Question: Can RMC, IMC and EMT be direct-buried?

Answer: The National Electrical Code (NEC) allows the direct burial of all three products as noted in their respective Articles:

Galvanized Steel RMC Section 344.10 (B) Corrosion Environments. Galvanized steel 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. Galvanized steel 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. Galvanized steel 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 approved as suitable for the condition.”

Members of the Conduit Committee of the Steel Tube Institute apply a zinc coating to galvanize steel RMC, IMC and EMT. Therefore, these products are “protected by corrosion protection” as the Code requires. However, in severe corrosive environments, the designer or AHJ may decide to require additional or supplementary protection.

UL Product IQ (https://iq.ulprospector.com/en) contains information relating to limitations or special conditions applying to products listed by UL. This information is provided by product category:

DYIX Guide Information for Rigid Ferrous Metal conduit states that galvanized steel RMC does not generally require supplementary corrosion protection when installed in soil unless: 1. Soil resistivity is less than 2000 ohm-centimeters. 2. Local experience has confirmed that the soil is extremely corrosive.

DYBY Guide Information for Intermediate Ferrous Metal Conduit states that galvanized steel IMC does not generally require supplementary corrosion protection when installed in soil unless: 1. Soil resistivity is less than 2000 ohm-centimeters. 2. Local experience has confirmed that the soil is extremely corrosive.

FJMX Guide Information for Electrical Metallic Tubing states that In general, galvanized steel EMT in contact with soil requires supplementary corrosion protection. Where galvanized steel EMT without supplementary corrosion protection extends directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.

Galvanized or stainless steel EMT that is provided with a metallic or nonmetallic coating, or a combination of both, has been investigated for resistance to atmospheric corrosion. Nonmetallic outer coatings that are part of the required resistance to corrosion have been additionally investigated for resistance to the effects of sunlight.

(Note: Soils producing severe corrosive effects have low electrical resistivity, expressed in ohm-centimeters. Local electric utilities commonly measure the resistivity of soils. The authority having jurisdiction (AHJ) has the authority to determine the necessity for additional protection.) EMT in direct contact with the soil generally requires supplementary corrosion protection. However, local experience in some areas of the country has shown this to be unnecessary.