Chapter 10 The Service Entrance
177
• Rod or pipe electrodes that are at least 8′
long, fully driven into the ground or buried
not less than 4′ below the surface
• Metal plate of no less than 2 ft2 surface area
Where two or more grounding electrodes are
used, they should be separated by a distance of
6′ and bonded (linked with a copper conductor).
The resistance between the grounding electrode
and the earth must not exceed 25 ohms
Grounding Electrode
Conductor
The grounding electrode conductor con-
nects the grounding bus bar to the grounding
electrode. This conductor should provide little
resistance. For that reason, the conductor is
typically copper, aluminum, or copper-clad
aluminum. The grounding electrode conductor
must also be fi rmly attached to grounding elec-
trode using approved fi ttings, Figure 10-22. As
with all conductors involved in grounding, the
grounding electrode conductor must never be
interrupted.
Sizing the grounding electrode conductor
Table 250.66 of the NEC indicates the proper
sizes for the grounding electrode conductor.
This is based on the service entrance conductor
size. See Figure 10-23.
For example, the installation of a 200 A
service entrance using 3/0 AWG copper service
wires would require a 4 AWG copper grounding
electrode conductor.
Figure 10-22. Always fi rmly attach the grounding electrode conductor to the grounding electrode using approved
fi ttings.
Grounding Electrode Conductor Sizing
Size of Largest Service-Entrance Conductor
(AWG/kcmil)
Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-Clad Aluminum
Size of Grounding Electrode Conductor
(AWG/kcmil)
Copper
2 or smaller
1 or 1/0
2/0 or 3/0
Over 350 – 600
Over 600 – 1100
Over 1100
Over 3/0 – 350
1/0 or smaller
2/0 or 3/0
4/0 or 250
Over 250 – 500
Over 500 – 900
Over 900 – 1750
Over 1750
8
6
4
2
1/0
2/0
3/0
6
4
2
1/0
3/0
4/0
250
Figure 10-23. Refer to NEC Table 250.66 when determining the size of the grounding electrode conductor.