Grounding Electrode Conductor

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manheng

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We have a new project with 2 new electrical services. Service #1 is a 4000 amp, 120/208v, 3 ph, 4 w service. Service #2 is a 5000 amp, 277/480v, 3 pf, 4 w service. Service #1 is supplied through 10 sets of 4#600 kcmil in (10) 4" schedule 80 pvc conduits, underground. Service #2 is 12 sets of 4#600 kcmil in (12) 4" schedule 80 pvc conduits, underground. My connections to driven rod, electrode, concrete encased electrode and ground ring is 3/0. Should the connection to the water service and building steel be sized at 12% of the total area of the incoming service conductors?
 
Re: Grounding Electrode Conductor

The largest GEC the NEC ever requires is 3/0 CU or 250 AL.

The main bonding jumpers if you where to install them would be 12.5% of the service conductors.

But I imagine your MBJ will come as a buss bar in the service gear.
 
Re: Grounding Electrode Conductor

yes the MBJ is internal within the switchboard. So if I read this correctly, 3/0 maxes out for all of my ground connections to satisfy all connections associated with 250.50?

from the servie switch out to equipment, I am sized based on overcurrent protection per 250.122.
the reason I ask is I have a plans examiner questioning my design and he is making my head spin

thanks for the reply
 
Re: Grounding Electrode Conductor

Even with this size of service, a GEC that runs only to a driven ground need not exceed #6 copper.
 
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