250.12 Clean Surfaces.

Notice the paint scraped off from the pipe before the grounding clamp was installed. Not a bad idea to paint the surface after the clamp is installed to avoid future rust.
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Notice the paint scraped off from the pipe before the grounding clamp was installed. Not a bad idea to paint the surface after the clamp is installed to avoid future rust.

In order to ensure a good ground/bonding connection, Section 250.12 requires nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded or bonded to be removed from surfaces to ensure good electrical continuity.

Some equipment has dimpled or flared holes where a bonging screw will be installed and is not required to have the paint scraped off.

For other items, such as gas piping like in the image, paint must be scraped off to ensure a good metal to metal contact between the pipe and the bonging clamp. Paint or other nonconductive surfaces will not ensure proper continuity between the object being bonded and the bonding device.

Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.

2020 Code Language:

250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded or bonded shall be removed from threads and other contact surfaces to ensure good electrical continuity or shall be connected by means of fittings designed so as to make such removal unnecessary.

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250.12 Clean Surfaces.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true of a gas pipe requiring bonding?

A: It must be nonmetallic.
B: Conductive coatings must be removed.
C: Nonconductive paint shall be removed from the contact surface to ensure good electrical continuity.
D: It is not permitted to be bonded.
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