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Thread: Ballast Replacement and Grounding

  1. #1

    Ballast Replacement and Grounding

    Here's a situation I hope someone can explain.

    I've had a couple of flouresent fixture ballast replacement installations. Both were two 40 Watt T-12 Rapid Start Magnetic ballast types. After the ballast installation I got very a dim glow out of the tubes. Also (in one of these cases) the new ballast hummed.

    In trying to remedy these problems I attached the power source ground directly to the metal frame of the fixtures. In both cases that stopped the problem.

    Can anyone explain why attaching the ground to the frame of the fixture solved the problem? The only thing I can think of is that it sets up a "field" around the tubes that helps throw the arc through them upon startup.

    This is really bugging me, so I hope someone can give me a technical explantion.
    _________________
    William R. Smith

  2. #2
    Join Date
    Sep 2003
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    381

    Re: Ballast Replacement and Grounding

    In the instructions it always says to ground the metal frame. I'm guessing there is an electronic switch, with a static circuit that must be grounded to allow the ballast to ignite the circuit. They couldn't be using the ground for the return path. Unless there might be an error in the manufacturing of these units, swapping the ground for the return? try putting an amprobe around the hot, ground and return wires. See where the current flows. I would be interested in the answer.
    Earl

  3. #3
    Join Date
    Feb 2003
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    Re: Ballast Replacement and Grounding

    Some instructions note that the Fluorescent tube must be with-in 1 inch of a grounded surface ( which is usually the metal reflector ) which would mean the reflector must be grounded.
    That should not be a problem since 250.134(B) requires the grounding conductor to be installed with the circuit conductors. And then all non-current carrying metal parts of an electrical system are to be bonded to the EGC. See 250.2 'Ground-Fault Current Path' and 250.4(A)(2) and (3).

    gwz2

  4. #4
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    Re: Ballast Replacement and Grounding

    The fixture or ballast does not have to be grounded through an equipment ground to operate. Yes, the ballast case has to be electrically connected to the sheet metal behind the lamps for them to ignite. If you notice, some "U" tubes have a foil stripe to further help with this.

  5. #5
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    Re: Ballast Replacement and Grounding

    The grounded metal cover within 1" of the lamp is required to permit proper excitement of the electrons in the gas in the lamp. If not, only some of the electrons will excite and the chain reaction will not occur to provide proper luminance.
    Dave Nix

  6. #6
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    Jul 2003
    Location
    Twin Cities, MN
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    16

    Re: Ballast Replacement and Grounding

    Here is a new thought. It is possible that grounding the metal housing provides shielding from radio frequency interference. The fluorescent tube may be excited by RF energy impressed in the wiring without this shielding. Experience with a home made Tesla coil found that a fluorescent tube provides brighter illumination when held in a hand than when powered normally from a ballast. Local RF sources such as broadcast radio, television, and 2-way radio communications can provide enough energy to dimly light a fluorescent tube given the right antenna.
    Amherst Class Demo

  7. #7
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    Re: Ballast Replacement and Grounding

    It is possible that grounding the metal housing provides shielding from radio frequency interference.

    Maybe to a small degree, but I absolutely doubt that that even crossed the minds of the fixture and ballast makers. The reason a flourescent fixture is connected to an equipment ground is the same as with any other type of fixture and like them will operate just fine without it.

  8. #8
    Join Date
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    Wisconsin
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    Re: Ballast Replacement and Grounding

    Rapid start lamps must be mounted "near" a grounded surface to start properly.

    Excerpts from an Advance Transformers ballast guide:
    "... it is necessary to excite the gas within the lamps by means of an external voltage...This external excitation is created by means of the capacity [capacitor circuit] that is present between the lamp and the reflector or channel."
    Just because you can, doesn't mean you should.

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