Controlling EMI & PLCs

[EEAutomEng]

I have heard different recommendations on methods of grounding when it comes to PLCs. What type of fasteners should I use when connecting the equipment grounding conductors to the ground bus? I have heard recommendations for zinc-plated screws and star washers. Can anyone offer a detailed explanation why plated screws should be used?

 

[dbaird]

Get a copy of "Industrial Automation Wiring and
Grounding Guidelines".

David Baird
Sr Controls Engineer

 

[bmsg]

We connect the equipment grounding conductors (usually copper wire) to the ground bus (usually, a copper bar, typically, about 25mm x 6mm cross-section, say, with holes every 25mm, say for fastening screws to secure different grounding conductors) using brass screws, and I have never encountered ant problem.
Regarding the use of zinc-plated screws, I believe the plating has to do with anodic corrosion, which occurs at the junction of dis-similar metals - a phenomenon which is probably accelerated by the flow of an electric current through the junction.