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

Units

Largest ungrounded conductor the GEC is associated with.

A

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

Terms of Service

Results

Please tick the box above to display the Result.

Engineering methodology

Two different conductors. The grounding electrode conductor (GEC) runs to the electrode. Under NEC 250.166 it is not smaller than the largest supplied conductor, not smaller than 8 AWG copper, and need not be larger than 3/0. The “rod, pipe or plate (sole connection)” choice adds the 250.166(C) cap: the GEC need not be larger than 6 AWG copper, so it is 8 AWG with small circuit conductors and 6 AWG once the largest conductor reaches 6 AWG. The narrower exemptions for a concrete-encased electrode (250.166(D) caps it at 4 AWG) and a ground ring (250.166(E) caps it at the ring conductor) are not implemented, so those electrodes may be oversized here. The equipment grounding conductor (EGC) follows a simplified NEC Table 250.122 by overcurrent-device rating. Metric mm² inputs are mapped up to the first AWG at least as large (25 mm² counts as 2 AWG), because the GEC must not be smaller than the conductor; displayed mm² are AWG equivalents, not an IEC 60364-5-54 earthing table.

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 a fault to a metal case has a path back to the source and the OCPD opens. 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 it is the sole connection 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. It is a cap, not a fixed size: with circuit conductors of 8 AWG or smaller the general 8 AWG minimum applies.

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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