250.30(A)(3) Exception No. 2 & it?s use

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tryinghard

tryinghard

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We?re installing a new feeder in a concrete building that has an existing CEE (ufer) at the source; and the water pipe is not a qualified electrode as per 250.52(A)(1). This new circuit includes a transformer downstream that would normally have a GEC to the building steel but there is none. We could install another driven type electrode but it will still need to bond to the existing per 250.53(C).

Regarding grounding this new transformer there are three obvious concerns: 1) electrode type, 2) grounding electrode conductor (GEC), & 3) If an additional electrode is installed I understand the bonding can terminate at distribution/panel bus locations if excising electrodes are not accessible. It appears the design below is compliant but it seems weird to use the circuit ground wire as the GEC and not provide another electrode at the transformer.

Is the use of 250.30(A)(3) Exception No. 2 appropriate with this design?

XFMRGrounding.jpg
 
I am not sold that the EGC may also be used as the GEC.

If that is the intention of the NEC there would be no reason for 250.30(A)(4).
 
250.30 (A) (3) exception 2 says where a separately derived system originates in listed equipment suitable as service equipment, that exception does not apply to your installation
 
iwire said:
I am not sold that the EGC may also be used as the GEC.
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I?m not necessarily either.

This building is on ground level, I could drive an electrode. If I do the bond between the electrodes (existing to new) will still be #4 cu (250.53(C)) and it will terminate at every bus to the service disconnect. I guess I don?t see the difference except the lack of another ground electrode?

I still wonder how exception #2 of 250.30(A)(3) & (7) apply?
 
mpd said:
250.30 (A) (3) exception 2 says where a separately derived system originates in listed equipment suitable as service equipment, that exception does not apply to your installation
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In what way though, the primary circuit does originate in suitable equipment the transformer just doesn?t reside there?
 
they are talking about service equipment switchgear that has a transformer section
 
So if another grounding electrode is installed for the transformer this particular application would have to be installed like this picture below, I suppose? The #4 cu ground from the 480V 125A circuit cannot be sized as equipment ground (Table 250.122) because it is also the electrode bonding jumper between the ground electrodes. What?s weird is it terminates at each distribution bus along the way and this appears to be compliant with 250.53(C). It also does not physically terminate to electrodes rather only busing that includes GEC?s.

Do you think the picture below is NEC compliant ? comments?

XFMRGroundingb.jpg
 
mpd said:
tryinghard

IMO you do not comply with 250.64 (C) & (F)
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But the grounding electrodes must connect as a system, and 250.53(C) qualifies this bonding.

250.53(C) is specifically devoid of mentioning 250.64's (C)(D) & (F), check it out.

The GEC would be from the new electrode to the transformer only.
 
Check this out, it is an ROP from 2002 where the CMP says a dedicated GEC is required in addtion to any EGC.

5-99 Log #2716 NEC-P05
(250-30(A)(4) Exception No. 2 (New) )
Final Action: Reject
Submitter: Donald A. Ganiere Ottawa, IL
Recommendation:
Renumber existing Exception as Exception No. 1 and add new Exception No. 2 as follows:
"Exception No. 2: Where a transformer is used as a separately derived system and where the transformer primary feeder circuit
originates in the same building or structure, a grounding electrode shall not be required."
Substantiation:
There is no electrical or safety related reason to require a grounding electrode for a transformer used as a separately derived system when
the primary power source for the transformer is located in the same building or structure. The requirements of 250.4(A)(1) are met
without the use of a grounding electrode at the secondary side of the transformer. Lighting is not a problem within the building or
structure. The only possible contact with a higher voltage system is a fault on the primary feeder and this fault will be cleared by the
primary feeder equipment grounding conductor. The bonding required by 250.30(A)(1) will stabilize the voltage to earth under normal
operating conditions. The same bonding in combination with the primary feeder equipment grounding conductor will limit the effect of
line surges. The addition of a direct connection from the secondary side of a separately derived system to a grounding electrode
provides no additional protection over that which is already provided by the primary feeder equipment grounding conductor.
Panel Meeting Action: Reject

Panel Statement:
The present requirements for separately derived systems to be grounded to a reference earth by a dedicated grounding electrode
conductor apply to all systems without regard of installation inside or outside the building or structure served. The primary reason is to
establish an earth ground reference and stabilize the system voltage around this reference. The equipment grounding conductor from the
source to the separately derived system does not meet the requirements for size, not having a choke effect when installed in metal
raceways, multiple terminations, etc. The equipment grounding conductor's primary purpose is to provide a low impedance path for
fault current in the event of a ground-fault on the system up to and including the primary of the transformer, not to act as the low
impedance earth reference conductor.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 15 Negative: 1
Explanation of Negative:
RAPPAPORT: The purpose of the grounding electrode conductor in the proposed Exception is to stabilize voltage. See my Comment
on Affirmative on Proposal 5-91. An equipment grounding conductor, run with the feeder to the separately derived system and sized for
the separately derived system, should be adequate.
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iwire said:
If I could use the EGC I would not need a that section.

See my post dirrectly above
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Okay I can understand this, but now in Post 9 the grounding electrode will be installed and the GEC will terminate from it to the transformer.

The bonding of the electrodes would now be as per 250.53(C), would you say this is this correct?
 
Did you read the ROP?

You must run a GEC from XO all the way to the buildings grounding electrode system, The EGC is not part of the GES.
 
iwire said:
Did you read the ROP?

You must run a GEC from XO all the way to the buildings grounding electrode system, The EGC is not part of the GES.
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Doesn't 250.53(C) qualify the bonding between multiple grounding electrodes and cause them to become a grounding electrode sysetm?

If so the new ground electrode would qualify and the new GEC is between the new electrode and transformer.

I did read the ROP I am not trying to use the EGC as part of the GES, I am proposing this #4 as the electrode "bonding jumper" as described in 250.53(C) if this is wrong I just wonder how so.

I wonder how else I could install this grounding?
 
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When I install another ground electrode how can it bond to the existing CEE, and aren?t 250.50 & 53(C) the qualifying codes for this bonding? :-?
 
tryinghard said:
When I install another ground electrode how can it bond to the existing CEE, and aren?t 250.50 & 53(C) the qualifying codes for this bonding? :-?
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tryinghard, You don't install another GE, follow 250.30(A) & 250.30(A)(7) , if the only GE

is the CEE, then you need to run from the SDS to the CEE.

IMO, 250.50 &53(C) are not for SDS,s.
 
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