How is an equipment grounding conductor sized?

Start with the overcurrent device, then account for conductor upsizing and local requirements.

Build an effective ground-fault current path as a complete system. Start with the protective device, then verify conductor sizing, raceway continuity, bonding, parallel paths, terminations, and any phase-conductor upsizing against the adopted code and equipment instructions.

Sizing starts with: The circuit overcurrent-protective-device rating
System objective: A permanent, continuous, low-impedance fault-current path
Final check: Adopted NEC edition, local amendments, listings, and AHJ

1. Record the circuit and wiring method

Record the protective-device type and rating, system voltage, conductor material and sizes, terminal ratings, and the equipment being supplied.
Identify every part of the fault-current path: wire-type equipment grounding conductor, metal raceway or cable armor, boxes, fittings, enclosures, flexible sections, bonding jumpers, and equipment terminals.
Note parallel raceways, separately derived systems, service equipment, feeders to separate structures, and any location where special bonding rules may apply.
Confirm whether ungrounded conductors were increased in size for voltage drop, derating, standardization, or another design reason.

2. Establish the sizing basis

Use the locally adopted NEC edition to establish the baseline equipment-grounding-conductor size from the rating or setting of the protective device ahead of the equipment.
Evaluate the adopted rule for proportional adjustment when ungrounded conductors are increased beyond the size that would otherwise be required.
For parallel installations, verify the required equipment grounding path in every raceway or cable and do not divide a required conductor size by the number of parallel paths without an applicable rule.
Check equipment listings and manufacturer instructions for terminals, bonding hardware, conductor ranges, and any supplemental grounding provisions.

3. Evaluate the physical fault path

Trace the path from the equipment enclosure back to the source bonding point; identify loose joints, concentric or eccentric knockouts, reducing washers, flexible raceway, painted surfaces, corrosion, and nonmetallic sections.
Verify fittings and raceways are listed for the wiring method and installed in a way that preserves electrical continuity.
Where a wire-type conductor is used, protect it from damage, route it with the circuit conductors, and terminate it with listed hardware at every required enclosure and device.
Treat an auxiliary grounding electrode or isolated-ground conductor as a special design feature; neither substitutes for the required effective fault-current path.

4. Install and document terminations

Prepare conductors and contact surfaces as the manufacturer directs; use compatible lugs, connectors, screws, bushings, and bonding jumpers.
Apply listed torque values with an appropriate tool and record critical terminations when the project procedure requires it.
Keep grounded conductors and equipment grounding conductors separated downstream of the system bonding point unless a specific rule requires otherwise.
Update one-lines, panel schedules, conductor records, and inspection notes so the sizing basis and bonding points are unambiguous.

5. Verify before turnover

Under the project’s approved safe-work procedure, inspect the complete route and confirm that covers, fittings, jumpers, and equipment grounding terminals are present and secure.
Use continuity or low-resistance testing only with equipment isolated as required and with an instrument and method suitable for the expected resistance range.
Confirm protective-device identification, conductor routing, neutral-to-ground separation, and the intended system bonding point.
Resolve discrepancies through the designer, manufacturer, inspector, or AHJ rather than treating a simple continuity beep as proof of adequate fault-current performance.

Common failure patterns

Sizing from normal load current instead of the upstream protective device.
Increasing phase conductors without evaluating the related equipment-grounding-conductor rule.
Assuming a metal raceway remains continuous through loose fittings, flexible sections, paint, corrosion, or field modifications.
Omitting the required path in one of several parallel raceways.
Creating an unintended neutral-to-ground connection downstream of the system bonding point.

Worked field example

Worked documentation example: feeder conductors increased for voltage drop

Record the feeder protective-device rating and determine the baseline phase-conductor and equipment-grounding-conductor sizes under the adopted edition.
Record the installed phase-conductor size and why it was increased.
Apply the adopted proportional-adjustment method, including conductor material and circular-mil basis where the rule requires it.
Check every parallel or flexible path, terminal range, raceway fitting, and equipment instruction.
Document the calculated basis and field-verified installation for review by the designer or AHJ.

What this proves: The protective-device table value is only the starting point. Upsizing, parallel paths, wiring methods, and termination details can change the required design and must remain traceable in the project record.

Verify before use

Official sources

Source set reviewed September 2026. Recheck the current adopted requirements before design, purchase, permit, or installation.

NFPA 70 — National Electrical Code ↗
Use the adopted edition for grounding and bonding, conductor sizing, wiring methods, and equipment rules.
OSHA — Control of Hazardous Energy ↗
Official overview of hazardous-energy control for service and maintenance work.