Stray voltage mystery question

[e57]

Been a bazillion years since I’ve posted here. Miss you guys sometimes. (Not posted much since a dad)

Nonetheless, got a little question - how much stray voltage is too much? And who you think is responsible for correcting it?

Last week disconnected a 200A feeder that goes from a main house panel board to a pool house then to a distant shed each building with its own electrodes etc and no MBJ’s in them. No other conductors building to building. Soil conditions mostly fractured serpentine rock.

During reconstruction of the equipment grounding conductor - the kid I had doing it got shocked. So he it it with proximity tester (because he questioned it) - nothing, but got shocked making the connection again and told me. So I had him pull out his meter and it was 63 volts. And I said well that’s interesting?!? I tapped them together and there was a little spark. Threw an ammeter on it - but got no current that registered after being connected… (figured enough to shock and enough to spark would at least register current?)

We broke the ground again just to check. At the building in the middle and got the same conditions and measurements. When reconnected it’s completely gone… And with the feeder fully connected there’s barely a volt between EGC/with electrodes and the separate structures neutral. Condition vanishes seemingly.

Nearest I can assume is a stray current in the earth from either or both the adjacent property and this and that property that is one which is in front of the property next door 500’ away. POCO Transformer unknown location but think it’s further away in the other direction (?)

It feels/seems like neutral current levels of voltage (if one was dumb enough to disconnect one) But 63v seems excessive? And seems to vanish with no current on the grounding conductor after connected.

Any thoughts?

 

[ActionDave]

Welcome back.

63V would be an easy target for phantom voltage as an explanation, but not when it is accompanied with a shock, so it's real. Way too much to be stray voltage. As far as tapping the wires, you can get a nice spark with less than an amps worth of current. What is the condition of the feeders? Are they in conduit or direct buried? Is there any current on the neutral?

 

[winnie]

'Phantom voltage' comes from the parasitic capacitance between energized and disconnected wires.

It can certainly cause a shock or spark if there is enough coupling between the energized wires and the disconnected wires.

I presume the feeder was not energized when these tests occurred.

 

[ptonsparky]

Are the conductors in laying parallel with overhead High Voltage transmission lines?
Both ends isolated or just one at time of shock/spark?

 

[Fred B]

main house panel board to a pool house then to a distant shed....... meter and it was 63 volts.

With the mention of a "Pool" this can be a serious concern for electric shock drowning. Proper EP bond should mitigate issue but it is rare to find one with 100% bonding on existing pools. Had a poor POCO neutral from a pad-mount cause a high voltage potential on the ground and to a pool.

Voltage can vary depending on soil conditions and loads applying to the transformer.

A check can include testing back toward the transformer. Voltage to remote earth at each panel on the way back will change, up or down depending on if it is a POCO neutral current from a multi-grounded system or an open or poor neutral.

 

[e57]

'Phantom voltage' comes from the parasitic capacitance between energized and disconnected wires.

It can certainly cause a shock or spark if there is enough coupling between the energized wires and the disconnected wires.

I presume the feeder was not energized when these tests occurred.

The entire downstream feeder disconnected - no adjacent feeders

 

[e57]

Are the conductors in laying parallel with overhead High Voltage transmission lines?
Both ends isolated or just one at time of shock/spark?

No over head and while the street feeders are likely parallel probably 75’ separation. (But if you drew a parallel line between say about where the main service of other properties they would be in line with these two structures)

Only one end isolated and later broke connection at the other structure just to check.

 

[e57]

With the mention of a "Pool" this can be a serious concern for electric shock drowning. Proper EP bond should mitigate issue but it is rare to find one with 100% bonding on existing pools. Had a poor POCO neutral from a pad-mount cause a high voltage potential on the ground and to a pool.

Voltage can vary depending on soil conditions and loads applying to the transformer.

A check can include testing back toward the transformer. Voltage to remote earth at each panel on the way back will change, up or down depending on if it is a POCO neutral current from a multi-grounded system or an open or poor neutral.

This is my thinking and concern as well. It’s not measurable when connected with any objectionable current on the conductors. But now “I know it’s there”…. But now I also know it’s adjacent to a pool… And fairly confident it’s not on this property service - but might device a means to check next time I’m out there…

 

[winnie]

I figured that the feeder was off, but worth checking.

I agree: likely not phantom voltage induced in the wires, but rather stray current flowing in the soil, with the different grounding electrodes picking up the voltage difference in the soil. Pretty much what you've already surmised.

My guess is that you actually do have current flow, just not enough to pick up with the meter you are using.

You can try mapping the voltage using short probes in the soil, and perhaps get a lead on the source.

 

[wwhitney]

I agree: likely not phantom voltage induced in the wires, but rather stray current flowing in the soil, with the different grounding electrodes picking up the voltage difference in the soil. Pretty much what you've already surmised.

I guess my question is how the 69V reading came about. Are there two points in the circuit (EGC 1, grounding electrode 1, earth, grounding electrode 2, EGC 2) that are actually 69V apart? Or is the reading an artifact of a high impedance meter?

Basically looking for an equivalent circuit diagram with remote source, remote sink, several grounding electrodes each with its own resistance, etc.

Cheers, Wayne