The National Electrical Code (NEC) allows RSC, IMC and EMT to be installed in concrete, as noted in their respective Articles:

RMC Section 344.10 (B) Corrosion Environments. "RMC, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."

IMC Section 342.10 (B) Corrosion Environments. "IMC, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."

EMT Section 358.10 (B) Corrosion Protection. "Ferrous or nonferrous EMT, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."

Rigid steel conduit, IMC and EMT are all "protected by corrosion protection" due to the zinc coating that is applied during the manufacturing process. However, in severe corrosive environments, the designer or AHJ may decide to require additional or supplementary protection.

Underwriters Laboratories' Electrical Construction Equipment Directory contains information relating to limitations or special conditions applying to products listed by UL.

The Directory states that supplementary corrosion protection is not required on rigid steel conduit and IMC when installed in concrete.

The Directory states the following for EMT: "Galvanized steel electrical metallic tubing installed in concrete on grade or above generally requires no supplementary corrosion protection. Galvanized steel electrical metallic tubing in concrete slab below grade level may require supplementary corrosion protection."

It also states that "Wherever ferrous rigid conduit (or intermediate metal conduit or electrical metallic tubing) runs directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil."

In the STI Guidelines for Installing Steel Conduit/Tubing (see "Resources/Downloads", then "Installation Guide" ), we recommend that supplementary corrosion protection be applied to the conduit/tubing a minimum of 4 inches on each side of the point where it emerges. This LINK will take you to an individual page from the Installation Guide pertaining to concrete installation.

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