Stray or Static

[selectric]

We have a light pole 16'(4 100watt hps heads) that we went to trouble shoot. We disconnected incoming 208v feed & at the top of the pole we still have 130v to pole or pole to ground.(oucH)
There is high voltage wire approximately 25' above this pole. Could it be static electricity? If pole is connected the voltage fluctuates from 130v at top of pole to appox. 26v at the bottom. I am concerned that someone will get hurt.
What do you think????

Steve

 

[tom baker]

Re: Stray or Static

Does the overhead feed have an equipment grounding conductor?
What type of meter are you using to measure the voltage and what is the reference?

 

[selectric]

Re: Stray or Static

It is fed from underground and there is a transmission line approximately 25 ' above the pole

We are using a Greenlee Cm1050 True rms meter.
If we measure from the pole itself to ground coming from underground going to the building we get 26v-130v
If we measure between two areas of the pole we get the same.

We also get a reading with only one probe on the pole and the other one touching nothing.


Steve

 

[petersonra]

Re: Stray or Static

Is the meter a digital meter? if so, you often get readings that make no sense due to the very high impedance input these meters usually have. the fact that you get a high reading when one side is connected to nothing makes me think this is the case.

is the EGC coming from the building bonded to the pole?

 

[selectric]

Re: Stray or Static

It is digital
My concern is my employee after everything was disconnected he still got a tingle shock from the pole. When I tested the voltage I got a spark from everything metal on the pole to the tester leads.


Steve

 

[pierre]

Re: Stray or Static

Is the lighting pole connected to an Equipment Grounding Conductor that goes back to the same panel as the lighting feed?

Pierre

 

[selectric]

Re: Stray or Static

yes,
it goes back to a timer then to the lighting panel

 

[petersonra]

Re: Stray or Static

If the pole is bonded to the EGC coming from the building, and you still get some kind of stray voltage, it makes me wonder if something else is going on, especially if you can feel it.

Is it possible the EGC is open?

 

[rattus]

Re: Stray or Static

Guys, I speculate that the pole is ungrounded and that you are seeing capacitive coupling between the pole and the overhead wire. The voltage would drop if you touch the pole or even attach a voltmeter to it. A low impedance meter should provide lower readings if this is the case.

Then too, maybe the EGC is hot for some reason. If it can happen it will!

 

[selectric]

Re: Stray or Static

We disconnected & removed everything to the pole fixtures/wire. Went to top of pole & received shock, I have a feeling that the overhead transmission line in inducing voltage on the pole. Have not figured this one out yet???

 

[peter d]

Re: Stray or Static

I have heard of the same occurance under similar circumstances. A local electrician complained of "hot" light poles that were directly under HV transmission lines.

 

[rattus]

Re: Stray or Static

Selectric, it is called capacitance. You are touching one plate of a poor capacitor. The other plate is the live HV line. The voltage is high enough though that you can get a tingle through this tiny capacitor. If it were a much larger capacitor you would be dead.

Also, it is remotely possible that the ground potential under the line is not zero which would indicate some unhealthy ground currents.

 

[petersonra]

Re: Stray or Static

so if there are issues with either the overhead HV line or some kind of elevated potential on the ground, just how would one go about fixing either situation?

 

[templdl]

Re: Stray or Static

It appears as though you are concerned about servicing. If so simply jumper the conductor in question to ground draining off the potential.
A cable set up similar to a jumper cable with an alligator clamp attached to each end should work fine.
I've been told by a high tension linesman that even the wind blowing across de-energized high tension wires can generate static electricity. It sounds posible and something that one wouldn't consider but I really haven't heard that from other sourses.

 

[George Stolz]

Re: Stray or Static

Wouldn't driving a ground rod next to the pole and grounding it out null any of this? Or does the ground tend to carry that inducted charge?

Would that potential matter if the pole was bonded to the ground anyway? Everything in the area would be 30 Volts, right?

 

[petersonra]

Re: Stray or Static

I am not sure that driving a ground rod is likely to help much. The pole is probably set directly onto a concrete support which is a pretty decent ground in itself.

 

[charlie]

Re: Stray or Static

I've been told by a high tension linesman that even the wind blowing across de-energized high tension wires can generate static electricity. It sounds possible and something that one wouldn't consider but I really haven't heard that from other source.

You just heard it again, it is true. If it is not grounded, it is not dead . . . period.

 

[rattus]

Re: Stray or Static

It is feasible that the wind blowing particles of dust, perhaps ions, or whatever across a pole might cause it to build up a charge. After all that is the way cloud charges are developed, I think. Now I would be interested to know if this is a static charge or capacitive coupling to the HV line overhead.

 

[apauling]

Re: Stray or Static

i am curious as to the actual physical connections of ladder and type, elec isolation of worker, height where sensate shock starts, etc..

i am not sure of the terms, but can't current be induced this way, although limited? does there need to be a full loop for any current? or is there some info about where the current stops being induced as a coil uncoils.

paul

 

[rattus]

Re: Stray or Static

And emf may be induced by a magnetic field which is certainly present here, but the pole is at right angles to the HV wire. Still I am not convinced that it could not happen. If so, an emf would appear between the ends of the pole even if one end is grounded. No current would flow however until the loop is completed. Think of the pole as the secondary of a transformer.