NEC 250.122 · Equipment grounding explained

How to size the equipment grounding conductor with NEC 250.122

Size by the breaker, not the wire — plus the proportional-upsizing, parallel-run, and motor-circuit rules that trip up inspections, with worked examples.

Need the actual numbers?

This page teaches you how to use NEC Table 250.122 — it deliberately does not reproduce the table. Look up Table 250.122 in the free NFPA 70 (NEC) online viewer (free NFPA account, read-only), or your printed code book (Article 250, Part VI).

Section numbers and values vary by NEC edition, and your jurisdiction may adopt an older edition or local amendments. The edition your AHJ enforces governs.

How to read Table 250.122, step by step

Step	What you do
1. Identify the OCPD	Find the rating of the breaker or fuse on the supply side of the circuit — the device that will have to clear a ground fault. Not the load current, not the wire size.
2. Find the row	Table 250.122 rows are "not exceeding" ratings. Go down the first column to the first row that is equal to or greater than your device rating.
3. Read the material column	Read the copper column or the aluminum / copper-clad aluminum column for the EGC material you are installing.
4. Apply the table footnote	The footnote reminds you that the EGC may need to be larger than the table to meet the fault-clearing requirement of 250.4(A)(5) / (B)(4) — usually a long-run or high-fault-current issue.
5. Apply 250.122(A)–(F)	Cap at the circuit conductor size (A); increase proportionally if the phase conductors were upsized (B); use the per-raceway rule for parallel runs (F); motor circuits use the motor short-circuit device rating (D).
6. Confirm the EGC type	If a raceway or cable armor is serving as the EGC, check 250.118 — some flexible wiring methods only qualify within length and OCPD limits.

Worked examples

Example	Inputs	Steps	Result
A. 100 A feeder, no upsizing	Copper conductors sized for ampacity, 100 A breaker.	Row for devices not exceeding 100 A, copper column: 8 AWG Cu per Table 250.122.	8 AWG Cu EGC
B. 20 A circuit upsized for voltage drop	20 A breaker; 12 AWG Cu would carry the load, but 10 AWG Cu was pulled for voltage drop.	Table minimum for 20 A is 12 AWG Cu. Area ratio of phase conductors: 10,380 cmil ÷ 6,530 cmil ≈ 1.59. Required EGC ≥ 6,530 × 1.59 ≈ 10,380 cmil (250.122(B)).	10 AWG Cu EGC
C. Parallel feeder in two conduits	Two parallel sets, one per conduit, one breaker protecting both.	Each conduit gets its own EGC sized from the full breaker rating — do not divide by the number of sets (250.122(F)).	Full-size EGC in each conduit

Table values are quoted only to illustrate the calculation. Circular-mil areas are the standard AWG conductor areas. Look up your own rating in the official table for your adopted edition.

Which rule applies?

Situation	Where to look
Ordinary branch circuit or feeder	Table 250.122 by the OCPD rating
Phase conductors upsized (voltage drop, future load, etc.)	250.122(B) — increase the EGC by the same circular-mil ratio
Parallel sets in separate raceways or cables	250.122(F) — a full-size EGC in each raceway, based on the OCPD protecting the whole set (not divided)
Motor branch circuit	250.122(D) — based on the rating of the motor short-circuit/ground-fault device, not the overload
Multiple circuits sharing one raceway	250.122(C) — one EGC sized for the largest OCPD of the circuits it serves
Service or separately derived system bonding to earth	Not an EGC question — that is the grounding electrode conductor (Table 250.66) or supply-side bonding jumper (250.102(C))

Common field mistakes

Mistake	What to do instead
Sizing the EGC from the phase conductor size	The table is keyed to the overcurrent device. Start there.
Upsizing phases for voltage drop but not the EGC	250.122(B) — grow the EGC by the same area ratio. A frequent inspection write-up.
Splitting the EGC across parallel raceways	Each raceway needs a full-size EGC per 250.122(F).
Using Table 250.66 for an equipment ground	250.66 is for grounding electrode conductors. Mixing up EGC and GEC is the classic grounding error.
Sizing a motor EGC from the overload	Use the motor short-circuit/ground-fault device rating (250.122(D)).
Relying on flex as the ground without checking limits	Flexible metal conduit and some fittings only count as the EGC within the length and OCPD limits of 250.118 — otherwise pull a wire-type EGC.

What changed between editions

Edition	What to know
2020 NEC	250.122(B) was reworded to tie the proportional increase to conductors increased beyond the minimum size that has sufficient ampacity for the installation — clarifying how upsizing interacts with correction and adjustment factors.
2023 NEC	Kept Table 250.122 and the 250.122(A)–(F) structure. Check the edition's change markers for revisions to the (B) wording and its exceptions.
2026 NEC and later	Being adopted state by state — confirm the table and subsection letters in the edition your AHJ enforces.

Orientation only — confirm in the edition your jurisdiction has adopted.

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When you need Table 250.122

The equipment grounding conductor (EGC) is the path that carries fault current back to the source so the breaker trips fast. Every branch circuit and feeder that needs one is sized from NEC Table 250.122, keyed to the rating of the overcurrent device ahead of the equipment.

The table is the minimum. The rules in 250.122(A) through (F) then modify it: never larger than the circuit conductors, proportionally larger when phases are upsized, full size in every parallel raceway, and motor circuits sized from the short-circuit device.

Grounding the service to earth is a different conductor — see the grounding electrode conductor (250.66) guide. For the phase conductors, see how to read NEC Table 310.16, and check long runs with the voltage drop calculator. Field PM keeps panel schedules, equipment lists, and inspection records together on the job.

FAQ

What size equipment grounding conductor for a 100 amp breaker?+

Per NEC Table 250.122, a circuit protected by a 100 A overcurrent device needs at least an 8 AWG copper equipment grounding conductor — unless the phase conductors were upsized, in which case 250.122(B) requires a proportional increase. For other ratings, look up Table 250.122 in the free NFPA viewer at nfpa.org/freeaccess.

Is the equipment grounding conductor sized by breaker or by wire size?+

By the rating of the overcurrent device (breaker or fuse) ahead of the equipment — not by the size of the ungrounded conductors. Two qualifiers: per 250.122(A) the EGC never has to be larger than the circuit conductors, and per 250.122(B) it must be increased proportionally if the ungrounded conductors are increased.

Do I upsize the ground wire if I upsize the conductors for voltage drop?+

Yes. When ungrounded conductors are increased above the minimum size needed for ampacity, 250.122(B) requires the EGC to be increased by the same ratio of circular-mil area. Example: going from 12 AWG to 10 AWG phase conductors on a 20 A circuit is a ratio of 10,380 ÷ 6,530 ≈ 1.59, so the 12 AWG EGC must grow to at least 10 AWG.

What is the difference between an EGC and the grounding electrode conductor?+

The equipment grounding conductor (EGC, Table 250.122) bonds equipment back to the source so faults trip the breaker; it is sized by the overcurrent device. The grounding electrode conductor (GEC, Table 250.66) connects the system to the earth electrode (rods, concrete-encased electrode, water pipe) and is sized by the service or derived-system conductor size. Different conductor, different table.

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