Homeowners hear “15 amp lighting circuit” and assume fifteen amps of bulbs is fine. Electricians plan twelve amps of continuous lighting on that breaker—because lighting stays on, breakers heat, and inspectors read 80% as the practical ceiling.
The 80% continuous-load rule
National Electrical Code (NEC) and similar standards limit continuous loads—expected to run 3+ hours—to 80% of the overcurrent device rating unless the breaker is listed otherwise.
| Breaker | Max continuous amps | ~120 V watts |
|---|---|---|
| 15 A | 12 A | 1,440 W |
| 20 A | 16 A | 1,920 W |
Why it exists:
- Breaker trip curves assume intermittent loads
- Heat builds in terminations when current runs for hours
- Margin absorbs inrush from LED drivers and cold filaments (legacy)
Count fixtures, not rooms
“Kitchen lights” is not a load—twelve recessed cans, two pendants, under-cabinet tape, and a hood light might share a circuit. Each needs watts at the wire, including remote drivers mounted in joists.
LED is lower—but not zero
LED retrofits cut amps 70–85% versus incandescent. Common mistakes after retrofit:
- Adding more fixtures because “the breaker handled it before”
- Using maximum tape-light wattage on dimmers set to 100%
- Mixing fan/light units without summing both motors and lamps
Always enter driver nameplate W, not “60 W equivalent” labels.
Symptoms of an overloaded lighting branch
- Breaker trips on hot summer nights when outdoor and kitchen loads coincide
- Voltage sag → dimming at the far end of the circuit (see voltage-drop tool)
- Dimmer buzz and shortened LED life from sustained overcurrent
Fix paths
- Split circuits — new homerun to panel for heavy kitchen or outdoor zones
- Reduce load — lower-watt luminaires or shorter tape runs
- Upsize breaker only with upsized wire — never swap 15 A → 20 A on #14 copper
Related reading
- Lighting Circuit Load Guide — full workflow
- Home Lighting Safety Check — remodel self-check
The breaker is not the budget—80% of the breaker is. Design there and your LEDs stay bright without drama.