STAR-WIRED NETWORK LED TO GROUNDING FAULTS
Prof. Max Felser of the PROFIBUS Competence and Training Center at the Bern University of Applied Sciences explains why a star-wired grounding system caused a prototype PROFIBUS drives network to keep failing.
Problem/challenge: A manufacturer had built a prototype machine using PROFIBUS. When running, the machine would work OK for around half an hour but would keep stopping because of PROFIBUS network errors.
Analysis: Having a look at the cabinet we see that it is cabled as described in a schoolbook: make the grounding in a star! So the integrator has mounted all rails and frequency converters on isolating bolts, and wires the ground with 2.5 mm2 cables to one central grounding point in the cabinet. The installation runs fine, but there is a considerable current flowing in these ground wires and this leads to voltage differences between the different devices inside the cabinet. As soon as the drives are running under load, the voltage differences get too high and the PROFIBUS network collapses.
Solution: Mount all devices and also the frequency converters directly to the metallic backplane of the cabinet and use that as the “central grounding” point. A similar cabinet installed in this way by a different installer runs perfectly, even with much larger drives!
Where you can get more help: Our PROFIBUS Competence and Training Center at the Bern University of Applied Sciences offers support in solving these and many other challenges in the field. You can find this guideline and other useful information in my “PROFIBUS Manual”, which can be DOWNLOADED HERE
PI Competence Centers, Training Centers and Test Labs can be found in all regions of the world. They provide a wide range of support services for PROFIBUS and PROFINET applications. There’s a full listing HERE