Parallel grounding electrode

[Paul Bates]

I recently inspected a 800 amp main breaker 3 Phase 4 wire 208/110 volt (parallel 500 mcm thhn) Service Entrance where the electrician used # 1/0 cu as the grounding electrode conductor to the metal water pipe ground. I instructed him to remove the #1/0 cu ground and install a 2/0 cu ground to the water pipe per table 250.66. He then installed an additional #4 cu ground in parallel with the 1/0 cu ground in the same conduit, and contends the cicular mill area of the two conductors is the same as 2/0 cu therefore it is sufficient. NEC 310.4 states parallel conductors used for grounded conductors must be the same cicular mill area and not smaller than # 1/0 cu, does this apply to gounding conductors as well or is he correct. Thanks

 

[George Stolz]

You are right as rain. 310.4.

 

[LarryFine]

. . . parallel 500 mcm thhn . . .

I'd bet he went by the conductor size, forgetting about Note 1. He's also forgetting about the division of current by even considering the paralleling of different sizes.

 

[infinity]

Maybe he should have asked if the additional #4 was OK before now having to do the job for a third time.

 

[Pierre C Belarge]

Article 100
Grounded Conductor.
A system or circuit conductor that is intentionally grounded. This conductor is either the grounded conductor or sometimes the neutral conductor - it depends on the installation which it would be. It is not the grounding electrode conductor. The GEC or the EGC are not considered "circuit" conductors.

I do not believe 310.4 applies to the GEC. "...comprising each phase, polarity, neutral, or grounded circuit conductor..."

With that said, based on the function of, and potentially how the GEC actually will work under conditions of lightning or high voltage being imposed on the circuit, I would say that installing two different sized conductors (in the manner described) instead of one conductor would be a problem.
Multiple GECs are premitted, but the size of each should be according to 250.66 and I cannot see how the described installation would meet 250.66 sizing requirements.