the GFI it exceeded the limitations of the receptacle or created some type of disfunction between the hot and neutral as you suggested.

Phil

[ December 15, 2003, 06:33 AM: Message edited by: goldstar ]
 
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