Engineering
Motor Current Calculator — Full Load Amps (FLA)
Calculate full load current (FLA) of an electric motor from power, voltage, power factor, and efficiency. Free electrical calculator for dairy plant engineers.
Formula
(motorPower * 1000) / (1.732 * voltage * powerFactor * efficiency)
motorPower
Motor Rated Power (kW)
voltage
Line Voltage (V)
powerFactor
Power Factor (PF)
efficiency
Motor Efficiency (η)
Worked Example
1
Given:
efficiency = 0.9
motorPower = 7.5
powerFactor = 0.85
voltage = 415
2
Apply the formula:
(motorPower * 1000) / (1.732 * voltage * powerFactor * efficiency)
3
Result:13.63 A
What is Full Load Current (FLA)?
Full Load Current (FLA or FLC) is the current drawn by an electric motor when running at its rated horsepower/kW output at rated voltage. It is the basis for:
- Cable sizing: Cables must carry FLA continuously
- Circuit breaker selection: MCB/MCCB rated at 125–160% of FLA
- Overload relay setting: Set to 100–105% of FLA
- Starter sizing: DOL, Star-Delta, VFD selection based on FLA
Formula — 3-Phase Motor
I (A) = P (kW) × 1000 / (√3 × V × PF × η)
Where:
- P = rated power (kW)
- V = line voltage (V) — typically 415V in India
- PF = power factor (typically 0.80–0.90 for induction motors)
- η = motor efficiency (typically 0.85–0.95)
- √3 = 1.732
Typical Values for Indian Motors
| Motor Rating | Typical FLA at 415V |
|---|---|
| 0.37 kW (0.5 HP) | 1.0–1.2 A |
| 0.75 kW (1 HP) | 1.8–2.2 A |
| 1.5 kW (2 HP) | 3.5–4.0 A |
| 3.7 kW (5 HP) | 8.0–9.5 A |
| 7.5 kW (10 HP) | 16–18 A |
| 15 kW (20 HP) | 30–35 A |
| 37 kW (50 HP) | 72–80 A |
Cable Sizing Rule of Thumb
Minimum cable size (mm²) = FLA / 4 for copper cables in conduit at 40°C ambient
Always verify against IS 694 / IS 1554 current ratings and apply applicable derating factors.