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Thread: 2 lamps on a 4 lamp t8 ballast

  1. #1
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    Apr 2007
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    2 lamps on a 4 lamp t8 ballast

    Does anyone know if it will damage a 3-4 lamp electronic t-8 ballast if it is only used with 2 lamps? It is a 48' 4 lamp fixture and i would like to inboard outboard the fixture using a relay on the leads feeding the sockets.

    Thanks for any help

  2. #2
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    Most electronic ballast just say to cap unused leads.

  3. #3
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    As Bob said, but I'm just cheap enough to swap out that ballast for a 2-tube model, and save the 3-4-tube one for a 3-4-tube application.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  4. #4
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    I haven't done a amp reading, but does anyone know if you waste energy using a four lamp ballast as a two lamp. I was at the Hertz Corporate office and noticed they are removing one lamp from hundreds of fixtures. I would think there is some energy savings, but could also waste money and damage the ballasts. Any thoughts

  5. #5
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    man that is complicated method of switching light. no sir it does not waste energy if only two are connected it only uses that amount of energy and when you are talking .045 amps on 4 bulbs it is minute. That is an approximation on the amp draw as I did not look up a ballast to be exact.
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  6. #6
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    Quote Originally Posted by LarryFine View Post
    As Bob said, but I'm just cheap enough to swap out that ballast for a 2-tube model, and save the 3-4-tube one for a 3-4-tube application.

    I am wanting to inboard outboard switch the fixtures by using a relay to kill power to 2 lamps(4 lamp fxture with 1 ballast). The fixtures are brand new, installed, have 2 switch legs and 1 4 lamp ballast.

    I know that at least one switch would have to be on to power ballast. It just like it would be a little easier and cheaper (I have the relay) then adding another ballast

  7. #7
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    Quote Originally Posted by cschmid View Post
    man that is complicated method of switching light. no sir it does not waste energy if only two are connected it only uses that amount of energy and when you are talking .045 amps on 4 bulbs it is minute. That is an approximation on the amp draw as I did not look up a ballast to be exact.
    Yes I know. I will probably be adding another ballast.

  8. #8
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    Quote Originally Posted by -=PEAKABOO=- View Post
    I am wanting to inboard outboard switch the fixtures by using a relay to kill power to 2 lamps(4 lamp fxture with 1 ballast). The fixtures are brand new, installed, have 2 switch legs and 1 4 lamp ballast.

    I know that at least one switch would have to be on to power ballast. It just like it would be a little easier and cheaper (I have the relay) then adding another ballast
    You'd need a multi-pole relay in each fixture, using the second line conductor to energize them. Plus, that relay would have to be capable of handling approx. 600v.

    I'd still go with two 2-lamp ballasts in each fixture. Didn't they know they would want separate-pair operation before the fixtures were ordered?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  9. #9
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    Quote Originally Posted by LarryFine View Post
    I'd still go with two 2-lamp ballasts in each fixture. Didn't they know they would want separate-pair operation before the fixtures were ordered?
    I mentioned it to them, there never said they wanted it that way. They claimed I bid it that way but I did not. I have 32 fixtures like this. The contractor that I am doing the work for is throwing a fit about having to pay claiming I told him I would do it this way. Just trying to way options here. It was kind of my mistake by not thinking to order fixtures with dual ballast. I am at least going to try to get him to cover the difference in ballast price which is roughly how much extra the proper fixtures would cost.

  10. #10
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    Have you considered running 1 4 lamp ballast for two fixtures and the other 4lamp ballast for two fixtures. That would give you inboard outboard. I don't know your arrangment but you said you had two switch legs. If the fixtures are end to end it would be really simple but if your in a grid you could throw an 18 gauge whip. I've don a thousand master/slaves using 4 lamp ballast with whips so it would be kinda the same thing. Maybe??

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