PLC & Controls
Motor runs manually but not in automatic mode
Successful manual operation often proves part of the motor and power circuit. Automatic operation still depends on permissives, sensors, sequence logic and mode selection.
If a motor runs in manual mode but not automatic, the fault boundary is narrower—but manual operation does not prove the complete automatic control path is healthy. The two modes may share the same power circuit while using different commands, permissives and sequence logic.
What manual operation may prove
Depending on the design, manual mode can confirm that the contactor or drive can run, the motor power circuit is available and the mechanical load can move. Some manual controls bypass parts of the normal sequence, however, so the exact circuit and software design matter.
Automatic permissives and interlocks
Automatic operation may require guards closed, pressure or level conditions satisfied, upstream and downstream equipment ready, no active alarms and the correct production mode selected. One missing input can legitimately prevent the command without producing an obvious electrical trip.
Sensor and sequence conditions
A sensor may work physically but never reach the PLC input, or the input may be present at the wrong point in the sequence. Timers, counters, latched faults and state-machine conditions can also hold the process before the motor command. The relevant status should be read in context rather than forcing the output.
Selector and command path
Worn selector contacts, incorrect HMI mode, remote/local selection and communications faults can prevent the automatic request reaching the controller. Recent software, maintenance or production changes are particularly relevant.
A useful diagnostic question
Instead of asking only why the motor is not running, identify the first expected condition in the automatic sequence that is missing. Drawings, PLC status and a clear understanding of the intended sequence help locate that boundary safely.
Bypassing a permissive or forcing a PLC output can create unexpected machine movement. It should not be used as a shortcut around proper diagnosis and site safety procedures.
When Truvo may help
Truvo Industrial supports automatic-sequence, PLC I/O and motor-control fault finding across Sheffield and South Yorkshire. The selected mode, sequence stage and indications present when automatic operation stops are useful details for an enquiry.