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Motors & Automation
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Guides to motor circuits, protection and variable-frequency drives. Compare the motor duty, supply conditions and protective functions before selecting equipment.Motor protection · VFD selection
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Motor Repair or Replacement: A Failure-Evidence and Lifecycle Decision
The right choice between repair and replacement depends on more than the price of a rewind and the price of a new motor. Repair is the better starting…
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Variable Frequency Drive Maintenance: A Condition-Led Checklist
A useful drive maintenance visit produces evidence, not just a cleaned cabinet. The sequence matters as much as the checklist: isolate and verify first, confirm the DC bus…
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Comparing Motor Starting Methods: DOL, Soft Start, VFD and MV Contactors
Choose a motor-starting architecture by matching the driven load, supply event, starting duty, run-speed requirement and consequence of failure—not by ranking device names. Direct-on-line (DOL) starting is a…
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Replacement Three-Phase Induction Motors: Fit, Speed and Duty Checks
Select a replacement three-phase squirrel-cage induction motor by checking the retained machine’s interfaces, not just matching its kilowatt rating. Mechanical fit, operating speed, starting behavior, cooling and control…
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Motor Operating Temperature: Separate Ambient, Cooling and Load Causes
Interpret a motor-temperature change by first identifying what was measured and under what conditions. A hotter frame, a higher winding-sensor reading and a warmer bearing are different observations.…
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Motor and VFD Sizing for Machine Loads: Torque, Inertia and Duty
Size the motor from the machine’s required shaft torque and speed over time, then check the variable-frequency drive (VFD) against the motor’s required current and overload duration. Matching…
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Induction Motor Calculations Every VFD User Should Know
A variable-frequency drive (VFD) controls the electrical frequency supplied to a motor, but frequency is not the same as actual shaft speed. For an induction motor, first calculate…
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Contactor Selection for a 60 Hz Control Supply
A 60 Hz control supply is a coil-compatibility input, not a complete contactor specification. First confirm the actual voltage and frequency at the coil terminals during pickup and…
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Control Transformer Sizing for Contactor Pickup and Holding
Do not size a contactor control transformer from coil holding VA alone. Build at least two load cases: the largest credible simultaneous pickup demand, and the steady sealed/holding…
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Motor Protection Circuit Breaker Design Basics
A motor protection circuit breaker (MPCB) is a low-voltage switching and protective device designed around motor-circuit behavior. It typically provides adjustable overload protection, rapid short-circuit protection, and manual…