How to use this calculator
- Enter the upstream OCPD rating. Use the breaker or fuse protecting the branch circuit or feeder, not the connected load or downstream panel bus rating.
- Choose EGC material. Select copper or aluminum/copper-clad aluminum so the correct material column is used.
- Enter any upsize ratio. Leave 100% if the ungrounded conductors were not upsized, or enter the circular-mil ratio when they were enlarged for voltage drop.
- Compare selected size. Pick the proposed EGC size and review the suggested listed size, selected area margin and utilization.
How it works
Equipment grounding conductor sizing starts with the automatic overcurrent device ahead of the equipment. This page finds the first table row whose ampere rating is not less than the entered breaker or fuse rating, then uses the selected material column for the base EGC size.
CM_req = CM_table x R_up
R_up is the phase-conductor upsize ratio. Leave it at
100% when the ungrounded conductors are not upsized. If the
phase conductors were increased for voltage drop, enter the actual
circular-mil ratio so the required EGC area is increased proportionally.
Grounding Conductor Formula Worksheet
Use this worksheet to translate the grounding-conductor formula into the calculator inputs. It is for wire-type equipment grounding conductors, not grounding electrode conductors or service bonding design.
| Sizing question | Calculator input | Design read |
|---|---|---|
| What protects the circuit? | Upstream breaker or fuse rating | Selects the first equipment-grounding row at or above that rating. |
| Starting from transformer kVA? | Transformer kVA to OCPD context | Estimate source current first, then enter the actual breaker or fuse rating selected for the circuit. |
| What material is the EGC? | Copper or aluminum | Uses the matching material column for the base wire-type EGC size. |
| Were phase conductors upsized? | Conductor upsize percent | Converts voltage-drop upsizing into a circular-mil area multiplier. |
| What area is required? | CM_req = CM_table x R_up | Reports adjusted required area before picking the next listed size. |
| Does the selected wire pass? | Selected EGC size | Compares selected area with required area and reports margin/utilization. |
| Are there parallel raceways? | Parallel raceway count | Shows total installed area; each raceway still needs its own full EGC screen. |
Use this after checking voltage drop, ampacity derating, conduit fill and box fill. For breaker-led searches, use the ground wire size by breaker page. For motor feeders, pair it with motor full-load amps and motor overload sizing. If the search starts with source capacity, use the transformer kVA calculator to estimate current before entering the actual protective-device rating here.
Worked example
Verified against the live calculator
A 60 A breaker with a copper wire-type EGC uses the
60 A row and a base #10 copper EGC. If the
ungrounded conductors were upsized by 150% for voltage drop,
the required circular-mil area becomes 10,380 x 1.5 = 15,570 cmil,
so the next listed copper EGC size is #8 AWG.
Frequently asked questions
How do you size an equipment grounding conductor?
For a wire-type equipment grounding conductor, start with the upstream breaker or fuse rating, use the table row at or above that rating, then select the copper or aluminum EGC size for that row.
Do I size the EGC from load current or breaker size?
Use the rating or setting of the overcurrent device ahead of the equipment, not the normal load current. A 150 A feeder breaker, for example, uses the row that covers 150 A.
Can I size a grounding conductor by transformer kVA?
Transformer kVA can help estimate full-load current and protective-device context, but this calculator still starts from the actual upstream breaker or fuse rating. Use the transformer kVA calculator first if current is unknown, then enter the selected OCPD rating here.
What if the phase conductors were upsized for voltage drop?
Enter the actual circular-mil upsize ratio. If the ungrounded conductors are doubled in area compared with the minimum required area, enter 200% so the EGC is proportionally increased.
Is this the same as a grounding electrode conductor?
No. This page is for equipment grounding conductors run with branch circuits or feeders. Grounding electrode conductors use different rules and are intentionally not modeled here.
Does this approve the installation?
No. It is a code-style sizing screen. The adopted code edition, local amendments, wiring method, equipment listing, conductor restrictions and AHJ interpretation still control the final installation.
Method & assumptions
- Models wire-type equipment grounding conductors for branch circuits and feeders.
- Uses the upstream breaker/fuse rating and the next table row at or above that rating.
- Proportional upsizing uses circular-mil area, not ampacity or diameter.
- Parallel raceways are shown as total installed area only; each raceway still needs the full per-raceway EGC screen.
- Does not size grounding electrode conductors, bonding jumpers, service conductors, conductor ampacity, short-circuit protection or permit-ready installations.