Before starting
The question “why doesn’t the engine start?” is too wide. Before the measurements, collect what is already visible: Does the engine try to start? Does the contactor turn on? Has a security intervened? Has the failure occurred after maintenance or modification?
Note the initial state before rearming or resetting. An immediate intervention can erase the most useful clue.
The 7 controls, in order
Define the symptom
Distinguishes between completely stationary motor, buzz, slow start, immediate protection or stop after a few seconds. Each behavior opens a different path.
Check permissive and command
Check the logical path: emergencies, selectors, switches, thermostats, PLCs and process consents. If the command does not arrive, the problem is not necessarily in the power circuit.
Observe contact and protection
An abnormal mechanical state, a coil that does not maintain or a relay intervened require specific causes. Do not limit yourself to the reset: record which device has intervened.
Check feeding according to procedure
Only if competent and authorized, controls the presence and consistency of the steps in the points provided for in the procedure. The instrument and the measurement category must be adapted to the point of the plant.
Square, cable and motor
Use the pattern to delimit the faulty trait. The continuity of the route and the integrity of the connections must be verified with system in the expected security state.
Evaluate insulation and winding
Motor measurements require preparation, insulation from sensitive equipment and correct interpretation. A single reading without conditions and temperature has limited value.
Exclude mechanical load
A locked compressor, a brake pump or damaged transmission can imitate an electrical failure. Mechanical control must be coordinated with safety procedures.
Three symptoms, three directions
| Symptom | First areas to discriminate |
|---|---|
| The contactor does not turn on | Command, permissive, coil, auxiliary and logical power supply. |
| The contactor turns on but the motor is still | Power circuit, protections, connections, motor and load. |
| Part and intervene protection | Currents, times, calibration, phase loss, load and mechanical conditions. |
Tools: few, but suitable
The kit depends on the type of plant and the authorized measures. In a definitive guide we will link each instrument to the precise phase of control, avoiding commercial CTA where they do not add value.
- updated scheme and machine documentation;
- proper and correctly classified verification tool;
- True RMS amperometric caliper when relevant;
- isolation meter only with correct procedure and preparation;
- protection devices and safety tools.
Checklist to bring with you
Use the operating report to note symptom, pattern, conditions, measures and outcome. You can print it or save it in PDF from your browser.