Grounding Electrode Conductor Sizing

With the 250.66(A)-(C) electrode caps applied: a rod/pipe/plate sole connection need not exceed 6 AWG copper, a concrete-encased (Ufer) 4 AWG copper, while a water-pipe or structural-steel electrode takes the full table size. The AHJ-adopted edition governs.

GEC from NEC Table 250.66 by the largest ungrounded service conductor (or equivalent parallel area), then the 250.66(A)-(C) electrode caps: rod/pipe/plate sole connection not larger than 6 AWG copper / 4 AWG aluminum; concrete-encased not larger than 4 AWG copper; ground ring not smaller than the ring conductor and not smaller than 2 AWG; water-pipe / structural-steel electrode takes the full table size.

NEC 2023 (NFPA 70). Section 250.66 and Table 250.66.

Free read-only access at nfpa.org/freeaccess.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: service_kcmil, material, electrode_type, required_gec, base_gec

• Table mapping only the threshold-to-size mapping is encoded (the egc-sizing / wire-ampacity precedent), not a reproduced NFPA tableNEC Table 250.66
• Electrode caps 250.66(A) rod/pipe/plate, 250.66(B) concrete-encased, 250.66(C) ground ring; the cap is the smaller of the table size and the electrode limitNEC 250.66(A)-(C)
• Material the chosen material sizes both the service-conductor column and the GEC; copper defaultuser input