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#62905 - 03/02/06 03:38 PM Mixing T12 and T8 ballast/lamps
drillman Offline

Registered: 03/24/03
Posts: 97
Loc: Somewhere in Texas
Does anyone know the long term effects of using T12 lamps with a T8 electronic ballast or using T8 lamps with T12 magnetic ballast?

I know they will work, at least in the short term.

The other thing I wonder about is on the diagram for the Advance electronic T8 ballasts it shows the bipin sockets shorted together. Does anyone know what the long term effect would be if that was not done. I know they make preshorted sockets but I do not have any right now.

This came up in an argument between me and a maintenance man that stated "they work just fine" when he mismatched the lamps and ballast. My response was "yeah for now". However, I have no real ammo except the label on the ballast.

Thanks for any help.

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#62906 - 03/02/06 04:16 PM Re: Mixing T12 and T8 ballast/lamps
renosteinke Offline
Cat Servant

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Change one, change the other...keep the fixture anf lampholders. What's the problem?

We have another thread going, where a manufacturer makes no excuses for his low opinion of "electricians." Ballast info is there for a reason.

On the plus side, there are now many self-regulating ballasts out there, that are capable of accepting a variety of lamps.

Just when you've made things "idiot proof"....they come out with a better idiot!

#62907 - 03/02/06 04:33 PM Re: Mixing T12 and T8 ballast/lamps
Rewired Offline

Registered: 01/01/06
Posts: 567
Loc: Hamilton, Ontario, Canada
I have seen this many a time.. like you said they will work "for now" but while doing so you will probably not be getting the correct light output, and its hard on the bulb and ballast.. As for " shorted" endsockets.. What we do if we are converting a fixture over to T-8 is to "short" them ourselves.. ( wire the 2 leads from the endsocket to the single wire from the ballast).. works fine.. Our local convention center is wired like that... I do not know of any long term effect if the sockets were not " shorted".. Possible hard starting of the lamp maybe, or premature failure of the electrodes in the lamp is all I can think of really...


#62908 - 03/02/06 04:45 PM Re: Mixing T12 and T8 ballast/lamps
Megawatt Offline

Registered: 03/11/04
Posts: 74
Loc: Lexington,Ky, USA
Here's what I found on a trouble call.
2 yr old Church. 5 2x4 lay ins, Customer rebulbed all, none would work.
Opened the first fixture, removed 4 T12's.
& found an electronic ballast, requiring 4 T8 tubes.
Had to replace all 5 ballasts, & replace tubes. These fixtures were in the main entrance, so they were on anytime the Church was occupied, so they failed first.
96 fixtures in all, & everyone had T12 tubes installed.
Ordered a truck load of T8's to replace all of them.
Needless to say, They were not very happy with the Electrical Contractor that made this mistake.

#62909 - 03/03/06 06:11 AM Re: Mixing T12 and T8 ballast/lamps
Rick Kelly Offline

Registered: 01/11/06
Posts: 60
Loc: Iqaluit, NU, Canada
Be very careful when playing with T8 lamps and instant start electronic ballasts. There have been documented fires caused by mis-wiring of T8 equipped fixtures.

You must enure that the pins are shorted together. If you do not have shorting sockets then short the conductors going to the socket together. Not doing so has caused at least one fire, that we know of, in a Canadian jurisdiction. The fire was caused by charring of the tubes due to excessive heating of the lamp cathodes due to high current.

My jurisdiction, I am a regional electrical inspector in the Canadian Territory of Nunavut, has published a "Notice to Industry" on this issue. The notice was based on material found at the following URL.


I just tried the link and NEMA has moved the document. Anyone want it? Send me a message and I will send you the "Notice to Industry" we published on this issue.

[This message has been edited by Rick Kelly (edited 03-03-2006).]


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