(a) A conductor for grounding a direct-current system must be the larger of:

(1) The largest conductor supplying the system; or

(2) No. 8 AWG (8.4mm2).

(b) A conductor for grounding the neutral of an alternating-current system must meet Table 111.05-31(b).

Table 111.05-31(b)—Neutral Grounding Conductor for Alternating-Current System

Open Table
Size of the largest generator cable or equivalent for parallel generators—AWG-MCM (mm2) Size of the system grounding conductor—AWG(mm2)
Greater than Less than or equal to
2 (33.6) 8 (8.4)
2 (33.6) 0 (53.5) 6 (13.3)
0 (53.5) 3/0 (85.0) 4 (21.2)
3/0 (85.0) 350 MCM (177) 2 (33.6)
350 MCM (177) 600 MCM (304) 0 (53.5)
600 MCM (304) 1100 MCM (557) 2/0 (67.5)
1100 MCM (557)     3/0 (85.0)

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