100 Amp Wire Size Calculator
Find the right wire gauge (AWG) for a 100 amp circuit. Enter voltage, conductor material, distance, and max voltage drop to get the recommended wire size.
About This Calculator
The 100 Amp Wire Size Calculator helps electricians, engineers, and DIY homeowners determine the correct wire gauge (AWG) for a 100 amp electrical circuit. Choosing the right wire size is critical for safety — undersized wires overheat and can cause fires, while oversized wires waste money on unnecessary copper or aluminum.
This calculator uses Pouillet's law combined with Ohm's law to compute the required cross-sectional area based on the voltage drop formula: A = (φ × I × ρ × L) / V_drop. For single-phase systems, φ = 2 (accounting for the return conductor); for three-phase systems, φ = √3. The resistivity ρ is temperature-corrected using the conductor's temperature coefficient, ensuring accurate results for real-world operating conditions up to the maximum wire temperature rating.
The result is the minimum wire gauge recommended to keep voltage drop within your specified limit. The calculator supports both copper and aluminum conductors, single-phase and three-phase AC systems, and any operating temperature from 20°C to 90°C. The AWG (American Wire Gauge) output follows the standard logarithmic scale where smaller numbers indicate thicker wires (e.g., 4/0 is thickest, 40 AWG is thinnest).
Regional Notes: This calculator uses the NEC voltage drop methodology, which is widely adopted globally. For North America (US/Canada), typical residential voltages are 120V and 240V. For the UK, Europe, and many other regions, standard single-phase voltage is 230V. Three-phase voltages vary: 208V (US commercial), 400V (EU/UK), and 415V (India/Australia). Always verify results against local electrical codes — this tool provides guidance only and does not replace a qualified electrician's assessment.
Frequently Asked Questions
What size wire do I need for 100 amps?
For a 100 amp circuit, the required wire gauge depends on voltage, conductor material, distance, and allowable voltage drop. At 120V single-phase with copper at 30.5m (100ft) and 3% voltage drop, you typically need 1 AWG copper. For 240V at the same distance, 3 AWG may suffice. Always consult a licensed electrician and follow local electrical codes.
How is wire size calculated for 100 amps?
Wire size is calculated using Ohm's law and Pouillet's law: A = (φ × I × ρ × L) / V_drop, where φ depends on system type (2 for single-phase, √3 for three-phase), I is the current (100A), ρ is the conductor resistivity, L is the one-way distance, and V_drop is the maximum allowable voltage drop. The result is the required cross-sectional area, which is then converted to the nearest AWG gauge.
What is the voltage drop for 100 amp service?
The National Electrical Code (NEC) recommends a maximum voltage drop of 3% at the farthest outlet for branch circuits and 5% total for feeder and branch combined. For a 100A, 120V circuit at 30.5m with 1 AWG copper wire, the voltage drop is approximately 3.1V (2.6%). Longer distances or smaller wire gauges increase the voltage drop.
Can I use aluminum wire for 100 amps?
Yes, aluminum wire can be used for 100 amp circuits, but it requires a larger gauge than copper due to higher resistivity. Aluminum has about 60% more resistance than copper, so you typically need to go up 2 AWG sizes (e.g., 1/0 aluminum instead of 1 AWG copper for the same application). Always use CO/ALR rated connectors.
How does distance affect 100 amp wire size?
Wire size is directly proportional to cable length. Doubling the distance requires doubling the cross-sectional area of the wire to maintain the same voltage drop. For a 100A, 120V single-phase circuit with copper: at 15m (50ft) you may need 3 AWG, at 30.5m (100ft) you need 1 AWG, and at 61m (200ft) you need 2/0 AWG to stay within 3% voltage drop.
What is the minimum NEC rating for 100 amp wire?
Per NEC Table 310.15(B)(16), copper wire rated for 75°C terminations must be at least 3 AWG (100A ampacity). Aluminum requires 1 AWG (100A at 75°C). However, voltage drop considerations over longer distances often require thicker wire than the minimum ampacity rating. Always verify with local codes.
Is this 100 amp wire size calculator suitable for three-phase systems?
Yes, this calculator supports both single-phase and three-phase AC systems. For three-phase, the formula uses the factor √3 instead of 2, reflecting that three conductors share the load. This results in a smaller required wire size compared to single-phase for the same voltage and distance.