Wire Sizing Calculator

Calculate proper wire gauge per NEC 310.16 ampacity tables. Accounts for temperature derating, bundling factors, and voltage drop.

Input Parameters

Load Current (A)

Maximum continuous current draw

System Voltage (V)

Wire Run Length (m)

One-way distance (calculator uses round-trip)

Conductor Material

Insulation Rating

Ambient Temperature (°C)

Conductors in Conduit

Max Voltage Drop (%)

NEC recommends 3% for branch circuits, 5% total

Circuit Type

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Enter parameters and click Calculate

Diameter

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Area

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Resistance

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Run calculation to see ampacity table

The maximum current a conductor can carry continuously without exceeding its temperature rating. Values come from NEC Table 310.16.

I_corrected = I_base × f_temp × f_bundle

When ambient temperature differs from the 30°C base, ampacity must be adjusted per NEC 310.15(B). Higher temperatures reduce the allowable current.

When more than 3 current-carrying conductors are bundled together, heat dissipation is reduced. NEC 310.15(C) provides adjustment factors.

Resistance causes voltage loss along wire length. NEC recommends ≤3% for branch circuits.

V_drop = I × R × L_roundtrip V_drop% = (V_drop / V_source) × 100

P_loss = I² × R