Equipment Grounding Conductor Troubleshooting

EGC Problems Quick Answer

Use this when an inspector red-tags the green wire, a receptacle tester shows open ground, or plan review rejects a size that “matches” the phase conductors.

1. Inspector Rejects an EGC That “Should” Pass

What it looks like: Plan or pull ticket shows a ground matching the phase conductors (or matching “what we always pull”). Calculator or table row for a different ampacity looks fine. Inspector cites undersized equipment grounding conductor against the breaker on the schedule.

Why it happens: Table 250.122 is keyed to the rating or setting of the automatic overcurrent device ahead of the equipment — not to ungrounded conductor ampacity and not to “whatever AWG is on the spool.” Crews habitually match green to black/red. That overshoots sometimes and undershoots when phase wire is smaller than the OCPD allows, or when someone used the ampacity of the wire instead of the handle rating.

Likely causes checklist:

• Wrong OCPD used as the sizing basis — looked up 60 A because the feeder is “60-amp wire,” but the breaker is 100 A (or vice versa).
• Schedule vs field mismatch — drawings say 60 A; panel got a 70 A or 100 A device after a late change.
• Parallel conductor blind spot — one EGC sized for a single set while phases are parallel; 250.122(F) applies in addition to the table minimum.
• Tap / motor / equipment special rules — Article 430 or tap rules change which OCPD “ahead of the equipment” actually governs.

Fixes:

• Stand at the panel: read the handle or fuse label that protects this run. That number is the Table 250.122 input.
• Re-run the EGC Calculator with that OCPD and copper/aluminum as installed.
• If phases are parallel, size EGCs per 250.122(F) — do not assume one green for the bank is enough.
• Document OCPD rating on the as-built next to EGC size so the next change order does not orphan the ground.

2. Confusing EGC with GEC (250.122 vs 250.66)

What it looks like: Branch or feeder ground sized from Table 250.66 (service conductor / electrode rules), or a fat conductor to a ground rod treated as if it replaces the green wire in the raceway. Subpanel “grounded” with a local rod and no EGC back to the source. Plan review asks why Table 250.66 appears on a 60 A feeder ground.

Why the names collide: Both say “grounding.” They do different jobs with different inputs.

• EGC (equipment grounding conductor) — runs with circuit conductors; bonds equipment; returns fault current to the source so the OCPD opens; sized from Table 250.122 by OCPD rating.
• GEC (grounding electrode conductor) — connects the grounded service conductor / bonding system to electrodes (rods, Ufer, water pipe at the service); sized from Table 250.66 by largest ungrounded service conductor (with electrode-type caps).

A #6 to a ground rod does not clear a branch-circuit fault the way a correctly sized EGC back to the panel does. Earth is a poor return path; the EGC is the intentional low-impedance path. Conceptual fork: Grounding vs Bonding Explained. Electrode sizing: GEC Calculator and GEC Guide.

Fixes:

• Ask: “Is this wire returning fault current with the circuit, or tying the service to electrodes?” That single question picks 250.122 vs 250.66.
• Never substitute a rod conductor for the EGC in a feeder or branch. Subpanels need the EGC (or metallic raceway acting as EGC where allowed) back to the supply — not a local rod alone.
• If someone already pulled 250.66 sizes on a branch schedule, re-size with the EGC Calculator and leave GEC work at the service.

3. Multiple Circuits Sharing a Conduit — Wrong EGC for the Bank

What it looks like: One equipment grounding conductor in a raceway that holds several circuits with different breaker ratings. Installer sized the ground for the smallest circuit, or for “a typical 20 A.” Inspector or engineer requires the EGC sized from the largest overcurrent device protecting conductors in that raceway when the installation method demands it — a common miscount on multi-circuit EMT and PVC pulls.

Why it bites: A single EGC serving multiple circuits must be adequate for the worst-case fault clearing duty those circuits present. Pulling a 14 AWG ground because “most of these are 15 A lighting” fails when a 60 A or 100 A circuit shares the same conduit and relies on that EGC path.

Likely causes:

• Takeoff counted conductors but not OCPD ratings per circuit in the raceway.
• Assumed cable-assembly logic (each NM cable has its own ground) still applies inside a multi-circuit conduit pull with one green.
• Added a larger circuit later without upsizing the shared EGC.

Fixes:

• List every OCPD that protects conductors in the raceway. Size the shared EGC from the largest applicable rating per Table 250.122 (and any parallel / upsizing rules that apply).
• When circuits are added, re-check the shared ground — the new breaker may become the controlling OCPD.
• Prefer dedicated EGCs per circuit set when logistics allow; shared grounds demand stricter bookkeeping.

4. Missed 250.122(B) After Voltage-Drop Upsizing

What it looks like: Phase conductors jumped from 10 AWG to 6 AWG (or larger) for a long run. Breaker still 30 A or 60 A. Ground left at the Table 250.122 minimum for that OCPD. Plan reviewer marks 250.122(B). Field “passes” the calculator’s base row and fails the proportional increase.

Why it happens: NEC 250.122(B) requires the EGC to increase in size proportionally when ungrounded conductors are increased in size for voltage drop (or similar reasons). The base table row is only the starting minimum. Upsizing phases without adjusting the EGC is one of the most frequent plan-check hits on long feeders and shop runs.

How to diagnose:

• Note minimum phase size for the circuit ampacity vs installed phase size (circular mils or AWG steps).
• Compute the upsizing ratio; apply it to the Table 250.122 EGC minimum for the OCPD.
• Round up to a standard size that meets or exceeds the proportional result.

Fixes:

• Re-size EGC after any intentional phase upsizing — same change order that grows the hots should grow the green.
• Use the Advanced Voltage Drop Calculator to justify the phase size, then return to the EGC Calculator / 250.122(B) math for the ground.
• Note both OCPD and upsizing ratio on drawings so inspection compares three numbers: breaker, phase, EGC.

5. Bonding Jumper / EGC Continuity Failures (Calc Cannot Catch)

What it looks like: Table size is correct. Outlet tester shows open ground. Metal box or equipment frame is hot to a known ground under fault or shows unexpected voltage. Continuity from device yoke to panel ground bar is open or high-resistance. Paint, powder coat, or corrosion under a ground lug. Missing bonding bushing / jumper at a concentric knockout. Plastic box with no ground pigtail to the device.

Why sizing tools are silent: The calculator answers “how big.” Continuity answers “is the path actually there?” An undersized wire fails math; a painted lug fails physics while the takeoff looks perfect.

Likely causes:

• Paint, powder coat, or rust under set-screw lugs and ground bars — metal-to-metal contact never made.
• Missing equipment bonding jumper at metallic boxes, reducing washers, or eccentric/concentric knockouts where required.
• Cut or pushed-back bare ground in NM; stab-back devices with loose ground clips; open ground in daisy-chained receptacles.
• Corroded Al EGC terminations without listed connectors / inhibitor where required.
• Flexible whip or cord with ground smaller than Table 250.122 for the supply OCPD — or ground pin never landed.

Fixes:

• De-energize safely. Continuity-test from equipment ground terminal to the supplying panel ground bar. Investigate any open or high reading before chasing “wrong AWG.”
• Clean lug lands to bare metal; torque to listing; use antioxidant on Al where the connector listing requires it.
• Install required bonding jumpers / bushings at metallic enclosures; verify box-to-device ground path.
• Screen receptacles with a known-good tester, then verify upstream with a meter — open ground at the last device often starts two boxes back.