Grounded Conductor Brought to Service Equipment

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The 2008 NEC, Article 250.24(C) states:
" Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run (i.e. from the utility point of service) to each service disconnect means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus..........."

Is there any reference in the NEC to systems at, or at greater than 1000 volts requiring a grounded conductor(s) when in similar conditions as in the above article?. I have not been able to find any reference.
In is my opinion for the conditions in Article 250.24(C),the need for a low impedance path to the utility source is needed.
 

Dennis Alwon

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Generally the NEC speaks of "600 volts or less" and "Over 600 volts". For article 250 they only appear to deal with up to 1000 volts.

Could it be that utilities don't deliver more than a 1000 volts and anything higher than that is on the utility side-- which is not governed by the NEC?????

I am sure there is a better answer than this one.
 

SG-1

Senior Member
Article 250 Part X deals with 1KV & over. Basically these systems must comply with Article 250 plus specific rules in Part X.

The building where I work has 12000 volts coming from the POCO into our switchgear.
 
Grounded Conductor Brought to Service Equipment

Thank you for the responses to date, and i am attempting to clarify my original question.
Should the service conductors, for a 4,160Y/2,400v service, from the service panel(s) to a utility point of service include a grounded conductor ?
Assume the conditions in Article 250.24(C) under which a grounded conductor is required exists.

It appears to me that the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts. But that is just my opinion............
Anybody has better arguments?
 

SG-1

Senior Member
Part of the problem with an answer is that a medium voltage system can be grounded in many different ways or be ungrounded. This depends upon how important continunity of service is to the customer. The other problem is the POCO does not fall under the NEC.

If the system is supposed to be solidly grounded I would full expect to see a grounded conductor pulled in with the ungrounded conductors, unless no line to neutral loads are served. In that case the steel conduit ( wiring method ) may be supplying the low impedance path back to the service.

Am I hitting nearer to the mark ??
 

don_resqcapt19

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I am not sure why 250.24(C) is limited to 1000 volts and less as it appears to me that 250.24(A) requires this for any premises wiring system that is supplied from a grounded AC service.
 

shepelec

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Palmer, MA
Grounded or grounding conductor? Unless you are counting concentric neutral on a MV cable, I have never seen a grounded conductor in MV. Of course I have not seen all the possible applications.:-?
 

Cold Fusion

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... Is there any reference in the NEC to systems at, or at greater than 1000 volts requiring a grounded conductor(s) when in similar conditions as in the above article?. I have not been able to find any reference.
In is my opinion for the conditions in Article 250.24(C),the need for a low impedance path to the utility source is needed.

References are 2005:
First look at 250.20.C. That says that 1kv and over you can either ground or not -no restrictions.

If the system is grounded, then as SG mentioned, go to Sec X. Specifically read 250.184.B and C. The only place the code specifically requires a neutral is mentioned in 250.184.B.6.

I think that the code panel is tellng us that they are not going to cookbook design systems 1kv and up. One is actually going to have to understand the systems and design accordingly. If so, this is one thing that code panel 5 got right. (Yes, there are several others:roll:)

cf
 

Cold Fusion

Senior Member
Location
way north
...Should the service conductors, for a 4,160Y/2,400v service, from the service panel(s) to a utility point of service include a grounded conductor ?
Assume the conditions in Article 250.24(C) under which a grounded conductor is required exists.

It appears to me that the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts. But that is just my opinion............
Anybody has better arguments?
Well, with no N-G loads, and single point grounded, there is no need for a neutral. There must be an equipment grounding conductor and that will be connected to the neutral back at the xfm.

So, my answer is: It depends :roll:

As for, "the reasons requiring the grounded conductor for a grounded AC system should be the same regardless if is operating at less, equal or over 600 volts." I agree. However under 1kv, the code requires cookie cutter design, regardless of the physics, science, or system requirements. 1kv and up, the code recognizes that cookie cutter design is impractical.

cf
 

don_resqcapt19

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I still believe that 250.24(A) applies and requires that a grounded conductor be brought to the service equipment if the utility system is a grounded system.
250.180 General.
Where high-voltage systems are grounded, they shall comply with all applicable provisions of the preceding sections of this article and with 250.182 through 250.190, which supplement and modify the preceding sections.
 

Cold Fusion

Senior Member
Location
way north
I still believe that 250.24(A) applies and requires that a grounded conductor be brought to the service equipment if the utility system is a grounded system.
(references are 2008)

You could well be right in that an AHJ could well cite this reference and demand that a grounded conductor be brought to the service equipment.

However, there is some evidence that 250.24.A applies to services less than 1kv. For example, look at the 250.24.A.2, Ex. The exception cites 250.36, which applies to services 1kv or less. If this section was meant to apply to services 1kv and up, then the exception would also include 250.186 - but it doesn't.

Take a look at 250.184.B.1 - 8. This is not a house service where the bare grounded conductor from the service doubles as an equipment grounding conductor.

Interestingly, I'm neither in-favor nor not-in-favor of running a neutral to the service disconnect. Mostly because I don't know what I would do. I've never worked with a solidly grounded MV service distributed through a plant. For the stuff I work that would be a design flaw.

cf
 
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