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Thread: Flourescent Lighting Fixture Starters

  1. #21
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    Quote Originally Posted by MTW View Post
    From an old Advance troubleshooting guide, for a preheat ballast using starters the minimum open circuit voltage is 176V for a F30T12 or a F40T12 lamp.
    Where would you get that voltage with a 120v light with a starter?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  2. #22
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    180703-1700 EDT

    Larry:

    I would expect that ballast is actually a transformer. Assuming the voltage is a sine wave read with either an RMS meter or an average reading meter calibrated with an RMS scale.

    The peak voltage of a 120 V sine wave is about 170 V.

    To drive a fluorescent bulb one has to use a source that limits current. A high impedance between a voltage source and a load can achieve this. A transformer can be designed to have a high internal impedance or a standard transformer can be used with an external high impedance.

    .

  3. #23
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    Quote Originally Posted by LarryFine View Post
    Where would you get that voltage with a 120v light with a starter?
    I am with you when it comes to single lamp preheat circuit like the wiring diagram early in this thread. Open the circuit at any point and you should read 120 volts across the "open part" if supply voltage is 120 volts.
    I live for today, I'm just a day behind.

  4. #24
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    180703-2415 EDT

    The initiation voltage to start conduction in a fluorescent bulb with a heated filament will be dependent upon bulb length, filament temperature, bulb gas temperature, gas pressure, gas mixture, and stray radiation.

    In a 4' T12 tube with a heated filament I saw initiation at about 150 to 175 V. Too high for straight line voltage of 120 with a simple inductor for current limiting. A shorter tube or differently designed tube might work without a transformer.

    .

  5. #25
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    Quote Originally Posted by LarryFine View Post
    Where would you get that voltage with a 120v light with a starter?
    I would think that you get it, 176V and higher the same way you get a 10KV spark ignition from 12VDC, interruption of the transformer coil current.

    Almost every other ballast type I looked at for a 48" lamp had a much higher open circuit voltage listed in the specs 200-300V.
    Rapid start and Instant start lack the pre-heat emissions, so they must strike at a higher voltage. All provided by the 120V source.

    It's not a number I picked, It's Advance's number for the preheat ballast in question. There is a link for substantiation.

  6. #26
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    Quote Originally Posted by Nardie View Post
    Just recently I had an E&I mechanic experience an electrical shock while reinstalling a fluorescent lighting fixture starter. The starter is a FS-4 30-40W. The mechanic was replacing the bulbs for the fixture, and noticed the starter seemed not to be installed correctly since the fixture did not illuminate once the bulbs were replaced. So the mechanic removed it, inspected the starter, and reinstalled it after noticing no damage. When he twisted the starter into place he felt an electrical shock, and described the sensation as "it lit me up". He was standing on a fiberglass ladder, and stated "that only his right hand touched the starter". When a voltage test was performed with a low voltage proximity tester on the starter and fixture, the tester did light up only in proximity of the starter not the fixture. When the starter was tested with a Tegam 110 voltage tester, the voltage measured was 5V to ground. There was several different grounds used to include the light fixture. The starter was removed and damage was noticed. During a continuity test between the starter's male terminals to its casing, one male terminal was shorted to the starter's casing. The starter was replaced, and the light fixture began operating. So my question is this since I'm not very familiar with fluorescent lighting starters, what is the voltage conducted through the starter? Is it the normal line voltage of 120V, or does it operate at a lower voltage? I am trying to understand why when tested, the voltage on the starter's casing was measured only at 5V, yet the mechanic stated he felt the shock enter his right side and exited his left while standing on a fiberglass ladder, i.e. note he also stated his left hand was touching nothing, not grounded. Is it due to the current of through the starter, or something else? Any help would be greatly appreciated. Also, the mechanic is fine and was released by medical personnel with no restrictions. Thanks
    Should he have been working on it live?
    Si hoc legere scis nimium eruditionis habes.

  7. #27
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    180704-1053 EDT

    I doubt that any ordinary fluorescent fixtures start bulb conduction by an inductive kick method.

    Conduction is started in one of two ways --- heating the cathode to a sufficient temperature to produce a large space charge of electrons (comes from a heated object) (note the cathode switches tube ends every half cycle), or from a large enough voltage gradient at the cathode to generate enough electron flow.

    This occurs every half cycle as can be seen when looking at the fluorescent tube voltage drop on a scope.

    Where a manual pushbutton or starter is used to initiate conduction it is used to provide current flow thru the heaters (cathodes) in the fluorescent tube to make them hot (temperature) to get a large amount of electron emission. When the pushbutton or starter opens, then conduction is initiated by adequate voltage and the electron space charge. The cathodes remain hot (temperature) from thermal storage and current flow thru the fluorescent tube.

    The ballast design, internal fixture wiring, and wiring to the fixture will determine what voltages may be present at the starter. Anything from near zero to full line voltage. When open there is considerable voltage across the two starter pins. Basically the voltage drop across the fluorescent bulb. During the start time the voltage across the starter is near zero. But this does not mean relative to earth.

    Because a 5 V voltage source can provide at least 1 A does not mean that if you touch your hands across that 5 V source that 1 A will flow thru you. On a low humidity day I would see about 5/500,000 A (10 micro amps) thru me.

    .

  8. #28
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    180704-1609 EDT

    In post #18 MTW provided a very good reference, "European paper". Study this.

    But I do not agree with MTW that inductive kick is what is normally used to initially start conduction. Separately note that every half cycle conduction has to restart but in the opposite direction. The electrode that is the cathode has to switch from one end of the tube to the other.

    Too many of the responses to this thread are based on someones imagination.

    Get a scope and other instruments, some components, and run controlled experiments. Then you may be able to accurately talk about what actually happens.

    .

  9. #29
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    Quote Originally Posted by MTW View Post
    I would think that you get it, 176V and higher the same way you get a 10KV spark ignition from 12VDC, interruption of the transformer coil current.
    But that 10kV is only momentary as the magnetic field collapses, open circuit voltage after that collapse is done is only 12 VDC.
    I live for today, I'm just a day behind.

  10. #30
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    Quote Originally Posted by gar View Post
    180704-1609 EDT

    In post #18 MTW provided a very good reference, "European paper". Study this.

    But I do not agree with MTW that inductive kick is what is normally used to initially start conduction.
    Gar, even your reference states otherwise:

    When applying the mains voltage a glow discharge is initiated inside the glow starter (Fig. 3.4) which heats up the bi-metallic contacts and causes them to close (Fig. 3.5). Now current flows from the mains via the ballast, the cathode filament, the starter and the second filament. This way the cathodes are pre-heated. But since the glow discharge has solely been shorted by the bimetallic contact, the bimetallic contact cools down and opens again few seconds after closing. By interrupting the current through the (relatively great) inductance of the ballast a substantial voltage surge is generated across the ends of the fluorescent lamp, starting a current flow through the tube.
    -Hal

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