NEC Quick Reference Tables
NEC Table 310.16 - Ampacity of Insulated Conductors
Based on 30°C (86°F) ambient, 3 current-carrying conductors in raceway or cable
| Wire Size | Copper | Aluminum | ||||
|---|---|---|---|---|---|---|
| 60°C | 75°C | 90°C | 60°C | 75°C | 90°C | |
| #14 | 15 | 20 | 25 | - | - | - |
| #12 | 20 | 25 | 30 | 15 | 20 | 25 |
| #10 | 30 | 35 | 40 | 25 | 30 | 35 |
| #8 | 40 | 50 | 55 | 35 | 40 | 45 |
| #6 | 55 | 65 | 75 | 40 | 50 | 55 |
| #4 | 70 | 85 | 95 | 55 | 65 | 75 |
| #3 | 85 | 100 | 115 | 65 | 75 | 85 |
| #2 | 95 | 115 | 130 | 75 | 90 | 100 |
| #1 | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 | 240 | 285 | 320 | 195 | 230 | 260 |
| 350 | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 | 320 | 380 | 430 | 260 | 310 | 350 |
Note: For ambient temperatures other than 30°C (86°F), apply correction factors per NEC 310.15(B)(1).
Temperature Correction Factors
Multiply ampacity by these factors for ambient temperatures other than 30°C
| Ambient °C | Ambient °F | 60°C | 75°C | 90°C |
|---|---|---|---|---|
| 21-25 | 70-77 | 1.08 | 1.05 | 1.04 |
| 26-30 | 78-86 | 1.00 | 1.00 | 1.00 |
| 31-35 | 87-95 | 0.91 | 0.94 | 0.96 |
| 36-40 | 96-104 | 0.82 | 0.88 | 0.91 |
| 41-45 | 105-113 | 0.71 | 0.82 | 0.87 |
| 46-50 | 114-122 | 0.58 | 0.75 | 0.82 |
| 51-55 | 123-131 | 0.41 | 0.67 | 0.76 |
Conduit Fill Adjustment Factors
Derate ampacity when more than 3 current-carrying conductors in raceway
| Current-Carrying Conductors | Percent of Table Value |
|---|---|
| 4-6 | 80% |
| 7-9 | 70% |
| 10-20 | 50% |
| 21-30 | 45% |
| 31-40 | 40% |
| 41+ | 35% |
Conduit Fill - NEC Chapter 9, Table 1
| Number of Conductors | Percent Fill Allowed |
|---|---|
| 1 | 53% |
| 2 | 31% |
| 3 or more | 40% |
EMT Internal Area (sq in)
| Trade Size | Total Area | 1 Wire (53%) | 2 Wires (31%) | 3+ Wires (40%) |
|---|---|---|---|---|
| 1/2" | 0.304 | 0.161 | 0.094 | 0.122 |
| 3/4" | 0.533 | 0.282 | 0.165 | 0.213 |
| 1" | 0.864 | 0.458 | 0.268 | 0.346 |
| 1-1/4" | 1.496 | 0.793 | 0.464 | 0.598 |
| 1-1/2" | 2.036 | 1.079 | 0.631 | 0.814 |
| 2" | 3.356 | 1.779 | 1.040 | 1.342 |
| 2-1/2" | 5.858 | 3.105 | 1.816 | 2.343 |
| 3" | 8.846 | 4.688 | 2.742 | 3.538 |
| 4" | 14.753 | 7.819 | 4.573 | 5.901 |
THHN/THWN Wire Area (sq in)
| Wire Size | Area (sq in) | Wire Size | Area (sq in) |
|---|---|---|---|
| #14 | 0.0097 | #1 | 0.1562 |
| #12 | 0.0133 | 1/0 | 0.1855 |
| #10 | 0.0211 | 2/0 | 0.2223 |
| #8 | 0.0366 | 3/0 | 0.2679 |
| #6 | 0.0507 | 4/0 | 0.3237 |
| #4 | 0.0824 | 250 | 0.3970 |
| #3 | 0.0973 | 300 | 0.4608 |
| #2 | 0.1158 | 350 | 0.5242 |
Box Fill - NEC 314.16
Volume Allowances per Conductor
| Wire Size | Volume (cu in) |
|---|---|
| #18 | 1.50 |
| #16 | 1.75 |
| #14 | 2.00 |
| #12 | 2.25 |
| #10 | 2.50 |
| #8 | 3.00 |
| #6 | 5.00 |
Standard Box Volumes
| Box Type | Volume (cu in) |
|---|---|
| 4 × 1-1/4 Square | 18.0 |
| 4 × 1-1/2 Square | 21.0 |
| 4 × 2-1/8 Square | 30.3 |
| 4-11/16 × 1-1/4 Square | 25.5 |
| 4-11/16 × 1-1/2 Square | 29.5 |
| 4-11/16 × 2-1/8 Square | 42.0 |
| 3 × 2 × 2 Device | 7.5 |
| 3 × 2 × 2-1/4 Device | 10.0 |
| 3 × 2 × 2-1/2 Device | 10.5 |
| 3 × 2 × 2-3/4 Device | 12.5 |
| 3 × 2 × 3-1/2 Device | 18.0 |
Box Fill Rules:
- Each conductor = 1× volume
- All internal clamps = 1× largest conductor
- Each support fitting = 1× largest conductor
- Each device/yoke = 2× largest conductor
- All equipment grounds = 1× largest conductor
Motor Full Load Amps - NEC Tables 430.248, 430.250
Single-Phase AC Motors (Table 430.248)
| HP | 115V | 200V | 208V | 230V |
|---|---|---|---|---|
| 1/6 | 4.4 | 2.5 | 2.4 | 2.2 |
| 1/4 | 5.8 | 3.3 | 3.2 | 2.9 |
| 1/3 | 7.2 | 4.1 | 4.0 | 3.6 |
| 1/2 | 9.8 | 5.6 | 5.4 | 4.9 |
| 3/4 | 13.8 | 7.9 | 7.6 | 6.9 |
| 1 | 16 | 9.2 | 8.8 | 8 |
| 1-1/2 | 20 | 11.5 | 11 | 10 |
| 2 | 24 | 13.8 | 13.2 | 12 |
| 3 | 34 | 19.6 | 18.7 | 17 |
| 5 | 56 | 32.2 | 30.8 | 28 |
| 7-1/2 | 80 | 46 | 44 | 40 |
| 10 | 100 | 57.5 | 55 | 50 |
Three-Phase AC Motors (Table 430.250)
| HP | 208V | 230V | 460V | 575V |
|---|---|---|---|---|
| 1/2 | 2.4 | 2.2 | 1.1 | 0.9 |
| 3/4 | 3.5 | 3.2 | 1.6 | 1.3 |
| 1 | 4.6 | 4.2 | 2.1 | 1.7 |
| 1-1/2 | 6.6 | 6.0 | 3.0 | 2.4 |
| 2 | 7.5 | 6.8 | 3.4 | 2.7 |
| 3 | 10.6 | 9.6 | 4.8 | 3.9 |
| 5 | 16.7 | 15.2 | 7.6 | 6.1 |
| 7-1/2 | 24.2 | 22 | 11 | 9 |
| 10 | 30.8 | 28 | 14 | 11 |
| 15 | 46.2 | 42 | 21 | 17 |
| 20 | 59.4 | 54 | 27 | 22 |
| 25 | 74.8 | 68 | 34 | 27 |
| 30 | 88 | 80 | 40 | 32 |
| 40 | 114 | 104 | 52 | 41 |
| 50 | 143 | 130 | 65 | 52 |
Overcurrent Protection Quick Reference
Standard Breaker Sizes (NEC 240.6)
Standard ampere ratings for fuses and inverse time circuit breakers
15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000
Branch Circuit Wire/Breaker Combinations
| Breaker Size | Min Wire (Cu) | Min Wire (Al) | Common Uses |
|---|---|---|---|
| 15A | #14 | #12 | Lighting, general receptacles |
| 20A | #12 | #10 | Kitchen, bathroom, garage receptacles |
| 30A | #10 | #8 | Dryer, water heater, small A/C |
| 40A | #8 | #6 | Range (small), large A/C |
| 50A | #6 | #4 | Range, EV charger, subpanel |
| 60A | #6 | #4 | Subpanel, large A/C |
| 100A | #3 | #1 | Subpanel, service |
| 200A | 2/0 | 4/0 | Main service |
Motor Branch Circuit Protection (430.52)
| Motor Type | Time Delay Fuse | Inverse Time Breaker | Instant Trip Breaker |
|---|---|---|---|
| Single-phase | 175% | 250% | 800% |
| AC polyphase (other than wound-rotor) | 175% | 250% | 800% |
| Wound-rotor | 150% | 150% | 800% |
| DC | 150% | 150% | 250% |
If the calculated value doesn't match a standard size, round up to the next standard size per 430.52(C)(1) Exception 1.