T8 vs T12

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The ballast voltages are quasi-secret, that's where the concern is, I think T-8 and T-12 use the same voltages but I've never actually checked and could easily be in left field.

If that's true a 32 watt T-8 will work on a 40 watt T-12 ballast and actually prolong ballast life.
 
t8 ballast

t8 ballast

I recently had this issue on a service call. Someone had installed the t8 bulbs in fixtures designed to burn t12 bulbs ( magnetic ballast) They were acting all screwy, just pulsating and blinking. Some times they came on, some times they didnt, and sometimes they pulsated like crazy. I changed out the ballast to electronic and they now work fine.
 
Copperclad said:
I recently had this issue on a service call. Someone had installed the t8 bulbs in fixtures designed to burn t12 bulbs ( magnetic ballast)
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It's not uncommon. Buildings get remodeled and they install new T8's right alongside the old T12's. Manager buys one kind of lamp for spares. The employees don't know the difference and they go to change lamps and BINGO, it's service call time when it doesn't work.
 
If you swap out a T-12 ballast and install a T-8 ballast, you must connect both contacts of each socket together and to the single ballast wire, where the T-12 ballast had a pair of wires.
 
Some universal ballasts can do both - some do not. But often the difference t-8 vs t-12 is series vs parralel connection of the lamps.
 
e57 said:
Some universal ballasts can do both - some do not. But often the difference t-8 vs t-12 is series vs parralel connection of the lamps.
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As Larry said, replacing a T12 with a T8 just requires a few more orange wire nuts and following the diagram on the ballast. One end you make up all the leads together. The other end, you have to separate the two sockets that are typically tied together and then wire them as shown.
 
steve66 said:
Some ballasts are made to drive either, but in general, the lamp must match the ballast.
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I agree, never use any lamps not listed on the ballast label.


LarryFine said:
If you swap out a T-12 ballast and install a T-8 ballast, you must connect both contacts of each socket together and to the single ballast wire, where the T-12 ballast had a pair of wires.
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In many cases you must swap out the sockets as well. Many times the sockets that shipped with T-12 type ballasts have the contacts internally connected. This type socket will have a large black "S" on the back side of the socket that stands for 'shunted'. If you have shunted sockets they must be swapped.
 
iwire said:
In many cases you must swap out the sockets as well. Many times the sockets that shipped with T-12 type ballasts have the contacts internally connected. This type socket will have a large black "S" on the back side of the socket that stands for 'shunted'. If you have shunted sockets they must be swapped.
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Iwire - good point. I have not personally ran in to that situation yet.
 
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