Beginner
NEC 125% Continuous Load Rule
NEC overcurrent device and conductor sizing for continuous vs non-continuous loads — the 125% rule explained with examples.
Formulas
OCPD ≥ 1.25 × I_continuous + 1.0 × I_non-continuous
Minimum overcurrent device rating
Conductor ≥ 1.25 × I_continuous + 1.0 × I_non-continuous
Minimum conductor ampacity
Variable Definitions
OCPD=Overcurrent protective device rating(amperes (A))
I_continuous=Continuous load current (3+ hours)(amperes (A))
I_non-continuous=Non-continuous load current(amperes (A))
1.25=Continuous load multiplier(dimensionless)
Worked Example
Circuit with 30A continuous lighting load and 10A non-continuous receptacle load.
- OCPD = (1.25 × 30) + (1.0 × 10) = 37.5 + 10 = 47.5A
- Next standard breaker: 50A
- Conductor: minimum 47.5A ampacity → 6 AWG copper (65A at 75°C)
Answer: 50A breaker with 6 AWG copper conductors
When to Use
- •Sizing branch circuit breakers for lighting circuits (always continuous)
- •Sizing feeders with mixed continuous and non-continuous loads
- •HVAC equipment circuit sizing
- •Any load operating for 3 hours or more continuously
Standards & References
- NEC 210.19(A) — Branch Circuit Conductor Sizing
- NEC 210.20(A) — Branch Circuit OCPD Sizing
- NEC 215.2(A) — Feeder Sizing
- NEC Article 100 — Definition of 'Continuous Load'