Hi Curt, Originally the enclosure was going to be conversion-coated Aluminum and the ground lugs were Tin-plated. In the unending quest for cost reduction, this changed to a galvanized steel enclosure with plain brass lugs. The zinc/brass match set off all sorts of galvanic corrosion alarm bells for me which is what prompted re-reading the standards. This machine will be sold worldwide, but mostly in the US, Canada, and the EU. We typically apply IEC 60204-1 for electrical safety and EN 415-10 (Packaging Machinery: General).
Thanks, Mark Stultz | CMSE® | Sealed Air | Automated Packaging Systems | Streetsboro, OH | 330-342-2402 From: Curt McNamara <[email protected]> Sent: Wednesday, December 16, 2020 12:50 PM To: Stultz, Mark <[email protected]> Cc: [email protected] Subject: Re: [PSES] Use of Electrical Enclosure as the Ground Bus CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe. In my experience enclosure metal is usually not satisfactory for a low impedance connection that remains corrosion free. Aluminum is typically anodyzed, and anodyzing is (mostly) non-conductive. Most steel is painted or plated. Clearing off the surface coating will allow corrosion to happen. There are some plating processes which could allow a low impedance connection. It is critical to examine the materials that come in contact with each other, as many combinations will lead to corrosion after installation. https://www.sharrettsplating.com/base-materials/aluminum<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.sharrettsplating.com%2Fbase-materials%2Faluminum&data=04%7C01%7Cmark.stultz%40sealedair.com%7C375bf7546088472689f008d8a1eafa81%7C2691a2514c384643af0b0c0982f197bd%7C0%7C0%7C637437377893605604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=FyHpw25kbguN8ifem2LppIQoWEV769Fm9WCg2nTE01w%3D&reserved=0> My understanding is that if the metal types are the same, the risk of corrosion is lower. Check out the chart on the lower right of this page. https://galvanizeit.org/corrosion/corrosion-process/galvanic-corrosion<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgalvanizeit.org%2Fcorrosion%2Fcorrosion-process%2Fgalvanic-corrosion&data=04%7C01%7Cmark.stultz%40sealedair.com%7C375bf7546088472689f008d8a1eafa81%7C2691a2514c384643af0b0c0982f197bd%7C0%7C0%7C637437377893615572%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=hNe0bmnjWcFoQ%2Fb4pg4%2BsfADOVBOQESf%2FYmZJHKUCFQ%3D&reserved=0> It is possible to get ground studs installed at time of enclosure manufacture, it will reduce these risks. What market is this for, and what safety standard will be applied? Curt McNamara, P.E. On Wed, Dec 16, 2020 at 11:04 AM Stultz, Mark <[email protected]<mailto:[email protected]>> wrote: Hello, I'm working with an engineering team that wants to use the electrical enclosure as the bus for the bonding circuit. The item is a smallish piece of machinery for indoor industrial use. The motivation is to save the cost of a separate copper busbar and reduce the length of bonding wires inside the enclosure. IEC 60204-1 appears to allow this with stipulations: Metal enclosures or frames or mounting plates of electrical equipment, connected to the protective bonding circuit, may be used as protective conductors if they satisfy the following three requirements: * their electrical continuity shall be assured by construction or by suitable connection so as to ensure protection against mechanical, chemical or electrochemical deterioration; * they comply with the requirements of 543.1 of IEC 60364-5-54:2011; * they shall permit the connection of other protective conductors at every predetermined tap-off point. NFPA 79 appears to not allow this (unless the enclosure were made of copper...): 8.2.2.1 Conductors used for grounding and bonding purposes shall be copper. Stipulations on stranding and flexing as outlined in Chapter 12 shall apply. What are your thoughts on connecting the bonding system this way? Is NFPA 79 as inflexible in this regard as I am reading it? 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