Bonding Jumper Sizing (Supply-Side and Equipment)

The main / supply-side bonding jumper from Table 250.66 by the service conductor (with the 12.5% rule above 1100 kcmil copper / 1750 kcmil aluminum), and the equipment (load-side) bonding jumper from Table 250.122 by the overcurrent device, a full-size jumper in each parallel raceway. NEC 250.28 / 250.102; the AHJ governs.

Supply-side (main / system) jumper from Table 250.66 by the service conductor; above 1100 kcmil copper (1750 kcmil aluminum) it is at least 12.5% of the largest phase area, rounded up to a standard size (250.102(C)(1) / 250.28(D)). Equipment (load-side) jumper from Table 250.122 by the OCPD, a full-size jumper in each parallel raceway (250.102(D)).

NEC 2023 (NFPA 70). Sections 250.28(D), 250.102(C) and 250.102(D).

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: mode, material, service_kcmil, required_jumper

• 12.5% rule applies only where service phase conductors exceed 1100 kcmil copper / 1750 kcmil aluminum; the jumper is at least 0.125 x the largest phase areaNEC 250.102(C)(1)
• Equipment mode Table 250.122 by the overcurrent device, the same mapping as the equipment grounding conductor; a full-size jumper in each parallel racewayNEC 250.102(D)
• Table mapping only the threshold-to-size mapping is encoded, not a reproduced NFPA tableNEC Tables 250.66 / 250.122