To remove paint or not to remove paint?

[Bob O]

Who removes the paint on the back panel when mounting a ground bar? I thought this was the right thing to do or it can’t hurt. I started to think”more” about it this morning and now I am thinking different. Removing the paint on the panel between the ground bar and the panel would only matter if you removed the paint between the panel mounting hardware [studs] and then the enclosure mounting tabs. You would then have good metal to metal contact from the back panel to the enclosure and then the enclosure to what ever it is mounted to but you still need the correct size ground wire to begin with. I may be out in left field and others do all this and I haven’t seen it or I am just wrong in my thinking. What are you opinons?

[ssommers]

Read through the NFPA-79 2007 chapter 8 on Grounding & chapter 11 on Enclosures. I make sure my electricians use threaded holes to screw the grounding bar to the back panel. This eliminates the need to scrape paint because the clean threaded hole has no paint. Then they use a bonding jumper directly from the ground bar to the ground point of the cabinet & door. The cabinet ground stud may need a bit of paint scraping, but not if the cabinet manufacturer put plastic cap on it before painting. HTH! Susan

[BudMan]

Chrysler (Do's & Don'ts) and Ford (VOSS) both require Bonding the ground bar to a unpainted area. Plant Inspectors will look for this. From Chrysler (Do's & Don'ts) Equipment grounding conductors shall be terminated in each electrical enclosure on a common ground bar or terminal strip which is bonded to the unpainted sub-plate. From NFPA-79 8.2.3.3 Bonding of equipment with bolts or other identified means shall be permitted where paint and dirt are removed from the joint surfaces or where the bonded members are effectively penetrated. Bud

[Bob O]

Susan and Bud, Thanks for the replies and the link. I didn't know that book was online. Happy Holidays

[motion guru]

We have switched almost entirely to zinc plated backpans for noise suppression and ease of grounding with large scale drive systems. We can get drive mounting brackets, EMI shields, shelves, etc. plated cheaper than painting as well. Makes a nice package. Here is a shot of a panel under shop test - pretty much all hardware and backpan components are zinc plated.

[Pierre]

Nice work