277/408 volt lighting

[Kopper]

I am troubleshooting a situation where there are three 277/408 volt 400W MH parking lot lights that do not work. The ballasts and bulbs were replaced about 10 months ago and recently they all went off. No breakers are tripped and there is power at the bottom of the light poles. Each individual leg measured 285V +/- but when i measured across the legs it gave no reading. I am a bit baffled... There is no known record of the type of ballasts and bulbs that were used when they were replaced. I plan to go up and check out the tops of the lights sometime next week...?

 

[chris kennedy]

I am troubleshooting a situation where there are three 277/408 volt 400W MH parking lot lights that do not work.

Are the luminaires tapped up for 277 or 480?

Each individual leg measured 285V +/- but when i measured across the legs it gave no reading.

This would lead me to believe they are tapped up to 480. If one ungrounded was lost you will read 277 on each ungrounded conductor through the ballast windings.

 

[big john]

I agree with Chris you have an open circuit conductor:If these are 277 volt lights you've got an open neutral which is why both conductors measure ~285 to ground.If these are 480v lights you've got an open phase which is why you measure nothing between them.

 

[iwire]

I agree with Chris and John, sounds like an open hot between the panel and the place you are taking the reading.

Kill the power, break the splices and ring the wires out with a continuity tester.

 

[Kopper]

I was unprepared and unable to get to the luminares today but plan to do that on Tuesday December 1. They are at the top of 20 or 30 foot poles.

 

[iwire]

I was unprepared and unable to get to the luminares today but plan to do that on Tuesday December 1. They are at the top of 20 or 30 foot poles.

I would start with breaking the spices in the handhole at the base.

With multiple poles out it is doubtful the problem is at the fixtures.

 

[chris kennedy]

I agree with Chris

I agree with Chris

If either of you guys are single, want to marry me? It would be cool to live with someone that agrees with me once in a while.:lol:

 

[iwire]

If either of you guys are single, want to marry me? It would be cool to live with someone that agrees with me once in a while.:lol:

 

[sparkyrick]

I am troubleshooting a situation where there are three 277/408 volt 400W MH parking lot lights that do not work. The ballasts and bulbs were replaced about 10 months ago and recently they all went off. No breakers are tripped and there is power at the bottom of the light poles. Each individual leg measured 285V +/- but when i measured across the legs it gave no reading. I am a bit baffled... There is no known record of the type of ballasts and bulbs that were used when they were replaced. I plan to go up and check out the tops of the lights sometime next week...?

You have a loose or broken wire somewhere or a bad breaker (one open pole). You get 285V on both legs, but 0V between legs, because you are reading the voltage from Phase A going through the ballast and being present on Phase B.

 

[peter d]

You have a loose or broken wire somewhere or a bad breaker (one open pole). You get 285V on both legs, but 0V between legs, because you are reading the voltage from Phase A going through the ballast and being present on Phase B.

The 285 volts could also very well be ghost voltage.

 

[Kopper]

I must do more testing... There were three wires at the base of the first pole that tested 285 volts. One was capped with a wire nut. I later discovered another wire with a wire nut cap which I did not test. All of the lighting is on double pole breakers in a three phase panel box....