Industrial fault scenarios in practice

Initial symptom

The equipment would not start, the motor protection repeatedly tripped, and from the operator side only the shutdown itself was visible.

Diagnostic direction

A protective trip on its own does not explain the actual cause. In cases like this, the starter circuit, load side, motor side, and control signal path all need to be checked separately.

What does this mean in practice?

The aim was not to replace the full system, but to pinpoint the fault accurately and define the necessary corrective action.

Initial symptom

The machine reported a fault and an alarm appeared on the display, but the reason for the shutdown was not immediately clear.

Diagnostic direction

In this type of case, the displayed message, power supply, communication path, and the condition of the related sensors have to be assessed together.

What does this mean in practice?

Effective troubleshooting depends on interpreting the visible symptom, the information shown on the display, and the current operating condition as one complete picture.

Initial symptom

The motor stopped after a short period of operation and would not restart afterwards. The inverter gave no clear feedback, the display was inactive, and the equipment appeared to be switched off.

Diagnostic direction

With this type of symptom, checking the inverter alone is not enough. The control signals, power supply, and the condition of the related sensors and protective devices also need to be checked.

What does this mean in practice?

Not every inverter-related fault points to an actual hardware failure. In many cases, the cause is an interrupted signal or a protective state. The right solution comes from evaluating the full system, not just the inverter on its own.

Initial symptom

The entire production line stopped and production could not be restarted. The system did not provide a clear fault indication, and the cause was not obvious at first glance.

Diagnostic direction

During troubleshooting, the control chain was checked step by step: the power supply, starter circuit, control signals, and the related connections.

What does this mean in practice?

A wire had partially slipped out of a connector, so the control signal no longer reached the required point. Once the faulty connection was restored, the line could be started again immediately. It is a clear reminder that not every fault requires redesign or major intervention. Even a simple connection fault can cause a complete shutdown, and precise fault finding often leads to the faster and more cost-effective solution.

Initial symptom

The refurbished 75 kW electric motor was scheduled for reinstallation. Before being returned to production service, it was necessary to verify that the motor could start correctly, operate reliably, and that its basic electrical parameters were within acceptable limits.

Diagnostic direction

The motor was started under test conditions. The inspection included evaluation of startup behavior, current consumption, temperature characteristics, and observation of any abnormal noise or vibration.

What does this mean in practice?

For high-power electric motors, performing a test run before reinstallation can significantly reduce the risk of unexpected downtime and the need for repeated removal or maintenance work.

Initial symptom

After every start attempt, the equipment remained in a locked-out state and the control system reported a safety system fault. The „FAULT” message shown on the operator interface alone did not make it clear what was blocking the start, so the machine was not operational.

Diagnostic direction

During troubleshooting it quickly became clear that some element of the safety system was preventing the start. This is especially critical because safety relays and monitoring modules perform person and machine protection functions. If the system detects an irregular condition, it blocks machine start for safety reasons. The goal of the investigation was to precisely determine which part of the safety system was blocking the start.

What does this mean in practice?

In case of a safety system fault, a shutdown is often not caused by a defective component, but by a state that does not meet the safety conditions required by the system. After checking the safety system and identifying the root cause, the equipment returned to normal operation in a safe manner.

Initial symptom

The customer experienced that starting the machine failed intermittently. In some cases the equipment started normally, while in other cases it did not respond under the same conditions. The fault was especially hard to pinpoint because it did not occur continuously; such intermittent issues can cause significant downtime since the problem may not appear during on-site inspection. During the on-site check, an additional warning was observed: the Siemens SIMATIC S7-300 CPU313 BATF (Battery Fault) LED was blinking.

Diagnostic direction

During troubleshooting, we first examined how the machine start chain works. The checks showed that the PLC always issued the start command, so the issue was not located in the control program. By checking the auxiliary relays in the control cabinet under load, we identified a relay that behaved abnormally: the control signal arrived, but the switching action did not occur in certain instances. Based on measurements, the relay’s internal contact defect caused the starting problem. In parallel, we also checked the PLC status indicators: the CPU313 BATF fault indication suggested that the PLC buffer battery had aged.

What does this mean in practice?

Intermittent relay faults are among the most difficult categories of industrial troubleshooting. An internal relay contact may not fail completely, but only lose proper contact under certain conditions. That is why the machine can start correctly one time and fail to start the next. The BATF indication observed during the investigation did not directly cause the starting issue, but it was an important warning: the Siemens S7-300 buffer battery maintains memory during power outages. With a depleted battery, a longer power interruption can lead to program loss or data loss, which can significantly increase downtime.

Initial symptom

The machine was intermittently and unpredictably unable to start. Sometimes the Siemens LOGO! controller would restart briefly; other times it would shut down completely and only resume operation after switching the main power off and back on.

Diagnostic direction

During the investigation, it became clear that the problem always resolved after the system was fully de-energized and restarted. Since there were no indications pointing to the control program or wiring, the diagnosis focused on the Siemens LOGO! Power 24 VDC power supply. Measurements showed that the power supply intermittently caused voltage drop-outs, which were sufficient to trigger a restart or shutdown of the LOGO! controller.

What does this mean in practice?

In PLC systems, power supplies near the end of their lifecycle often do not fail completely at once. Instead, they typically indicate the problem through short, periodic voltage drop-outs. This fault is particularly difficult to identify because after switching the main power off and on again, the system may work properly—although the power supply has merely ‘recovered’ from a cooler state. After replacing the faulty LOGO! Power supply, the controller ran stably: the random restarts stopped, and the machine became reliably startable in every case.

Initial symptom

After starting, the dust extraction motor ran only briefly for about half a minute and then stopped. The motor protection tripped during every start attempt, meaning the extraction system could not run continuously. Sawdust remained on the conveyor belt.

Diagnostic direction

Since the motor did start but stopped regularly after a short time, the troubleshooting focused on the motor control. The investigation showed that the star-delta motor starter did not switch correctly: the motor stayed in star connection and did not transition to the delta stage. In star connection, the motor produces only about one third of its rated power—this may be enough for the short, unloaded running time, but under real load the motor draws excessive current, which is indicated by the motor protection tripping.

What does this mean in practice?

In star-delta starters, the switchover is controlled by the time relay and contactors. If the time relay does not provide the switching signal or the delta contactor does not pull in, the motor remains in star connection. Even though it ‘runs’ briefly, it stops inevitably under sustained load. After identifying and replacing the faulty time relay, the star-delta switchover worked correctly again. The motor reached its rated speed, and the dust extraction system operated continuously and reliably once more.