Motor Voltage Drop Calculator
Use this motor voltage-drop workflow when you want separate running and starting-current voltage-drop estimates for a motor circuit.
- Running voltage drop
- V
- Running voltage drop
- %
- Running remaining voltage
- V
- Starting voltage drop
- V
- Starting voltage drop
- %
- Starting remaining voltage
- V
Calculation details
- Phase multiplier
- x
- Calculation basis
- Selection boundary
Recent results
Formulas
- Phase multiplier = 2 for single-phase two-conductor; sqrt(3) for balanced three-phase
- Running voltage drop = phase multiplier x running current x one-way length x conductor resistance / 1000
- Starting voltage drop = phase multiplier x starting current x one-way length x conductor resistance / 1000
- Voltage-drop percent = voltage drop / system voltage x 100
- Remaining voltage = system voltage - voltage drop
Use this calculator
Estimate running voltage drop, starting voltage drop, and remaining motor terminal voltage from entered current and conductor assumptions.
Read the result
Review the calculated values with their displayed units and assumptions. The result is a planning aid for the stated inputs, not a final equipment or installation decision.
Check before final work
This motor voltage-drop estimate is a screening calculation. It does not verify motor starting torque, source impedance, utility flicker limits, conductor ampacity, protection, equipment ride-through, or code compliance.
FAQs
Why does the calculator show running and starting drop separately?
Motor current can be much higher during starting. Showing both values keeps normal-operation and start-condition screening separate.
Does this include source impedance?
No. It only applies the entered conductor resistance. Use source-impedance or voltage-sag studies when the supply system matters.
Can this approve a motor circuit?
No. Ampacity, protection, controller, voltage tolerance, utility, and code checks are separate.