[Shop-talk] T8 and T12

[David C.]

OK, this may be old news to a lot of you, but I just found out it's 
fairly easy to retrofit a 2 lamp T12 fixture to T8 lamps.  All you need 
is a new electronic ballast.  As I found out (below) this will work with 
either a T8 or a T12 electronic ballast.  At least it will with 
Phillips/Advance ballasts.

First of all, it's probably not worth the effort and expense to retrofit 
a bunch of old shoplight fixtures that have magnetic ballasts.  You 
would be time and money ahead to just replace the whole fixture. 
However, in my utility room I have two 48" T12 fixtures that are about 
12 years old, and I didn't want to go to the hassle of pulling them down 
and replacing them with new fixtures.  I already did that in the master 
walk in closet before I found out about this.

Anyway, a while back the ballast in one utility room fixture went out. 
I replaced it with a T12 electronic ballast from H.D. and put the 
regular T12 lamps back in.  Installation was normal; the new ballast had 
all the same wires as the old one.  (Apparently magnetic ballasts are no 
longer available, which is probably a good thing.)  A few days ago I 
read on another forum that ANY electronic ballast will usually drive T8 
lamps (as long as it's for the same number of lamps).  So today I got 
two T8 ballasts (one for a spare) and four T8 lamps.  In the fixture 
that had the "new" electronic ballast,  I just put two T8 lamps in and 
it fired right up.

I took the other fixture apart and removed the ballast, and unwrapped 
the new T8 ballast.  It's a little different- it only has half the wires 
as a T12 ballast.  Where the T12 ballast had two yellow leads to one 
end, and two blue and two red to the other end, the T8 has two blue and 
one red.  No yellow.  After studying the wiring diagram on the ballast, 
I figured you attach the one red lead to the two yellow (fixture) leads 
on one end, and then one each of the blue leads goes to two red and two 
blue leads on the other end of the fixture.

So now I have lots of light in the utility room, new ballasts, and, I 
hope, a happier wife. Plus I can take the extra ballasts back to H.D. 
and put about $18 back in my wallet.  I just wish I had known this trick 
before I spent an hour taking the old fixture down and putting a new one 
up in the closet.