The 2014 NEC has added language that affects only metal-clad (MC)
cables with phase conductors 250 kcmil or larger. You may think of MC cable as primarily a branch circuit wiring method, but larger size MC cables are often used for feeder circuits in high-rise buildings or other large installations. Many of the support and securement requirements are the same regardless of the size of the cable; however, there are different securing requirements for MC cable with very small or very large conductors.
A proposal and comment submitted during the 2014 NEC revision cycle, along with testing performed at UL, resulted in a change to the securing requirements in 330.30(B). For vertical installations, any listed MC cable is allowed to be secured at 10 foot intervals (rather than the 6 foot interval required in the 2011 NEC) as long as the cable contains ungrounded conductors 250 kcmil or larger.
Note that the language says that the MC cable must be listed, not “listed for the purpose.” UL 1569 is the product standard used to list MC cable, and there is no special test in the standard for MC cable used in a vertical installation. Additionally, there are no requirements in the NEC for supporting the conductors inside the cable, unlike the requirements for conductors in raceway.
Any of the commercially available MC cables listed to UL 1569 having ungrounded conductors 250 kcmil or larger can be used with this new less stringent securing requirement. This change will allow for fewer clamps in vertical installations, while still providing a safe and secure installation.