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5150 Views 37 Replies 9 Participants Last post by  frank
A switch controls a bank of 2x4 drop in, 277v, 3 tube bi-pin, fluorescent lights. One fixture is not working, I change the ballast, put in two tubes and it works, put in the third tube and it goes out. Put two new tubes in and it works, put in the third and it goes out again. I replace that fixture and the third tube goes out again. I replace that tube and turn on the switch, the light comes on, but then goes out with the one next to it. I flip the switch a couple of times and all of the lights come on. I turn off the switch and leave. I get a call that another light, two down from the one that I replaced comes on and then goes out. Flip the switch and they all come on. The original fixture that I took out was put in another location and it works fine.
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Just guessing, maybe a loose neutral wire in that circuit???I assume that you checked the voltage???Maybe some "noise" in that circuit from an inductive load somewhere messing with the electronic ballast???

Let us know what you find out and don't let it drive you mad!!!!

The voltage is fine, the light in question is in the middle of the run.
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I second the motion for a voltage issue or a loose wirenut in one of the fixtures upstream.
check all wires to the tombstones.
They are wired wrong from the factory

(verify the the wires to the lampholders match the diagram)

oops, then I read the rest of the story. still pondering.....
Have to check all junctions, the problems could be unrelated.
The problems will reveal themselves if you maticulously inspect every part of the local system. And grounding is very important with flourescents
The light that is in question is in the middle of a run of lights. The lights before and after this fixture all work. I checked the voltage and it is ok.
Are they MC cabled together? light to light?
MC from fixture to fixture. The first fixture that I had problems with, I replaced the tubes and the ballast. I thought that it was the sockets, but I relocated that fixture and it works fine.
Grounding; check the ground connections in the problem fixtures, don't just look at them, but redo them. Every flourescent fixture nowadays say right on the box "fixture will not work properly if not properly grounded".

And also check all the wires in the problem fixtures. I can't count how many times a fixture come from the factory wired wrong or the push in connections were not pushed in all the way.
the only time I've seen the 2 lamps light and third not is when tombstones are miswired or misplaced in the fixture.

Sorry to say you have me stumped also. BUT there is an answer, there always is. Look again closely and measure. There really isn't that much to a fluorescent fixture.

I'd have to put my hands on it.:001_huh:
I am going back to that job in the morning. I talked to another 'lectrician an he said the same thing as you Joe Momma. I will keep you guys posted.
Joe Momma for president!! Joe you were right about the grounds. I started at the first fixture that was giving me problems and worked back to the switch. I could see that the fixtures were daisy chained. I checked all connections and found that the fifth fixture back had a problem with the grounds. All of the fixtures contained two MC cables, with the grounds spliced together with a tail to the plate that snaps into the fixture for your connector. The one that was bad did not have a ground tail, one MC ground went to the plate and then was spliced to the other MC ground. One ground was stripped longer than the other and they were not making contact. I spliced them together and everything worked fine.
I hate how the fixtures just use that little slide in cover to ground the fixture.

I've always thought that might pose a problem, but apparently it's usually installer error that causes the problems.
Thanks Joe, I also re-spliced all of the connections on the fixtures that I opened up. The MC hot and neutrals were skined about 3/4 " and the leads for the ballast were about 1/4". I always strip the leads from ballast as long as the MC's and twist them all together, for a better connection.
The leads from the fixture were stripped by the factory(if they were installed brand new). And it's tough to redo connections on troffers as you probably noticed.
I know I usually cut my wires down to about 3 inches so I can get them back into the small opening they provide.
I would think it's a grounding issue also, I once had a bank of new lights not work unless you physically touched the lamps with your finger.
I received a call yesterday, the lights that I worked on are not working again. This is crazy, I cannot understand it!:mad:
No Robert, it is down at the U of P, a new building , only 3yrs.
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