City water network creates parallel neutrals (parallel conductors)

[LarryFine]

To add:

We can't instantly switch electrode connections in or out in response to emergency situations, so they stay. When an electrode carries excess current, it's usually due to a defect in the supply's neutral pathway.

We prefer that the cause is a short-duration event to be quickly corrected, but until it is, that pathway carrying this current is preferable to the alternative: a much greater voltage imbalance and possible fires.

I once increased the neutral size of a new high-leg service to a multi-occupancy (one store, two apartments, old building), simply because there were no qualifying electrodes beyond the two new rods I added.

 

[don_resqcapt19]

In that one case of the open neutral, I measured more than 1 amp on a ground rod. I shut everything down and didn't do further testing at the risk of frying things and having a fire start, of course. But I did snag that measurement on rod and was pretty amazed that so much current could run through the soil. Good, moist, compacted soil can provide good connections to the rod though. There are so many parallel connections in the earth that a lot of current can run. Tapping into it is the hard part, but the parallel paths are there once you do tap in. Of course we should NOT be using the earth as a conductor, either, and should be using intended cables only. While some current on the earth is inevitable in our multi-grounded system, it can be limited through good and proper practices.

...

120 ohms would let 1 amp flow with a 120 volt circuit. Often ground rods have less resistance that that.

Yes the earth itself, because of its huge cross sectional area has almost zero resistance. All of the resistance is the connection between the grounding electrode and the earth.

The current in the earth at dwelling units could be limited with a change in installation practices, but the general current in the earth from the multi-grounded neutral cannot be limited unless you do away with multi-grounded neutral systems. One thing that would pretty much eliminate that issue would be to require the primaries of all of the utility distribution transformers to be connected line to line and not line to neutral like most of them in my area are.

 

[kwired]

I have a very sensitive clamp meter that detects "leaking" current - PM me if you'd like info. It goes down to .01 milliamps. So far I have never measured current through water (in a pex/cpvc pipe). Obviously it depends on the situation, but it certainly could happen if the voltage were high enough and the impedance of the water were low enough. But in real practice I have never seen it go through water.

I have frequently, however, seen small amounts of current making it through dielectric unions. These unions aren't the most reliable devices. I prefer a piece of pex pipe.

I've seen enough current pass through water in non metallic section of drain pipe to introduce shock hazard in a shower before.

customer said they were feeling tingling when using shower, I measured a low neutral to earth voltage at the service but couldn't measure voltage between anything in the tub area. They called me back some time later and I actually ran water through shower once there was water in drain pipe I started getting similar neutral to earth voltage from water faucet to metal drain fitting even though there was plastic water pipe leaving from that drain fitting.

Of course there is likely more possible contaminants in the drain that could increase conductivity of the water than there probably is in the supply lines.

 

[GoldDigger]

...

Of course there is likely more possible contaminants in the drain that could increase conductivity of the water than there probably is in the supply lines.

I also would not be surprised to see conduction through a coating of gunk on the inside surface of the pipe which is conductive when wet.

 

[kwired]

Guys, just remember there are different distribution systems and not all are MGN's. Come to upstate NY and most of the distribution is ungrounded delta.

For remote areas with only single phase, I would assume they run two ungrounded conductors as well as a "shield wire"?

Part of the idea behind wye distribution with an MGN is the ability to run just two wires for a single phase circuit.

 

[kwired]

Stray voltage from the utility using MGN systems is easy to solve for farms by the installation of a neutral isolator, something most utilities will do for dairy farms and other livestock farms on request.
However many of the dairy issues have been from incorrect wiring practices on the load side of the service point and the neutral isolator will not fix that.

Not using the grounded conductor as much as possible goes a long way in minimizing voltage drop on the grounded conductor also.

 

[kwired]

I'm not sure I follow how this would solve the issue.

With MGN, the primary neutral is earthed along the distribution line. So to the extent that the primary neutral is carrying a net current, it has a voltage drop along its length, and the multi-point earthing imposes a voltage gradient in the earth. This is all true for a primary wye system with only ungrounded delta secondaries.

So is it this earth voltage gradient that livestock experience as a step potential between two legs?

Now if instead of an ungrounded delta secondary you have a grounded wye secondary, with the secondary neutral solidly connected to the primary neutral, the customer's Grounding Electrode System will be an additional earthing of the primary neutral, and so that earthing will change the pattern of earth voltage gradient imposed by the primary system. If there would otherwise be a voltage difference between earth near the customer's GES and the primary neutral at the transformer, the secondary neutral will now be carrying some current from that voltage difference.

The Ronk Blocker can block that current on the secondary neutral. But I don't see how that would change the step potential on the property other than in the immediate vicinity of the customer GES.

Cheers, Wayne

All it blocks is anything coming from utility side. Stray voltage originating on premises wiring won't be blocked. This is why it is a good idea to not use grounded conductor as a current carrying conductor as much as practical in such places. Use 208-240 for single phase loads instead of 120 or 277 whenever possible.

 

[kwired]

OK, but take the simplest case of a single service disconnect, where the EGC system (including bonded parts), the GEC from the GES, and the service neutral come together in a single point, with no other connections elsewhere. And suppose the GES is spatially compact so all the earth connection(s) are at the same potential.

Then if the primary neutral is at an elevated potential from the earth at the GES, you certainly will have current flowing from the GES along the GEC and the service neutral to that primary neutral. But the EGC system and the GES (earth) are separated only by that GEC, and they will have a voltage difference only equal to the voltage drop from that current on the GEC. E.g. if the primary neutral is say 6V above GES/earth, and the service neutral is 90' while the GEC is 10' of the same conductor type and size as the service neutral, the EGC to earth/GES voltage will be 6V * 10'/100' = 0.6V.

So how sensitive are livestock to small voltage differences like that? What's the acceptable threshold?

Of course, the voltage divider of GEC/service neutral may be more balanced than my example. And much more complicated topologies are likely to be common, e.g. where multiple points along the EGC system are in fact earthed, putting current from a primary neutral elevated above earth on the EGC system itself.


Seems like if there's a potential difference between two earthed points (two different points on the MGN, when the primary neutral is carrying current), there must be a voltage gradient through the earth. But maybe where those points are far apart, the voltage gradient at the surface of the earth is negligible, other than in the vicinity of the earth electrodes?

Cheers, Wayne

Just like there is voltage drop across the conductors, there is pretty much never a grounding electrode that has zero resistance to it.

Earth is a good conductor but is difficult to make a zero/near zero resistance connection to it. Therefore there is often at least a small voltage between grounded current carrying conductors (and any extensions that originate at them) and actual earth. These cattle are not any more suspect to being effected than people are, they just happen to have a longer "wheel base" and can span across larger zones when present in the ground when they are near a bonded object that is also in contact with the ground, plus they don't wear shoes that may increase insulation value between foot and earth like people often do. And are typically standing in wet conditions with increased levels of salts, minerals, etc. that also will increase conductivity of what they are standing in/on.

 

[kwired]

How many dairies are on shared utility transformers? I would of think most have only one secondary side neutral.
How many dairies are serviced by a metallic municipal water system?
How many dairies have had multiple buildings added and service upgrades over many decades by many people who wired the way 'grandpa' taught them, often with little regard to maintaining neutral and grounding conductor integrity and separation?

Most of those have pretty much disappeared around here. Or at least are no longer operating. What dairy farms are left are 1000 head of cows and larger and have 480/277 @ 600-800 amps or greater for main supply.

No longer profitable to do this on small scale unless maybe some kind of specialty thing involved. "organic" milk might be one those things.

 

[electrofelon]

For remote areas with only single phase, I would assume they run two ungrounded conductors as well as a "shield wire"?

Part of the idea behind wye distribution with an MGN is the ability to run just two wires for a single phase circuit.

No shield wire, just two hot wires. I don't think I've ever seen a shield wire on a distribution line regardless of topology.

 

[kwired]

This was allowed prior to 2008 for feeders to separate buildings. It also happens when multiple buildings get their service from the same transformer, even if the primary neutral is isolated. Neighborhoods are going to have this problem unless the public wants to pay more for infrastructure such that every building or house has its own transformer.

I think having the utility isolate the primary neutral from the secondary neutral sounds like a good idea. Not sure why they don't do this unless they want a ground electrode at the pole for both primary and secondary neutrals. To me, the secondary electrode should not be needed at the transformer since there is a ground electrode at the building being served. This will make the loose neutral problem worse, but hey the NEC is really pushing GFCIs so they could just mandate one for the main breaker now too.

Isolating the plumbing is also a good idea. Every house I have had used a poly water pipe from the street. It is the old cities based on metal water distribution where this is a problem. Could be retrofitted away, but it will take time. It would help though if the code pushed or forced a non metallic section when pipes are upgraded or repaired. Heck, it seem like some cities still have lead pipes which seems like a much bigger problem.

Finally, it is good to remember why we have the system we do (MGN), and the bad things that happened long ago to drive what we have today. Mandating an electrical distribution change could have some unintended consequences making things that are rarely a problem come into the forefront.

They are "grounded conductors" and need to be bonded to prevent voltage potential between them. POCO distribution often can have just one conductor serving both primary and secondary between poles. Does no good to bond them at both ends, it just becomes a parallel set then.

Would you want an ungrounded primary conductor to fall onto your isolated secondary "grounded conductor"? it needs to be bonded to primary grounded conductor so it will operate primary overcurrent devices quicker. Even then it still may cause over voltage related damages at times within your premises wiring.

 

[kwired]

No shield wire, just two hot wires. I don't think I've ever seen a shield wire on a distribution line regardless of topology.

No lightning protection or are they just from ungrounded line to an electrode?

 

[jim dungar]

No shield wire, just two hot wires. I don't think I've ever seen a shield wire on a distribution line regardless of topology.

I think there is a terminology issue. The bare wire strung between utility poles serves many purposes, but it is a grounded conductor and is integral to the proper functioning of a Multi Grounded (common) Neutral utility distribution system.

 

[electrofelon]

No lightning protection or are they just from ungrounded line to an electrode?

Typically they have a lightning arrestor on the primaries of the transformer, and ground the can and secondary center tap to a rod at the base of the pole.

 

[electrofelon]

I think there is a terminology issue. The bare wire strung between utility poles serves many purposes, but it is a grounded conductor and is integral to the proper functioning of a Multi Grounded (common) Neutral utility distribution system.

I don't think so. I was referring to a Delta system and I'm sure Kwired knows there would not be a neutral on a delta system.

 

[tortuga]

Yeah its pretty easy to avoid NEV that in utility distribution design, its actually an older topology that works best for dairy farms.
Here you have delta distribution in rural areas, 12.5 kV L-L so you get a two bushing transformer 12.5:120/240.
The problems can occur if you convert that to underground and use a single cable and set 7.2kv pad mounts, the the concentric is the neutral.

 

[kwired]

I don't think so. I was referring to a Delta system and I'm sure Kwired knows there would not be a neutral on a delta system.

Yes. Transmission lines are usually from a delta source, that fourth wire has no place to connect to at the source other than metal frame and is grounded multiple times but is called a shield wire more so than a neutral or grounded conductor.

MGN systems are usually from a wye secondary and is also the neutral of the system.

 

[kwired]

Yeah its pretty easy to avoid NEV that in utility distribution design, its actually an older topology that works best for dairy farms.
Here you have delta distribution in rural areas, 12.5 kV L-L so you get a two bushing transformer 12.5:120/240.
The problems can occur if you convert that to underground and use a single cable and set 7.2kv pad mounts, the the concentric is the neutral.

I think you would need to run two cables. The concentric is not "insulated" but rather "covered". Seen older cables where the concentric not even covered it is the outer layer of the cable.

 

[suemarkp]

They are "grounded conductors" and need to be bonded to prevent voltage potential between them. POCO distribution often can have just one conductor serving both primary and secondary between poles. Does no good to bond them at both ends, it just becomes a parallel set then.

Would you want an ungrounded primary conductor to fall onto your isolated secondary "grounded conductor"? it needs to be bonded to primary grounded conductor so it will operate primary overcurrent devices quicker. Even then it still may cause over voltage related damages at times within your premises wiring.

The systems would be grounded to the earth, but not solidly grounded to each other. Think of two separate power systems side by side each with ground electrodes but no solid connection between the grounded conductors, just earth. This should be a low enough impedance connection for high voltage systems to trip yet greatly reduce currents from voltage drop cross connects.

 

[kwired]

The systems would be grounded to the earth, but not solidly grounded to each other. Think of two separate power systems side by side each with ground electrodes but no solid connection between the grounded conductors, just earth. This should be a low enough impedance connection for high voltage systems to trip yet greatly reduce currents from voltage drop cross connects.

Maybe so.

I know I seen some aftermath in a small town where the 34.5kV transmission supplying the town dropped a conductor onto 4.16/2.4kV distribution for the town. Got service calls from around town, most would be in groups like a few all on same block next group in different area of town. I think there was a surge on one particular phase conductor and it happened to be the one feeding those particular customers. Mostly had incidents of damaged electronics items. One house I recall replacing nearly every GFCI receptacle it had in it. Another one had burned out circuit board on a range and a few other consumer electronics items that were not working anymore.