By Dovydas Kersys · Chapter 55 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Symptom
The PLC issues a run command and the drive status changes to running, yet the motor remains stationary.
Diagnostic approach
A running status does not prove torque reaches the shaft. Check frequency reference, motor current, brake state and output wiring.
What the team found
The drive output frequency rises, current remains low, and the motor brake coil has no voltage. The brake output relay was wired to the wrong auxiliary supply. After correction, brake timing is adjusted and the motion is retested at low speed.
Commissioning lesson
When the command path looks correct, follow the energy path to the load.
Use the same layered isolation method even when the symptom seems to point at software.
FIELD RULE: Preserve evidence before making changes: values, states, diagnostics, timestamps and the exact machine condition.
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Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.