Grounding Electrode Conductor Sizing

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Butler

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On a Dwelling unit 200 amp or larger service with use of a ground "rod" what size copper grounding electrode conductor is required? Article 250.66(A) states 6AWG?
 
Thanks, I keep being told to use Table 250.66, but Article 250.66(A) states not larger than 6 AWG. I assume this is due the the rods impedance?
 
Butler said:
I assume this is due the the rods impedance?
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That's correct.

Actually the #6 is probably overkill considering the rods impedance. :wink:

Roger
 
The reason that a GEC to a ground rod need not be larger than #6 AWG is because the Ground Rod CANNOT carry fault current. If one leg of a 240-volt service becomes shorted to the GEC and the ground rod has a 25-ohm resistance the GEC will carry 4.8 amps (120/25= 4.8 amps). What purpose would be served by installing a larger GEC?
 
haskindm said:
The reason that a GEC to a ground rod need not be larger than #6 AWG is because the Ground Rod CANNOT carry fault current. If one leg of a 240-volt service becomes shorted to the GEC and the ground rod has a 25-ohm resistance the GEC will carry 4.8 amps (120/25= 4.8 amps). What purpose would be served by installing a larger GEC?
Click to expand...

Is the rod supposed to carry fault current?

(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

I was under the impression that the bonding of the equipment grounding conductors and the grounded neutral was for the purpose of clearing a fault.
 
jwelectric said:
Is the rod supposed to carry fault current?

(1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

I was under the impression that the bonding of the equipment grounding conductors and the grounded neutral was for the purpose of clearing a fault.
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Your impression is correct.
 
Mike,
You are absolutely correct, but many people do not understand that concept. Many people think that ground rods play a part in clearing faults. 250.122 requires larger conductors than 250.66 because those conductors may be called upon to carry fault current.
 
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