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.
Formula and source
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).
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