Circuit Load and Overload Risk Calculator
Calculate total circuit load, capacity utilization percentage, and assess overload risk for residential or commercial electrical circuits.
Connected Devices / Loads
Formulas Used
Total Real Power (W): Ptotal = Σ (Pdevice × Quantity)
Apparent Power (VA): S = Ptotal / PF | where PF = Power Factor (0–1)
Total Current (A): I = S / V | where V = Circuit Voltage
Capacity Utilization (%): U = (I / Ibreaker) × 100
NEC 80% Safe Limit (A): Isafe = Ibreaker × 0.80
Available Headroom (W): Premaining = (Ibreaker − I) × V × PF
Assumptions & References
- Based on NEC (NFPA 70) Article 210.19(A)(1): continuous loads must not exceed 80% of the overcurrent device rating.
- Wire ampacity values follow NEC Table 310.15(B)(16) for copper conductors at 60°C (140°F) in conduit.
- Power factor accounts for reactive loads (motors, transformers, switching power supplies). Purely resistive loads (heaters, incandescent bulbs) have PF = 1.0.
- Device wattage values are nameplate or rated power; actual consumption may vary.
- Calculations assume a single-phase circuit. Three-phase circuits require different formulas (P = √3 × VLL × I × PF).
- Voltage drop along wire length is not calculated here; long runs may require upsizing wire gauge.
- Always consult a licensed electrician before modifying electrical circuits.