VFD Calculator

Variable Frequency Drive circuit breaker, wire sizing, and output filter recommendations

VFD / Motor Parameters

Phase

Motor HP

Input Voltage

Cable Length VFD → Motor (ft)

Motor Full Load Amps

13.4A

10 HP @ 480V 3Φ

Input Circuit Breaker

175% of VFD input current

25A

Input Wire Size (75°C Cu)

125% of input current = 16.8A

12 AWG

Output Wire Size (VFD → Motor)

125% of motor FLA = 16.8A

12 AWG

Cable Length VFD → Motor

50 ft

✓ Cable length within typical limits — no additional filtering required

NEC 430.122VFD circuit breaker: max 175% of VFD rated input current

NEC 430.122(A)If 175% does not correspond to standard size, next higher standard size permitted

NEC 430.124Conductor sizing: based on VFD input current rating, not motor FLA

Best PracticeOutput wire cannot be smaller than motor wire — VFD output is PWM, not sine wave

> 100 ft cableAdd 3-5% line reactor to reduce reflected wave voltage spikes

> 200 ft cableAdd dV/dt or sine wave output filter; use inverter-duty (NEMA MG1 Part 31) rated motor