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Thread: T8 bulbs working on T12 ballast

  1. #1
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    T8 bulbs working on T12 ballast

    I went to a job today and on all their F40T12 fixtures where 1 or 2 of the 4 bulbs had burned out they had replaced them with T8 bulbs and they were all working. Why would a T8 bulb work on a F40T12 ballast, and will the T8 bulbs burn out faster? I just always assumed T8 bulbs would not work on a T12 ballast, but aparently they do.

  2. #2
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    If you run a t8 bulb on a t12 ballast you will have premature bulb life as the t12 ballast will over "tax" the bulb. If you run it vice versa and have a t8 ballast running a t12 bulb you will have premature ballast life as the t12 bulb takes more to run and will over work the ballast.

  3. #3
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    Quote Originally Posted by fireryan View Post
    If you run a t8 bulb on a t12 ballast you will have premature bulb life as the t12 ballast will over "tax" the bulb. If you run it vice versa and have a t8 ballast running a t12 bulb you will have premature ballast life as the t12 bulb takes more to run and will over work the ballast.
    Thank you for the info. Do you happen to have any link to a site I could print some manufaturers data stating what you just told me. i wanted to show these customers something "official" looking. They seem to think since they are working like they are that there is no problem.

  4. #4
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    Quote Originally Posted by GG View Post
    i wanted to show these customers something "official" looking.
    Just point them to this thread.

    After all, what's more official than the Mike Holt forum?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  5. #5
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    Quote Originally Posted by GG View Post
    Thank you for the info. Do you happen to have any link to a site I could print some manufaturers data stating what you just told me. i wanted to show these customers something "official" looking. They seem to think since they are working like they are that there is no problem.
    GG
    Here's a link for sylvania ballast info guide.http://assets.sylvania.com/assets/do...968ee0a7cb.pdf

  6. #6
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    Ok. Let's keep in mind one thing. Unlike incandescent lamps where the filament is the load, the fluorescents and HID lamps are actually a conductor, where the gas gets ignited by the amperage created by the load we call ballast. Both the T12 and T8 use same kinda gases, but the t12 need higher amperage to be pushed thru (and voltage) to ignite the gas. So a T8 should definitely work on a t12 ballast(as the t12 use higher voltage and amperage to ignite the gas). Would they have a premature life? Hard to say, if the gas stays intact and doesn't leak, no. Remember, the lamps is a conductor here, so look at it as a piece of #12 wire.

    Quote Originally Posted by GG View Post
    I went to a job today and on all their F40T12 fixtures where 1 or 2 of the 4 bulbs had burned out they had replaced them with T8 bulbs and they were all working. Why would a T8 bulb work on a F40T12 ballast, and will the T8 bulbs burn out faster? I just always assumed T8 bulbs would not work on a T12 ballast, but aparently they do.

  7. #7
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    Quote Originally Posted by LEO2854 View Post
    GG
    Here's a link for sylvania ballast info guide.http://assets.sylvania.com/assets/do...968ee0a7cb.pdf

    Bad link

    RC
    It's my name going on that drawing, not yours. If what you want ain't right, it ain't going on the drawings!

  8. #8
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    Quote Originally Posted by Strife View Post
    Ok. Let's keep in mind one thing. Unlike incandescent lamps where the filament is the load, the fluorescents and HID lamps are actually a conductor, where the gas gets ignited by the amperage created by the load we call ballast. Both the T12 and T8 use same kinda gases, but the t12 need higher amperage to be pushed thru (and voltage) to ignite the gas. So a T8 should definitely work on a t12 ballast(as the t12 use higher voltage and amperage to ignite the gas). Would they have a premature life? Hard to say, if the gas stays intact and doesn't leak, no. Remember, the lamps is a conductor here, so look at it as a piece of #12 wire.
    Not quite accurate. The lamps and ballast are a system designed to work with thier complimentary parts. T8 lamp life does decrease when run on a T12 ballast. We used to catch retrofit cheaters by looking for the premature blackening on the ends of the T8 lamps.

  9. #9
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    Quote Originally Posted by BullsnPyrs View Post
    Not quite accurate. The lamps and ballast are a system designed to work with thier complimentary parts. T8 lamp life does decrease when run on a T12 ballast. We used to catch retrofit cheaters by looking for the premature blackening on the ends of the T8 lamps.
    Speaking of such, how many of you have done retrofits? Do the kits work well and fit a wide range of fixtures? I'm sure I'll get a call for one sometime soon.
    Yes, I'll be happy to do a first class job for less than anyone else and take a dollar a week for 10 years.

  10. #10
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    Yes, if you pay attention to fixture depths.

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