# T8 bulbs in T12 fixture



## Mr Rewire

Hotlegs said:


> I'm no lighting expert so I wanted some input on what I came across in an office building. I get there and the owner tells me he relamped the fluorescent light fixtures that had burned out bulbs.
> 
> He had replaced burned out T12's with T8's and they were all working. The ballast specifically stated they were for T12's. So I told him he screwed up and he asked me why then were the T8's working, and I didn't have an answer. So what would have happened leaving the T8's on a T12 ballast?


 How long ago was it that he called because he will be calling soon. I have gotten calls like this and they usually dont burn long.


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## B4T

Had a call last week about 4' lamps flickering.. the maintenance guy got them mixed up..:no:

This is going to be a constant problem for years to come.. BUT.. a money maker for us.. :thumbup:


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## Hotlegs

Mr Rewire said:


> How long ago was it that he called because he will be calling soon. I have gotten calls like this and they usually dont burn long.


 Well I made sure I replaced them all with the proper T12's so they were only in there a few hours. I remeber the T8's were very hot when removing them.


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## frenchelectrican

Because with 4 foot 32 w T8 bulbs in 40 watt T12 ballast will overdrive them a bit and the amprage will be somehow higher and majorty of the T12 ballast I ran into are wired for rapid start which the electrodes always stay warm all the time.

It is a common item when someone get mixed up and not realized that they still have old T12 ballast in there.

So the soluation is either relamp with proper lamps or reballast to T8 ( which I always try to upsell it due they can save little more electrique right there and more quiet as well )

Merci.
Marc


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## noarcflash

The T8 ballast in a 2x4 fixture, they don't last more than 3 or 4 years. It's cheaper running the old T12 ballast forever, than the small amount of energy savings.


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## Dennis Alwon

I am pretty sure I have seen ballast that will do T-8 or T-12 tubes. Not sure if they are junk but they are out there


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## mattdolan16

Hotlegs said:


> I'm no lighting expert so I wanted some input on what I came across in an office building. I get there and the owner tells me he relamped the fluorescent light fixtures that had burned out bulbs.
> 
> He had replaced burned out T12's with T8's and they were all working. The ballast specifically stated they were for T12's. So I told him he screwed up and he asked me why then were the T8's working, and I didn't have an answer. So what would have happened leaving the T8's on a T12 ballast?


The
Lights will burn out. Try putting a t12 in. T8 ballast. Won't work.


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## Fredman

I just replaced several T-8's that were installed less than 3 months ago in t-12 fixtures. Go maintenance guy, go!! :thumbup:


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## Cletis

*m*

My personal opinion would be to put in extra efficient instant start ballast with some high efficiency t-8's. It seems to be the best bang for the buck, bulb life, and energy savings...


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## noarcflash

today I saw an 8' fixture. 96"
1) T8 bulb
1) T12 bulb
Both lamps were working !
I was curious, so I pulled the ballast cover. It was a T8 ballast.

But it was firing both lamps. no problems. The T8 was obviously brighter than the T12.

Then I had to explain to the maintenance personel to differences.


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## DEelectrician88

noarcflash said:


> The T8 ballast in a 2x4 fixture, they don't last more than 3 or 4 years. It's cheaper running the old T12 ballast forever, than the small amount of energy savings.


Better get me while u still can. I saw a memo at our local supply house the other day that said they were gonna stop making certain t-12 an a few t-8 lamps next july due to some new government efficiency laws.


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## dthurmond

My supplier says if you use the wrong bulbs t12 in t8 it voids their warranty on the ballast. Not sure how they would know if the wrong bulbs were used though.
I had this exact problem last week in a kitchen. They would light up but had a very bad flicker. Maint had even put in a new fixture.


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## Scott Paullin

*T-8 lamps on T-12 ballast*



Mr Rewire said:


> How long ago was it that he called because he will be calling soon. I have gotten calls like this and they usually dont burn long.


You can expect the T-8 lamps to burn about a week or a little longer


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## BLohman

For what it's worth, I just replaced the ballast in a 96" T12-60W single pin 2-lamp fixture. The new ballast, though rated/labeled for T12's, was small like a 4' T8 ballast would be - not like a huge and heavy 96" ballast is typically. Anyhow...works fine. I left the T12's in it, but after reading this am tempted to see how it does on single pin T8's. Totally appeared to be an electronic ballast.

FYI... T12 AND Incandescent lamps are all going to cease being manufactured shortly, as stated earlier in the feed.


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## Stickshaker

You can overdrive a ballast with a 4 tube ballast running 2 tubes and they will run a loooong time while giving 1.7 times the light.


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## tscardwell

This is an incredibly old thread but I was googling searching for an answer to an issue of mine and came upon this. I work in an office building with at least 30 light fixtures if not more with each having 4 fluorescent bulbs. I waited awhile to change them and now there's like 20 burnt out. I bought 2 boxes of the t12's and started to change the ones that were out and it was SO hard to remove and even harder to put the new bulbs back in - the fit was SO tight. There was NO room to move the bulb diagonally and I was getting frustrated so a quick google search told me that t8's and t12's were identical besides the diameter. We had a fixture not working at all regardless of the bulb so maintenance came in and he jumped all over me about putting t8's in there, saying the ballast was made for t12's. I decided to research further, and it seems to be that the real difference is the t12 ballast is made for 40w bulbs, t8 made for 34w bulbs. t12 ballast will burn a t8 much much quicker. However, the ballasts in my fixtures say Electronic Ballast Basic 12, use 40w or 34w T12. SOOOO what's the difference between using a 40w t12, and a 34w t8???????


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## McClary’s Electrical

tscardwell said:


> This is an incredibly old thread but I was googling searching for an answer to an issue of mine and came upon this. I work in an office building with at least 30 light fixtures if not more with each having 4 fluorescent bulbs. I waited awhile to change them and now there's like 20 burnt out. I bought 2 boxes of the t12's and started to change the ones that were out and it was SO hard to remove and even harder to put the new bulbs back in - the fit was SO tight. There was NO room to move the bulb diagonally and I was getting frustrated so a quick google search told me that t8's and t12's were identical besides the diameter. We had a fixture not working at all regardless of the bulb so maintenance came in and he jumped all over me about putting t8's in there, saying the ballast was made for t12's. I decided to research further, and it seems to be that the real difference is the t12 ballast is made for 40w bulbs, t8 made for 34w bulbs. t12 ballast will burn a t8 much much quicker. However, the ballasts in my fixtures say Electronic Ballast Basic 12, use 40w or 34w T12. SOOOO what's the difference between using a 40w t12, and a 34w t8???????


A T 12 ballast is un-shunted between the two post, a T 8 ballast is shunted between the two post. Even though the pin diameter is the same, and the pin distance is the same, they are most certainly under no circumstances inter changeable. Ever. Period. No doubts about it.


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## Almost Retired

I always cut the ballast loose, and rewire the fixture for self ballasted, 110V LED bulbs.  IF you get the correct LED bulb, then neither T8/T12, polarity, or which end matters. Yeah, i am working myself out of a job, but i dont like florescent fixtures anyway.


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## u2slow

Early T8 ballasts were magnetic rapid-start and tombstones were unshunted. (I had a whole site with these. ) Instant-start took over almost as soon they went electronic. Many of the retrofit electronic ballasts are T8 or T12 compatible. 

Read the ballast and install the correct lamps... or retrofit to ballast-bypass LED as you wish.


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