TradeToolsElectrical · in the TradeTools app
Grounding & Bonding Calculator
The equipment grounding conductor for a circuit, sized by the rating of the breaker or fuse ahead of it rather than by the load it carries — plus the grounding electrode conductor and bonding jumper sizing this same tool covers.
NEC Tables 250.122 · 250.66 · 250.102(C)(1)
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Worked example
60 A subpanel feeder on 6 AWG copper — does the ground have to be 6 AWG too?
| Conductor | Equipment grounding (EGC) |
|---|---|
| Material | Copper |
| Overcurrent device rating | 60 A |
| Conductors upsized for voltage drop | off |
| Conductor size | #10 AWG |
|---|---|
| Equivalent in the other material | #8 AWG |
| Code references | NEC Table 250.122 |
No — the equipment grounding conductor isn't sized to match the circuit's hot conductors. NEC Table 250.122 sizes it by the rating of the overcurrent device ahead of the circuit: a 60 A breaker or fuse calls for 10 AWG copper, or 8 AWG aluminum or copper-clad aluminum. Under 250.122(A), the equipment grounding conductor is never required to be larger than the circuit conductors it grounds.
How it's calculated
The table behind the number
The equipment grounding conductor is looked up in NEC Table 250.122 by the rating of the breaker or fuse protecting the circuit, in the material selected — not by the ampacity of the circuit's hot conductors and not by the connected load. If the ungrounded conductors have been upsized for a reason other than the temperature or conductor-count adjustments of 310.15(B)/(C) — most often to control voltage drop — the equipment grounding conductor grows proportionately to the increase in circular-mil area, under 250.122(B); this tool's voltage-drop toggle applies that adjustment when it's switched on.
- NEC 2023 Table 250.122Minimum size equipment grounding conductors, by the rating of the circuit's overcurrent protective device — 60 A: 10 AWG copper or 8 AWG aluminum/copper-clad aluminum
- NEC 250.122(A)The equipment grounding conductor is sized by the overcurrent device ahead of the circuit, not by the load, and is never required to be larger than the circuit conductors supplying the equipment
- NEC 250.122(B)If the ungrounded conductors are upsized for a reason other than 310.15(B)/(C) adjustments, wire-type equipment grounding conductors grow proportionately to the circular-mil area of the ungrounded conductors
Questions
Before you trust the number
Does the ground wire have to be the same size as the hot conductors?
No. An equipment grounding conductor is sized from NEC Table 250.122 by the rating of the breaker or fuse ahead of the circuit, and under 250.122(A) it's never required to be larger than the circuit conductors supplying the equipment — a 6 AWG hot doesn't call for a 6 AWG ground.
What sizes the equipment grounding conductor, if not the load?
The rating of the overcurrent protective device — the breaker or fuse — ahead of the circuit. A 60 A OCPD calls for 10 AWG copper or 8 AWG aluminum from Table 250.122, whatever the connected load actually draws.
Does a subpanel feeder use a different table?
No — a feeder to a subpanel is sized the same way, by Table 250.122 and the rating of the overcurrent device protecting that feeder.
When does the ground wire have to grow?
When the hot conductors are upsized for a reason other than the ambient-temperature or conductor-count adjustments — typically to control voltage drop. NEC 250.122(B) then increases the equipment grounding conductor proportionately to the circular-mil area of the hots.