Printable cheat sheet
Hit ⌘ + P. Designed to print to 8.5×11 portrait; folds in half for the pocket.
Forward · field cheat sheet
NEC quick reference
Ampacity, voltage-drop K, breaker pairing, conduit fill. Sanity-check only — verify with the engineer of record.
Table 310.16 — copper ampacity (most common temps)
| Size | 60°C | 75°C | 90°C |
|---|---|---|---|
| 14 AWG | 15 | 20 | 25 |
| 12 AWG | 20 | 25 | 30 |
| 10 AWG | 30 | 35 | 40 |
| 8 AWG | 40 | 50 | 55 |
| 6 AWG | 55 | 65 | 75 |
| 4 AWG | 70 | 85 | 95 |
| 3 AWG | 85 | 100 | 115 |
| 2 AWG | 95 | 115 | 130 |
| 1 AWG | 110 | 130 | 145 |
| 1/0 AWG | 125 | 150 | 170 |
| 2/0 AWG | 145 | 175 | 195 |
| 3/0 AWG | 165 | 200 | 225 |
| 4/0 AWG | 195 | 230 | 260 |
| 250 kcmil | 215 | 255 | 290 |
| 350 kcmil | 260 | 310 | 350 |
| 500 kcmil | 320 | 380 | 430 |
Reminder: NEC 110.14(C) terminations limit the effective column. ≤100 A circuits use 60°C; >100 A use 75°C — even if your insulation is 90°C-rated.
Voltage drop K-factors (75°C)
- Copper: K = 12.9
- Aluminum: K = 21.2
VD (single-phase) = 2·K·I·L / cmils; VD (three-phase) = √3·K·I·L / cmils.
NEC informational: 3% branch / 5% total.
Common breaker / wire pairings
| Breaker | Cu (75°C) | Al (75°C) |
|---|---|---|
| 15 A | 14 AWG | — |
| 20 A | 12 AWG | 10 AWG |
| 30 A | 10 AWG | 8 AWG |
| 40 A | 8 AWG | 6 AWG |
| 50 A | 6 AWG | 4 AWG |
| 60 A | 6 AWG | 4 AWG |
| 100 A | 3 AWG | 1 AWG |
| 125 A | 2 AWG | 1/0 AWG |
| 150 A | 1/0 AWG | 3/0 AWG |
| 200 A | 2/0 AWG | 4/0 AWG |
| 400 A | 500 kcmil | 750 kcmil |
Conduit fill — 40% max for ≥3 conductors (NEC 300)
- 1 conductor max: 53% fill
- 2 conductors max: 31%
- ≥3 conductors max: 40%