Objectional Current in Grounding Conductors.

[david]

A grounding conductor is not required between a service transformer and the service disconnecting means of a grounded system, regardless of who owns the transformer. Non-current-carrying metal parts must be bonded to the grounded conductor.

That said, what usually establishes a path for [objectionable] system current on or through non-current-carrying metal parts on a grounded-system service is electrically continuous metallic raceway.

True,

and I think it would be agreeable to avoid them when we can, recognizing they all cannot be avoided.

 

[al hildenbrand]

I think it would be agreeable to avoid them when we can, recognizing they all cannot be avoided.

Why?

All conductive paths, ALL, between the service disconnect main bonding jumper and the power supply have NORMAL current on them. The grounded service conductor is neither a neutral nor an equipment grounding conductor. The neutral and equipment grounding conductor are smushed together at the service disconnect main bonding jumper and are connected to the grounding electrode system. Any load current that arrives from the Premises Wiring (System) splits into however many paths that there may be at the service disconnect main bonding jumper. This splitting is NORMAL. Therefore the current on ANY conductive paths between the service disconnect main bonding jumper and the power supply is excluded by 250.6(A).

 

[Smart $]

.. Therefore the current on ANY conductive paths between the service disconnect main bonding jumper and the power supply is excluded by 250.6(A).

Installation requirements do not explicitly prohibit conductive paths other than the grounded service conductor, such as metallic conduit between service equipment. Neutral current on these paths is technically objectionable, though many do not consider it as such and take no remedial action.

 

[al hildenbrand]

Why?

All conductive paths, ALL, between the service disconnect main bonding jumper and the power supply have NORMAL current on them. The grounded service conductor is neither a neutral nor an equipment grounding conductor. The neutral and equipment grounding conductor are smushed together at the service disconnect main bonding jumper and are connected to the grounding electrode system. Any load current that arrives from the Premises Wiring (System) splits into however many paths that there may be at the service disconnect main bonding jumper. This splitting is NORMAL. Therefore the current on ANY conductive paths between the service disconnect main bonding jumper and the power supply is excluded by 250.6(A).

Installation requirements do not explicitly prohibit conductive paths other than the grounded service conductor, such as metallic conduit between service equipment. Neutral current on these paths is technically objectionable, though many do not consider it as such and take no remedial action.

Where is this definition that makes any current in any of ALL of the conductive paths that any one service has between the service disconnect main bonding jumper and the power supply, EXCEPT for the current in the insulated grounded service conductor, objectionable?

The problem is that the "neutral current", the Premises Wiring (System) unbalance current, arriving from the load side at the main bonding jumper in the service disconnect is NOT the same current on the line side.

And add (or subtract) any currents that are contributed by neighbor's load unbalance, and currents contributed by the power company distribution itself. To ignore these and then to require excluding conductive raceways or transformer XO bonding jumpers because a part of the currents present is thought to be the "neutral current" is willful hoodwinking.

 

[Smart $]

Where is this definition that makes any current in any of ALL of the conductive paths that any one service has between the service disconnect main bonding jumper and the power supply, EXCEPT for the current in the insulated grounded service conductor, objectionable?

The problem is that the "neutral current", the Premises Wiring (System) unbalance current, arriving from the load side at the main bonding jumper in the service disconnect is NOT the same current on the line side.

And add (or subtract) any currents that are contributed by neighbor's load unbalance, and currents contributed by the power company distribution itself. To ignore these and then to require excluding conductive raceways or transformer XO bonding jumpers because a part of the currents present is thought to be the "neutral current" is willful hoodwinking.

You know as well as I that the NEC does not define objectionable current.

For the most part, neutral current on paths other than the grounded conductor is not explicitly spelled out in the Code. I will provide one instance where it is noted...

250.30(A)(1)

Exception No. 2: If a building or structure is supplied by afeeder from an outdoor transformer, a system bonding
jumper at both the source and the first disconnecting means
shall be permitted if doing so does not establish a parallel
path for the grounded conductor.

I'll leave it to you to find the rest and implement them (or not :roll into your understanding.

 

[al hildenbrand]

250.30(A)(1)

Exception No. 2: If a building or structure is supplied by a feeder from an outdoor transformer, a system bonding
jumper at both the source and the first disconnecting means
shall be permitted if doing so does not establish a parallel
path for the grounded conductor.

I believe David has been talking about a "utility transformer". Therefore, the conductors and method in question are the service entrance and service conductors, not a feeder.

 

[Smart $]

I believe David has been talking about a "utility transformer". Therefore, the conductors and method in question are the service entrance and service conductors, not a feeder.

I realize that... but conductive normally non?current-carrying metal parts on the line side of the service disconnecting means are not service entrance and service conductors. There is nothing in the Code which explicitly prohibits parallel grounded conductor current paths on the line side, other than 250.6... and we have no explicit definition of objectionable current.

With that said, I ask you to show me where Code permits conductive normally non?current-carrying metal parts to be a parallel conductor for anything other than fault current or surge current from lightning. I'll save you some time and tell you, there is no where in the Code that does... but being considered a permissive text, it does not explicitly prohibit such either. The closest it comes is prohibition of connecting the grounded conductor to the grounding system on the load side of the service disconnecting means.

 

[david]

to require excluding conductive raceways or transformer XO bonding jumpers because a part of the currents present is thought to be the "neutral current" is willful hoodwinking.

if I have six conduits each. one 500mcm neutral in each and one 3/0 neutral in each I can take an amp probe and measure the current on each of the 12 conductors.

If I have six conduits each. One 500 MCM neutral in each one 3/0 conductor I now identify with green insulation and move them to the transformer enclosure with a main bonding jumper connecting the XO to the 3/0 conductors in the transformer.

The only thing being excluded is the 3/0 "equipment grounds" no one is excluding the main bonding jumper from the XO to the enclosure no one is excluding the choice of rigid metal conduit.

If I was however the design engineer I would not use metal conduit as a design choice.

 

[al hildenbrand]

I realize that... but conductive normally non?current-carrying metal parts on the line side of the service disconnecting means are not service entrance and service conductors. There is nothing in the Code which explicitly prohibits parallel grounded conductor current paths on the line side, other than 250.6... and we have no explicit definition of objectionable current.

First, I apologize for using an undefined term "service entrance" when what I meant is embodied by the Article 100 term "Service". To reiterate my point, David, in one illustration of how to control "objectionable current" is altering the connection at the XO of a power company transformer. We don't know yet, from David, whether the transformer low voltage terminals are the "service point", but, regardless, the transformer is not customer owned nor part of a supply that is other than an electric power utility.

The Code does not permit ONLY current on the grounded service conductor. The Code DOES permit multiple current paths between the service main bonding jumper and the service source when the service is supplied by an electric power utility. The Code permits metallic raceways in the assembly of a "service" supplied by an electric power utility.

That's it. It's that simple. An electric power utility supplied "service" will, by Code , have current in ALL of the conductive paths present between the service disconnect main bonding jumper and the supply. I submit that, because of Code requirements for the bonding of conductive enclosures and raceways of a service, current in them is NORMAL.

Thinking of David's metallic raceway between a CT cabinet and a utility transformer cabinet, current in the metal of the raceway, by Code bonding requirements, is NORMAL. David's raceway is "normally current carrying", and, as such, doesn't meet the description of "normally non?current-carrying metal parts of equipment" in NEC 250.6(A).

. . . show me where Code permits conductive normally non?current-carrying metal parts to be a parallel conductor for anything other than fault current or surge current from lightning. I'll save you some time and tell you, there is no where in the Code that does... but being considered a permissive text, it does not explicitly prohibit such either. The closest it comes is prohibition of connecting the grounded conductor to the grounding system on the load side of the service disconnecting means.

No problem. Answered above, in this post. I'm not making my point about anything other than the "service" connected to an electric power utility supply.

if I have six conduits each. one 500mcm neutral in each and one 3/0 neutral in each I can take an amp probe and measure the current on each of the 12 conductors.

If I have six conduits each. One 500 MCM neutral in each one 3/0 conductor I now identify with green insulation and move them to the transformer enclosure with a main bonding jumper connecting the XO to the 3/0 conductors in the transformer.

The only thing being excluded is the 3/0 "equipment grounds" no one is excluding the main bonding jumper from the XO to the enclosure no one is excluding the choice of rigid metal conduit.

If I was however the design engineer I would not use metal conduit as a design choice.

David, you are absolutely correct to the technical reduction of current in the rigid metal conduit. I have no trouble understanding this. But, the basis for your request requires rejecting the permissions of the Code that describe the materials used and electrical assembly of the same into a "service" that is supplied by an electric power utility. In my opinion, excluding Code permitted service assembly is above the minimum standard of the Code. If your requirement of applying 250.6(A) stands in your RMC connection to the utility transformer enclosure, then 250.6(A) HAS TO apply to a metallic conduit installed between a 100 Amp 120/240 volt single phase residential service center and the electric power utility meter socket enclosure.

 

[david]

You are making assumptions that are not correct. the transformer is utility owned and the utility owned bonding strap is never removed.

The design of the service conductors and the service conductors supplying the building are in fact the customers responsibility not the utilities.

I never said the conduit is metal in fact most of the time the design submitted is 40 PVC.
I did say we would make no comment about a design using rigid metal conduit. I also said if I was the design engineer I would not design the service lateral using metal conduit.

What we are talking about is what is being called an "equipment ground" that is installed from the utility transformer to the building service equipment passing through a CT cabinet

 

[Smart $]

First, I apologize for using an undefined term "service entrance" when what I meant is embodied by the Article 100 term "Service". To reiterate my point, David, in one illustration of how to control "objectionable current" is altering the connection at the XO of a power company transformer. We don't know yet, from David, whether the transformer low voltage terminals are the "service point", but, regardless, the transformer is not customer owned nor part of a supply that is other than an electric power utility.

The Code does not permit ONLY current on the grounded service conductor. The Code DOES permit multiple current paths between the service main bonding jumper and the service source when the service is supplied by an electric power utility. The Code permits metallic raceways in the assembly of a "service" supplied by an electric power utility.

That's it. It's that simple. An electric power utility supplied "service" will, by Code , have current in ALL of the conductive paths present between the service disconnect main bonding jumper and the supply. I submit that, because of Code requirements for the bonding of conductive enclosures and raceways of a service, current in them is NORMAL.

Thinking of David's metallic raceway between a CT cabinet and a utility transformer cabinet, current in the metal of the raceway, by Code bonding requirements, is NORMAL. David's raceway is "normally current carrying", and, as such, doesn't meet the description of "normally non?current-carrying metal parts of equipment" in NEC 250.6(A).


No problem. Answered above, in this post. I'm not making my point about anything other than the "service" connected to an electric power utility supply.

...

Okay... I'll accept your answer as...

Installation requirements do not explicitly prohibit conductive paths other than the grounded service conductor, such as metallic conduit between service equipment. Neutral current on these paths is technically objectionable, though many do not consider it as such and take no remedial action.

Now, let me put it to you as such...

You have installed a system as you have described as permitted or otherwise not prohibited. The grounded neutral service conductor becomes completely compromised somewhere between adequately bonded normally non?current-carrying metal parts which establish a parallel current path for grounded neutral current. Will the system show signs of a open fault? Is the current on these bonded parts, under this condition, considered objectionable current?

 

[al hildenbrand]

You are making assumptions that are not correct. the transformer is utility owned and the utility owned bonding strap is never removed.

The design of the service conductors and the service conductors supplying the building are in fact the customers responsibility not the utilities.

I never said the conduit is metal in fact most of the time the design submitted is 40 PVC.
I did say we would make no comment about a design using rigid metal conduit. I also said if I was the design engineer I would not design the service lateral using metal conduit.

What we are talking about is what is being called an "equipment ground" that is installed from the utility transformer to the building service equipment passing through a CT cabinet

If you make no comment on RMC, in this situation, and I go to 250.118(2) and see that RMC is an EGC, how am I then to determine that a wire (copper or aluminum, insulated or not, stranded or solid), a wire shown in 250.118(1) also as an EGC is now different and subject to containing "objectionable current"?

Answering my own rhetorical question: I can't. More importantly, when I read the Article 100 definition of "Grounding Conductor, Equipment (EGC), I again find that an EGC is

The conductive path(s) installed to connect normally non?current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.

That is, an EGC is "normally non?current-carrying", BUT this wire you are talking about and calling an "equipment ground" being installed on the line side of the service disconnect main bonding jumper HAS to normally carry current, therefore, again, my point.

 

[al hildenbrand]

Okay... I'll accept your answer as...

Originally Posted by Smart $ Installation requirements do not explicitly prohibit conductive paths other than the grounded service conductor, such as metallic conduit between service equipment. Neutral current on these paths is technically objectionable, though many do not consider it as such and take no remedial action.

But, you see, I'm not agreeing with you that the neutral current "on these paths is technically objectionable." The fallacy I see, with applying 250.6 is the repeated statements that this or that electrical path between the service disconnect main bonding jumper and the electric power utility supply is a normally non-current-carrying metal part (or parts). My point is that the parts are, in fact, normally carrying current.

 

[kwired]

If you make no comment on RMC, in this situation, and I go to 250.118(2) and see that RMC is an EGC, how am I then to determine that a wire (copper or aluminum, insulated or not, stranded or solid), a wire shown in 250.118(1) also as an EGC is now different and subject to containing "objectionable current"?

Answering my own rhetorical question: I can't. More importantly, when I read the Article 100 definition of "Grounding Conductor, Equipment (EGC), I again find that an EGC is
That is, an EGC is "normally non?current-carrying", BUT this wire you are talking about and calling an "equipment ground" being installed on the line side of the service disconnect main bonding jumper HAS to normally carry current, therefore, again, my point.

If the raceway on service side equipment incidentally ends up being parallel component of the grounded conductor, NEC doesn't consider that current objectionable. But if a wire conductor is installed and is a parallel component then that wire is part of a "parallel conductor" and both must be same size, type, length and terminate at same points with similar termination methods. Must also meet minimum size requirements no matter what ampacity is needed. There is no EGC on the service side everything non current carrying is bonded to the grounded conductor (which does subject it to non intentional current carrying possiblities). Any kind of "bonding jumper" used on the service side is sized to 250.66 and not 250.122, partly because it technically is not an EGC.

 

[al hildenbrand]

But, you see, I'm not agreeing with you that the neutral current "on these paths is technically objectionable." The fallacy I see, with applying 250.6 is the repeated statements that this or that electrical path between the service disconnect main bonding jumper and the electric power utility supply is a normally non-current-carrying metal part (or parts). My point is that the parts are, in fact, normally carrying current.

AND, really, in my thinking, the application of 250.6 gets even harder to do when one throws in the reality of the electric power utility distribution system unbalance currents and the neighbor(s) normal unbalance currents also finding parallel paths in the single hypothetical Premises Wiring (System) we are discussing.

 

[Smart $]

But, you see, I'm not agreeing with you that the neutral current "on these paths is technically objectionable." The fallacy I see, with applying 250.6 is the repeated statements that this or that electrical path between the service disconnect main bonding jumper and the electric power utility supply is a normally non-current-carrying metal part (or parts). My point is that the parts are, in fact, normally carrying current.

Well thanks for letting me know how you (and perhaps others) justify your interpretation. No point in continuing to debate the issue, as I see your opinion is firmly rooted and the Code as currently written does not provide any recourse.

 

[al hildenbrand]

But if a wire conductor is installed and is a parallel component then that wire is part of a "parallel conductor" and both must be same size, type, length and terminate at same points with similar termination methods.

I'm not arguing the pros or cons of 310.10(H). I am trying to speak to the OP.

I agree that 310.10(H) can probably by grounds for removal of this second grounded service conductor.

 

[kwired]

I'm not arguing the pros or cons of 310.10(H). I am trying to speak to the OP.

I agree that 310.10(H) can probably by grounds for removal of this second grounded service conductor.

I'm just trying to say that throwing in this "EGC" causes other complications with other things - like it effectively becomes a parallel conductor, but common practices for EGC's would make it undersized and unacceptable to other code sections.