Article 640 of the 2017 NEC provides different requirements for permanent installations of this equipment (Part II) than it does for installing portable versions (Part III). One of several places we can see that is in the requirements for flexible cords and cables [Sec. 640.21 and Sec. 640.42].
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NEC Rules for Flexible Cords and Cables for Audio Signal Processing Equipment
Understanding Article 640 of the 2017 NEC