Overview
The grounding and bonding calculator sizes two distinct types of grounding conductors:
Equipment Grounding Conductor (EGC): The conductor that provides a fault return path from equipment back to the source. Sized per NEC Table 250.122 based on the ahead OCPD rating.
Grounding Electrode Conductor (GEC): The conductor that connects the system ground to the grounding electrode (ground rod, water pipe, etc.). Sized per NEC Table 250.66 based on the largest ungrounded service-entrance conductor.
These are frequently confused, but they serve different purposes and use different sizing tables.
EGC Sizing (Table 250.122)
The equipment grounding conductor is sized based on the overcurrent protection device (breaker or fuse) rating ahead of the circuit:
| OCPD Rating | Copper EGC | Aluminum EGC |
|---|---|---|
| 15A | 14 AWG | 12 AWG |
| 20A | 12 AWG | 10 AWG |
| 30A | 10 AWG | 8 AWG |
| 40A | 10 AWG | 8 AWG |
| 60A | 10 AWG | 8 AWG |
| 100A | 8 AWG | 6 AWG |
| 200A | 6 AWG | 4 AWG |
| 300A | 4 AWG | 2 AWG |
| 400A | 3 AWG | 1 AWG |
| 500A | 2 AWG | 1/0 AWG |
| 600A | 1 AWG | 2/0 AWG |
GEC Sizing (Table 250.66)
The grounding electrode conductor is sized based on the largest ungrounded (phase) service-entrance conductor:
| Largest Service Conductor (Cu) | Copper GEC | Aluminum GEC |
|---|---|---|
| 2 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 AWG | 6 AWG | 4 AWG |
| 2/0 or 3/0 AWG | 4 AWG | 2 AWG |
| Over 3/0 through 350 kcmil | 2 AWG | 1/0 AWG |
| Over 350 through 600 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 through 1100 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | 3/0 AWG | 250 kcmil |
NEC References
- NEC Table 250.122 — minimum size equipment grounding conductor
- NEC Table 250.66 — grounding electrode conductor sizing
- NEC 250.28 — main bonding jumper and system bonding jumper
- NEC 250.102 — supply-side bonding jumper sizing
- NEC 250.118 — types of equipment grounding conductors
Try it yourself
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