National Electrical Installation Standards

Standards as High as Your Own

Tuesday, October 31, 2023


Hello Charlie, Regarding the CQD from Thursday, August 3, 2023, relating to whether it is permissible for NM Cable to be exposed to weather elements during construction. The answer referenced Section 334.12(B)(4) specifying NM Cable is not permitted in Damp or Wet Locations:

 NM-B Cable is designed and rated for dry locations only.  However, it may be temporarily exposed to clean and uncontaminated rainwater during building construction (before being energized) without damage to the cables. The 2023 NEC® addresses this in Article 100 in the definition of “Location, Dry” stating that “A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.” Clean and uncontaminated rainwater in temporary contact with the cable prior to being energized will not have any adverse effects on the electrical properties or operation of the cable. Allow any moisture to dry before the cable is energized.  It is good practice to limit or eliminate the entry of water into the ends of the cables since the paper used in the NM-B Cable construction can wick water far into the cable.


Dave Watson

Principal Engineer



Hello Dave, thank you for sharing Southwire’s perspective regarding the installation of NM Cable in a building under construction. This is often a point of contention in today’s fast paced construction world. It is also important to remember that some local jurisdictions have local ordinances or clauses that address this practice, it is always best to consult the local AHJ on these types of matters.  

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