Grounding Electrode Conductor (GEC) Sizing
NEC 2023 — Section 250.66 & Table 250.66
Select a conductor size above to see the required GEC.
Equipment Grounding Conductor (EGC) Sizing
NEC 2023 — Section 250.122 & Table 250.122
Enter the OCPD rating above to see the required EGC.
250.122(B) — Increased Size: Where the circuit conductors are increased
in size from the minimum required, the EGC shall be increased proportionately.
This calculator gives the minimum size per Table 250.122.
Main Bonding Jumper (MBJ) & Supply-Side Bonding Jumper (SSBJ)
NEC 2023 — Sections 250.28, 250.102 & Table 250.66
Select a conductor size above to see the required bonding jumper size.
250.102(C)(1) — Multiple Conductors in Parallel: Where the service-entrance
conductors are installed in parallel, the bonding jumper shall be sized based on the
equivalent area of the largest phase conductor per phase (sum of parallel conductors of
the same size and material), and the result looked up in Table 250.66.
12.5% Rule (250.102(C)(1) Exception): Where the service-entrance conductors exceed the maximum in Table 250.66, the bonding jumper is permitted to be sized at not less than 12.5% of the equivalent circular mil area of the largest phase conductor, selecting the next standard size from Table 250.66 or higher.
12.5% Rule (250.102(C)(1) Exception): Where the service-entrance conductors exceed the maximum in Table 250.66, the bonding jumper is permitted to be sized at not less than 12.5% of the equivalent circular mil area of the largest phase conductor, selecting the next standard size from Table 250.66 or higher.
NEC 2023 Table 250.66 — GEC & Bonding Jumper Sizing
Section 250.66; also governs MBJ/SSBJ per 250.28 & 250.102
| Largest Service-Entrance Conductor (or Equivalent for Parallel) |
GEC / Bonding Jumper Size | ||
|---|---|---|---|
| Copper (Cu) | Aluminum / CCA (Al) | Copper GEC | Aluminum GEC |
| 2 AWG or smaller | 1/0 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 AWG | 2/0 AWG or 3/0 AWG | 6 AWG | 4 AWG |
| 2/0 AWG or 3/0 AWG | 4/0 AWG or 250 kcmil | 4 AWG | 2 AWG |
| Over 3/0 thru 350 kcmil | Over 250 thru 500 kcmil | 2 AWG | 1/0 AWG |
| Over 350 thru 600 kcmil | Over 500 thru 900 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 thru 1100 kcmil | Over 900 thru 1750 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | Over 1750 kcmil | 3/0 AWG | 250 kcmil |
NEC 2023 Table 250.122 — EGC Sizing
Section 250.122 — based on OCPD rating ahead of circuit
| OCPD Rating (A) | Copper EGC | Aluminum / CCA EGC |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 30 | 10 AWG | 8 AWG |
| 40 | 10 AWG | 8 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 |
| 500 | 2 AWG | 1/0 AWG |
| 600 | 1 AWG | 2/0 AWG |
| 800 | 1/0 AWG | 3/0 AWG |
| 1000 | 2/0 AWG | 4/0 AWG |
| 1200 | 3/0 AWG | 250 kcmil |
| 1600 | 4/0 AWG | 350 kcmil |
| 2000 | 250 kcmil | 400 kcmil |
| 2500 | 350 kcmil | 600 kcmil |
| 3000 | 400 kcmil | 600 kcmil |
| 4000 | 500 kcmil | 750 kcmil |
| 5000 | 700 kcmil | 1200 kcmil |
| 6000 | 800 kcmil | 1200 kcmil |
Conductor Area Reference (kcmil)
Used for 12.5% rule calculations
| Size | Circular Mils (CM) | 12.5% of CM |
|---|
Study aid only — verify against the adopted code edition / a licensed
professional before use in real project/estimate documentation. This calculator
implements NEC 2023 Table 250.66 and Table 250.122 logic. Local amendments,
parallel conductor configurations, and special conditions (e.g., 250.66(A)–(C)
caps for certain electrode types) may alter the required size.