Ground Wire Size Calculator
// SIZE EQUIPMENT GROUNDING CONDUCTORS FROM THE OVERCURRENT DEVICE AND CHECK PROPORTIONAL UPSIZING WHEN PHASE CONDUCTORS ARE ENLARGED //
Use the rating or setting of the upstream breaker or fuse.
Smallest ungrounded conductor that would have satisfied ampacity.
Actual ungrounded conductor size installed in the circuit.
Shown as an installation reminder. Each raceway still needs its own EGC.
For a 100A device with a Copper grounding conductor, the base minimum is 8 AWG. Minimum phase size is 3 AWG, installed phase size is 3 AWG, so the recommended grounding conductor is 8 AWG.
Required grounding conductor area: at least 16,510 circular mils before rounding to the next standard size.
One raceway is selected. In parallel installations, each raceway or cable set normally carries its own full-sized equipment grounding conductor sized from the overcurrent device, not a divided share.
NEC Table 250.122 sizes the equipment grounding conductor from the breaker or fuse rating, not directly from the calculated load.
If ungrounded conductors are increased beyond the minimum size for ampacity, NEC 250.122(B) generally requires the equipment grounding conductor to be increased proportionately by circular-mil area.
This tool is a planning reference. Verify local amendments, conductor type limits, and installation-specific grounding rules before construction.
Voltage-drop corrections are the most common reason phase conductors are increased above their ampacity minimum.
When that happens, the grounding conductor often has to move up as well even if the breaker size does not change.
The proportional increase is based on conductor area, then rounded up to the next standard grounding conductor size.
Equipment grounding conductor sizing is different from grounding electrode conductor sizing and from neutral conductor sizing.
Small-conductor rules, flexible cords, service equipment, and separately derived systems can introduce exceptions not modeled here.
Use the related voltage-drop, ampacity, and conduit-fill tools to finish the rest of the wiring design check.
| Breaker / Fuse Rating | Copper EGC | Aluminum EGC |
|---|---|---|
| Up to 15A | 14 AWG | 12 AWG |
| Up to 20A | 12 AWG | 10 AWG |
| Up to 60A | 10 AWG | 8 AWG |
| Up to 100A | 8 AWG | 6 AWG |
| Up to 200A | 6 AWG | 4 AWG |
| Up to 300A | 4 AWG | 2 AWG |
| Up to 400A | 3 AWG | 1 AWG |
| Up to 500A | 2 AWG | 1/0 AWG |
| Up to 600A | 1 AWG | 2/0 AWG |
| Up to 800A | 1/0 AWG | 3/0 AWG |
| Up to 1000A | 2/0 AWG | 4/0 AWG |
| Up to 1200A | 3/0 AWG | 250 kcmil |
| Up to 1600A | 4/0 AWG | 350 kcmil |
| Up to 2000A | 250 kcmil | 400 kcmil |
| Up to 2500A | 350 kcmil | 600 kcmil |
| Up to 4000A | 500 kcmil | 800 kcmil |
| Up to 5000A | 700 kcmil | 1200 kcmil |
| Up to 6000A | 800 kcmil | 1200 kcmil |
Check if larger phase conductors are needed for long runs.
Confirm the minimum ungrounded conductor size for the load.
Verify raceway fill after adding the grounding conductor.
Run a broader feeder or branch-circuit sizing check.
Estimate resistance and loss on upsized conductors.
Estimate material weight for feeders and pull planning.