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Steve G.
Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 17978
Experience:  Spent 20 years as an Electrical Engineer, designing electrical plans and specifications.
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Hi, I just replaces a T12 ballast with a T8 for an 8 two lamp

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Hi, I just replaces a T12 ballast with a T8 for an 8' two lamp fixture. My problem is now one lamp will light and the other will not. I'm confident I wired it correctly.
Hello there and welcome to Just Answer. My name is XXXXX XXXXX I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

Now..can you give me the make and model number of the ballast please?

Please let me know so that we can continue.

Customer: replied 3 years ago.

Thanks. It is a Philips Advance Centium - ICN-2P32-N Instant Start Electronic Ballast.

Here is the wiring diagram:

Let me know if you need more help.

Customer: replied 3 years ago.

The wiring diagram is on the front of the ballast. It is wired correctly. The fixture is properly grounded. The lamp connections look clean and free from corrosion. I've tried two different, brand new lamps and still have the same issue.

Swap the blue wires and see if the other lamp fires.
Customer: replied 3 years ago.

Ok I swapped the blue wires but it did not fix the problem. So just for kicks I took the lamp that wouldn't light out and swapped it with the lamp that did light. Now the lamp that would light on one side lights on the other, and the lamp that didn't light on the one side still doesn't light on the other side. Could it be that I got two bad lamps in a row?

Sure. I have seen whole boxes of faulty lamps.

I'd probably get two more from a different store and give them a try.

This is a head scratcher for sure.

Customer: replied 3 years ago.

Ok, this is getting weirder. Hold on to your seat.


We went and got 2 new lamps and put them in. Same problem, one would light and one wouldn't.


So I did this: I stuck one end of the lamp we knew would light into one of the blue wire side socket, and it partially lit. When I placed the other end in the corresponding red wire socket it fully lit, like it should.


I then removed the lamp and did the same thing on the other side of the fixture and had the same result. I tried this with all 4 lamps and had the same result.


But when I placed two lamps that I know work into the fixture one of them lights and the other doesn't. I'd be pulling my hair out if I had any left.

Well now I would have to suspect the ballast.

If you just put one lamp into either pair of sockets, does it work?

Then move it to the other set of sockets, does it work?

Please let me know so that we can continue.

Customer: replied 3 years ago.

Yes. It works on both sets of sockets alone. Whichever lamp I plug in first works on either sockets. But the lamp I plug in second never works.

And when I say "works" I mean it lights along the whole length of the lamp. But it doesn't look like it is at full brightness.


I'm sorry this is taking so long. I'm not an electrician so I figured it would be a simple answer at first, just something I overlooked.

Don't worry about it taking so long.

Do you have a full 120V supply on the black and white wires?

If not, I think you have a bad ballast.

Let me know.

Customer: replied 3 years ago.

I'm getting 114.4 volts when I check the incoming white to black wires.

Ok, that's good.

You stated that you replaced a T12 ballast. I assume that you had T12 sockets.

How many wires went to each socket originally?
Customer: replied 3 years ago.

Yes our fixtures are 14 years old T12 fixtures. The ballast I replaced was a MagneTek Slimline Ballast 806-SLH-TC-P.


It had one red wire going to one socket & a blue wire going to the other socket on the same end of the fixture.


On the other end it had a white wire from the ballast going to one socket along with the white wire from the line in. This white wire side was on the same lamp as the red wire on the opposite end.


The other socket on this end had the black wire from the ballast as well as the black wire from the line in wired to it. It was on the same lamp as the blue wire from the opposite end.

Ok, >>>READ THIS<<<

Go down to the bottom of page 3 and read up.

You may need to modify those sockets.

I'll be here if you need further help with this issue. Please let me know.


Steve G. and other Electrical Specialists are ready to help you
Customer: replied 3 years ago.

Ok I fixed it. The problem was I asked the store for a T8 ballast to replace a T12 ballast for an 8 foot light fixture, and they gave me a T8 ballast to replace a T12 ballast for a 4 foot light fixture. The lesson here is just because you don't know what you're doing doesn't mean you can trust people that should know what they're doing. Anyways, once I put the correct ballast on everything else worked as it should. The sockets are the same ones that have been on there forever.