[angiosperm]

Wires from panels in parallel will all be at, typically, 48VDC. Voltages add only when you wire in series. No "live parts" are exposed in modern systems.

The quoted regulations govern construction. Residents have much greater latitude. All the appliances mentioned are approved for use with rated extension cords.

[thereisnospork]

Notably, even in construction/industrial settings, there are typically broad exemptions for 'low voltage' wiring[0], typically defined as < 50V or < 48V, justified because there is no/little 'hazard' associated with voltage that low. To wit you can, for instance, just duct tape/zip tie some flexible wire/cabling to the wall if it is only carrying e.g. a 5V power to a sensor, some LEDs, or other equipment. Which I have done and passed fire marshal inspection on multiple occasions in multiple jurisdictions[1].

The regs (and by extension a fire marshal) would probably be unhappy about the extension cord, but a. 'everyone does it'[2], b. 'surge protecting' cords are generally exempt (at least in my jurisdictions), and c. trivially rectified by hard wiring one or both ends of the extension cord to hard wire or create a 'wire + receptacle'.

[0]Current limitations, watt-hr limitations, etc. may apply in this case.

[1]Obligatory disclaimer: not advice, follow your local regulations, etc.

[2]The response would be a 'please fix this' and not fines or worse.

[millebe]

NEC chapter 7, article 720 covers wiring of less than 50V. It's important to note that elsewhere in the NEC and other codes, "low voltage" is defined as <600V, <1000V, or <2000V, depending on the code and code cycle.

Your fire marshal might have passed 5V cabling duct taped to a wall, but it would be in violation of 720.11:

    720.11 Mechanical Execution of Work
    Circuits operating at less than 50 volts shall be installed in a neat and workmanlike manner. Cables shall be supported by the building structure in such a manner that the cable will not be damaged by normal building use.

[thereisnospork]

Good point about 'low voltage' -- which does not mean the same thing in all contexts.

>Circuits operating at less than 50 volts shall be installed in a neat and workmanlike manner. Cables shall be supported by the building structure in such a manner that the cable will not be damaged by normal building use.

The only possible violation of 720.11 for duct taping <50V cables to walls I can see is 'neat and workmanlike' which is vague at best; there is nothing intrinsically 'un-neat' about an attachment method unless maybe using like literal chewing gum or something else absurd or just categorically unfit for purpose. I'm hardly going to call it best practice, but duct taping a (small to modest-sized) zip-tied bundle of low voltage cables to say route it up and around a door is perfectly cromulent in my experience.

Likewise I'd feel perfectly comfortable (from both a safety and code/inspection perspective) supergluing cables to dry wall (on the more absurd end), or p clamp'ing w/ drywall screws, or using adhesive zip tie mounts, etc.