Parking lot lighting strange voltage.

[H.L.]

I am trouble shooting parking lot lighting problems. One circuit that I am having an issue with is 480V single phase. At the poles, which are about 3000-4000' from the panel, i get 275V to ground on one leg and about 288V to ground on the other leg. Phase to phase I get about 40V. I am thinking that I may have a high resistance phase to phase short or that one phase is open before the first light pole and the downstream side of the open leg is shorted to a third phase that is on a different circuit in the same pipe.

What are your thoughts?

 

[ActionDave]

Sounds like an open hot. Time to break out the fault finder.

 

[kingpb]

So what is your voltage to ground on either phase if you turn the breaker off? If a phase is shorted to a another circuit, then you will still have voltage on the the phase that is turned off. Also, what is the chance that your 480V single phase circuit is actually using two phases off the same leg, i.e. A, B, C. instead of A-B 480V, your using A-A from two different breakers, or something similar. Maybe it got mixed up in a a j-box or pole.

 

[greenspark1]

I have also received strange voltage readings after 1 or 2 fuses in a 3-phase circuit blow. Goodluck troubleshooting, let us know what you find out.

 

[Smart $]

...

What are your thoughts?

Open fault on one line, supply side of test points.

Test supply voltage after disconnecting [safely] all load conductors at first pole.

 

[H.L.]

So what is your voltage to ground on either phase if you turn the breaker off? If a phase is shorted to a another circuit, then you will still have voltage on the the phase that is turned off. Also, what is the chance that your 480V single phase circuit is actually using two phases off the same leg, i.e. A, B, C. instead of A-B 480V, your using A-A from two different breakers, or something similar. Maybe it got mixed up in a a j-box or pole.

Zero volts to ground when the breaker is off. Chances of the 480 single phase circuit being two wires on the same phase of different breakers is naught as these poles were working. Until they were not.

 

[H.L.]

Open fault on one line, supply side of test points.

Test supply voltage after disconnecting [safely] all load conductors at first pole.

That is what I did when I got the 40V to ground.
I will open all fuseholders on the circuit and check voltage. Could it be something caused by the ballasts and or capacitors for the HID lighting?

 

[H.L.]

Sounds like an open hot. Time to break out the fault finder.

I think that I will be calling the thumper man

 

[Smart $]

...i get 275V to ground on one leg and about 288V to ground on the other leg. Phase to phase I get about 40V....

Zero volts to ground when the breaker is off...

That is what I did when I got the 40V to ground.

Your numbers are not jiving. First post you said 40V L-L... last post you said 40V L-G.

Typical outside lighting is pole to pole: 1) fixtures, 2) supply, and 3) "continue circuit" conductors spliced in pole base. Either that or there's a handhole somewhere with all the splicing. Which is yours?

Exactly how did you measure voltages posted? With pole fixtures and downline fixtures still connected? If you have fuses at each pole, with or without fuses pulled?

You need to be specific or this online method of troubleshooting is gonna take forever (unless you get lucky).

 

[rt66electric]

Start at the 1st pole.

Start at the 1st pole.

Start troubleshooting at he 1st pole.
disconnect all poles.
check voltage.


Connect 1st pole only ..... Does it work??

connect 2nd pole only.... does it work???

connect 3rd pole only.... does it work ???

connect 4th pole only ... it does NOT work... then go back to check the connections at the top/bottom of the 3rd pole....


somewhere there is a open in "B " phase, and your meter is reading "A" phase and through a ballast and back to "phantom A" phase instead of "B" phase

be sure to wear your gloves . this is the type of fault troubleshooting that will fling a loose wirenut off and get a live wire on the back of your hand.

 

[Smart $]

...somewhere there is a open in "B " phase, and your meter is reading "A" phase and through a ballast and back to "phantom A" phase instead of "B" phase...

Just want to point out it can easily be a "stiff" voltage, so take proper precautionary measures. The phantom, as you are calling it, is not the same as indicated on a voltage detector or high-impedance-input meter on a totally disconnected wire run with energized conductors.

 

[electricalist]

Start troubleshooting at he 1st pole.
disconnect all poles.
check voltage.


Connect 1st pole only ..... Does it work??

connect 2nd pole only.... does it work???

connect 3rd pole only.... does it work ???

connect 4th pole only ... it does NOT work... then go back to check the connections at the top/bottom of the 3rd pole....


somewhere there is a open in "B " phase, and your meter is reading "A" phase and through a ballast and back to "phantom A" phase instead of "B" phase

be sure to wear your gloves . this is the type of fault troubleshooting that will fling a loose wirenut off and get a live wire on the back of your hand.

I agree I have seen guys chase problems all over parking lots.
They all work now these went out now these work and those but no not for long.
When I'm by myself I disconnect the first junction, then disconnect 2 of 3 phase .checke that phase from breaker to whatever it goes through til my first junction. Doing each phase on its own. I find weak or bad breaker , in line fuse blown at pole, and a false hot because someone tested phase to ground not phase to phase, therefore I think its a called in series when volts 267 ish or less. It seems good but not nor will it be as light begin to come on.

 

[H.L.]

Your numbers are not jiving. First post you said 40V L-L... last post you said 40V L-G.

Typical outside lighting is pole to pole: 1) fixtures, 2) supply, and 3) "continue circuit" conductors spliced in pole base. Either that or there's a handhole somewhere with all the splicing. Which is yours?

Exactly how did you measure voltages posted? With pole fixtures and downline fixtures still connected? If you have fuses at each pole, with or without fuses pulled?

You need to be specific or this online method of troubleshooting is gonna take forever (unless you get lucky).

Where I said the L-G voltage was 40 was a typo. I meant L-L. That was whit all fuses at the base of the Poles connected. After removing all fuses I retested the voltage at the pole bases. There are three poles on this circuit in aisle B11. all three had zero volts any way I checked. There are two poles on this circuit in aisle B13. both poles had one leg 277 to ground and one leg zero to ground. I want back to the Panel and tested voltage at the breaker and found that "A" phase of the load side of the breaker had zero volts to ground. After putting in a new breaker the poles in aisle B13 have 480 L-L and 277 L-G. B11 I have not been back to yet but the lights are not working on those three poles.

 

[Smart $]

.... B11 I have not been back to yet but the lights are not working on those three poles.

They won't work until you put the pole base fuses back in... :slaphead:

:angel:

 

[frank everingham]

harpo

harpo

I am trouble shooting parking lot lighting problems. One circuit that I am having an issue with is 480V single phase. At the poles, which are about 3000-4000' from the panel, i get 275V to ground on one leg and about 288V to ground on the other leg. Phase to phase I get about 40V. I am thinking that I may have a high resistance phase to phase short or that one phase is open before the first light pole and the downstream side of the open leg is shorted to a third phase that is on a different circuit in the same pipe.

What are your thoughts?

there may be nothing wrong with your system. you have an ungrounded 480 volt delta system. they were common years ago. your primary is a 208 Y. your secondary is a 440 volt ungrounded delta. since there is no grounded conductor, the voltage between the pole and earth floats. you are reading capacitance. the grounded conductor is only required at the service. your system still requires an equipment grounding conductor. something interesting about these systems is that if the poles have in line fuses, if you take out one fuse, some times the pole still lights.

 

[meternerd]

Probably been said in other posts in a different way, but....here's my opinion. 480 single phase can likely either be from a 480/277 grounded Wye or a 480 ungrounded Delta. If it's the Wye, each phase should read around 277 to ground depending on phase voltage imbalance. But reading through a still connected device will read through the load to the de-energized wire if you have an open circuit, so both wires will show voltage. Voltage with one open leg would be as you are describing. With an ungrounded Delta, you can read anything up to 277 or so even with no grounded conductors due to capacitance. If it was me, I'd do an ohm check from the source to the load (across the load wires). If it reads open or high resistance, ground both wires on the load side and then read each leg (at the source end) to ground. That should show you which leg is open. A megger might give you a better reading than an ohmmeter with that long of wires. Sure sounds like an open leg to me. Also check line voltages to ground and line to line with the load disconnected. Should show 480 L/L and even voltages L/G. Use of a digital (high impedance) meter will add to any confusion.