I/we normally don't see the signal wire marked if the sensor cable wires are all landed beside each other in the panel. None are marked on most to all systems we have here or that I have seen in recent years elsewhere. For any panels we build in-house (not a lot) we would only mark the sensor cables and none of the actual wires. An exception may be where the signal wire is landed some distance away in the panel from the other wires in the same sensor cable. But normally they are kept together where possible. For industry standard DC M12 sensor cables it is usually pretty obvious to Electricians that the Brown is 24V, Blue is 0V, Black is N/O signal and White is N/C signal (if used). But yes, I have also seen systems where not only the signal wire is marked, but all wires are marked. It does no harm but costs a little in time, money and effort. I'm sure for professional panel builders there may often be customer specifications where each wire must be designated and marked, especially in higher level or Government facilities. Maybe petrochemical, pharmaceutical, nuclear, I'd imagine?
Our cables are marked with two designations -
1st Designation > =
Schematic Page-
Device Designation
Example:
=100-WS1/2
100 = Schematic Page
WS1/2 = Device Designation
2nd Designation > (+
Terminal Group-
Terminal Section)
Example:
(+1C-XL4)
+1C = Terminal Group
XL4 = Terminal Section
The schematics are of course important for sensor designation. It's good practice to illustrate both the pin numbers of the M12 plug socket arrangement and the wire colours. A Cable Designation list should also be drawn up to cross reference each cable in the system. A panel layout schematic can also guide you to where the terminal designation physically is in the panel.
This is a sample from one of our latest systems from a very reputable global OEM who would be adhering the the very best in wiring standards...
(Note: the photos are just samples and not intended to represent the sensor cable in the schematic)
Note how even multi-core cable wires are not individually marked. The colours are illustrated in the schematic so it's not really essential. If it was done though, I wouldn't complain.
Regards,
George