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Conductor Protector
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Discussion Starter · #1 ·
I got a call to look at a problem (I’d never been there before), where someone had felt a tingle between the ground (dirt, earth) and the metal frame of a trailer on tires with a sub panel in it. I didn’t have a ground rod or plate with me, but I put a piece of rebar in the ground and measured 12 VAC (Greenlee true RMS multimeter) between that rod and the bonded metal of the trailer, or the bond wire back to main service, or the sub panel metal etc. I Shut off feed (ACWU- 3 aluminum conductors plus ground in an armoured/ jacketed cable- this is Canada) to this sub panel and the voltage was still there! I removed the neutral, bond wire and connector from the main service ( all paths back to system ground) and the voltage went away. As soon as those connections were re-established in the main service it was back. I could even read it just by putting one probe in the dirt and the other to grounded metal! The property has a house with a 200 A service with at least one out building fed from that as well as a shop with a 400 A service which feeds the trailer with the 12VAC potential from surrounding earth back to the system ground of the 400 Amp service. I had someone shut off the main at the house the voltage went down to 10 VAC. With house back on, they shut off the entire shop- voltage again went down about 2 volts to around 10VAC. I don’t know why I didn’t try killing both services at the same time, but I’m not sure it would have mattered... It seems to me this is too high of a potential to be “normal “. Here in Canada we don’t have to re establish the ground in out buildings, unless they house livestock- the bond wire back is fine. I could however put in a ground and bond the neutral in the sub panel and that would eliminate the potential to earth there, but if there is a high impedance ground fault somewhere on one of the systems, wouldn’t that cause current flow back through the bonding conductor to the 400 amp service ground? I’m guessing it would be a pretty negligible current though... I’m thinking that since the voltage was still there with either service turned off, that it could be a power utility (POCO) issue? Am I on the right track with this? Is re establishing the ground at the sub panel the solution? What are the best ways to troubleshoot this issue? Different multimeter? Could a loose neutral connection cause this even with the mains shut off? Sorry for long winded post, but hopefully it gives enough info that I can get some helpful feedback. Thanks in advance!
 

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the only time i ever saw a fault like that was a screw into the wire conducting to the outside metal. (not bonded to the metal frame or sub panel) (and it was a bear to find)
the service was bonded at the disconnect on the riser (mobile home)
 

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I got a call to look at a problem (I’d never been there before), where someone had felt a tingle between the ground (dirt, earth) and the metal frame of a trailer on tires with a sub panel in it. I didn’t have a ground rod or plate with me, but I put a piece of rebar in the ground and measured 12 VAC (Greenlee true RMS multimeter) between that rod and the bonded metal of the trailer, or the bond wire back to main service, or the sub panel metal etc. I Shut off feed (ACWU- 3 aluminum conductors plus ground in an armoured/ jacketed cable- this is Canada) to this sub panel and the voltage was still there! I removed the neutral, bond wire and connector from the main service ( all paths back to system ground) and the voltage went away. As soon as those connections were re-established in the main service it was back. I could even read it just by putting one probe in the dirt and the other to grounded metal! The property has a house with a 200 A service with at least one out building fed from that as well as a shop with a 400 A service which feeds the trailer with the 12VAC potential from surrounding earth back to the system ground of the 400 Amp service. I had someone shut off the main at the house the voltage went down to 10 VAC. With house back on, they shut off the entire shop- voltage again went down about 2 volts to around 10VAC. I don’t know why I didn’t try killing both services at the same time, but I’m not sure it would have mattered... It seems to me this is too high of a potential to be “normal “. Here in Canada we don’t have to re establish the ground in out buildings, unless they house livestock- the bond wire back is fine. I could however put in a ground and bond the neutral in the sub panel and that would eliminate the potential to earth there, but if there is a high impedance ground fault somewhere on one of the systems, wouldn’t that cause current flow back through the bonding conductor to the 400 amp service ground? I’m guessing it would be a pretty negligible current though... I’m thinking that since the voltage was still there with either service turned off, that it could be a power utility (POCO) issue? Am I on the right track with this? Is re establishing the ground at the sub panel the solution? What are the best ways to troubleshoot this issue? Different multimeter? Could a loose neutral connection cause this even with the mains shut off? Sorry for long winded post, but hopefully it gives enough info that I can get some helpful feedback. Thanks in advance!
Paragraphs, please. :blink:

That's brutal to read. :eek:
 

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I’ve broken all that into paragraphs- thanks telsa- hope that it makes it easier to make sense of and someone is able to pass along some ideas. Cheers.
Thanks, it really does make a difference reading it :thumbsup:

I'd focus on the incoming service. Either a bad Tx, or a neighbour is passing neutral current to this service.

Measure the current on the ground wire, I think you'll see current. If it stays there when you shut off the main, you know it's from someone else.
If you don't find anything there, then do the same with the neutral on the service.

*edit* adding a ground rod at the trailer will only hide the problem, but will fix the tingle problem
 

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Out in the sticks, some utilities actually use the Earth as a neutral return for THEIR power scheme.

( Then they can save on a conductor. )

This results in a voltage gradient over distance -- right out of the soil.

It's something to look into if you're out in the sticks.

Yes, in such schemes, you can't take it for granted that everywhere is at the same earth potential.

If you're not aware that this is going on -- then you are truly lost.

The above working scheme is not common in urban areas -- just the sticks.

When the money is available, the Poco can always change over.
 

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Conductor Protector
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Discussion Starter · #9 ·
Out in the sticks, some utilities actually use the Earth as a neutral return for THEIR power scheme.

( Then they can save on a conductor. )

This results in a voltage gradient over distance -- right out of the soil.

It's something to look into if you're out in the sticks.

Yes, in such schemes, you can't take it for granted that everywhere is at the same earth potential.

If you're not aware that this is going on -- then you are truly lost.

The above working scheme is not common in urban areas -- just the sticks.

When the money is available, the Poco can always change over.

Really? I may be truly lost. Ya I think this place could be considered in the sticks- it’s way out there for sure. Probably at the end of the lines. So are you saying this is normal enough that I should just do a ground at the trailer and bond it there and call it good? It will get rid of the tingle.
 

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Really? I may be truly lost. Ya I think this place could be considered in the sticks- it’s way out there for sure. Probably at the end of the lines.

So are you saying this is normal enough that I should just do a ground at the trailer and bond it there and call it good? It will get rid of the tingle.
You can double check with the Poco... but I'd say you're on the right track.
 

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Conductor Protector
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Discussion Starter · #11 ·
Thanks, it really does make a difference reading it :thumbsup:

I'd focus on the incoming service. Either a bad Tx, or a neighbour is passing neutral current to this service.

Measure the current on the ground wire, I think you'll see current. If it stays there when you shut off the main, you know it's from someone else.
If you don't find anything there, then do the same with the neutral on the service.

*edit* adding a ground rod at the trailer will only hide the problem, but will fix the tingle problem
Thanks for your reply! I can’t get at the ground wire cause it’s in the meter base of the 400 A service with utility seal on it. It comes out in a PVC conduit straight into the ground. Everyone uses plate electrodes around here.

I suppose I could clamp over the PVC or dig a little, but I don’t think there would be much current- there wasn’t at the other end.

Thanks!
 

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Is not a Hydro issue, you are just dealing with different potential.

I would start confirming the neutral connection at the service entrance panel is solidly connected to a grounding electrode.

I would then, confirm the neutral and bonding wire at the trailer panel are not connected together, either by a wire jumper or by the green screw at the bonding bar. CEC 10-208 (1) (b)

I would also take a look at the wiring of the load being fed from this sub-panel, any possible leakage?

if stray current is still there, then I would drive a grounding rod by the trailer CEC 10-208 (1) (a); the idea is to stablish equipotential.

Any fault will follow the path of less resistance, no need to worry if it will go back to the shop.

cheers
 

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So we're reading 400A shop 200A house ,and trailer all off one service ?

The problem apparently being return paths to the serving Xformer , which is where? proximal or distal to these structures?

My Q's would be how many earthed neutrals exist?

How many metallic systems are common? IE> water, cable coax, phone, etc

~CS~
 

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Thanks, it really does make a difference reading it :thumbsup:

I'd focus on the incoming service. Either a bad Tx, or a neighbour is passing neutral current to this service.

Measure the current on the ground wire, I think you'll see current. If it stays there when you shut off the main, you know it's from someone else.
If you don't find anything there, then do the same with the neutral on the service.

*edit* adding a ground rod at the trailer will only hide the problem, but will fix the tingle problem
:thumbsup:

^^^this phenomenon happens more than most realize ..... apt advise starting with the concept of an internal Vs. external malady ~CS~
 

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Drive a ground rod about 50 ft away and run an insulated wire, like #12 THHN back to the area. Start testing for voltage using the rod as ground.
I found voltage leaking from a POCO sub-station like that once.
Another time I found the entire industrial building had 120V on the metal frame.
 

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Conductor Protector
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Discussion Starter · #17 ·
So we're reading 400A shop 200A house ,and trailer all off one service ?

The problem apparently being return paths to the serving Xformer , which is where? proximal or distal to these structures?

My Q's would be how many earthed neutrals exist?

How many metallic systems are common? IE> water, cable coax, phone, etc

~CS~
Hi thanks for responding. On the property there is a 400A service on the shop- this is where the trailer is fed from.
There is also a 200A service on the house which also feeds at least one out building.
The voltage exists even with the mains off, though for some reason I didn’t test with both services off at the same time.
The transformer is pole mounted. I didn’t pay much attention to it while on site. Pretty sure it does both services, both of which are overhead.
 

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Conductor Protector
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Discussion Starter · #18 ·
Is not a Hydro issue, you are just dealing with different potential.

I would start confirming the neutral connection at the service entrance panel is solidly connected to a grounding electrode.

I would then, confirm the neutral and bonding wire at the trailer panel are not connected together, either by a wire jumper or by the green screw at the bonding bar. CEC 10-208 (1) (b)

I would also take a look at the wiring of the load being fed from this sub-panel, any possible leakage?

if stray current is still there, then I would drive a grounding rod by the trailer CEC 10-208 (1) (a); the idea is to stablish equipotential.

Any fault will follow the path of less resistance, no need to worry if it will go back to the shop.

cheers
Hi thanks for thoughtful reply. The neutral and grounding conductor bonding point is in the 400 Amp meter base, so I can’t get in there to check it. It’s a pretty new looking service- not that that means much.

It then splits into two 200A panels, one of which feeds the trailer. The neutral at the trailer is currently NOT bonded.

Voltage is there with sub panel feed CB shut off and/or Mains shut off, so it’s not associated with loads from the sub panel.

I guess I’ll do some more testing when I’m able to make it back and then re establish the ground at the trailer to get rid of that potential. Still doesn’t really solve the problem though.
 

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:thumbsup:

^^^this phenomenon happens more than most realize ..... apt advise starting with the concept of an internal Vs. external malady ~CS~
Agreed. Re-reading his post, he didn't have everything shut off at the same time. Definitely rule out internal first.

Wonder if that trailer has batteries and an Inverter too ... Worth disconnecting that too.
 
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I had a similar problem. Plumber working in house and valves wouldn't hold so he could solder. He loosend the nut on the water meter to let the water drip and disrupted the ground clamp and got an arc and sparks.

Amprobe around the water pipe showed amps...loose neutral by POCO current going back to the transformer through the earth.

Even with the service shut off current went down but not completely gone. Suspect POCO had loose neutrals on other houses nearby and they were called to make repairs.

If your closer to the transformer you get the stray current
 
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