NEC 250.122 Equipment Grounding Conductor Lookup
NEC 250.122 is the starting reference for sizing wire-type equipment grounding conductors based on the rating or setting of the overcurrent protective device protecting the circuit. Use it after the breaker or fuse basis is known and before assuming the grounding conductor still fits the raceway or cable plan.
| Field Item | NEC Reference | Field Meaning |
|---|---|---|
| Overcurrent device basis | NEC 250.122(A) | The equipment grounding conductor is generally sized from the rating or setting of the circuit overcurrent protective device. Use the Breaker Size Calculator when the OCPD basis needs to be checked first. |
| Minimum wire-type EGC size | NEC 250.122 | The table provides a minimum equipment grounding conductor size tied to the upstream breaker or fuse rating. Do not reproduce the table from memory in the field. |
| Copper or aluminum grounding conductor | NEC 250.122 table context | Material matters. A copper EGC and aluminum EGC are not interchangeable without checking the applicable table basis and installation suitability. |
| Ungrounded conductor upsizing | NEC 250.122(B) | When ungrounded conductors are increased in size, wire-type equipment grounding conductors may also need proportional upsizing by circular mil area. This often appears after Voltage Drop Calculator review. |
| Parallel raceways or cable sets | NEC 250.122(F) | Parallel installations need a separate grounding review for each raceway or cable set instead of assuming one grounding conductor covers every path. |
| Approved EGC path | NEC 250.118 | Wire-type grounding conductors are not the only possible equipment grounding path. Raceway type, fittings, cable assembly, and equipment instructions still matter. |
| Raceway fill handoff | NEC Chapter 9 | A bare or insulated equipment grounding conductor still occupies physical raceway area and must be included in NEC Chapter 9 Conduit Fill Tables review where applicable. |
Field Workflow
EGC Sizing Workflow
Treat NEC 250.122 as a grounding-conductor sizing checkpoint after the upstream overcurrent device is known. The rule does not replace conductor ampacity, breaker sizing, voltage-drop review, raceway fill, or equipment grounding path verification.
Identify the OCPD. Start from the breaker or fuse rating protecting the circuit; do not size the EGC from load amps alone.
Check EGC material. Confirm whether the grounding conductor is copper, aluminum, bare, insulated, or part of an approved wiring method.
Review conductor upsizing. If ungrounded conductors were increased for voltage drop or another reason, check whether the EGC also needs proportional upsizing.
Verify raceway fit. Include the grounding conductor in physical raceway fill review and check the grounding path for the actual installation method.
Voltage-Drop Upsizing
Voltage-Drop Upsizing
When ungrounded conductors are increased in size, NEC 250.122(B) can require a wire-type equipment grounding conductor to be increased proportionately. This is why a voltage-drop upsizing decision needs a grounding review before the raceway plan is trusted.
The grounding conductor does not stay frozen automatically. A larger phase conductor for voltage drop may create an EGC upsizing check even when the breaker size did not change.
The OCPD still sets the minimum table basis. NEC 250.122 starts from the overcurrent device rating, then the upsizing review adds another step when the ungrounded conductors were increased.
Grounding Path Review
Grounding Path Review
NEC 250.122 helps size wire-type equipment grounding conductors, but the installed grounding path still has to match the wiring method, raceway, fittings, cable assembly, equipment instructions, and local inspection requirements.
Conduit fill is a separate physical check. A grounding conductor may not count as a current-carrying conductor for ampacity adjustment in many common cases, but it still occupies raceway area and can change pull conditions.
Field Sequence
OCPD rating → EGC material → upsizing check → grounding path → conduit fill
If the breaker, phase conductor size, wiring method, or raceway changes, rerun the EGC and fill checks before relying on the field plan.
Field Example
EGC Sizing and Voltage-Drop Upsizing
If a circuit starts with a 60 amp overcurrent device, NEC 250.122 starts the wire-type equipment grounding conductor from the OCPD basis. If the ungrounded conductors are later upsized for voltage drop, the EGC may also need proportional upsizing before the raceway fill result is trusted.
- Step 1: size the EGC from the circuit OCPD rating or setting.
- Step 2: if phase conductors are upsized for voltage drop, recheck the EGC upsizing requirement.
- Step 3: include the final bare or insulated EGC size in conduit fill and box-fill review where applicable.
Calculator Use
TradeHub Calculator Application
Use the OCPD rating or setting as the starting point for NEC 250.122 EGC sizing, then recheck voltage-drop upsizing, raceway fill, and conductor selection.
Related TradeHub Calculators
Field Checks
Common Field Misses
Sizing from load amps instead of OCPD rating. The equipment grounding conductor review starts from the protective device basis, not just the calculated load.
Forgetting voltage-drop upsizing. Larger ungrounded conductors may require proportional EGC upsizing even when the breaker size stays the same.
Ignoring the EGC in conduit fill. Bare or insulated grounding conductors still occupy raceway area and can change the raceway fill result.
Assuming the raceway path is automatically acceptable. Metal raceways, fittings, boxes, concentric knockouts, and equipment instructions still need installation-specific grounding review.
Changing breaker size without revisiting the EGC. Any OCPD change can change the minimum equipment grounding conductor basis.
RELATED REFERENCES
Related NEC Field References
Source Scope
Source Alignment and Use Scope
This NEC 250.122 page is a field reference based on equipment grounding conductor sizing, NEC 250.122(B) upsizing review, NEC 250.118 grounding path context, and Chapter 9 raceway fill handoff. It is for screening and planning only; it does not replace the adopted NEC, local amendments, equipment markings, manufacturer instructions, engineered design documents, or AHJ review. Review the TradeHub Code Citation & Source Log for source alignment records and the TradeHub Methodology page for how field references are scoped.
FAQ
Equipment Grounding Conductor FAQ
Is an equipment grounding conductor sized from load amps or breaker size?
For NEC 250.122 field checks, the equipment grounding conductor is generally sized from the rating or setting of the overcurrent protective device protecting the circuit, not from the calculated load alone.
Does voltage-drop upsizing require a larger equipment grounding conductor?
When ungrounded conductors are increased in size, NEC 250.122(B) requires wire-type equipment grounding conductors to be increased proportionately by circular mil area where that rule applies.