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Thread: T8 Ballast lead length

  1. #1
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    T8 Ballast lead length

    Retrofitting 2 x 4 Fluorescent Troffers from T12 to T8 components, it is suggested to maintain the Factory lead length and new shunted sockets to get the most out of the ballast and bulb lifespan.

    I came across Fixtures that were T12 with the two leads on every socket with an T8 ballast. The original leads were full length from being cut off the old T12 Ballast and the Factory Length of wire from the T8 ballast were spliced without shortening anything. I am assuming it reduces the lifespan of ballast and tubes and wondering by how much? ...does this reduce light output? ..reduce ballast life by a percentage? ... burn out the tubes more quickly? ...potential for overworked ballast to cause a fire?

    Thanks for any feedback!

  2. #2
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    I am unaware of any reduction in lifespan from cutting either tombstone or ballast leads short. Usually when I do this type of replacement, I cut the leads from the tombstones about halfway from the ballast because it's convenient and leave the leads from the ballast full length again because it's convenient. The ballast leads are already stripped. If I cut the ballast leads, I would have to strip them which takes time. There is usually plenty of space in the wiring compartment for the extra wire.

  3. #3
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    I always cut the ballast leads right at the ballast so it doesnt get mistaken for a new/good one. There's usually plenty of room behind the cover for extra wire, tho I also twist the wire together a bit to get it tight and not get mashed by the cover.

    eta: I dont see where the resistance of +/-3' of short/extra copper wire is going to affect tube/ballast life, output, etc.
    Last edited by JFletcher; 04-09-17 at 03:21 PM.
    Electricians do it until it Hertz!

  4. #4
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    I carry only T8 IS (instant start) ballasts on my truck. If I demo a T12 or T8 RS (rapid start), I try to shunt the tombstones as close as I can with out pulling the socket rail, usually about six inches from where the leads leave the belly pan and enter the socket rail.

    I read somewhere the IS ballast requires the socket to be shunted within six inches of the socket but I keep it practical.

    I see that a lot of electricians use the entire lead length supplied with the replacement ballast because they don't want to waste time stripping out shortened leads. I cut the replacement ballast leads and try to offset the manufacturer's suggestion to minimize lead length against the "not to exceed" time from the service provider and my minimum standard of craftmanship.

    As I'm replacing these ballasts, my mind races around considerations of luminaire efficacy, ballast performance and lamp life. All that thinking while I'm working, but in the end, if the troffer comes on, I walk away and don't look back.

  5. #5
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    Quote Originally Posted by jeremysterling View Post
    I carry only T8 IS (instant start) ballasts on my truck.
    What happens when you need to repair a T12 fixture where the tubes are still usable. Do you replace the tubes with T8 tubes? Are your clients fine with the extra cost? Just curious.

  6. #6
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    Quote Originally Posted by Coppersmith View Post
    What happens when you need to repair a T12 fixture where the tubes are still usable. Do you replace the tubes with T8 tubes? Are your clients fine with the extra cost? Just curious.
    If the customer has T8 lamps on-site, I will retro-fit a T8 ballast in a heartbeat.

    Eight years ago, I had a dispatcher/purchaser "service coordinator" that refused to put T12 ballasts in will-call for me even if the customer had plenty of brand-new T12 lamps on site. He insisted that T12 were being outlawed and phased-out. I was not expected to up-sell, so his policy put me in an awkward position with the customer. If I looked around and there was no and I mean no T8 anywhere on the customer's property, I would obtain T12 ballast at the counter.

    Does "where the tubes are still usable" mean "used tubes"? For "best practice", if I install a ballast on fluorescent or HID, I will install new lamps. New lamps will also lengthen the time before you get that phone call, "The light your guy just worked on is off now." I only reuse lamps if its 4pm on Friday and the supply house is two hours away.

  7. #7
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    Quote Originally Posted by powerplay View Post
    Retrofitting 2 x 4 Fluorescent Troffers from T12 to T8 components, it is suggested to maintain the Factory lead length and new shunted sockets to get the most out of the ballast and bulb lifespan.

    I came across Fixtures that were T12 with the two leads on every socket with an T8 ballast. The original leads were full length from being cut off the old T12 Ballast and the Factory Length of wire from the T8 ballast were spliced without shortening anything. I am assuming it reduces the lifespan of ballast and tubes and wondering by how much? ...does this reduce light output? ..reduce ballast life by a percentage? ... burn out the tubes more quickly? ...potential for overworked ballast to cause a fire?

    Thanks for any feedback!
    Not bridging the two together close to the socket would be the biggest impact. 4' away rather than at the socket slash the lamp life to roughly half according to one source.


    There are four holes per rapid start socket, two per each lamp connection.
    AB CD

    So you have one wire in A, one in C. What's fine to do is cut the A a few inches from the socket, strip, and loop it into D.
    You can pull the C out or trim it flush to the socket. Stab the new ballast lead into B.

    For the common end, join the three wires together as near as reasonably practical (new ballast wire + two wires that went to old ballast)

    Who suggested leaving all the factory wire in place to maximize component life? This isn't true.

    New sockets are recommended, because T12 systems with original sockets are usually old enough many sockets are brittle or already broken. You can use a push-in connector and mechanical stripper to speed things up and reduce strain on yourself.

    Quote Originally Posted by jeremysterling View Post
    If the customer has T8 lamps on-site, I will retro-fit a T8 ballast in a heartbeat.
    This is a poor practice. You shouldn't spot replace a fixture to require a lamp that is physically interchangeable but not compatible with the type of lamps used in rest of the fixtures. Replacement application T12 electronic ballasts as well as modified formula T12 lamps are readily available at big box stores. These modified consumer grade T12 lamps are much better than the workaround used when T12s were initially banned.

    The early workaround was using high CRI lamps like Chroma 50 that is only 2,000 lumens. Reformulated consumer lamps are 87 CRI with 2900 lm.
    Last edited by Electric-Light; 04-18-17 at 03:31 AM.

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