When routing power and I/O signal wiring to and within a PLC enclosure, you should:

A) use the shortest possible wire runs for I/O signals.
B) never run signal and power wiring in the same conduit.
C) run low-level signal conductors as shielded twisted pair.
D) all of these.

It is best to use the shortest possible wire runs for I/O signals to minimize electrical interference and noise, especially in high-speed applications. Running power and signal wiring in the same conduit can introduce electromagnetic interference and noise into the signal lines, so it is best to keep them separate. Low-level signal conductors, such as analog signals or sensor inputs, are susceptible to noise and interference, so using shielded twisted pair cable can help to reduce these effects. Therefore, all of these options should be followed when routing power and I/O signal wiring to and within a PLC enclosure.