Conventional Wiring | Marshalling Rack | PLC Panels

Conventional Wiring is one in which each individual instrument is wired separately to the marshalling rack.

The signal travel from each instrument to the IO card on separate wire /terminal dedicated for the same.

Typical type of Conventional wiring contains following steps for wiring.

  • Generally a paired cable with shield wireruns from field instrument like transmitter, positioner etc connecting with + & - terminal of instrument to the terminals in Junction Box.

  • Junction Box is generally metallic enclosure consisting long strip of terminal where wire from various field devices comes and terminate

  • From Junction Box generally a multi-pair cable runs to the marshalling cabinet kept at safe shelter.

  • Each pair of multi- pair cable carries signal of one device etc.

  • Generally these multi pair cables thick cable in which each pair of cable has their individual shield and as well as overall shield wire.

  • This multi- pair cable terminates at FTA( Field Terminal assembly) in Marshalling Cabinet.

  • From these FTA arises cross cabling in which each signal is carried to their respective cards. i.e. Analog Input to Analogue Input Card , Digital Output to Digital Output card for Automation system to process.

Few things you should remember while performing conventional wiring instrument

  • Instruments are not connected with ground wire and it is generally Cut & Taped at instrument.

  • Ground wire is generally connected to grounded at marshalling end only to avoid forming the ground loop which completes the circuit and leads to flow of current and faulty signal

  • Instruments , Junction Boxes and marshalling racks generally have Protective Body earthing which help protection from current discharges in body, lightning etc

  • Generally it is advisable for longer length signal connection.

  • It is more reliable but requires more cable and laying/maintenance of cables.