277 Lighting back feeding neutral

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Chancelong

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Location
Wisconsin
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Electrician
I have been working on replacing 277volt T8 fluorescent tubes with ballast bypass LED's in a commercial kitchen. I have slowing been replacing them as they go out, they already had luminaire disconnects installed so power wasn't shut off during ballast removal. I after converting to led I put the new bulbs in and they stayed on for 10 seconds then both went out, then every other light on that circuit, and a few on another circuit went out. Pulled the light apart and it had 480v at the disconnect with no tripped breakers. I checked another light that went out at the same time and it also had 480v across the switch leg and neutral. Knowing that multiple circuits feed this area, with a possible shared neutral, could another ballast be back feeding this neutral and the ballast I removed, somehow caused the other lights to receive 480 volts?
 
You most likely have a floating neutral.
The good news is you are about to learn alot of important things about messing with things...
And you didnt get magnetized w/480v.
Go back to the first box and start there.
Visually w/the power off..
 
Welcome to the forum.

Yikes! It sounds like you may have delta instead of wye.

Measure from each line conductor to ground.

You should have 277v and 0v, not 277v and 277v.
 
So I checked voltage on the lights on a different circuit, but still not working. I had the 277 volts from the hot conductor to ground, 0 volts between hot and neutral, and 277 volts between the neutral and the ground. So that tells me something is causing one circuit to back feed the neutral. Would a loose neutral wire cause such a strange situation?
 
Found the issue, a neutral wire pulled out of a wire nut. With the neutral being shared between two circuits, when one circuit back fed the other and sent 480v to each light fixture, it cooked the ballast and LED bulbs. Now just to replace some bulbs and its good to go. Thanks for the help
 
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