Table 250.66 Grounding Electrode Conductor
for Alternating-Current System
Size of Largest Ungrounded
Service-Entrance Conductor
or Equivalent Area for
Parrell Conductorsa
(AWG/kcmil)		 Size of Grounding
Electrode Conductor
(AWG/kcmil)
Copper Aluminum or
Copper-Clad
Aluminum		 Copper Aluminum or
Copper-Clad
Aluminum
2 or smaller 1 or smaller 8 6
1 or 1/0 2/0 or 3/0 6 4
2/0 or 3/0 4/0 or 250 4 2
Over 3/0
through 350		 Over 250
through 500
2
1/0
Over 350
through 600		 Over 500
through 900		 1/0 3/0
Over 600
through 1100		 Over 900
through 1750		 2/0 4/0
Over 1100 Over 1750 3/0 250
Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No.2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.
2. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.
 aThis table also applies to the derived conductors of seperately derived ac systems.
 bSee installation restrictions in Section 250-64(A).