How do 2023 NEC updates protect NM and NMC cable from physical damage?

334.15 (B) Protection from Physical Damage 

Overview 

NM (Nonmetallic Sheathed) and NMC (Nonmetallic Sheathed Cable with Corrosion-Resistant Covering) cables are often chosen for exposed installations due to their ease of installation and cost-effectiveness. However, these installations are particularly vulnerable to physical stresses such as abrasion and environmental factors. NEC Section 334.15(B) mandates physical protection using various types of conduits and coverings to prevent damage to NM and NMC cables. The 2023 NEC update added an additional requirement, now mandating the installation of bushings or adapters to provide abrasion protection where cables enter and exit conduits and tubing.

Applying the 2023 Code 

NM (Nonmetallic Sheathed) and NMC (Nonmetallic Sheathed Cable with Corrosion-Resistant Covering) cables are commonly installed in exposed works, where they are placed on or attached to surfaces or behind panels. These installations are favored for their ease of installation, cost-effectiveness, and the ability to quickly modify or expand wiring systems. However, exposed installations are subject to physical stresses such as abrasion, impact, and environmental factors like moisture and temperature fluctuations. 

Section 334.15(B) of previous NEC versions outlined the physical protection measures for exposed NM and NMC cables. This section mandated that cables be protected from physical damage by using rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, Type RTRC marked with the suffix -XW, or other approved means. When cables pass through floors, they must be enclosed in the aforementioned conduits extending at least 150 mm (6 in.) above the floor. Type NMC cables installed in shallow chases or grooves in masonry, concrete, or adobe must be covered with plaster, adobe, or a similar finish. These requirements made certain that NM and NMC cables were adequately protected in most operating scenarios. However, the previous versions did not guide installers on how to protect cables at points where they emerge from the protective conduits and tubing. Such considerations were often made in the field based on the experience and intuition of the installers. To rectify this issue, the 2023 NEC version introduced new requirements for exposed NM and NMC cable installations. According to the updated language, when these cables are installed in conduits or tubing that protect them from physical damage, a bushing or adapter must be used to provide abrasion protection at the points where the cables enter and exit the raceway. This additional requirement guarantees that the cables are shielded from wear and tear caused by the sharp edges of conduits, which can lead to insulation damage and electrical faults. 

What’s New for the 2023 NEC? 

The comparison of 2020 NEC and 2023 NEC in terms of Section 334.15(B), is given in the Table below.