Parallel path for neutral current?

[Steelhead]

Hi guys. This is something I came across in a home I was doing some work in:

-Meter pedestal with 100A breaker located on exterior of home

-GEC connected to grounded conductor at pedestal. One ground rod installed

-SE cable (3 conductor) from pedestal feeds panel inside house

-Galvanized water piping connected to neutral bus in interior branch circuit panel with #6 solid

My question is isn't the connection of the galvanized water piping to the neutral bus in the panel creating a parallel path for neutral current?

The homeowner says this was installed 20+ years ago. My guess is that the installer was using the water piping as an additional grounding electrode seeing as there is only one rod outside (at least that I can see)

 

[G._S._Ohm]

Re: parallel path, you can do a no fuss, no muss test of the current in that piece of #6 by using it as a shunt and measuring the drop across it.

0.395 = ohms/1000' for #6 copper
10 = current in the wire in amps
8 = length of the wire in feet
0.0316 = volts across the length of wire

Adjust the current in the neutral by loading only one side of the 120/240.

 

[iwire]

It is a parallel path for sure and it is very common. Nothing to worry about in my personal opinion. Almost impossible to code compliantly avoid in some situations.

 

[ptonsparky]

NdWater pipe if it meets the qualifications of a GEC must always be used. The rod supplements the pipe. The standard practice is now 2 rods.

The water pipe will often provide a parallel path for neutral return current to the transformer in areas that have community wide metallic piping.

I would consider the disconnect under the meter when installed on the house as the service disconnect and would have used 4 wires to the interior panel. I am not inclined to replace a 20 year old installation unless they are having issues. My attitude has modified over the years to where I pick my battles. Just let the customer know.

 

[ptonsparky]

Water pipe if it meets the qualifications of a GEC must always be used. The rod supplements the pipe. The standard practice is now 2 rods.

The water pipe will often provide a parallel path for neutral return current to the transformer in areas that have community wide metallic piping.

I would consider the disconnect under the meter when installed on the house as the service disconnect and would have used 4 wires to the interior panel. I am not inclined to replace a 20 year old installation unless they are having issues. My attitude has modified over the years to where I pick my battles. Just let the customer know.

 

[kwired]

I would consider the disconnect under the meter when installed on the house as the service disconnect and would have used 4 wires to the interior panel. I am not inclined to replace a 20 year old installation unless they are having issues. My attitude has modified over the years to where I pick my battles. Just let the customer know.

I question that myself. How is a pedestal installed "on the building"? Aren't pedestals intended to be freestanding separate structures?

If the main in the pedestal is somehow considered the main disconnect for the home then the GEC needs run to the main panel and not the sub panel. The three wire feeder to the house was probably acceptable at the time of installation assuming the house was a separate structure supplied by a feeder.

If I were upgrading anything here I would make it right to todays codes, otherwise I would let it be.

If this were a mobile home, then the pedestal makes more sense, if it is freestanding structure of its own, but a four wire feeder to the home has always been a requirement for mobile homes.

 

[Steelhead]

Water pipe if it meets the qualifications of a GEC must always be used. The rod supplements the pipe. The standard practice is now 2 rods.

The water pipe will often provide a parallel path for neutral return current to the transformer in areas that have community wide metallic piping.

I would consider the disconnect under the meter when installed on the house as the service disconnect and would have used 4 wires to the interior panel. I am not inclined to replace a 20 year old installation unless they are having issues. My attitude has modified over the years to where I pick my battles. Just let the customer know.

Those were my thoughts too. The branch circuit panel in the house has no main breaker. I was thinking that the installer should have used 4 wires to that panel as well and treat it as a sub panel. The costumer hasn't experienced any problems that I am aware of so I was just going to leave it as is.

 

[Steelhead]

It is a parallel path for sure and it is very common. Nothing to worry about in my personal opinion. Almost impossible to code compliantly avoid in some situations.

Thanks

 

[al hildenbrand]

-Galvanized water piping connected to neutral bus in interior branch circuit panel with #6 solid

Out of curiosity, is the water supply a private well, or is it a municipal water system? And, if it is municipal, are there neighbors on the same transformer?

 

[Steelhead]

Out of curiosity, is the water supply a private well, or is it a municipal water system? And, if it is municipal, are there neighbors on the same transformer?

They are on a municipal system. Not sure if the neighbors are on the same trans.

 

[al hildenbrand]

They are on a municipal system. Not sure if the neighbors are on the same trans.

Assuming a couple of the neighbors are on the same transformer, and, if the municipal water system is all metal, from house to main in the street, the main, and to the neighbors, then this actually stands a chance of being as low an impedance path as your client's home neutral. So, the water pipe grounding electrode conductor (GEC) is a parallel path. . . but, a parallel path required by the NEC.

You see, each of the neighbor's GEC to Main Bonding Jumper to Service Neutral connection are all in parallel to each other, reducing their impedance.

 

[Steelhead]

Assuming a couple of the neighbors are on the same transformer, and, if the municipal water system is all metal, from house to main in the street, the main, and to the neighbors, then this actually stands a chance of being as low an impedance path as your client's home neutral. So, the water pipe grounding electrode conductor (GEC) is a parallel path. . . but, a parallel path required by the NEC.

You see, each of the neighbor's GEC to Main Bonding Jumper to Service Neutral connection are all in parallel to each other, reducing their impedance.

I thank you for your input. Very helpful as grounding/bonding issues can be or at least seem complicated at times. Your example is probably the case for this neighborhood.

 

[kwired]

It doesn't matter if the neighbors are on same transformer or not. The secondary grounded conductors will be bonded to the primary grounded conductors. If your neighbor is on a separate transformer and loses a service neutral, say in his meter socket, he still has a low impedance path through the water pipe, through your service, and back to his transformer via the primary neutral.

 

[Steelhead]

It doesn't matter if the neighbors are on same transformer or not. The secondary grounded conductors will be bonded to the primary grounded conductors. If your neighbor is on a separate transformer and loses a service neutral, say in his meter socket, he still has a low impedance path through the water pipe, through your service, and back to his transformer via the primary neutral.

I drew that out on paper to better visualize and I can see how this would work. So if this scenario were to take place would there be anything to indicate a problem with the neighbor's service? Also wouldn't there be more of a load on my customers neutral?

 

[al hildenbrand]

I drew that out on paper to better visualize and I can see how this would work. So if this scenario were to take place would there be anything to indicate a problem with the neighbor's service? Also wouldn't there be more of a load on my customers neutral?

You're getting it.

It is common that the first indication of a problem comes when the neighbor has a plumber replace something around the water service that results in the plumber lifting the GEC from connection with the water pipe coming into the dwelling. That neighbor's house starts experiencing voltage swings from a floating neutral.

That is, with all these parallel paths, a home can run for years with the electrical service entrance grounded conductor completely open and never give an indication until the GEC gets loose.

If it is your customer's house that has the open service entrance grounded conductor (neutral), then your customer's unbalance current is going out the GEC, through the municipal metallic water system, and back to the transformer neutral connection via the neighbor's neutrals.

Putting an amprobe on the GEC that heads to the water pipe can help to get a handle on this.

But, additionally, there is one more current source: As Kwired notes in his post above, the secondary neutral is bonded to the primary neutral. That means that the power company high voltage transmission system (primary line) with its own "unbalance" currents may well be flowing through that primary - secondary bond, down the dwelling service grounded conductor, and on into the Earth via the GEC.

 

[Steelhead]

You're getting it.

It is common that the first indication of a problem comes when the neighbor has a plumber replace something around the water service that results in the plumber lifting the GEC from connection with the water pipe coming into the dwelling. That neighbor's house starts experiencing voltage swings from a floating neutral.

That is, with all these parallel paths, a home can run for years with the electrical service entrance grounded conductor completely open and never give an indication until the GEC gets loose.

If it is your customer's house that has the open service entrance grounded conductor (neutral), then your customer's unbalance current is going out the GEC, through the municipal metallic water system, and back to the transformer neutral connection via the neighbor's neutrals.

Putting an amprobe on the GEC that heads to the water pipe can help to get a handle on this.

But, additionally, there is one more current source: As Kwired notes in his post above, the secondary neutral is bonded to the primary neutral. That means that the power company high voltage transmission system (primary line) with its own "unbalance" currents may well be flowing through that primary - secondary bond, down the dwelling service grounded conductor, and on into the Earth via the GEC.

Interesting. If this problem were to occur (loosing the neutral conductor) and the GEC were carring the neutral current back to the source and a plumber or homeowner disconnects or removes a section of the metallic plumbing to make a repair or something like that and that person completes the circuit by touching both ends of the plumbing couldn't that person receive a shock or be electrocuted by completeing the path for the current back to the source?

 

[al hildenbrand]

. . . couldn't that person receive a shock or be electrocuted by completeing the path for the current back to the source?

Yup, the "potential" is there, the more unbalanced the running load of the dwelling at that instant, the further the neutral "swings" towards one leg, approaching 120 Volts.

 

[Steelhead]

Yup, the "potential" is there, the more unbalanced the running load of the dwelling at that instant, the further the neutral "swings" towards one leg, approaching 120 Volts.

Thanks Al!

 

[kwired]

Interesting. If this problem were to occur (loosing the neutral conductor) and the GEC were carring the neutral current back to the source and a plumber or homeowner disconnects or removes a section of the metallic plumbing to make a repair or something like that and that person completes the circuit by touching both ends of the plumbing couldn't that person receive a shock or be electrocuted by completeing the path for the current back to the source?

That does happen at times. Where it is most dangerous is if the plumber is working in a trench, worse yet if trench has water in it, and he "opens" the conductor (pipe).

 

[Steelhead]

That does happen at times. Where it is most dangerous is if the plumber is working in a trench, worse yet if trench has water in it, and he "opens" the conductor (pipe).

Would it be safer for a plumber/homeowner if I were to move the GEC from the sub panel to the disconnect in the meter pedestal? The end result would be the GEC connected to the grounded conductor terminal at the disconnect and then terminated to the galvanized piping in the house probably down by the meter where the supply from the city enters the basement. Thoughts?