Grounding & Conduit Fill Card — GEC, EGC Sizes & EMT Wire Capacity

One-page card: NEC grounding electrode and equipment grounding conductor sizes, EMT conduit fill percentages, and THHN capacity per trade size.

Updated August 22, 2026

The two NEC grounding tables and the conduit fill arithmetic, on one card: grounding electrode conductor sizes from Table 250.66 (sized from the largest ungrounded service conductor), equipment grounding conductor sizes from Table 250.122 (sized from the breaker or fuse ahead of the circuit — the ampere column is a "not exceeding" band, so a 50 A breaker uses the 60 A row), the Chapter 9 Table 1 fill percentages, and the maximum count of same-size THHN conductors per EMT trade size at 40% fill.

Every cell is generated from the constants behind the grounding conductor size and conduit fill charts — the THHN counts are computed with the same 40%-fill, Note (7)-rounding function the chart uses, never retyped. Print it for the panel room; the full 14 AWG–500 kcmil matrix, EMT areas, and the GEC made-electrode caps of 250.66(A)–(C) live on the linked charts.

Grounding & Conduit Fill Card — GEC, EGC Sizes & EMT Wire Capacity — updated August 22, 2026

Grounding electrode conductor (NEC 250.66)

Service — CuService — Al / CCAGEC — CuGEC — Al / CCA
2 AWG or smaller1/0 AWG or smaller8 AWG6 AWG
1 or 1/0 AWG2/0 or 3/0 AWG6 AWG4 AWG
2/0 or 3/0 AWG4/0 AWG or 250 kcmil4 AWG2 AWG
Over 3/0 AWG through 350 kcmilOver 250 through 500 kcmil2 AWG1/0 AWG
Over 350 through 600 kcmilOver 500 through 900 kcmil1/0 AWG3/0 AWG
Over 600 through 1100 kcmilOver 900 through 1750 kcmil2/0 AWG4/0 AWG
Over 1100 kcmilOver 1750 kcmil3/0 AWG250 kcmil

Sized from the largest ungrounded service conductor. To a rod, pipe, or plate electrode the GEC need not exceed 6 AWG Cu / 4 AWG Al; to a concrete-encased electrode, 4 AWG Cu (250.66(A)–(C)).

Equipment grounding conductor (NEC 250.122)

OCPD ≤ (A)CopperAl / CCA
1514 AWG12 AWG
2012 AWG10 AWG
3010 AWG8 AWG
4010 AWG8 AWG
6010 AWG8 AWG
1008 AWG6 AWG
2006 AWG4 AWG
3004 AWG2 AWG
4003 AWG1 AWG
5002 AWG1/0 AWG
6001 AWG2/0 AWG
8001/0 AWG3/0 AWG
10002/0 AWG4/0 AWG
12003/0 AWG250 kcmil
16004/0 AWG350 kcmil
2000250 kcmil400 kcmil
2500350 kcmil600 kcmil
3000400 kcmil600 kcmil
4000500 kcmil750 kcmil
5000700 kcmil1200 kcmil
6000800 kcmil1200 kcmil

Rating column is a ceiling — use the first row the breaker does not exceed. Upsize the EGC proportionately when circuit conductors are upsized for voltage drop (250.122(B)).

Conduit fill limits (NEC Ch. 9 Table 1)

Wires in racewayMax fill
1 conductor53%
2 conductors31%
Over 2 conductors40%

Percent of the raceway internal area. Nipples ≤ 24″ may fill to 60% (Note (4)); equipment grounding conductors count toward fill.

Max same-size THHN per EMT — computed at 40% fill

EMT1412108642
1/2″12953211
3/4″2216106422
1″3526169743
1-1/4″614528161275
1-1/2″8461382216107
2″1381016336261611
2-1/2″24117611164462820
3″36426616796694330
3-1/2″476347219126915640
4″6084432791611167151

THHN/THWN/THWN-2 sizes in AWG; counts per Ch. 9 Note (7) (fraction ≥ 0.8 rounds up). Same-size conductors only. Sizes 1 AWG–500 kcmil: conduit fill chart.

Sources

  • NEC (NFPA 70) Tables 250.66 and 250.122 — digit-verified against independent reproductions (zing2.app, buildmyowncabin.com, TEP SR-453)
  • NEC Chapter 9 Tables 1, 4 (EMT), and 5 (THHN) with Notes (4)/(7); THHN counts computed at 40% fill

Try the Calculators

Grounding Conductor Size Calculator (NEC 250.66 & 250.122)Cable Tray & Conduit SizingVoltage Drop CalculatorConduit Bending Calculator (Offset, Saddle, Stub-Up)

Grounding & Conduit Fill Card — GEC, EGC Sizes & EMT Wire Capacity — reuven.tools/cheat-sheets/grounding-conduit-card — verified against: NEC (NFPA 70) Tables 250.66 and 250.122 — digit-verified against independent reproductions (zing2.app, buildmyowncabin.com, TEP SR-453); NEC Chapter 9 Tables 1, 4 (EMT), and 5 (THHN) with Notes (4)/(7); THHN counts computed at 40% fill