Grounding Separately Derived Systems

[kevin]

Section 250.30(A)(4) spells out the requirements for the required grounding electrode for a grounded separately derived system. If there is an effectively grounded metal water pipe available and there are no effectively grounded structural metal members, the underground water pipe must be utilized as the grounding electrode.
Must it be supplemented by an additional electrode per 250.53(D)(2)?

 

[bennie]

Re: Grounding Separately Derived Systems

I promise not to get into this one

 

[iwire]

Re: Grounding Separately Derived Systems

Bennie, it must be taking all your will power.

 

[don_resqcapt19]

Re: Grounding Separately Derived Systems

Kevin,
There is no need to install another supplemental grounding electrode. There must already be one for the service grounding electrode system.
Don

 

[kevin]

Re: Grounding Separately Derived Systems

Don,
That is a very insightful answer. What if the building, though, was built and wired before the Code required the supplemental electrode for underground water pipes?

 

[don_resqcapt19]

Re: Grounding Separately Derived Systems

Keven,
The code does not require a supplemental grounding electrode for the SDS.
Don

 

[kevin]

Re: Grounding Separately Derived Systems

Don,
Thanks for your reply. I tend to agree, but do you, or anyone, have an opinion on why the Code should not require a supplemental grounding electrode for a separately derived system, but mandate it for a main service [250.53(D)(2)]? Is there a logical inconsistency here? The rationale for requiring the supplemental grounding electrode is apparently based on the assumption that at some future date the underground metal water pipe will be replaced by plastic water pipe, thus rendering it useless as a grounding electrode. Why shouldn't the same concern hold true for a separately derived system?