250.66 (A)

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arnettda

Senior Member
If I have a 600 amp disconect at my remote service with parallel conductors and my only grounding electrodes are two driven ground rods.I only need to run a #6 awg copper to it? My question is why? If you used the table values it would need to be larger. I then use feeder tap rules to feed 3 separate 200 amp panels.
Thanks
 
arnettda said:
If I have a 600 amp disconect at my remote service with parallel conductors and my only grounding electrodes are two driven ground rods.I only need to run a #6 awg copper to it? My question is why? If you used the table values it would need to be larger. I then use feeder tap rules to feed 3 separate 200 amp panels.
Thanks
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Mainly because the rod itself is only as good as the #6 so anything bigger does nothing to help improve the impendence
 
Dennis Alwon said:
Mainly because the rod itself is only as good as the #6 so anything bigger does nothing to help improve the impendence
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In theory, if you have multiple rods you could get an impedance below 10 ohms, and with a CEE, plate electrode or ground ring much lower than that.
I guess the idea is that for any reasonable number of rods exclusively the GEC to each rod need not be bigger than #6.
If you parallel many rods to make your GES, it might make sense to use a larger bonding jumper and a larger wire to the point where the rods are brought together. But that would be design rather than requirement.
 
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