Wire Ampacity Table

Lighting circuits must use wire rated for their current. This table focuses on the gauges used in fixture wiring and lighting branch circuits.

Wire (AWG) Ampacity Lighting use
18 7 A Fixture whips, low-voltage
16 10 A Fixture leads
14 15 A Branch lighting circuits
12 20 A Larger lighting and load circuits
10 30 A Feeders and long runs
Most lighting is 15 A. A standard 15 A lighting circuit uses 14 AWG copper. Step up the gauge for long runs (voltage drop) or heavily loaded circuits.

See the Voltage Drop Calculator and Voltage Drop Formula.

Wire ampacity for lighting circuits

Lighting circuits must use wire rated for the current they carry, sized so the breaker never lets the wire exceed its safe capacity. For typical copper branch wiring: 14 AWG suits 15-amp lighting circuits, 12 AWG 20-amp circuits, and 10 AWG 30-amp loads. Fixture whips and internal wiring often use smaller gauges rated for the specific load and temperature. Over long runs, voltage drop becomes the limiting factor — for low-voltage lighting especially (12V/24V landscape and tape systems), thicker wire or higher voltage is often needed to keep brightness consistent along the run. Always follow local electrical code; this is general reference, not a substitute for a licensed electrician.

Two common pitfalls: using lamp-cord-gauge wire on a branch circuit (under-rated), and ignoring voltage drop on long low-voltage runs, which dims the far end. As a rough guide, keep voltage drop under about 3% for lighting; if a run is long, step up a wire size or move to a higher system voltage. On a branch circuit, when in doubt match the wire to the breaker: 15A → 14 AWG, 20A → 12 AWG.

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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.