Conductor Size Calculator
Choose the US NEC or the IEC standard. For the NEC, enter the breaker or fuse rating and the material. For IEC, enter the phase conductor size in mm². The calculator gives the grounding or protective conductor size.
- NEC Table 250.122
- IEC 60364 Table 54.2
- Copper or aluminium
Under the NEC, use the breaker rating. Under IEC, use the phase conductor size. The other field is ignored.
The grounding conductor carries fault current long enough for the breaker to trip. Because it only carries current for a moment, it can be much smaller than the circuit wires. The NEC sizes it from the breaker rating, while IEC rules size it from the phase conductor.
Grounding conductor chart
NEC Table 250.122. Search for a rating.
| Breaker up to (A) | Copper | Aluminium |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 60 | 10 AWG | 8 AWG |
| 100 | 8 AWG | 6 AWG |
| 200 | 6 AWG | 4 AWG |
| 300 | 4 AWG | 2 AWG |
| 400 | 3 AWG | 1 AWG |
| 600 | 1 AWG | 2/0 AWG |
| 800 | 1/0 AWG | 3/0 AWG |
| 1000 | 2/0 AWG | 4/0 AWG |
Copper and aluminium sizes for the equipment grounding conductor.
Breaker rating and conductor
Copper. Slide the breaker rating.
The green core is the grounding conductor, drawn to scale against the circuit wires.
How to size a grounding conductor
From the breaker. Step through it.
Breaker rating
Of the circuit.
The grounding conductor never needs to be larger than the circuit conductors it runs with.
Grounding, bonding or grounding electrode
Conductor types. Compare them.
Runs with the circuit.
Joins metal parts.
To the earth rod.
The grounding electrode conductor to the earth rod or water pipe is sized from a different table, NEC 250.66.
Before wiring
Earth checks. Tick each item.
Tick each item as you go.
Conduit or armoured cable can count as the grounding path in some cases, but a separate wire is the safest choice.
What you get
Grounding size. Each tile explains one result.
AWG or kcmil.
mm².
Copper or aluminium.
Table row.
For voltage drop.
In parallel runs, each raceway needs its own full-size grounding conductor.
Frequently Asked Questions
No question matches that search.
What size ground wire do I need for a hundred amp breaker?
8 AWG copper or 6 AWG aluminium, from NEC Table 250.122.
How is a grounding conductor sized?
Under the NEC, by the rating of the breaker or fuse protecting the circuit.
Does the ground wire need to be the same size as the hot wires?
No. It is usually smaller, but never needs to be larger.
What if I upsize wires for voltage drop?
Upsize the grounding conductor by the same proportion.
How is the earth conductor sized under IEC rules?
The same as the phase up to 16 mm², 16 mm² up to 35 mm², then half the phase size.
What is the difference between grounding and bonding?
Grounding connects equipment to earth. Bonding joins metal parts so they stay at the same voltage.
Can I use aluminium for grounding?
Yes, but it must be one size larger than copper.
A safe path for fault current
Size the grounding conductor from the breaker or the phase conductor, upsize it with the circuit if needed and keep it with the circuit all the way.
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