Not being an electrician but being an electrical engineer. I am not a PE.
If you are talking about modifying a piece of equipment, I don't think the NEC applies in this application.
If you are talking about a switchboard type application where you are monitoring multiple power sources, I do not know what standards applies. I will venture a GUESS that as long as the maximum voltage difference between adjacent conductors is less than 600 V, any suitable insulated conductor would be OK.
Aside from that, the general concerns I have dealt with in these applications are:
1) Wire insulation has be suitable for the highest voltage it could be in contact with, assuming ANY single fault insulation failure.
2) Sensitive signals should be shielded and or seperated from power wiring.
3) Anchor wiring so it does not rub thru insulation.
4) Make as easy as possible to service. Nylocks are your friend. Loose split and flat washers will fall into undesired locatings.
5) DOCUMENT CHANGES and make it easy to find the documents. SUITABLE LABELS are your friend.
When I assembled control panels for automated equipment, we typically used THHN stranded for all control and power wiring 16 AWG and larger. TFFN stranded was used for 18 AWG and smaller. All wiring I dealt with were typically 600 V and less.
Red was for AC wiring less than 300 V.
White was Neutral only.
Black was AC wiring between 600 and 300 V.
Blue was all low voltage DC wiring.
Blue with a white tracer was for the DC common IF IT WAS BONDED TO CHASSIS.
Green was for chassis / ground.
YELLOW was used for power from other systems that were not deenergized when the main disconnect was opened.
All hinged doors and removable covers had braid or Green bonding wires.
Fuses were grouped logically.
Leave approximately 10 % open space, terminals, DIN rails, ground terminals, etc. for expansion.
Label all wires. NEATNESS COUNTS !
Convience outlets and cabinet lighting, if appropriate, are nice.
Larry C
