Introduction to Industrial Automation

6.10.3   Grounding

The elementary prerequisite for a seamless and safe operation of an industrial installation with 

one or more PLCs is the proper grounding of all the involved plant units, specifically PLCs. Poor 

grounding of a PLC is often the cause of operating problems that:

  1. Are not easily identifiable and cannot even be categorized if they are due to software (incor-

rect programming) or hardware failures

  2. Can only be explained by very specific measurements; many times, the programming engi-

neer wastes a lot of time searching for the cause of the malfunction in the program, while in 

reality it is a hardware problem

  3. Are not only relevant to the functionality of the PLC, but also to the safety of the personnel

  4. Are directly connected to the sources of electric noise and interference that are obscure, 

multiple, and multiform

Thus, in order to be sure from the beginning that similar problems will not be encountered, 

special attention should be paid to the implementation of the ground circuit. A primary source 

of technical information on how to ground a PLC comes directly from its manufacturer. With 

the help of electrical diagrams, the method of power supplying and grounding should be clearly 

defined, not only for the central unit and the power supply of the PLC but also for the different 

I/O modules. A second basic source of technical information is the industrial electrical installa-

tion regulations. Due to the fact that the electrical grounding is quite a huge field in electrical 

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