Motor current, starting, contactors, voltage quality, and VFDs
Motor Current Calculator
Estimate motor full-load current and a starting overload relay setting range from motor power, voltage, efficiency, and power factor.
Open calculatorMotors, Contactors & Drives
Tools for motor current, starter and contactor selection, starting voltage drop, voltage unbalance, and VFD sizing.
10 calculatorsMotor current, starting, contactors, voltage quality, and VFDs
Motor Starter Selection Calculator
Estimate motor current, starting current, contactor duty, overload-relay range, and preliminary short-circuit protection for a motor starter.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Three-Phase Voltage Unbalance Calculator
Calculate three-phase voltage unbalance, voltage-window thresholds, and select a starting VIOX FCP18 monitoring-relay function.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Insulation Resistance Temperature Correction Calculator
Correct a measured insulation-resistance value to a reference temperature using a selectable doubling-temperature or entered correction coefficient.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Motor Torque Calculator
Calculate motor shaft torque, output power, input power, angular speed, and lb-ft from kW or hp, rotational speed, and efficiency.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Motor Control Panel Load Calculator
Estimate an MCC or motor-control-panel feeder ampacity from the largest motor, remaining motors, non-motor load, demand, and spare capacity.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Contactor Selection Calculator (AC-1 / AC-3)
Estimate a contactor current class from load type, power, voltage, utilization category, and operating frequency.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Motor Starting Voltage Drop Calculator
Estimate bus voltage dip during motor starting from motor current, starting method, transformer impedance, and feeder impedance.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
VFD Sizing, Protection and Panel Calculator
Estimate the minimum VFD output-current class and screen input protection, bypass contactor, filtering, braking, and panel heat requirements.
Open calculatorMotor current, starting, contactors, voltage quality, and VFDs
Solid State Relay Selection & Heatsink Calculator
Calculate SSR load current, minimum nameplate-current screen, conduction loss, heatsink thermal resistance, junction temperature, surge margin, and semiconductor-fuse IΒ²t checks.
Open calculatorSize the complete motor operating path
Motor circuits must carry normal load, tolerate starting current, provide overload and short-circuit protection, and switch the load at the required duty. Motor current is only the first step.
Contactor utilization category, starter method, acceleration time, starts per hour, voltage quality, service factor, and VFD derating can govern the final equipment selection.
Separate running duty from starting duty
Full-load current determines continuous current paths, while locked-rotor or controlled starting current affects voltage dip, magnetic trip compatibility, contactor making duty, and source capacity.
VFD and soft-starter applications require manufacturer data for output current, overload class, carrier frequency, ambient temperature, altitude, cable length, EMC, harmonics, and motor compatibility.
Applications
Where these calculators fit
Motor operating point
Estimate current, input power, efficiency, torque, and phase behavior.
Starting and switching
Compare DOL, star-delta, soft starter, VFD, contactor, and overload requirements.
Motor control panels
Screen feeder load, starting voltage drop, voltage unbalance, heat, and protection.
FAQ
Why is motor nameplate current preferred?
It reflects the actual motor design and rating basis. Formula current is useful when nameplate data is unavailable, but efficiency and power factor assumptions introduce uncertainty.
Does a VFD remove motor starting-current concerns?
It reduces line-side starting impact but introduces drive current, overload, harmonic, thermal, EMC, and protection requirements.
Can one contactor rating cover every motor application?
No. AC-1, AC-3, AC-4 and other utilization categories have different making, breaking, and endurance duties.
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