parallel path for neutral current created by multiple grounding electrode connections

[mwm1752]

It is funny how we can discuss a simple drawing. Technically there is a parallel path as the earth is connected to all. Take power lines that are 1/4 mile apart technically they have parallel paths with the earth and the grounded conductor. Is there a measurable current? 1/1000000000 A maybe but if we are in contact with the earth we have the same potential. Know one knows how far apart the disconnects are and what they feed by this drawing. Realistically there in no applicable current due to the resistance of earth. The electrode system has never been considered a current carrying conductor even though its purpose is to mitigate induced voltage safely to earth.
Final answer there is no realistic parallel path that would cause harm.

 

[electrofelon]

It is funny how we can discuss a simple drawing. Technically there is a parallel path as the earth is connected to all. Take power lines that are 1/4 mile apart technically they have parallel paths with the earth and the grounded conductor. Is there a measurable current? 1/1000000000 A maybe but if we are in contact with the earth we have the same potential. Know one knows how far apart the disconnects are and what they feed by this drawing. Realistically there in no applicable current due to the resistance of earth. The electrode system has never been considered a current carrying conductor even though its purpose is to mitigate induced voltage safely to earth.
Final answer there is no realistic parallel path that would cause harm.

I did a panel swap yesterday in a rural area (no municipal water) and with the meter pulled, I had small sparks from the GEC's (both water and rods) to the service disconnect housing (service neutral still landed) as I took them out. I would guess it was a tenth of an amp, maybe less.

 

[mwm1752]

I did a panel swap yesterday in a rural area (no municipal water) and with the meter pulled, I had small sparks from the GEC's (both water and rods) to the service disconnect housing (service neutral still landed) as I took them out. I would guess it was a tenth of an amp, maybe less.

That could be a number of circumstances most likely the nuetral is rebonded to the equipment grounds on the load side of the first disconnect. the drawing does not depict the same instance.

 

[GoldDigger]

That could be a number of circumstances most likely the nuetral is rebonded to the equipment grounds on the load side of the first disconnect. the drawing does not depict the same instance.

With "the meter pulled", there should be no load current in the service neutral and so no effect from rebounding between GES and neutral on the customer side.
What the OP is seeing is the result of a voltage gradient in local earth from local ground to the POCO MGN. This could be the result of POCO current (most likely primary) flowing through the surface layer of earth or a voltage drop across the POCO service ground electrode, possibly the result of a non-ideal MGN connection set.

 

[don_resqcapt19]

I did a panel swap yesterday in a rural area (no municipal water) and with the meter pulled, I had small sparks from the GEC's (both water and rods) to the service disconnect housing (service neutral still landed) as I took them out. I would guess it was a tenth of an amp, maybe less.

You were providing an additional parallel path for the utility primary and, assuming more than one service is supplied by the utility transformer, the secondary neutral. The current (spark) is driven by the voltage drop on the utility conductors.

 

[mbrooke]

I truly believe all forums TN_C (even that which comes from a POCO) be forbidden.

 

[retire09]

As to the original drawing. This is one structure and each space is divided by a two hour firewall which in Washington can now be considered four separate buildings and have a service for each one. They will all have a main breaker panel and bond the neutral to the can. They will all connect to the common UFER ground in their space. For this situation all four meters are in one enclosure on the end of the structure and have no equipment ground but rigid metal conduit. Wouldn't this be a parallel path, but accepted per the code.

My opinion is that this is one building for the purpose of applying electrical code. The building code allowance to treat this as separate buildings with fire walls has no bearing on the electrical design. The building should have one electrode system and one service point where bonding is made. All other panels are subpanels and no additional electrode is required.

 

[PetrosA]

My opinion is that this is one building for the purpose of applying electrical code. The building code allowance to treat this as separate buildings with fire walls has no bearing on the electrical design. The building should have one electrode system and one service point where bonding is made. All other panels are subpanels and no additional electrode is required.

I agree this sounds wrong. It also implies that they're allowing unfused service conductors surface mounted in RMC over great distances. I could see it if each unit had a separate drop and meter, but all the meters grouped together? No.

 

[iwire]

My opinion is that this is one building for the purpose of applying electrical code. The building code allowance to treat this as separate buildings with fire walls has no bearing on the electrical design.

It cannot work that way.

Consider a single structure deemed as separate buildings and owned by different people.

You cannot force owner 1 to coordinate their electrical systems with owner 2.

 

[al hildenbrand]

. . . and why is better to only have 1 neutral to ground bond at the supply/transformer as opposed to having multiple points of ground paths?

This is a great question. I remember well what an eye-opener it was for me to finally learn about this ancient and pervasive practice of power company distribution wiring.

Understanding the "why" includes accepting that the answer is largely: "Because that's the way all the rest of it is." The PoCo stepdown transformer, supplying a specific building, has a single neutral to ground bond because that's the way it's been done since the electrification of the country really got going back at the turn of the Twentieth Century. This single point bond is regulated under the PoCos wiring Code, which is NOT the National Electrical Code (NEC). Back in the Early Twentieth Century assumptions were made, and this was definitely one of them. The Article 100 Definition of Service Point explains the boundary between PoCo wiring regulations and the NEC. The NEC then establishes another single point bond inside the Premises Wiring (System), (see Art. 100), AND combines the equipment grounds and neutrals from the LOAD side of the Main Bonding Jumper into the single grounded supply conductor on the LINE side of the Main Bonding Jumper.

Those two bonds, the PoCo distribution transformer and the NEC Premises neutral to ground bonds, send the neutral current along any, and all, parallel conductive paths that happen to exist. On a rural PoCo distribution spur there will tend to be fewer low resistance parallel paths than there will be inside a neighborhood of occupancies that are supplied by municipal water and sewer through conductive piping systems. The parallel electrical paths through the municipal piping systems and the NEC required Grounding Electrode System can result in surprising current flows, even when all the connections are good and solid.

Consider this example:

By CODEs (PoCo and NEC), this is not considered a problem. I assume all connections are solid and good. The only thing goofy is the unbalance current in House #3. A HUGE amount of that unbalance current travels in the neighbor's houses even if their meters are pulled from the sockets.

You ask me why? I'll tell you. I don't know. It's TRADITION. (Quoting Tevye in Fiddler On The Roof)

 

[mbrooke]

Adding to the above. TN-C is a POCO creation that is unsafe and dangerous (and yes, the NESC & NEC is fine with it). All one has to do is look at stray voltage lawsuits and the answer is clear. Take a few milligauss reading around those parallel paths and you see another issue. And those 2 are only part of it.



Multi grounded neutral systems basically came about like this. Most distribution systems started out as 3 wire 2,400 or 4,800 ungrounded delta 3 wire. As loads continued to rise POCOs discovered they could run a neutral and ground it repeatedly along with jumping it to the customers neutral. This meant they could raise the voltage to 4160 or 8,300 volts. Cans were re-used and connected phase to neutral. Economical at the time, the practice continued when they discovered only 1 bushing was needed, one arrestor, and any voltage could be used with a wye grounded primary without the risk of ferroresonance when one cutout blows or single phase switching takes place.


To give you an idea, If POCOs wired homes 14/2 with ground would be 2 circuits with the bare EGC acting as the ground and neutral to all outlets and lights. Random jumping from junction boxes to cold water lines just in case the EGC broke. If I wired a home like that I would eaten alive, but when POCOs do it its legal :happyno:





Outside of that more and more issues are cropping up each day. California and the rest of the world already made a solution: insulate all current carrying conductors back to the source. Stray voltage is not a problem for California dairy farmers. In California this doesn't apply to low voltage 120/240, but a huge step forward none the less.

In some parts of the world (like France) ground current is inconceivable. The 11 or 22kv is 3 wire, fed to a delta wye transformer. The secondary spits out 230/400Y, and the neutral and ground are run all the way back to the transformer X0 (TN-S) from the customers; or a TT system is employed where the customer does not connect his neutral to the building's grounding system. A main RCD (GFP) makes sure a neutral can not become grounded in the building where it will pass current onto the grounding system.



If people only knew I think they would feel betrayed a North American POCO practices. California is got it right, kudo to them.

 

[PetrosA]

It cannot work that way.

Consider a single structure deemed as separate buildings and owned by different people.

You cannot force owner 1 to coordinate their electrical systems with owner 2.

Why not?

The example given is where all the meters are fed from one service but with no disconnects located there. I've seen a lot of strip mall type buildings with meter stacks, but the meter stacks also contains the service disconnects, so any panels in the units are then treated as sub panels. I have NEVER seen a service feeding a bunch of meters, then continuing on 25', 50' or a 100' to "individual" units with unfused service feeders in rigid conduit without being encased in some amount of concrete for protection. That design (around here at least...) would put all that wiring and its maintenance in the hands of the POCO, which they likely don't want to deal with. The only thing close to that that I've seen would be when the POCO maintains an aerial quadplex or triplex attached to the back of the building or underground distribution and each owner has an individual drop or lateral to their unit's meter.

Considering the situation where all the meters and main disconnects are located in one place and fed from one service, these buildings are generally built by one investor and the units are rented out. If those units were sold individually, the meter stack would still be common and by nature any individual owner would have to coordinate their electrical system with the other owners there. Whether it's legally allowed to sell off units in a building like that is another question that I don't have an answer to.

 

[sandsnow]

Adding to the above. TN-C is a POCO creation that is unsafe and dangerous (and yes, the NESC & NEC is fine with it). All one has to do is look at stray voltage lawsuits and the answer is clear. Take a few milligauss reading around those parallel paths and you see another issue. And those 2 are only part of it.



Multi grounded neutral systems basically came about like this. Most distribution systems started out as 3 wire 2,400 or 4,800 ungrounded delta 3 wire. As loads continued to rise POCOs discovered they could run a neutral and ground it repeatedly along with jumping it to the customers neutral. This meant they could raise the voltage to 4160 or 8,300 volts. Cans were re-used and connected phase to neutral. Economical at the time, the practice continued when they discovered only 1 bushing was needed, one arrestor, and any voltage could be used with a wye grounded primary without the risk of ferroresonance when one cutout blows or single phase switching takes place.


To give you an idea, If POCOs wired homes 14/2 with ground would be 2 circuits with the bare EGC acting as the ground and neutral to all outlets and lights. Random jumping from junction boxes to cold water lines just in case the EGC broke. If I wired a home like that I would eaten alive, but when POCOs do it its legal :happyno:





Outside of that more and more issues are cropping up each day. California and the rest of the world already made a solution: insulate all current carrying conductors back to the source. Stray voltage is not a problem for California dairy farmers. In California this doesn't apply to low voltage 120/240, but a huge step forward none the less.

In some parts of the world (like France) ground current is inconceivable. The 11 or 22kv is 3 wire, fed to a delta wye transformer. The secondary spits out 230/400Y, and the neutral and ground are run all the way back to the transformer X0 (TN-S) from the customers; or a TT system is employed where the customer does not connect his neutral to the building's grounding system. A main RCD (GFP) makes sure a neutral can not become grounded in the building where it will pass current onto the grounding system.



If people only knew I think they would feel betrayed a North American POCO practices. California is got it right, kudo to them.

In the SoCal desert area around 29 Palms, the POCO runs about a 9 kV, 2 wire circuit with one grounded conductor overhead to a pole top XFMR by our cabin. That grounded conductor is grounded at every second or third pole. There only one cutout for their pole top XFMR.

 

[mbrooke]

....

 

[mbrooke]

In the SoCal desert area around 29 Palms, the POCO runs about a 9 kV, 2 wire circuit with one grounded conductor overhead to a pole top XFMR by our cabin. That grounded conductor is grounded at every second or third pole. There only one cutout for their pole top XFMR.

The line is most likely a hold over from back in the day, probably pre 1993. I went on Google earth looking at the central part of the city. All the new lines from the past 20 years have double bushing transformers, including substation VTs, are hooked phase to phase (phase to phase substation VTs are extremely rare in North American POCOs) California hasn't had this rule forever, so older multi grounded lines are still out there. Anything new built by a POCO bound to PUC95 must have all continuous current carrying conductors insulted from earth in some manner which often translates into phase-phase connected equipment or having the neutral up on insulators.

 

[al hildenbrand]

In the SoCal desert area around 29 Palms, the POCO runs about a 9 kV, 2 wire circuit with one grounded conductor overhead to a pole top XFMR by our cabin. That grounded conductor is grounded at every second or third pole. There only one cutout for their pole top XFMR.

That basic assembly, the pole top XFMR you describe by your cabin, is all over my metro area of 3+ million souls. Very common.

 

[sandsnow]

The line is most likely a hold over from back in the day, probably pre 1993. I went on Google earth looking at the central part of the city. All the new lines from the past 20 years have double bushing transformers, including substation VTs, are hooked phase to phase (phase to phase substation VTs are extremely rare in North American POCOs) California hasn't had this rule forever, so older multi grounded lines are still out there. Anything new built by a POCO bound to PUC95 must have all continuous current carrying conductors insulted from earth in some manner which often translates into phase-phase connected equipment or having the neutral up on insulators.

It is old where I am. Dating back to the fifties. We're in the boonies outside of town. The neutral is insulated on the crossarm FWIW.

 

[sandsnow]

That basic assembly, the pole top XFMR you describe by your cabin, is all over my metro area of 3+ million souls. Very common.

So I was at my cousins house in Edina, and could swear there was only one HV wire on top of poles in his backyard. I remember making a point to look because at the there had been lots of discussion about POCO earth return. I could be mistaken, it was ten years ago and I might have had "one" beer.

 

[mbrooke]

It is old where I am. Dating back to the fifties. We're in the boonies outside of town. The neutral is insulated on the crossarm FWIW.

Ok, that would make sense. MGN systems where typical in California back then. If I am correct (could be wrong) it was somewhere in 1993 when they changed the rules indirectly disallowing them. Let me see if I can find them...


IMO, I believe the practice should be applied in all 50 states... but I don't think POCOs would like me for that.


http://docs.cpuc.ca.gov/PublishedDocs/Published/G000/M146/K646/146646565.pdf

 

[al hildenbrand]

IMO, I believe the practice should be applied in all 50 states... but I don't think POCOs would like me for that.

It would definitely be an argument for job security to upgrade the distribution system.