Grounding electrode conductor in the same raceway as transformer feeders?

[kwired]

The

250.30 (4) says must be grounded to the building grounding electrode system. The bar in the MDP is part of the system’s so this shouldn’t be a problem

If you had smaller gear, like 200 amp gear with a rather small bar in comparison to what you do have there might be a problem, but I think would still be ok to tap onto the GEC itself, and probably doesn't even need to be something irreversible. There is only one "GEC" that needs to be continuous to the electrode, all other connections to it are a bonding jumper.

 

[Tulsa Electrician]

A common GEC would resolve this issue.

 

[wwhitney]

There is only one "GEC" that needs to be continuous to the electrode, all other connections to it are a bonding jumper.

There is only one "GEC" per service or SDS, but with one service and one SDS, you have two GECs, no?

A common GEC would resolve this issue.

Common GECs are allowed for multiple services, or for multiple SDSs, but I don't see an allowance for a common GEC with one service and one SDS. Perhaps an oversight.

I thought the reference to 250.30(A)(5) Exception 2 would settle this question. Here's the 2017 text for reference:

Exception No. 2: If the source of a separately derived system is located within equipment listed and identified as suitable for use as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, if the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.

Cheers, Wayne

 

[jaggedben]

But I think the 'source' a separately derived system is (typically) the transformer (the second winding, to be precise), not the place where the primary feeder receives its supply?

It other words that exception seems intended for when the service equipment contains a transformer. But I could be wrong.

 

[wwhitney]

But I think the 'source' a separately derived system is (typically) the transformer (the second winding, to be precise), not the place where the primary feeder receives its supply?

I guess you're right, it's not specifically defined anywhere that I can see, but that's the usage. So scratch that idea.

Cheers, Wayne

 

[don_resqcapt19]

But I think the 'source' a separately derived system is (typically) the transformer (the second winding, to be precise), not the place where the primary feeder receives its supply?

It other words that exception seems intended for when the service equipment contains a transformer. But I could be wrong.

That is correct based on the action on proposal 5-90 for the 2014 code.

5-90 Log #826 NEC-P05 Final Action: Accept in Principle
(250.30(A)(5) Exception No. 2)
Submitter: Michael J. Johnston, National Electrical Contractors Association
Recommendation: Revise text to read as follows:
Exception No. 2: Where a separately derived system originates and is located in listed equipment suitable as service equipment, the grounding
electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the
separately derived system, provided the grounding electrode conductor is of sufficient size for the separately derived system. Where the equipment
grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.
Substantiation: This exception has been widely interpreted to conflict with the purpose of the grounding electrode conductor as described in an informational note under 250.4(A)(1) and 250.30(A)(4) because it allows a grounding electrode conductor of unlimited length to be used in lieu of an electrode located near the transformer. The proposed change makes clear that this exception is intended to apply to separately derived systems that are an integral part of listed equipment. A companion proposal has been submitted for 250.30(A)(6)(b) Exception
Panel Meeting Action: Accept in Principle
Revise the text of 250.30(A)(5) Exception No. 2 to read as follows:
If the source of a separately derived system originates is located within equipment listed and identified as equipment suitable as service equipment
Suitable for Use as Service Equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, provided the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.
Panel Statement: The revised text incorporates the intent of the submitter and clarifies the location for the separately derived system relative to the equipment. In addition the revision clarifies the required marking as well as corrects the marking indicated to be consistent with the markings required in the product safety standards.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 15 Negative: 1
Explanation of Negative:
DOBROWSKY, P.: No substantiation was given indicating any problems are being created. The grounding electrode conductor for a service or separately derived systems such as in a unit substation should be permitted to be used for other separately derived systems that are not within the same enclosure. This same concept is permitted for common grounding electrode conductors
red text = new language blue text = deleted language

 

[wwhitney]

the action on proposal 5-90 for the 2014 code.

Don, do you have easy way to look up (at least recent) past PIs from different years for a given code section? Or do you just have to check each year one by one?

Cheers, Wayne

 

[don_resqcapt19]

Don, do you have easy way to look up (at least recent) past PIs from different years for a given code section? Or do you just have to check each year one by one?

Cheers, Wayne

The new system is actually easier, as you can look at the first and second drafts by section number. The new system does make it harder to look at PIs that were rejected in the first draft, but they are there. However in many cases the person is not interested in PI that have been resolved (rejected). One of the issues I see with having the resolved PIs hidden, that very few of those resolved PIs come back in the Second Revision Report. That was fairly common with the old system, and I had one that was rejected unanimously in the ROP, but accepted unanimously in the ROC as a result of a comment. You really don't see that now, and the number of comments as compared to the number of proposals has dropped with the new system.

For the 2014 and earlier some of the PDFs of the ROPs and ROCs are online, but I have hard copies of those back to the 84 code cycle. Those are in section order, so not real difficult to find things, and the PDFs are searchable.

The key for both systems is knowing when the change was made, so you can look at the correct documents.

To find the documents you go to nfpa.org/70, select the edition, and then select "archived revision information". For new system you can view the first draft or second draft, but for the old system you view the Report on Proposals (ROP) or Report on Comments (ROC). If you go to the 1993 and earlier codes, the ROP was known as the Technical Committee Report (TCR) an the ROC as the Technical Committee Documentation (TCD).

For 2014 and earlier, you can often download the documents, and in some editions, there is a draft report, which is how the code would look if the results of the first draft had not changed. One thing the draft has is the proposal number for any change that was made, making it easier to find the proposal information. The current system First Draft Report, really combines what was in the ROP and the Draft.

Over the years, I have found changes where I could not find any supporting documentation, but those have been rare.
The ones that are difficult are the ones where a section is rewritten or reorganized by a code making panel, but the rewrite included accepted proposals. Those you have to go back and read all of the proposals associated with the rewrite.

 

[wwhitney]

The new system is actually easier, as you can look at the first and second drafts by section number. . . .

Thanks for the long answer. Just to confirm, it sounds like you still need to check each year separately? I was hoping that at least for the years that are through the new system, there might be a way to look at the history of a particular section across years.

Cheers, Wayne

 

[don_resqcapt19]

Thanks for the long answer. Just to confirm, it sounds like you still need to check each year separately? I was hoping that at least for the years that are through the new system, there might be a way to look at the history of a particular section across years.

Cheers, Wayne

You are correct, everything is by the code edition.