Grounding and bonding sizes

Equipment grounding conductor — choose the breaker or fuse and copper or aluminium. If the circuit conductors were made bigger than the load needs (usually for voltage drop), tick the box and give the minimum size and the size installed: the EGC grows by the same ratio of circular mils (250.122(B)). Parallel raceways each get a full-size EGC (250.122(F)).

Service or supply conductors — the largest ungrounded service-entrance conductor (or a transformer’s secondary conductors), its material and how many parallel sets. The GEC and the bonding jumpers are sized from these.

Grounding electrode conductor — copper or aluminium and the electrode it runs to: rods, pipes and plates need no more than 6 AWG copper, a concrete-encased electrode no more than 4 AWG, a ground ring no more than the ring conductor; water pipe and building steel take the full Table 250.66 size.

Bonding jumpers — the main bonding jumper, a separately derived system’s system bonding jumper and supply-side bonding jumpers, from Table 250.102©(1) or 12.5 % of the area for very large services; with parallel sets in separate raceways, a jumper per raceway (250.102©(2)).

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Related: wire size and voltage drop, box fill, conduit fill, the shop power planner and the wire gauge table.

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