EGC (Equipment Grounding Conductor)

What the EGC Does

The Equipment Grounding Conductor is a dedicated bonding conductor, not a current-carrying conductor under normal operation. Every metallic part of the system that a technician could touch — module frames, racking rails, combiner box enclosures, conduit, and inverter chassis — gets bonded to it. If an ungrounded conductor ever faults to a metal frame or enclosure, the EGC gives that fault current a deliberately low-impedance path back to the source, which is what allows the overcurrent protective device (OCPD) to trip fast instead of leaving the equipment “live” at a dangerous touch voltage. This is why EGC sizing under NEC 250.122 is driven by the OCPD rating rather than by the load current the circuit normally carries, and why it sits alongside the broader grounding, bonding, and overcurrent requirements laid out across NEC 690 for grid-tied PV systems — the conductor only needs to survive briefly during a fault, not carry continuous current.

Worked Example

A rooftop PV source circuit is protected by a 20 A breaker at the combiner box. Per the NEC 250.122 table above, the minimum copper EGC for a 20 A OCPD is 12 AWG. If the same circuit is on a DC-coupled subarray where NEC 690.45(B) requires a larger conductor to account for solar-specific fault current considerations, the EGC gets upsized beyond the 250.122 minimum — the designer always checks both rules and uses whichever calls for the larger conductor.

NEC 250.122 EGC Sizing

Key Takeaways

• EGC = safety grounding conductor.
• Sized per NEC 250.122 by OCPD rating.
• Bonds all metallic equipment to ground.
• NEC 690.45(B) may require larger than 250.122 minimum.
• Always copper for solar source circuits.

Related Reading

EGC sizing rarely gets calculated in isolation — it sits next to conductor ampacity and conduit fill as one more line item on the same circuit schedule, since a designer has to confirm the current-carrying conductors, their derated ampacity, and the bonding conductor all fit correctly within the same raceway. On drawing sets, the EGC callout shows up directly on the one-line: our breakdown of solar SLD software and NEC 2023 auto-generation walks through how these grounding and bonding annotations get pulled onto the single-line diagram automatically rather than hand-drafted circuit by circuit. For projects where the EGC path runs through ground-mounted racking and piers rather than a rooftop, it’s worth cross-checking against the structural side too — see our pile foundation design guide for solar ground-mount for how grounding and structural bonding points interact on that racking type.