If you ask a seasoned electrician how many No. 12 AWG conductors will fit into a 3/4″ EMT conduit system, you may get a response such as “one more!” While this is amusing (and typically true), there are precautions that must be taken according to the NEC whenever conductors are bundled together in a raceway, cable, or even in a ditch in the earth.
Changes to the 2020 NEC include the addition of several paragraphs in section 430.122. These changes will help the user to determine the correct ampacity for conductors used with power conversion equipment. The Adjustable Speed Drive is one type of power conversion equipment that provides a means of adjusting the speed of an electric motor, 100. A Variable Frequency Drive, VFD, is an adjustable speed drive that controls the speed, the RPM, of a motor by controlling the frequency and voltage supplied to a motor. The changes made in 430.122 Conductors – Minimum Size and Ampacity apply to Adjustable Speed Drive Systems.
New for the 2017 NEC Code-cycle is section 330.15, entitled “Metal-Clad Cable: Type MC Exposed Work.” This new Code section requires an exposed run of MC Cable to closely follow the surface to which it is mounted while enjoying a new permission that allows the MC cable to be installed on the underside of floor joists.
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