In the past week, we acquired a new piece of equipment from Germany equipped with Siemens controls. While our company typically uses A.B. controls for most equipment, this new addition has posed a challenge. I am currently troubleshooting an issue with very little success. The equipment features 3 drive motors on VFDs that are functioning properly for Start/Stop/pause/increase, decrease speed commands. However, there is a pump/motor (not on a VFD) that, when selected on the HMI, instantly trips the main panel disconnect. Even after removing the motor leads from the contactor, the issue persists. It appears that the PLC is detecting a ground fault immediately, despite efforts to isolate the line/lead cables or the motors' overload. The output card shows the correct voltage and appears to be functioning properly. Could this problem be related to programming?
If your Main Breaker is not tripping, it is likely an issue separate from the PLC or program. To determine the cause, it is important to thoroughly investigate the wiring of your machine or system.
If the circuit trips only when the pump is running and not when other equipment is on, there may be another issue causing increased current draw. It is important to check the current draw without the pump, including the contactor. It is possible that a previous similar problem was due to the main switch tripping. Disconnecting one motor or contactor control resolved the issue, but no matter which one was disconnected, the circuit would not trip. This was despite the actual current draw being well within the disconnect's rating. The problem was eventually traced back to a faulty isolator, potentially with a magnetic trip circuit. This unexpected issue highlights the importance of thorough troubleshooting in identifying the cause of the trip.
Parky suggested that if the breaker only trips when the pump is running, it could indicate a different issue causing increased current draw. It's important to check the current without the pump and including the contactor, as an extra load could be the culprit. In a similar situation, a main switch was found to be tripping due to a faulty isolator, even though the disconnect was rated higher than the actual current drawn. Sometimes, disconnecting a motor or contactor control can help determine the source of the problem. Even after removing motor leads, the breaker continues to trip when the contactor engages, hinting at a potential cross phase issue within the panel.
One essential step would be to lift and adequately insulate the wires leading to the motor contactor's top. In your mention of a "motor/pump", it's important to clarify if it's a pump or a reversing starter. There may be an issue causing both forward and reverse functionalities to engage simultaneously, which could lead to serious malfunctions. It's crucial to address this issue promptly to prevent any potential dangers.
Is the main breaker equipped with a trip coil? It is common to find control panels that utilize this feature to automatically trip the breaker under various circumstances. I have come across multiple Italian control panels that are set up to trip the breaker when the cabinet door is opened. Additionally, in an older German control cabinet, I have observed the use of this mechanism to provide two disconnects for emergency stops - one at the main breaker and another at the individual contactors for all the motors. This setup may interact with the Programmable Logic Controller (PLC), as it could potentially bypass the automatic trip if a single motor without a Variable Frequency Drive (VFD) is selected. It is possible that VFDs have integrated Safe Torque Off (STO) functionality to stop in the event of an emergency, with Direct Online (DOL) motors being the only exception.
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Answer: - The issue of the main panel disconnect tripping when selecting the pump/motor on the HMI could be due to a ground fault detected by the PLC, even after isolating motor leads and checking the overload. Further troubleshooting may be required to pinpoint the exact cause.
Answer: - While the issue could potentially be related to programming, it's essential to thoroughly check and test the connections, cables, and components to rule out any physical faults before focusing on the programming aspect.
Answer: - Troubleshooting steps may include verifying the wiring connections, checking for any shorts or faults in the system, inspecting the grounding, and reviewing the programming logic to ensure proper operation and prevent false ground fault detections leading to the main disconnect tripping.
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