PLC panel wiring Considerations

Wiring guidelines:

  • Use the shortest possible wire length.
  • Use wire trays for routing where possible.
  • Avoid running wires near high energy wiring.
  • Avoid running DC wiring in close proximity to AC wiring where possible.
  • Avoid creating sharp bends in the wires
  • Avoid running input wiring close to output wiring where possible.

I/O Lines Noise

Hand ducts:

Leave at least 300mm between the power cables and the I/O or control wiring as shown:

Floor ducts:

Leave at least 200mm between the wiring and the top of the duct, as shown:


Separate CPM*A I/O lines, power and control lines, and power cables, as shown


Be sure to ground the functional earth and protective earth terminals together to less than 100ohm in order to protect against electric shock and incorrect operation from electrical noise. Be sure to sue a wire of at least 2mmsqre for grounding.

Crimp connector:

Always use crimp connector for the CPM*A’s power lines and I/O lines or else use a single wire line. Stray wire strands could accidentally short out.

Power supply wiring:

Wire a separate circuit for the CPM*A’s power supply wire so that there isn’t a voltage drop from the inrush current that flows when other equipment turned on.

When several CPM*A’s PLC’s are being used, it is recommended to wire the PCs on separate circuits to prevent a voltage drop from the inrush current or incorrect operation of the circuit breaker.

Use a twisted power supply wire to prevent noise from the power supply lines. Adding 1:1 isolating transformer reduces electrical noise even further.

Connecting inductive loads:

When connecting an inductive load such as relays and solenoids, connect a surge protector, diode etc., parallel with the load or contact. If the load is relay or solenoid there is a time lag between the moment the circuit is opened and the moment the load is reset.

C-R method:


If the supply voltage is 24 or 48V, insert the surge protector in parallel with the load. If the supply voltage is 10V to 200V insert the surge protector between the contact.

Diode method:


The diode-connected in parallel with the load changes energy accumulated by the coil into a current, which then flow into the coil so the current will be converted into Joule heat by the resistance of the inductive load.

Varistor method:


The varistor method prevents the imposition of the high voltage between the contacts by using the constant voltage characteristic of the varistor. There is time lag between the moment the load is reset.