Equipment Grounding Conductor: EGC Sizing
An equipment grounding conductor is the conductive fault-current path that connects equipment metal parts to the source so an overcurrent device can open during a ground fault.
The EGC is often called the ground wire, but its job is not to carry normal load current or make earth clear a fault. It provides a low-impedance fault-current path back to the source so the OCPD can operate.
Fault path, not normal return path
The equipment grounding conductor bonds equipment metal parts into an effective fault-current path.
Under normal operation it should not carry load current. Its purpose is to help a ground fault create enough current to open the OCPD.
How the starting size is selected
The usual starting point is the rating or setting of the upstream OCPD.
That rating maps to a minimum copper or aluminum EGC size. The load current alone does not choose the EGC size.
Fill, derating and raceway boundaries
The EGC counts for conduit fill because it occupies physical area in the raceway.
It is not counted as a current-carrying conductor for ampacity adjustment. Metal raceways, cable armor, bonding jumpers and grounding electrode conductors follow different rules.
Where the Term Decides Something
Four points in the work where the figure is the answer to a question, not vocabulary.
Sizing a branch-circuit EGC
Start with the rating of the OCPD ahead of the circuit and select the minimum copper or aluminum wire-type EGC size from the sizing table.
Sizing a subpanel feeder
For a feeder, the EGC is separate from the neutral downstream of the service bonding point. The feeder breaker rating sets the starting EGC size.
Reviewing voltage-drop upsizing
When ungrounded conductors are larger than the minimum size needed for ampacity, a wire-type EGC may need a proportional increase.
Calculating conduit fill
The EGC counts as a conductor for raceway fill area even though it is not counted as a current-carrying conductor for ampacity adjustment.
Which Figure to Use
Reading the term correctly in practice.
Size from the OCPD, not the load
The table input is the rating or setting of the overcurrent device ahead of the circuit, not the calculated load current by itself.
Do not confuse EGC and neutral
A neutral can carry normal return current. An EGC is a fault-current path and is kept separate from neutrals downstream of service bonding points.
Revisit EGC after conductor upsizing
If ungrounded conductors are upsized for voltage drop or another reason beyond minimum ampacity, check whether the wire-type EGC must increase proportionally.
Confirm the grounding path type
Some metal raceways and cable assemblies can serve as the EGC when installed as permitted. The sizing chart is for wire-type equipment grounding conductors.
FAQs
Is the equipment grounding conductor the same as the neutral?
How is an EGC sized?
Does the ground wire count in conduit fill?
When do I upsize the EGC for voltage drop?
Calculated against the NEC 2023 edition using Article 100, 250.4(A)(5), 250.118, 250.122, 250.122(B). Confirm the edition adopted by your AHJ, which may differ and may carry local amendments.
Not covered by this tool
- Grounding electrode conductor sizing and bonding jumper sizing.
- Metal raceway installation quality, continuity fittings and listed cable armor rules.
- Fault-current study, clearing-time analysis and utility grounding requirements.
Data last verified