Mike Dolt Enterprises
Mike Dolt Enterprises
User: whiplash68, Location: Massachusetts
Asked on: Tuesday, March 29, 2011 at 7:54 am EDT
Answered on: Thursday, May 23, 2024 at 6:07 pm EDT
Question: Hello,New member here. Our Company is an OEM for the water/wastewater industry. We also design and build our own control Systems and panels. Our panel shop is UL-508A approved.I?m not sure if this is the right forum but I have an ongoing issue with our shop foreman regarding the service ground lug of control panels. He currently taps and bolts the ground lug right on the painted back panel (next to the service main breaker). I finally noticed he doesn?t (and learned he never has) scraped or grinds the paint off the back panel prior. To me it seems like common sense which is why I never took notice.I am looking for documentation in the NEC and/or UL that is specific to control panel grounding. I do see some articles referencing the NEC 250-96 but this seems to be regarding conduit grounding and not necessarily industrial control panel service power grounding.Any help on this would be greatly appreciated.Thanks!Steve
NEC Requirements NEC 250.146(A) requires that a metal enclosure for electrical equipment shall be grounded. NEC 250.146(B)(2) specifies that the grounding connection shall be made to the enclosure by a grounding conductor of the type specified in NEC 250.118.
UL Requirements UL 508A does not have specific requirements for grounding control panels. However, Section 18.1.
2.1 states that "the enclosure shall be grounded in accordance with the National Electrical Code (NEC)."NFPA 70E NFPA 70E Article 110 also requires that metal enclosures for electrical equipment be grounded.
Common Industry Practice
In the industrial control panel industry, it is common practice to: Remove any paint or other non-conductive material from the surface of the enclosure where the grounding lug will be attached. Use a tooth washer or other appropriate means to ensure good electrical contact between the grounding lug and the enclosure. Tighten the grounding lug securely to ensure a low resistance path to ground.
Reasons for Removing Paint Paint is a non-conductive material that can impede the flow of electrical current. Grounding connections rely on a low resistance path to ground to function properly. Removing paint ensures that the grounding lug is in direct contact with the conductive metal of the enclosure.
Conclusion
Based on the NEC, UL, and common industry practice, it is clear that removing paint from the back panel of a control panel before attaching the service ground lug is necessary for proper grounding. The shop foreman should be instructed to modify his current practice to comply with these requirements. Flag for review