Equipment Grounding Conductor Size Calculator
Enter the rating of the breaker or fuse protecting the circuit and get the minimum equipment grounding conductor from NEC Table 250.122, in copper or aluminum. Optional inputs apply the 250.122(B) proportional increase when the ungrounded conductors are upsized for voltage drop and flag the 250.122(F) rule for parallel raceways.
How to use this calculator
- Enter the rating of the overcurrent device (breaker or fuse) ahead of the equipment, and pick copper or aluminum for the grounding conductor.
- If the ungrounded conductors were increased in size (most often to hold voltage drop on a long run), check the 250.122(B) box and enter the required and installed conductor sizes.
- If the circuit conductors run in parallel across more than one raceway, check the 250.122(F) box to confirm a full-size ground goes in each raceway.
- Read the minimum grounding conductor. The notes show the table row used, any proportional upsize arithmetic, and the 250.122(A) cap when it applies.
NEC reference
Sizing follows NEC 2020 Table 250.122, which lists the minimum copper and aluminum equipment grounding conductor for each overcurrent-device rating (the left column is a "not exceeding" ceiling, so a nonstandard setting maps up to the next row). The tool also applies 250.122(B) (proportional increase when ungrounded conductors are upsized), 250.122(A) (the ground need not exceed the circuit conductors), and 250.122(F) (a full-size ground in each parallel raceway). Table 250.122 is unchanged across the 2017, 2020, and 2023 editions.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
NEC Table 250.122 minimum equipment grounding conductors
| OCPD rating (A) | Copper | Aluminum / copper-clad |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1000 | 2/0 | 4/0 |
| 1200 | 3/0 | 250 kcmil |
| 1600 | 4/0 | 350 kcmil |
| 2000 | 250 kcmil | 400 kcmil |
| 2500 | 350 kcmil | 600 kcmil |
| 3000 | 400 kcmil | 600 kcmil |
| 4000 | 500 kcmil | 750 kcmil |
| 5000 | 700 kcmil | 1250 kcmil |
| 6000 | 800 kcmil | 1250 kcmil |
Values from NEC 2020 Table 250.122 (identical in the 2017 and 2023 editions). The aluminum column is aluminum or copper-clad aluminum. Sizes are AWG unless marked kcmil.
The 250.122(B) upsize for voltage drop, worked out
When you increase the ungrounded conductors above the minimum ampacity, most often to keep voltage drop in check on a long feeder, NEC 250.122(B) says the wire-type equipment grounding conductor has to grow by the same proportion of circular-mil area. The base ground from the table is multiplied by the ratio of installed area to required area, then rounded up to a standard size.
Example: a 200 A feeder needs 3/0 copper (167,800 cmil) for ampacity but is run in 250 kcmil (250,000 cmil) for voltage drop. The ratio is 250,000 / 167,800 = 1.49. The Table 250.122 base ground for 200 A is 6 AWG (26,240 cmil), so the grounding conductor becomes 26,240 x 1.49 = 39,094 cmil, which rounds up to 4 AWG copper. Check the 250.122(B) box in the tool to run this on your own numbers.
EGC vs. grounding electrode conductor
These two are easy to mix up because both are "grounding" conductors sized from a 250-series table. The equipment grounding conductor (this tool, Table 250.122) bonds equipment and raceways back to the source so a ground fault clears the breaker; it is sized on the overcurrent-device rating. The grounding electrode conductor (Table 250.66) ties the grounded service to the earth electrode and is sized on the service-entrance conductor area. A 200 A service, for instance, calls for a 6 AWG copper equipment grounding conductor but a 4 AWG copper grounding electrode conductor. Size the electrode conductor with the Grounding Electrode Conductor Size Calculator.
Frequently asked questions
What size ground for a 100 amp subpanel?
A 100 A feeder to a subpanel uses an 8 AWG copper or 6 AWG aluminum equipment grounding conductor per NEC Table 250.122. The feeder to a separate structure or subpanel keeps the grounded (neutral) and equipment grounding conductors separate, so this ground wire is run in addition to the neutral.
What size ground wire for a 60 amp circuit?
10 AWG copper or 8 AWG aluminum. The same 10 AWG copper ground covers every overcurrent device from 21 A through 60 A, because Table 250.122 lists the rating "not exceeding 60 A" in one row.
Can the equipment grounding conductor be smaller than the neutral?
Usually yes. The equipment grounding conductor is sized from Table 250.122 on the breaker rating and is normally smaller than the ungrounded and grounded (neutral) conductors, which are sized for load current. It only has to match the circuit conductors when 250.122(A) caps it, never exceed them.
Does a metal raceway count as the ground?
It can. NEC 250.118 recognizes rigid metal conduit, intermediate metal conduit, EMT, and several other wiring methods as equipment grounding conductors in their own right, in which case a separate wire ground may not be required. This tool sizes the wire-type conductor per 250.118(1); confirm the wiring method your installation relies on.
Related calculators
- Grounding Electrode Conductor Size Calculator: the grounding electrode conductor (Table 250.66) from the service conductor size.
- Service Size Calculator: service disconnect, conductor, and grounding electrode conductor from a known load.
- Breaker Size Calculator: the overcurrent-device rating that indexes this table.
- Wire Size Calculator: size the ungrounded conductors and check voltage drop, then bring the sizes here for 250.122(B).
- Wire Gauge Calculator: minimum AWG for a required ampacity.
Studying for the licensing exam? Our own NEC Code Quickstart works all twelve exam calculations start to finish, each with the code reference. Also in paperback.
Running an electrical contracting business? Jobber handles scheduling, invoicing, and job management. Start a 14-day free trial.
For deeper NEC training on grounding and bonding, Mike Holt's NEC courses are the industry standard.
Working from the printed code? NEC code books and tab sets are available from Mike Holt.
This page contains affiliate links. ElectricalToolbox may earn a commission when you sign up or buy through them, at no additional cost to you.