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NEC 250.12 Often Overlooked

jar546

jar546

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With so many different types of electrical equipment, more specifically cabinets and other assemblies, upon inspection we often don't know if ground lugs and bars are factory installed, field installed, or if they have proper metal-to-metal surface contact which is the purpose of NEC 250.12 - Clean Surfaces. Certain fittings, like locknuts and star washers, are engineered to maintain reliable electrical continuity through nonconductive coatings by ensuring a strong contact surface. The installer needs to secure these connections tightly, as this guarantees the locknut effectively establishes a solid electrical connection. This is one of the reasons why inspectors need to be familiar with changes in equipment and take a closer look at grounding and bonding during site visits.

Do you have a story to share about a violation you came across concerning NEC 250.12?
 
It happens with nearly every solar installation. The AC disconnect arrives with no ground bus. The label specifies a ground bus for the disconnect. The installers have lay-in lugs so that is what they use. Note the locknut.

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This is an example of the bus bar listed on the label.

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Since you mentioned locknuts, I tossed in a couple pictures. Seeing locknuts done wrong makes me suspect all of the work.

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