TROUBLE SHOOTING 480v MH PARKING LOT LIGHTS ISSUE

[coachj]

I've been working on a parking lot this week thats had numerous problems , which Ive fixed but this last one is killing me . I know im overlooking the obvious . I have 3 light poles with 3 heads 1000w480v ballast . The poles are being fed by 3phase circuits . When i test my power feeds at the hand hole 277v from each phase to ground but nothing from phase to phase when i should be gettin 480v. What should i be checking.

 

[Dennis Alwon]

If you are getting 277 from each phase to ground then either the 3 feeds are on the same phase or 2 phases are out and you are reading thru the light ballast back to ground.

 

[qcroanoke]

If you are getting 277 from each phase to ground then either the 3 feeds are on the same phase or 2 phases are out and you are reading thru the light ballast back to ground.

Are you testing with the pole lights still connected? I would clear them all from the feeds and then test.
Maybe even clear the feeds at the hand holds, find the first in line then re-connect 1 by 1.

 

[coachj]

I thought of it reading threw ballast so I did disconnect my feed going up the pole. There are three different panels that feed the parking lot and all breakers are 3phase breakers

 

[Dennis Alwon]

Have you disconnected all the lights on the circuit that you were reading 277 to ground on? Not sure how you can have 277 to ground but nothing across each phase. I guess it is possible that the lines are cut and there is leakage across the earth only from one phase???????

 

[growler]

When i test my power feeds at the hand hole 277v from each phase to ground but nothing from phase to phase when i should be gettin 480v. What should i be checking.

They are right, you are missing some phases.

Now the idea is to find the last place power is still good. Check at the panel and then the contactor (if one is used).

If the power is good at the panel or contactor (last place available ) then check to see which feeds are cut.

Hate to say it but it sounds like shovel time.

Also if the cable is cut and you can pull one of the feeds out this will help determine where to dig or if you have one use an underground locator/tracer. Or you can use my favorite trick and try to find out where they have been digging.


Make sure to check the contactor it could just be bad contacts ( they don't last forever).

 

[cowboyjwc]

They are right, you are missing some phases.

Now the idea is to find the last place power is still good. Check at the panel and then the contactor (if one is used).

If the power is good at the panel or contactor (last place available ) then check to see which feeds are cut.

Hate to say it but it sounds like shovel time.

Also if the cable is cut and you can pull one of the feeds out this will help determine where to dig or if you have one use an underground locator/tracer. Or you can use my favorite trick and try to find out where they have been digging.


Make sure to check the contactor it could just be bad contacts ( they don't last forever).

Could be a bad breaker too. Always start at the source and work back to the problem. Which could mean you'll need a shovel.

And when I say the source. If panel b is feeding the lights and panel a is feeding panel b then check the breakers at panel a. Though if the issue was at panel a you would probably be having other issues too.