Off-Grid Solar Calculators

Wiring and electrical safety

Grounding Rod & Wire Sizer

Two different conductors. The grounding electrode conductor (GEC) runs to the rod or other electrode. The equipment grounding conductor (EGC) follows the circuit so metal cases have a fault path.

Inputs

Largest ungrounded conductor the GEC is associated with.

A

Fuse or breaker rating used to pick the EGC from Table 250.122.

Results

GEC (to the electrode)
6 AWG
EGC (with the circuit)
10 AWG

Recommended gear

Engineering methodology

Two different conductors. The grounding electrode conductor (GEC) runs to the electrode. For a rod, pipe or plate used as the sole connection, NEC 250.166(C) says the GEC need not be larger than 6 AWG copper. For other electrodes the GEC is not smaller than the largest supplied conductor, not smaller than 8 AWG, and need not be larger than 3/0. The equipment grounding conductor (EGC) follows a simplified NEC Table 250.122 by overcurrent-device rating.

Frequently asked questions

What is the difference between a GEC and an EGC?

The GEC connects the system to the grounding electrode (rod, pipe, plate, ring). The EGC runs with the circuit so metal cases have a fault path back to the source so the OCPD can open. This tool sizes both; it does not design the whole grounding-electrode system.

Why is a ground-rod GEC capped at 6 AWG copper?

NEC 250.166(C): where connected to a rod, pipe or plate electrode, the GEC need not be larger than 6 AWG copper. A 4/0 battery cable does not force a 4/0 GEC to a single rod.

Does Table 250.122 apply to DC off-grid systems?

EGC sizing by OCPD rating is the usual NEC approach this tool copies in simplified breakpoints. DC bonding of negative, chassis and AC equipment grounds is a separate design choice for a qualified electrician.

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