Corrosion and deterioration can happen to almost everything; however, it is especially serious when it happens to an electrical system and the wiring methods supplying power to the system.

Article 300 is an introductory article to Chapter 3 in the National Electrical Code and covers methods and materials. Section 300.6 provides information and requirements for protection of wiring methods and materials against corrosion and deterioration, and it was rewritten and reorganized for the 2005 NEC. 

Staying relatively unchanged (for the most part) since 2005, Panel 3 (of which I was a member from 2002–2020) has struggled to provide the proper wording to cover the replacement of any galvanizing of ferrous metal raceways that may have been removed due to cutting and rethreading of these raceways. I believe Panel 3 has finally discovered the specific text in the 2023 NEC that will provide the necessary way to deal with all aspects of protection for these raceways.

New text in 2002

In 300.6 of the 2002 NEC, new text was added: “Ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, metal elbows, couplings, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material, such as zinc, cadmium, or enamel.”

The last sentence in this text stated that, “Where corrosion protection is necessary and the conduit is threaded in the field, the threads shall be coated with an approved electrically conductive, corrosion-resistant compound.”

We were relying on the electrical inspector, who is going to “approve” the installation, to determine whether the coating being used as a replacement for the factory-applied corrosion protection was appropriate. The replacement for the factory coating must be able to provide the necessary physical protection and be electrically conductive as part of the effective ground fault current path. How could the electrical inspector know if the field-applied coating was electrically conductive just by looking at it? Impossible at best, unless the coating material was available when the inspector was there.

For repair, some electricians used spray-on galvanizing that had never been tested for conductivity. On top of that, many electricians would say that they did not thread the raceway in the field. Some would state that the threading was done at the shop or supply house. Technically, they were correct, but that way of thinking needed to be corrected so appropriate protection could be applied.

2005 edition

In the 2005 NEC, we totally revised the layout of the section to make it easier to use. We also added an exception to 300.6(A) that stated protective coatings were not required for stainless steel raceways. That exception read, “Exception: Stainless steel shall not be required to have protective coatings.” 

We did not add any further requirements within the exception for when electricians would field cut and thread stainless steel raceways. We probably should have added a requirement for that field modification. No changes occurred on this issue until the 2014 NEC when we added an informational note that stated: “Field-cut threads are those threads that are cut in conduit, elbows, or nipples anywhere other than at the factory where the product is listed.”

However, the problem with putting that information into an informational note is that they are not enforceable. We provided further background information that reinforced the intent of providing added protection when conduit, elbows or nipples were threaded in the field.

The 2023 Code

Finally, 300.6(A) has been modified in the 2023 NEC by inserting the following: “Ferrous metal raceways, cable trays, cablebus, auxiliary gutters, cable armor, boxes, cable sheathing, cabinets, enclosures (other than surrounding fences and walls), elbows, couplings, nipples, fittings, supports, and support hardware shall be suitably protected against corrosion inside and outside (except threads at joints) by a coating of approved corrosion-resistant material. Where corrosion protection is necessary and the conduit is threaded anywhere other than at the factory where the product is listed, the threads shall be coated with an approved electrically conductive, corrosion-resistant compound.”

By removing the informational note and inserting the text into mandatory requirement within 300.6(A), we now have text that should make corrosion protection very clear. 

Unfortunately, an electrician told me at a meeting where we were doing 2023 NEC changes that rigid nipples often come from the electrical supply house that do not appear to have appropriate factory-applied galvanizing. My solution is to apply a surface coating on the nipple, on any field-threaded elbow and on any metal raceway that is field-threaded with an approved conductive anti-corrosion material. Ensure conductivity while providing substantial corrosion protection.

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