Hoping this is related enough to ask here, and not start a new thread . . .
For a wall-mounted TV installation, I usually place a typical old-work box with a standard or recessed receptacle behind the TV, with a length of 14-2 NM fed from a second old-work box installed below, at normal receptacle height. In this box, I run a power cord through a 1-hole wall plate and wire-nut the conductors to the 14-2.
I have in effect constructed an in-wall extension cord made with code-compliant in-wall components. The customer then plugs the cord into whatever power strip or surge protector the rest of the audio/video equipment plugs into, providing the same protection and avoiding any chance of different-circuit electrical noise or currents.
My question is whether the NEC has jurisdiction over, or rules covering such an installation. Having no direct connection to the premises wiring, is it nonetheless an installation that, technically speaking, is subject to permitting and inspection requirements? I have seen similar in-wall kits that actually use a rubber extension cord.
If i understand how you are doing this, I don't believe this is compliant. Flexible cords cannot be installed through holes in walls unless you meet the conditions in 400.10(A)(11).
400.12 Uses Not Permitted. Unless specifically permitted in 400.10, flexible cables, flexible cord sets, and power supply cords shall not be used for the following:
(2) Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors
400.10 Uses Permitted. (A) Uses. Flexible cords and flexible cables shall be used only for the following:
(11) Between an existing receptacle outlet and an inlet, where the inlet provides power to an additional single receptacle outlet. The wiring interconnecting the inlet to the single receptacle outlet shall be a Chapter 3 wiring method. The inlet, receptacle outlet, and Chapter 3 wiring method, including the flexible cord and fittings, shall be a listed assembly specific for this application.