Wire Size for 100 Amp Circuit at 250 Feet
Official National Electrical Code (NEC) sizing recommendation for a 100 Amp breaker over a 250-foot one-way conduit run on a 240V supply circuit.
Full Installation & Conduit Specifications
Interactive CalculatorVoltage Drop Alert: Base #3 AWG Wire Exceeds 3% (5.1%)
NEC Section 210.19(A) Informational Note 4 recommends that feeder and branch circuits maintain voltage drop under 3% (and 5% total) to protect appliances from motor burnout and voltage sagging. Using upsized 1/0 AWG copper wire successfully brings voltage drop back under safe limits.
Frequently Asked Technical Questions
What size copper wire is required for a 100 amp breaker at 250 feet?
Due to voltage drop over 250 feet (5.1% on base wire), the National Electrical Code (NEC) recommends upsizing copper wire from #3 AWG to 1/0 AWG. This keeps the voltage drop under 3%, protecting your equipment from overheating and brownout damage.
Can I use aluminum wire for 100 amps at 250 feet?
Yes, you can use aluminum or copper-clad aluminum wiring. For 100A at 250ft, you will need 3/0 AWG aluminum conductors with terminals rated AL7CU or AL9CU and anti-oxidant paste where required.
What is the maximum continuous load permitted on a 100 amp breaker?
Per NEC Article 210.20, continuous loads (operating for 3 hours or longer, such as EV chargers or heaters) cannot exceed 80% of the breaker rating. For a 100A breaker, your maximum continuous draw is 80.0 Amps.
What size conduit is recommended for this 250 ft run?
Based on Chapter 9, Tables 1 and 4 of the NEC for up to 3-4 current-carrying conductors plus ground at a 40% maximum conduit fill, we recommend using 1-1/4" EMT or Schedule 40 PVC.