GEC daisy chain between transformers?

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marcosgue

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Hello forum, I was watching at Main Elect Room that have two transformers and they're bonded theirs enclosure together with ground wire and only one ground wire go to ground bar on the wall and front there the GEC direct buried to ground rod grounding electrode conductor. I personally think this's nec violation, is this installation with GEC daisy chained is correct or I'm missing something? Please clarify this with some nec references
 
250.30(A)6 discusses a common Grounding Electrode Conductor for multiple SDSs. If the GEC is properly connected, a common conductor is compliant.
 
LarryFine said:
Of course, that doesn't apply to the GEC to solely the rod(s).
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I don't see any wording in 250.30(A)(6)(a)(1) that would allow a common grounding conductor to be smaller than a #3/0 copper conductor regardless of the electrode type.
 
I get the sense that maybe the OP is saying that these are not taps from a common GEC but rather chained to each xformer. That in my view would not be allowed.
 
infinity said:
I don't see any wording in 250.30(A)(6)(a)(1) that would allow a common grounding conductor to be smaller than a #3/0 copper conductor regardless of the electrode type.
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Unless the discussion excludes the conductor to a rod or two, which otherwise never needs larger than #6 cu.
 
LarryFine said:
Unless the discussion excludes the conductor to a rod or two, which otherwise never needs larger than #6 cu.
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You can use a separate #6 from each transformer to the rods but if you use a single common grounding electrode it cannot be smaller than #3/0. Doesn't make much sense but that's what it says. :oops:
 
infinity said:
I don't see any wording in 250.30(A)(6)(a)(1) that would allow a common grounding conductor to be smaller than a #3/0 copper conductor regardless of the electrode type.
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If I remember correctly the common part of the common grounding electrode conductor has to be 3/0 but the connection to the rod doesn't have to be.
 
texie said:
I get the sense that maybe the OP is saying that these are not taps from a common GEC but rather chained to each xformer. That in my view would not be allowed.
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I don't follow the OP's description, but I would say that any configuration for which cutting one wire and then resplicing it would be compliant is itself compliant. E.g. if a ground bar with 3 attachments, one GEC to each transformer and one common GEC to the GES, is compliant, then merging two of those wires, so that a single wire loops through the ground bar, would be fine. Assuming all the sizes are still good.

Cheers, Wayne
 
I agree with Texie because they're not taps, only one conductor 4awg bonding the two transformers metal enclosures and landing in the ground bar and from the ground bar one common attachment for GEC to the GES, so just two attachments in the ground bar, one for that bonding conductor 4awg and another for the common GEC #4awg that go to GES with 3 ground rod in triangle configuration.
 
I think the first part of this installation is a violation of 250.30 because there isn't taps from the ground bar to the SDS, but the use of wire #4 as GEC from the ground bar to GES is compliant because the minimum size is #6 to ground rod according to 250.66
 
I'm having difficulty with this installation, pertaining to compliance w/ 250.30(A)(6) Multiple Separately Derived Systems.
It's basically where your depending on the connection @ first SDS .

I've always been taught that difference in being in compliance w/NFPA 70 could possibly being the difference in -one word-..

250.30(A)(6) A grounding electrode conductor tap -*shall then be installed*- from each separately derived system to the common grounding electrode conductor as specified in 250.30(A)(4). A -grounding electrode conductor tap- *shall be installed* from each separately derived system to the common grounding electrode conductor.

How does this installation comply w/ the above (?) Don't you essentially have an extention of the GEC, to the first SDS(?)

* it appears in the above "shall" complies w/the mandatory rules of 90.5(A)..
 
RWC/NC. said:
How does this installation comply w/ the above (?) Don't you essentially have an extention of the GEC, to the first SDS(?)
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Perhaps mine is the minority interpretation, but I'm going to say an extension of a wire is a tap in the context of that code section.

I.e. if the supposed defect could be cured by cutting a wire and then (say) split bolting both cut ends back together, that's a sufficiently stupid end result that we should use our discretion in interpreting the words without Article 100 definitions to avoid an interpretation that would require that.

Cheers, Wayne
 
RWC/NC. said:
In all due respect, I never quoted Art.100 Definitions.. I quoted Art 90.5 Permissive and Mandatory rules.
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I only mentioned Art 100 for the comparison of definitions that are spelled out, vs other terms like "tap" that aren't formally defined.

My point is why not consider an extension a tap? Why require an extra splice? This is not a situation like 230.75 where it explicitly tells you a conductor needs to be disconnectable and can't run through unspliced.

[To reiterate: I'm not clear on what configuration the OP is describing. I'm referring to a configuration where you'd typically have 3 separate wires terminating on a ground bar (one to the GES, one for each transformers), with each wire having connections only at the ends. And then instead of that you have a wire that loops through the ground bar, so it is connected to the ground bar in the middle, plus the two end connections.]

Cheers, Wayne
 
marcosgue said:
Hello forum, I was watching at Main Elect Room that have two transformers and they're bonded theirs enclosure together with ground wire and only one ground wire go to ground bar on the wall and front there the GEC direct buried to ground rod grounding electrode conductor. I personally think this's nec violation, is this installation with GEC daisy chained is correct or I'm missing something? Please clarify this with some nec references
Click to expand...
Isn’t two grounding electrodes required within 6 feet apart unless resistance from electrode to ground is 25 ohms or less?
 
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