What Size Wire for a 100 Amp Circuit Breaker? (NEC Table 310.16)

Complete Copper vs. Aluminum AWG wire size, continuous load limit (80A max), ground wire gauge, and conduit sizing for 100A circuits (100A detached garage/workshop subpanels & small residential services).

Direct NEC Table 310.16 Answer for 100 Amps

3 AWG

Minimum Copper Wire (75°C)

THHN / THWN-2 / XHHW in Conduit

1 AWG

Minimum Aluminum Wire (75°C)

SER / XHHW-2 Feeder Cable

80 Amps

Max Continuous Load (80% Rule)

For loads running 3+ hours (EVs, lighting)

1-1/4" EMT

Recommended Conduit Size

Fits 3x 3 AWG + Ground under 40% fill

Common Applications for a 100A Circuit

100A detached garage/workshop subpanels & small residential services. Remember that under the NEC 125% continuous-load rule (NEC 210.19 & 210.20), a standard 100A breaker can only supply up to 80A of continuous load (any load that runs for 3 hours or more without stopping, such as an EV charger or commercial lighting).

When to Upsize for Voltage Drop (Over 100 Feet)

If your one-way wire run exceeds 100 feet at 240V (or 50 feet at 120V), step up one wire gauge from 3 AWG to keep total line voltage drop under the NEC 3% branch-circuit recommendation. Use our Voltage Drop Calculator to check your exact footage.

2. NEC Wire Size & Ampacity Calculator (Table 310.16)

Load Current (Amps)

Conductor Metal

Terminal Temp Rating

Conductors in Raceway

Continuous Load (runs 3+ hours continuously — apply NEC 125% rule)

What Size Wire for a 100 Amp Circuit Breaker? (NEC Table 310.16)

Direct NEC Table 310.16 Answer for 100 Amps

Common Applications for a 100A Circuit

When to Upsize for Voltage Drop (Over 100 Feet)

2. NEC Wire Size & Ampacity Calculator (Table 310.16)

Recommended Wire, Breakers & Termination Tools