Electrical Load & Ampacity Calculator (1Φ & 3Φ)
Computes full load running current and recommended circuit breaker ampacities according to the NEC 125% continuous load rule.
Full Load Current & NEC Wire Ampacity Sizer
Single-Phase (1Φ) and Three-Phase (3Φ) branch circuit and feeder ampacity calculator with 125% continuous rule
I = P / (√3 · V · PF) = 30000 W / (1.732 × 415 V × 0.85) = 49.1 A
Design Current: 61.38 A (includes 125% factor)
13.3 mm² • Rated 65 A (75°C THHN)
Electrical Load Sizing
Electrical load calculation determines the electric current drawn by equipment under continuous operation, essential for properly sizing feeder cables and circuit breakers.
Formula & Step-by-Step Calculation
Full load current equations for single-phase and three-phase circuits.
Worked Step-by-Step Examples
Calculate full load current of a 30 kW, 415V 3-phase motor operating at 0.85 PF
Common Real-World & Academic Use Cases
- ✓ Commercial building distribution panelboard sizing
- ✓ Industrial motor feeder cable and breaker selection
- ✓ HVAC chiller electrical disconnect sizing
How to Use the Electrical Load & Ampacity Calculator (1Φ & 3Φ)
Select Phase Type
Choose 1-Phase (1Φ) or 3-Phase (3Φ).
Enter Power & Voltage
Input equipment power (kW) and line voltage (V).
Read Operating Current
Inspect running current (A) and recommended breaker ampacity.
Frequently Asked Questions
Q: Why apply a 125% factor for circuit breakers?
The National Electrical Code (NEC) mandates that overcurrent protection devices for continuous loads (running 3+ hours) be sized at 125% of the continuous current.