EGC (Equipment Grounding Conductor)

NEC 250.122 is the table that sets equipment grounding conductor (EGC) size, and it is the rule solar permit designers and electricians apply on every PV circuit. This entry explains what an EGC does, gives the 250.122 sizing table, and shows how NEC 690.45 applies it to solar arrays.

What is an EGC in electrical and solar systems?

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. NEC 690.45 points PV circuits back to the same table. Where a PV circuit has no overcurrent device, the designer sizes the EGC from an assumed OCPD rating per 690.9(B).

NEC 250.122 table: EGC size by OCPD rating

Key Takeaways

• EGC = safety grounding conductor.
• Sized per NEC 250.122 by OCPD rating.
• Bonds all metallic equipment to ground.
• NEC 690.45 applies Table 250.122 to PV circuits, using an assumed OCPD where none exists.
• Upsizing the EGC for voltage drop is not required on PV 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.