Grounded Conductor in 15KV UG Service

[jwilson3]

NEC 250.24 (B) requires a grounded conductor in "under 1000 volt" services. Does the NEC require a grounded conductor for over 1000 volt, and if so, what article specifically addresses this?

 

[peebee]

Nope.

And read 250.24(B) again and you'll realize that, contrary to your post, NEC does NOT "require a grounded conductor in 'under 1000 volt' services" as you stated, it just details some requirements IF you ground the system. See 250.21(B) and 250.21. Read the NEC more carefully and quote it more accurately next time.

IEEE does strongly recommend grounding medium voltage systems for several reasons. See the Red Book for details.

There's lots of threads on ungrounded medium voltage systems in eng-tips. Try the search engine.

 

[jwilson3]

Response to peebee's underwhelming yet caustic comments:

I re-read 250.24(B) and stand by my original statement. Maybe you should get yourself a NEC "Handbook" and you'll see that a "grounded service conductor" IS REQUIRED if the ac system is grounded at any point.
Where's 250.21(B) you referred to? Are you looking at the 2002 NEC, or is it really 250.20(B) you meant. At any rate neither 250.20 nor 250.21 are germane to my question.

I guess the smartest thing you said in your comments was "Nope", which I agree with.

Thanks anyway for your comments. You at least reinforced my feeling that people aren't created equal.

 

[peebee]

Re: "if the ac system is grounded at any point". Well, that's a big if. There's still no requirement that in the NEC to provide a "grounded conductor in 'under 1000 volt' services" as you posted.

Yup, 250.20(B). You got me on that one. Sorry about the typo, but I can guarantee only that it will happen again.

Sorry if I'm sounding caustic. It seems I deal daily with people misquoting the NEC, or just outright making complete falsehoods up about it, and these people argue passionately about their misconceptions without ever checking to see if the code actually says anywhere what they think it does.

At least you took the time to read it, and I do appreciate that.

Re: "You at least reinforced my feeling that people aren't created equal." Well, I have just no idea what that means. But I'll assume you stated that with the best possible interpretation.

250.24(B) requires that if there's grounded system, that the grounded conductor be bonded to the service disconnecting means (it does not require a grounded system). So, it sounds like what you actually want to know is, "if the MV system is grounded, do you need to bond a grounding conductor to the service disconnecting means?" This is a much different question than "Does the NEC require a grounded conductor for over 1000 volt".

This is also a question that I'd be much more hesitant in answering. My answer is now more like "probably not" rather than a simple "nope." If you'd stated the question this way to begin with, I probably would not have responded to it at all, preferring instead to see how others responded. There's still no need to ground an MV system. But you still need to bond a grounding conductor to the SE equipment. The grounding conductor will also be bonded to a phase or neutral conductor. So the SE enclosure is clearly bonded. I do not believe there is any requirement, however, to run a grounded conductor with the phase conductors to achieve this bond. I'd invite other responses and certainly would not take this to be a definitive answer.

At the risk of sounding causting or equal or unequal to other people, whichever is worse, I might suggest trying to be a bit more specific in the phrasing of your questions.

 

[dpc]

If anyone is interested, I think the answer to your original question is that a grounding electrode conductor bonded to the grounded service conductor IS required for services over 1000 volts IF the service is grounded. The service is "permitted" to be grounded, but not required to be.

250.24(A) requires this and I don't see anything in 250.24(A)(1)through (5) that would exempt high voltage systems.

But keep in mind that the NEC was developed based on low voltage services so often the wording and interpretation for high voltage systems leaves a lot to be desired. It's getting better, but there are still gaps related to high voltage systems.

From a practical standpoint, I think you would want to intentionally bond your grounding system to the utility's system, since this will generally drastically improve your grounding system's resistance to earth.

There might be some cases where there is a concern about ground potential rise from a utility system if you were located extremely close to their substation. But if your grounding system is adequate you should be OK and not bonding it might be worse.

 

[peebee]

Some related news from the mikeholt.com newsletter:

"IEC Members Vote on Proposals for NEC Code-Making Panels
February 13, 2003,

http://www.ieci.org/default.asp?PID=434

". . .For example, in CMP-1, the panel voted to accept proposal 1-2 to change the term “equipment grounding conductor” to “equipment bonding conductor” everywhere those terms appear in the NEC. This panel also voted to include the definition of “Neutral Conductor” in Article 100. Panel members accepted this proposal (1-122) in principle, and they referred this action to Panels 2, 4, 5, and 13 for comments.

". . .Several panels were faced with proposals dealing with the change from “grounding” to “bonding.” CMP-4 voted to reject proposal 4-1 to change the term “equipment grounding conductor” to “equipment bonding conductor” throughout the NEC. “This is an issue that would have to be taken up by the correlating committee, and we would need direction from them,” said Terry Cole, CMP-4 Panel Representative.

"CMP-5 also reviewed numerous proposals to change the word “grounding” to “bonding” throughout. “After extensive debate and a task group report, CMP-5 made a panel proposal (5-78a) to handle the change in code language deleting the word “grounding” and replacing it with “bonding,” said Ted Robertson, CMP-5 Principal.

"Jerry Kent, Principal on CMP-6, said that they rejected proposal 6-1 to change “grounding” to “bonding.” He said, “The panel statement was general acceptance; however, the issue should have resided with Panel 5 first and then be reviewed on an item-by-item basis to ensure the global change does not affect the meaning of the written word.” Kent added that the hottest item for his panel was proposal 6-45, which deals with using raised ambient temperature to calculate the wire size for conduits installed on rooftops in direct sunlight. CMP-6 accepted 6-45.

"CMP-8 rejected the grounding to bonding name change proposal; CMP-12 accepted it; and CMP-19 rejected the universal change. Bill Zanicchi, Principal on CMP-19, said, “This proposal is repeated at least 16 times within panel 19’s scope, which meant that the panel just rejected each one without discussion after rejecting the first one. I believe this change would clarify the dmitted ‘confusion’ in the present language. It appears that panel 5 also sees merit in this proposal and accepted its concept by creating a panel proposal to change the term to ‘bonding.’ I applaud their efforts as I can only imagine the debate that went on in that meeting room.” . . ."