# t12 to t8



## Bkessler

When your rewiring 4'f 40t12's to t8's do you need both sides of each tombstone to be wired to the ballast? This would be for a 4 lamp electronic ballast where one end has two yellows that correspond to the four red and blue on the opposite side.


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## kbsparky

It's my understanding that the "electronic" sockets are internally connected to supply both prongs of the lamp with a single wire.

A jumper wire or pigtail can be utilized on older type sockets to accomplish the same thing on retro-fits.


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## Speedy Petey

According to the diagram you do. This may not be the case though in a fresh wire (as opposed to a retrofit).


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## Bkessler

Thanks, I thought you had to but was not sure. So brand new tombstones are internally connected but older retrofit ones need to be jumped. Thanks again. bk


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## Simux

I tend to pull the wires all the way to the tombstones. Seems to work, not had to go back on any of the retrofits I've accomplished.


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## k2x

Rapid start electronic are series wired and the leads need to be seperated. Instant start electronic are parallel wired and need to be shunted or jumpered or pigtailed. Rapid starts were pretty popular a few years ago because of a better lamp start and longer lamp life. The instant starts of five to 10 years ago you will often see blackened lamp ends because of the way they start. I think the instant starts today have a little better start and i don't see many rapid starts anymore. 

Anyway a rapid start won't work on a shunted tombstone. Also, as far as I know dimmable ballast are only rapid start and they won't work on a shunted tombstone.

Oh and instant starts will work off of one side of the tombstone but that will shorten the lamp life. This can be a problem with some older fixtures with starters. Guys think they pigtailed it but in reality they did not.


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## Nodoggie

Easy answer to this: always rely on the schematic of the particular ballast you are using. It's always on the ballast. keep life simple, bro.


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## Bkessler

Nodoggie said:


> Easy answer to this: always rely on the schematic of the particular ballast you are using. It's always on the ballast. keep life simple, bro.


I can read the schematic bro, my question was on the end sockets.


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## nap

Bkessler said:


> I can read the schematic bro, my question was on the end sockets.


 
I think nodoggie was trying to provide an answer that would allow you to make the determination based upon each individual situation. As others have posted, there are some types of ballasts that require a shunted socket, some that don't and the answer would llie within the schematic.


In your specific situation, the answer would be the terminals must be shunted (whether by an actual shunted socket or by connecting each terminal on the socket to the 1 wire feeding that socket) but as k2x posted, if you have a rapid start ballast, the must have seperate connections to each terminal on the socket.

If you had an instant start ballast with shunted sockets, you cannot use a rapid start ballast but you can convert the other direction simply by tying both terminals on each of the sockets to the repective feed wire on the ballast. (your situation apparently)

If you have shunted sockets and want to use a rapid start ballast as a retrofit, you would have to replace the sockets with seperated terminal sockets.


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## Nodoggie

per Nap:

exactly. The common practice is to get a new instant start ballast(s), and new t8 tombstones. It's a quick and reliable fix. Using all new components, the schematic makes it an easy job. Trying to mix new components with phased-out or antiquated components is always a bad idea, IMO. The only exception is when adding an emergency ballast to pre-existing fixtures.


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## Speedy Petey

Nodoggie said:


> The common practice is to get a new instant start ballast(s), and new t8 tombstones.


Not that common. I have never heard of anyone replacing sockets during a retrofit. Unless they're broken of course.
I myself just wire the old fixtures according to the schematic, which with the new ballasts is super simple.
On a two-light 4' fixture for example; one wire to all four yellows, one wire to both reads, one wire to both blues. Done.


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## Nodoggie

Maybe not that common in your neck of the woods, but very common in mine. T8 lamps don't always fit in T12 tombstones. Also, as you mentioned, tombstones crack; they also suffer from polymer deterioration. The higher-quality route (IMO) would be to get the new tombstones (for 35 cents each) and use those instead. The extra labor would be minimal and the end-product would be more reliable.


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## nap

Nodoggie said:


> T8 lamps don't always fit in T12 tombstones..


Not arguing with the rest of your post but I have never had a t-8 not fit a t-12 socket. The tube is smaller so if anything, there would be more clearance all the way around for the lamp.

Now, I have had the experience of having intereference with a t-12 and the wrong sockets.


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## Nodoggie

Fair enough. ;-) However, when doing ltg retro-fits for some establishments (industrial complexes, utility companies, especially, etc.) there is quite often a spec calling for tombstone replacement, as well.

That "extra space" in the T12 tombstone means--according to them--it doesn't fit correctly. It's not the right component. T8 lamps are often "barely" staying in T12 tombstones; the lack of a tight fit also increases vulnerability to arcing. A lot of things in our trade can "be made" to work; it doesn't mean they should.

Once again, just the humble opinion of one itsy-bitsy electrician.


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## Speedy Petey

nap said:


> Not arguing with the rest of your post but I have never had a t-8 not fit a t-12 socket. The tube is smaller so if anything, there would be more clearance all the way around for the lamp.
> 
> Now, I have had the experience of having intereference with a t-12 and the wrong sockets.


I completely agree.


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## nap

Nodoggie said:


> Fair enough. ;-) That "extra space" in the T12 tombstone means--according to them--it doesn't fit correctly. It's not the right component. T8 lamps are often "barely" staying in T12 tombstones; the lack of a tight fit also increases vulnerability to arcing. A lot of things in our trade can "be made" to work; it doesn't mean they should.
> 
> .


 
You apparently are under the misunderstanding that there is a difference in the pins of a T-8 and T-12. There isn't. They are identical. The only outward physical difference between these 2 lamps are the diameters of each.

that being said, I am not "making anything work". There is nothing wrong with using a short or tall socket as long as it fits the fixture properly and the lamp fits within the fixture properly using that socket.


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## Bkessler

nap said:


> You apparently are under the misunderstanding that there is a difference in the pins of a T-8 and T-12. There isn't. They are identical. The only outward physical difference between these 2 lamps are the diameters of each.
> 
> that being said, I am not "making anything work". There is nothing wrong with using a short or tall socket as long as it fits the fixture properly and the lamp fits within the fixture properly using that socket.


The tall sockets are not supposed to be used in T8's (i thought) because you need to maintain a 1/4" max from the lamp to the metal fixture.


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## nap

Bkessler said:


> The tall sockets are not supposed to be used in T8's (i thought) because you need to maintain a 1/4" max from the lamp to the metal fixture.


 
not sure where everybody gets these things. I have had t-12 fixtures and t-8 fixtures that use the tall sockets and the same that used short sockets. 

I'm trying to remember where it was (since everybody here seems to say the proximity to steel is a requirement of the lamps operating properly) but I know I had a situation where there was no steel housing at all. Everything worked just fine.

I just remembered one of the situations with no metal housing. One of the local television stations used fluorescent lights for backlighting some of their sets. There were no metal housings. The sockets were mounted on wood and the ballast was somewhat remotely mounted.

Another such "fixture". A church I was doing some work for had a cross made by one of the parishoners. It was all wood with fluorescent lamps used to backlight a stained glass front cover. The ballast had stand-offs so it would not be mounted directly to the wood. 

In both of those situations, the lighting worked just fine.


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## Nodoggie

Bkessler said:


> The tall sockets are not supposed to be used in T8's (i thought) because you need to maintain a 1/4" max from the lamp to the metal fixture.


that is correct.



nap said:


> I'm trying to remember where it was (since everybody here seems to say the proximity to steel is a requirement of the lamps operating properly) but I know I had a situation where there was no steel housing at all. Everything worked just fine.


The proximity to metal has nothing to do with operation; it has to do with safety. Ballasts can put out extreme voltages. 




nap said:


> I just remembered one of the situations with no metal housing. One of the local television stations used fluorescent lights for backlighting some of their sets. There were no metal housings. The sockets were mounted on wood and the ballast was somewhat remotely mounted.


nah. no misunderstanding. Both lamps use 5/8" spacing (except single pin T12s, obviously), and a T12 fixture will even usually run a T8 lamp, though with reduced lamp life. The reason why you use T8 tombstones is _to prevent arcing._ Our entire trade is not about "get 'r done," but rather, protection of personell. That is the entire basis of NFPA 70.



nap said:


> Another such "fixture". A church I was doing some work for had a cross made by one of the parishoners.


Stay close to the cross, my child :innocent:


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## Bkessler

nap said:


> not sure where everybody gets these things. I have had t-12 fixtures and t-8 fixtures that use the tall sockets and the same that used short sockets.
> 
> I'm trying to remember where it was (since everybody here seems to say the proximity to steel is a requirement of the lamps operating properly) but I know I had a situation where there was no steel housing at all. Everything worked just fine.
> 
> I just remembered one of the situations with no metal housing. One of the local television stations used fluorescent lights for backlighting some of their sets. There were no metal housings. The sockets were mounted on wood and the ballast was somewhat remotely mounted.
> 
> Another such "fixture". A church I was doing some work for had a cross made by one of the parishoners. It was all wood with fluorescent lamps used to backlight a stained glass front cover. The ballast had stand-offs so it would not be mounted directly to the wood.
> 
> In both of those situations, the lighting worked just fine.


Md had a real good explanation why the proper distance needs to be maintained between lamps and metal housing for electronic ballast on CT a couple of years ago.


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## MDShunk

I have never replaced, on my own or by spec requirement, all the tombstones in a T8 retrofit job. There are always broken one's to replace, however. My luck is that the fixtures with the most broken lampholder ends are the one's with tombstones of a style that take 3 weeks to get because they haven't been used in new fixtures for 30 years.


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## Nodoggie

That, my friend, is bad luck. It's never been a problem for me. However, I have had other ordinarily easy jobs quickly get overly complex due to extremely long lead times.


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## k2x

Bkessler said:


> Md had a real good explanation why the proper distance needs to be maintained between lamps and metal housing for electronic ballast on CT a couple of years ago.


I've done thousands of those acordian type reflector retros in troffers and the tolorance for bulb to reflector distance is pretty much wild. I've never had a problem.


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## Nodoggie

I'm a contractor so I'm a little more keen on liability, and having to return to a job. i don't like the prospect of being called out on a Code or safety violation in the future, even if I know it will fly in the present, nor on the prospect of burning down a building or killing someone years from now because I didn't pay a little more attention to quality in my installation. The NEC is not about how to do it; it's ultimately about how to do it right....fire prevention and personnel safety.

I understand there are others here who have their own way. To each his own. I, however, change out the tombstones. It takes all of 60 seconds.


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## Speedy Petey

Nodoggie said:


> I'm a contractor so I'm a little more keen on liability, and having to return to a job. i don't like the prospect of being called out on a Code or safety violation in the future, even if I know it will fly in the present, nor on the prospect of burning down a building or killing someone years from now because I didn't pay a little more attention to quality in my installation.


Well then you know how many of us here feel. :thumbsup:


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## Nodoggie

:thumbup1:


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## nap

> Nodoggie said:
> 
> 
> 
> t
> 
> 
> 
> The proximity to metal has nothing to do with operation; it has to do with safety. Ballasts can put out extreme voltages.
> 
> 
> 
> So what does that have to do with proximity of the lamps to steel?
> 
> 
> 
> 
> 
> 
> nah. no misunderstanding. Both lamps use 5/8" spacing (except single pin T12s, obviously), and a T12 fixture will even usually run a T8 lamp, though with reduced lamp life. The reason why you use T8 tombstones is _to prevent arcing._ Our entire trade is not about "get 'r done," but rather, protection of personell. That is the entire basis of NFPA 70.
> 
> Click to expand...
> 
> I have changed oh so many sockets. Can you define T-8 sockets and T-12 sockets?
> 
> before you do, let me simply tell you, (actually repeating myself here), I have had shorter sockets in both t-12 and t-8 fixtures and taller sockets in both t-12 and t-8 fixtures (all factory stock) so please, tell me the difference.
> 
> here is an example of a few items from a supplier.
> 
> http://www.1000bulbs.com/T8---T12Standard-Sockets/3774/
> http://www.1000bulbs.com/T8---T12Standard-Sockets/33918/
> http://www.1000bulbs.com/T8---T12Standard-Sockets/3775/
> 
> Now, there are some newer sockets that will accept only T-8 lamps
> 
> http://www.1000bulbs.com/T8---T12Standard-Sockets/4572/
> 
> but I believe we are talking about the typical tombstone style sockets, yes?
> 
> I sure would like somebody to come up with this explanation for the clearance you guys are talking about.
> 
> Oh, and for a non-self manufactured fixture that does not have any metal in it yet uses electronic ballasts;
> 
> I can't tell you if this specific manufacturer uses steel in their fixture but there are fixtures of this type that have a plastic backing for the lamps and the entire housing is plastic.
> 
> http://www.aeilighting.com/t8frezr.htm
> 
> What have you to say to that and your proximity to some sort of metal in the fixture?
Click to expand...


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## nap

Nodoggie said:


> I'm a contractor so I'm a little more keen on liability, and having to return to a job. i don't like the prospect of being called out on a Code or safety violation in the future, even if I know it will fly in the present, nor on the prospect of burning down a building or killing someone years from now because I didn't pay a little more attention to quality in my installation. The NEC is not about how to do it; it's ultimately about how to do it right....fire prevention and personnel safety.
> 
> I understand there are others here who have their own way. To each his own. I, however, change out the tombstones. It takes all of 60 seconds.


please alert me to any code violation in what I have been stating, or safety problem.


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## k2x

Yeah most of my work got inspected , analyzed, and inspected again by the Army corps of too many engineers. I'm comfortable that it is as safe as it can be.


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## MDShunk

Nodoggie said:


> ... To each his own. I, however, change out the tombstones. It takes all of 60 seconds.


Are you something like an Olympic gold medalist tombstone changer? Sometimes it takes me 60 seconds of fighting to get the thing apart on one end that holds the tombstones in, on a troffer.


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## nap

MDShunk said:


> Are you something like an Olympic gold medalist tombstone changer? Sometimes it takes me 60 seconds of fighting to get the thing apart on one end that holds the tombstones in, on a troffer.


when did you get the promotion MD? First time I noticed the "moderator" tag.


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## Speedy Petey

nap said:


> when did you get the promotion MD? First time I noticed the "moderator" tag.


Hell, he is the original. 

He pioneered this site. :thumbsup:


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## Nodoggie

MDShunk said:


> Are you something like an Olympic gold medalist tombstone changer? Sometimes it takes me 60 seconds of fighting to get the thing apart on one end that holds the tombstones in, on a troffer.


 
hehehe. yup. me, too, sometimes.


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## frenchelectrican

Most case to change the tombstone it will useally take me more than 60 seconds due the sheetmetal can get warped pop the old one is not a issue but to *install* the new one now that is a challange to install them without breaking them :blink:.


Merci,Marc


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## MDShunk

nap said:


> when did you get the promotion MD? First time I noticed the "moderator" tag.


You gotta know people who know people. :laughing:


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