Neutral Wants to Follow Ground

[flashlight]

Hello Alll,
I am semi retired these days and wiring a small barn I built last summer.

I have a temporary 30A 240V SOW cord running from the house to the barn for temporary power.

The house only has a 100A service, so the barn will have its own 200A service.
I was finishing up the panel inside and I looked at the bonding jumper and thought, well, this
will be service equipment so I might as well do it now.

The strange thing is, before I did this I had measured how much power I was drawing from the house.
I was drawing 12A on one side, for a small heater, and 3A on the other for work lights. The neutral showed
9A which seemed normal since it was the unbalanced current.

But after I installed the bonding jumper, it showed 6A on the neutral and 3A on the green ground wire of the SOW cord.
Why would this happen ? Is the neutral just searching for the easiest return path ?

 

[rjniles]

It is not a service yet. You have provided parallel neutral paths and the current is using them both. Demonstrates why you keep neutrals and grounds separate past the first disconnect


Sent from my Moto E (4) Plus using Tapatalk

 

[oldsparky52]

I believe SOW cords have full size ground conductor, so I would think the current would divide pretty close to equally across the white and green. There is some resistance in that green wire that maybe shouldn't be there.

 

[oldsparky52]

The house only has a 100A service, so the barn will have its own 200A service.
I was finishing up the panel inside and I looked at the bonding jumper and thought, well, this
will be service equipment so I might as well do it now.

Is the power company brining a separate service drop to a meterbase on the barn?

 

[flashlight]

Is the power company brining a separate service drop to a meterbase on the barn?

Yes. I am now doing the mast and the meter pan, then have to drop a couple trees, call for inspection and yadda yadda.

oldsparky52, yes same size conductors. Just for kicks, I went and measured the wire going to the ground rod out of the house. No current there. So there must be some resistive element in the ground sequence. I did not just rely on conduit, ran a ground conductor. But in the main house, 30 years ago, I did not run a green wire.

rjniles, excellent point, it is not service yet.

 

[oldsparky52]

Is the SOW hard wired into the house panel?

 

[kwired]

Is the SOW hard wired into the house panel?

Good question, if it is hardwired into the service panel then neutral and equipment ground should be connected to same point, and if same size and length current should divide evenly enough you would need pretty sensitive measuring equipment to tell any difference. But if tied into some point along a branch circuit or feeder there could be differences in resistance of each "parallel path" and current will not divide evenly.

 

[synchro]

Good question, if it is hardwired into the service panel then neutral and equipment ground should be connected to same point, and if same size and length current should divide evenly enough you would need pretty sensitive measuring equipment to tell any difference. But if tied into some point along a branch circuit or feeder there could be differences in resistance of each "parallel path" and current will not divide evenly.

True. Also the neutral conductor on a branch circuit or feeder could be tied to loads along the way that are drawing current through either or both (if a MWBC) phase conductors. This could create voltage potentials along this neutral conductor because of its resistance in between such loads and the panel. This would effect the way the current from the OP's loads divides on the two parallel paths.
One way to check if this is happening is to turn off all loads in the barn and then see if there's any current on the neutral and green wire on the SOW cord. This should be done right after confirming the original measurements to make sure that other loads have not changed.

 

[flashlight]

SOW is hardwired into a subpanel at house that is not service equipment and therefore neutral and ground are not connected, as in main panel.
So other loads at subpanel could be affecting neutral conductor as synchro suggests.

Am thinking I should probably unbond at barn until I am ready for actual service drop.

 

[oldsparky52]

SOW is hardwired into a subpanel at house that is not service equipment and therefore neutral and ground are not connected, as in main panel.
So other loads at subpanel could be affecting neutral conductor as synchro suggests.

Am thinking I should probably unbond at barn until I am ready for actual service drop.

Well based on your current divide stated, I'd be checking the bonding of the ground to neutral at the service equipment, then follow it until you find the problem. You do have a problem based on the current divide. You ground has too high of a resistance.

 

[kwired]

SOW is hardwired into a subpanel at house that is not service equipment and therefore neutral and ground are not connected, as in main panel.
So other loads at subpanel could be affecting neutral conductor as synchro suggests.

Am thinking I should probably unbond at barn until I am ready for actual service drop.

Subpanel you are tied to likely doesn't have same size and type EGC as the neutral conductor, and on top of that other neutral loads from that subpanel are further adding to this. If there would be any other neutral to ground bonds (intentional or not) anywhere they can further complicate how current divides.

 

[flashlight]

Kwired, subpanel is powered by type AC cable with no EGC, just the metal casing and the little continuity strip that runs with the current carrying conductors. SOW green wire is bonded to cabinet of subpanel. Lack of a green wire in the AC cable is likely the problem oldsparky52 suspects.

 

[kwired]

Kwired, subpanel is powered by type AC cable with no EGC, just the metal casing and the little continuity strip that runs with the current carrying conductors. SOW green wire is bonded to cabinet of subpanel. Lack of a green wire in the AC cable is likely the problem oldsparky52 suspects.

All I am saying is the EGC and neutral in your feeder are not the same size and type of material, which will make them different resistances and will change how current divides between them when they are parallel to one another. Apparently your neutral conductor does have the lesser overall resistance since it is carrying more of the current.

 

[hillbilly1]

Kwired, subpanel is powered by type AC cable with no EGC, just the metal casing and the little continuity strip that runs with the current carrying conductors. SOW green wire is bonded to cabinet of subpanel. Lack of a green wire in the AC cable is likely the problem oldsparky52 suspects.

There you go, probably a locknut or cable clamp is not tight, or metal is corroded or painted under the locknut.

 

[ramsy]

Am thinking I should probably unbond at barn until I am ready for actual service drop.

Yes, when EGC carries current --it can shock people in the path-- when they touch appliance frames, plumbing, or cover plate screws.

 

[kwired]

Yes, when EGC carries current --it can shock people in the path-- when touching appliance frames, plumbing, or cover plate screws.

Because of voltage drop on the EGC. You also need to be touching something else that would typically be at true earth potential. Standing on wood floor or other insulated surface your risk of shock is not great at all in that situation.

 

[ramsy]

..Standing on wood floor or other insulated surface your risk of shock is not great at all in that situation.

That doesn't matter when shocked by static electricity, which blasts thru everything to Zap the crap out of me, why should power line transients be any different?

 

[ActionDave]

That doesn't matter when shocked by static electricity, which blasts thru everything to Zap the crap out of me, why should power line transients be any different?

Because the static electricity is not coming from any of the electrical wires.

 

[flashlight]

This has me thinking about a typical residential service installation--the ground wire is not normally supposed to be carrying current. But it's joined to the neutral so the current will go the way of least resistance. I haven't checked many ground wires coming out of services toward electrode for current, but I have a handful of times and only seen current once. The one coming out of my house doesn't show any current. I guess this means the "neutral" coming in from POCO is less resistive than the grounding wire to grounding electrode installation. I know that stray currents to ground are a problem in some places.

 

[chrismarcellino]

This has me thinking about a typical residential service installation--the ground wire is not normally supposed to be carrying current. But it's joined to the neutral so the current will go the way of least resistance. I haven't checked many ground wires coming out of services toward electrode for current, but I have a handful of times and only seen current once. The one coming out of my house doesn't show any current. I guess this means the "neutral" coming in from POCO is less resistive than the grounding wire to grounding electrode installation. I know that stray currents to ground are a problem in some places.

There wont (shouldn't) be any unwanted current on the EGC if the only interface of the grounded conductor (neutral) and EGC is the service equipment/service point, unless if there is a ground fault (which will hopefully either be very small and due to equipment or outlet insulation issues, or a large one that will close a GFCI/AFCI or OCPD, etc.) In any case, we are talking single digit milliamps ideally and not amps) Yes, there can be multiple paths for current before the service disconnect (e.g. metallic conduit versus ungrounded conductor), but this does not pose any safety issue as there are no customer facing devices here. Incorrectly wired (to current standards) ovens and dryers will bond the neutral and EGC. Same for subpanel with a bonding screw in, etc. This will happen less in future years after everything gets GFCI'd.

See the graphic at post #4 https://forums.mikeholt.com/threads/ground-neutral-at-sub-panel.122455/
and
https://www.ecmweb.com/content/article/20894272/get-to-the-heart-of-objectionable-current