Outdoor Lighting Circuit Load Calculator
Calculate total circuit load, current draw, and recommended breaker/wire sizing for outdoor lighting circuits per NEC guidelines.
Enter up to 6 fixture groups:
Formulas Used
Apparent Power: S (VA) = Ptotal (W) ÷ Power Factor
Single-Phase Current: I = S ÷ V
Three-Phase Current: I = S ÷ (√3 × V)
NEC Derated Current (NEC 210.20): Idesign = I × 1.25 (continuous loads > 3 hours)
Breaker Size: Next standard OCPD size ≥ Idesign (NEC 240.6)
Wire Gauge: Copper conductor ampacity ≥ Idesign per NEC Table 310.15(B)(16)
Headroom: (Breaker Rating − Idesign) × V × PF
Assumptions & References
- Wire ampacity based on NEC Table 310.15(B)(16), copper conductors, 60°C rating, not more than 3 current-carrying conductors in conduit.
- Continuous load derating of 125% per NEC 210.20(A) applies when load operates for 3 or more hours continuously.
- Standard breaker sizes per NEC 240.6(A): 15, 20, 30, 40, 50, 60, 70, 80, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400A.
- Outdoor circuits must use GFCI protection per NEC 210.8(B) and weatherproof enclosures (NEMA 3R or better).
- Low-voltage systems (12V/24V) are typically Class 2 circuits; verify transformer rating independently.
- Three-phase calculations assume balanced load across all phases.
- Always verify with a licensed electrician and local AHJ (Authority Having Jurisdiction) before installation.
- References: NEC 2023 Articles 210, 215, 225, 240, 310; NFPA 70.