# 250.64 (d)(2)



## erics37 (May 7, 2009)

No, D(2) is basically saying run a dedicated GEC from each enclosure to the grounding electrode system. So, like, three enclosures would get three separate GECs to the water pipe or whatever.

D(1) is the one that permits a common GEC (sized by 250.66) with individual "taps" to each enclosure, sized per 250.66 based on the conductor sizes feeding that specific enclosure.


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## RIVETER (Sep 26, 2009)

Magnettica said:


> Interpretation: Each service disconnecting means gets a GEC 'tap' correct?


I know I will receive some flack but here goes. The ONLY purpose of a grounding conductor is to take an aberrant
current to ground. Let's say, in the case of a lightning event, I really don't see why the service conductor size comes into play...the source of the aberrant voltage is not coming from the service source transformer. Unless...unless someone thinks that a parallel path for the fault current should go back through the neutral and then back to the transformer which MAY be grounded.


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## KGN742003 (Apr 23, 2012)

RIVETER said:


> I know I will receive some flack but here goes. The ONLY purpose of a grounding conductor is to take an aberrant
> current to ground. Let's say, in the case of a lightning event, I really don't see why the service conductor size comes into play...the source of the aberrant voltage is not coming from the service source transformer. Unless...unless someone thinks that a parallel path for the fault current should go back through the neutral and then back to the transformer which MAY be grounded.


Most times your GEC is also bonding things like water pipes and building steel so it does need to scale up with the size of the ungrounded conductors to be able to handle fault currents.


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## erics37 (May 7, 2009)

KGN742003 said:


> Most times your GEC is also bonding things like water pipes and building steel so it does need to scale up with the size of the ungrounded conductors to be able to handle fault currents.


Bonding jumpers bond all those electrodes into a grounding electrode system. The GEC is the connection between that system and your electrical service.


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## GEORGE D (Apr 2, 2009)

RIVETER said:


> I know I will receive some flack but here goes. The ONLY purpose of a grounding conductor is to take an aberrant
> current to ground. Let's say, in the case of a lightning event, I really don't see why the service conductor size comes into play...the source of the aberrant voltage is not coming from the service source transformer. Unless...unless someone thinks that a parallel path for the fault current should go back through the neutral and then back to the transformer which MAY be grounded.


Ok I think I made no sense at all so I deleted that.


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## chicken steve (Mar 22, 2011)

RIVETER said:


> I know I will receive some flack but here goes. The ONLY purpose of a grounding conductor is to take an aberrant
> current to ground. Let's say, in the case of a lightning event, I really don't see why the service conductor size comes into play...the source of the aberrant voltage is not coming from the service source transformer. Unless...unless someone thinks that a parallel path for the fault current should go back through the neutral and then back to the transformer which MAY be grounded.


While Mother nature can't be sized to a conductor, i do believe most strikes enter switchgear via transmission line conductors, thus some relevance in GEC relation to the system served.

That said, a current free GEC is essentially a dead end. The more GEC's earthed from proximal MBJ's , *or* the more GEC's from separate services made to a common entity _(water pipe)_ simply invites Mr Kirchoff's laws into play



~CS~


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