Ground Wire Size Calculator

Size the equipment grounding conductor from the breaker (NEC Table 250.122) or the grounding electrode conductor from the service conductors (Table 250.66). For AC NEC work only — not 12 V DC earthing, and not phase-wire ampacity.

Ground wire inputs

What are you sizing?

Breaker / fuse rating Amperes of the OCPD ahead of the circuit (example: 200)

EGC material

About this calculator

EGC size follows the overcurrent device. GEC size follows the service conductors, then may be capped by electrode type. Continue on the protection calculators hub after you size phase conductors.

Result

Planning estimate. Confirm the published NEC edition and local amendments before you pull wire.

Assumptions: wire-type EGC or GEC. Raceway used as the EGC is not sized here. Parallel service equivalent area is not auto-summed. This screen does not size phase conductors.

Continue Your Calculation

Next, size the ungrounded (phase) conductors for ampacity and length. Ground-wire size does not replace cable ampacity.

Cable size →

NEC ground wire quick tables

Same screening values as the calculator. EGC uses Table 250.122 (OCPD not exceeding). GEC uses Table 250.66 (largest ungrounded service conductor).

OCPD not exceeding	EGC copper	EGC aluminum
15 A	14 AWG	12 AWG
20 A	12 AWG	10 AWG
60 A	10 AWG	8 AWG
100 A	8 AWG	6 AWG
200 A	6 AWG	4 AWG
300 A	4 AWG	2 AWG
400 A	3 AWG	1 AWG
600 A	1 AWG	2/0 AWG
800 A	1/0 AWG	3/0 AWG
1200 A	3/0 AWG	250 kcmil

Largest Cu service conductor	GEC copper	GEC aluminum
2 AWG or smaller	8 AWG	6 AWG
1 or 1/0 AWG	6 AWG	4 AWG
2/0 or 3/0 AWG	4 AWG	2 AWG
Over 3/0 through 350 kcmil	2 AWG	1/0 AWG
Over 350 through 600 kcmil	1/0 AWG	3/0 AWG
Over 600 through 1100 kcmil	2/0 AWG	4/0 AWG
Over 1100 kcmil	3/0 AWG	250 kcmil

Rod/pipe/plate only: GEC not required larger than 6 AWG copper or 4 AWG aluminum (250.66(A)). Concrete-encased only: not required larger than 4 AWG copper (250.66(B)).

Formula & method

EGC: look up the overcurrent device in Table 250.122. If ungrounded conductors were increased for voltage drop, EGC_cmil = Table_EGC_cmil × (actual_phase_cmil ÷ minimum_phase_cmil), then round up to the next standard size (250.122(B)).

GEC: look up the largest ungrounded service-entrance conductor in Table 250.66, then apply electrode caps 250.66(A)/(B)/(C) when the conductor connects only to that electrode type.

Example: 200 A breaker → EGC 6 AWG copper. Same 200 A service with 2/0 copper feeders → GEC table size 4 AWG copper; to rods only → may stop at 6 AWG copper under 250.66(A).

200 amp ground wire worked example

Question	Answer on this page
EGC with a 200 A feeder / breaker	6 AWG copper or 4 AWG aluminum (250.122)
GEC from 2/0 Cu or 4/0 Al service (full table)	4 AWG copper or 2 AWG aluminum (250.66)
Same GEC to ground rods only	Not required larger than 6 AWG copper / 4 AWG aluminum (250.66(A))

Phase conductors for a 200 A dwelling service are a different task — use the cable size calculator (and the future 200 A service table on that page).

FAQ

What size ground wire is required for a 60-amp circuit?

For an equipment grounding conductor on a 60 A overcurrent device, NEC Table 250.122 requires 10 AWG copper or 8 AWG aluminum.

What size ground wire for a 200 amp service?

It depends which ground wire you mean. The EGC with a 200 A feeder is typically 6 AWG copper (Table 250.122). The GEC from a typical 2/0 copper or 4/0 aluminum 200 A service is 4 AWG copper by Table 250.66, but if that conductor connects only to ground rods, 250.66(A) does not require larger than 6 AWG copper.

What is the difference between an EGC and a GEC?

An equipment grounding conductor (EGC) runs with the circuit conductors and is sized from the breaker by Table 250.122. A grounding electrode conductor (GEC) bonds the service or separately derived system to earth electrodes and is sized from the service conductors by Table 250.66.

Does a ground rod always need 4 AWG copper?

No. NEC 250.66(A) says a GEC that connects only to rod, pipe, or plate electrodes is never required to be larger than 6 AWG copper or 4 AWG aluminum. Some local rules still require 4 AWG copper; that is an AHJ amendment, not the national rod cap.

Does this calculator size phase conductors?

No. Phase and neutral ampacity stay on the cable size calculator. This page only sizes EGC and GEC ground wires.