Code Change Summary: Electrical metallic tubing (EMT) is now permitted to be used underground where conductors are subject to physical damage.

This code section must be read carefully and the gray shading that points out the code change was missing in the first published edition of the 2017 NEC^®.

NEC section 300.5 is all about underground installations. Subsection 300.5(D)(4) provides specific requirements for protecting underground enclosures and raceways from physical damage. In the 2014 NEC^®, underground conductors subject to physical damage were required to be installed in rigid metal conduit, intermediate metal conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent. This is still true but in the 2017 NEC^®, EMT was added to the list of suitable protection methods.

This new code change has dumbfounded many inspectors and electricians. Even though the 2017 NEC^® allows EMT to be used to protect underground conductors from physical damage, there are many who will never install EMT underground or allow it to be installed in this manner.

Though the concept of protecting underground conductors with EMT is new in subsection 300.5(D)(4), EMT has been allowed underground for many code cycles in Article 358.

Section 358.10(B)(1) allows galvanized steel and stainless steel EMT, elbows, and fittings 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”.

Most installers prefer to use a more robust wiring method underground in order to avoid potential service calls from EMT corroding underground or where it emerges from grade.

Below is a preview of Article 300. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.