Replacing Ballast Question

bjp999November 3, 2011

I have a 2 (8 ft T-12) bulb fixture in my garage, about 10 years old. The old ballast is too weak to light the fixture. It has a black and white wire, and a blue and red wire (one each). The blue and red wires go to the lamp holders on one end of the fixture only. I have not disassembled the other side to see what is over there.

I was unable to find a replacement ballast with this exact configuration - but came close. I found a ballast with 1 black, 1 white, 1 red, and 2 blue. The salesman said just not to hook up one of the blue wires and it would work. I hooked up as he suggested and sure enough, the light comes on.

But the instructions warn that you need to hook up both blue wires for the balast to work properly, so I have turned the fixture off pending further research. Can someone confirm that hooking it up as I have done is acceptable and not putting undue stress on the balast? Do I need to rewire the fixture so the red wire goes to the lamp holders on one side of the unit, and a separate blue wire to the lamp holders on the other side for this to be a good long-term solution?


Brian in VA

Here is a link that might be useful: New Ballast Data Sheet

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For 1 lamp application, cap unused blue lead, insulate for 600 Vrms

That's what it says on the bottom of the page that you linked to.

    Bookmark   November 3, 2011 at 8:11AM
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But I have two bulbs, not one.

Can't help but think I am running the two bulbs in series rather than in parallel. I'm thinking running them in parallel may be less stressful on ballast.

Tonight I am going to open the far end of the fixture and see if the wires are accessible to the lamp holders over there. If so I am going to rewire the fixture. But if the wires are inaccessible or too short, I'm not sure how big an issue this is.

    Bookmark   November 3, 2011 at 9:22AM
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"I found a ballast with 1 black, 1 white, 1 red, and 2 blue."

Wire color is not what tells you if the new ballasts s correct.

The ballast will be marked with what bulbs it supports and a wiring diagram showing how it should be connected.

The voltage would be VERY high to power 2 bulbs in series, and would likely fail quickly if one of them had a problem.

The open circuit striking voltages of ballasts are already very high.

    Bookmark   November 3, 2011 at 3:12PM
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I replaced some ballasts not long ago on fixtures I installed in 1958 in a church. They were used perhaps 8 hours per week with few on-off cycles. Amazing service life. But the new ballasts had wiring diagrams not even remotely resembling the old ones. I used the diagram on the new ballast. Go and do thou likewise.

    Bookmark   November 3, 2011 at 5:40PM
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I was able to rewire the fixture with no trouble. The light comes on almost instantly, while with the ballast hooked up using only one blue wire, it took several seconds to come fully on.

Thanks so much for your replies! Garden web is great!

    Bookmark   November 4, 2011 at 7:42AM
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Next time go T8.

    Bookmark   November 4, 2011 at 1:53PM
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