Half of a 6 lamp fixture outtage

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Eddy Current

Senior Member
Ive got a 2X4 fixture with two feeds of 277V and 6 T8 lamps and 3 of them are out. Its acting like its one of the ballasts that's out, because when I unplug the disconnect in the fixture and swap it with the other ballast it works. I have changed both ballasts though, checked all the connections, even changed the disconnects out and still can only get 3 lamps to light. I checked with a meter and I have 277 coming in on both feeds, but when I check the tombstones the three that are out are reading a lower voltage.
 
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Eddy Current

Senior Member
ActionDave said:
Do you get 480V if you check phase to phase on the two feeds? You can't check voltage at the tombstones. I guess you can, but I wouldn't.
Click to expand...

I didn't get a chance to look at it anymore today, but I noticed there are several in that same row that are half working, so its probably something with the circuit. Its those plug in type whip lights.
 
Electric-Light

Electric-Light

Senior Member
Eddy Current said:
Ive got a 2X4 fixture with two feeds of 277V and 6 T8 lamps and 3 of them are out. Its acting like its one of the ballasts that's out, because when I unplug the disconnect in the fixture and swap it with the other ballast it works. I have changed both ballasts though, checked all the connections, even changed the disconnects out and still can only get 3 lamps to light. I checked with a meter and I have 277 coming in on both feeds, but when I check the tombstones the three that are out are reading a lower voltage.
Click to expand...

Feel the ballasts. Do they both feel warm? It's a high possibility that they're on two switches to select between two levels.
You could be reading a stray voltage.

I dunno, maybe a box fell over and hit the switch that's seldom used.
 
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Eddy Current

Senior Member
Electric-Light said:
Feel the ballasts. Do they both feel warm? It's a high possibility that they're on two switches to select between two levels.
You could be reading a stray voltage.

I dunno, maybe a box fell over and hit the switch that's seldom used.
Click to expand...

When I first thought it was the ballast, I checked and only one was warm.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Do you have one neutral or two to the luminaire(s)? What are you testing to when you had 277 on each "hot" conductor. If the circuit not working has separate neutral and is open somewhere - the kind of thing you described is happening can be expected.
 
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Eddy Current

Senior Member
kwired said:
Do you have one neutral or two to the luminaire(s)? What are you testing to when you had 277 on each "hot" conductor. If the circuit not working has separate neutral and is open somewhere - the kind of thing you described is happening can be expected.
Click to expand...


Two neutrals two hots.
 
Electric-Light

Electric-Light

Senior Member
kwired said:
Do you have one neutral or two to the luminaire(s)? What are you testing to when you had 277 on each "hot" conductor. If the circuit not working has separate neutral and is open somewhere - the kind of thing you described is happening can be expected.
Click to expand...

This is a good point. It can be very dangerous. If you take an extension cord and plug a lamp into it so that only "hot" is plugged in, you'll find 120v from the neutral prong to ground. The presence of lamp makes such a little difference in electrocution hazard, because the resistance is so low relative to your body.

Measure the voltage between a known good ground and neutral. If it's floating, you'll get line voltage when power is applied.
 
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