kolyur
Lifetime Supporting Member + Moderator
Here's the setup: I have a small piece of equipment that runs on 120vac. The main panel has a grounded steel backplane in a plastic (FRP) enclosure. An additional small steel enclosure houses an HMI, which is powered by 24vdc through a cable that runs back to the main (plastic) box. Both boxes are bolted to the steel machine frame. The only high voltage external to the main box is the power cord and a cable running to a motor.
My question is this: What extra steps do I need to take for proper grounding? If I had used a metal box, the frame and second enclosure would already be grounded. But in this case the plastic box was not my choice. Should the HMI box be separately grounded even though it only contains 24v? Should I bond the machine frame to the backplane with a separate wire, which would also ground the second box? None of the above?
My question is this: What extra steps do I need to take for proper grounding? If I had used a metal box, the frame and second enclosure would already be grounded. But in this case the plastic box was not my choice. Should the HMI box be separately grounded even though it only contains 24v? Should I bond the machine frame to the backplane with a separate wire, which would also ground the second box? None of the above?
