What is Marshalling Cabinet?

Between the system cabinet and the field junction boxes, the marshalling cabinet serves as an interface. From the field junction boxes to the marshalling cabinet, the major cables are run. The system cabinet IO cards’ prefab cables are likewise terminated in the marshalling cabinet.

Table of contents

  • Marshalling Cabinet
  • Cabinet Types
    • System Cabinet
    • Marshalling Cabinet
    • System cum Marshalling Cabinet
    • Electronic Marshalling
  • Common Mistakes
  • Electronic Marshalling Cabinets
  • Dedicated Marshalling Cabinets
  • System Cabinet Photo
  • Marshalling Cabinet Photo
  • Closure view of marshalling cabinet components

The major termination point for incoming field cables is the marshalling cabinet. Furthermore, the wires’ other ends are connected to system cabinets, which house the I/O modules and controllers.

Marshalling Cabinet

As shown in the diagrams below, traditional cabling involves connecting field inputs and outputs to a field junction box, then using a home run (Multipair/Multi-core) cable to connect the signals from the field junction box to a marshalling panel in a control room / Instrument Technical Room, and finally using cross-wiring to connect the signals to their respective termination assemblies.

Marshalling cabinets, to put it simply, are situated between junction boxes and the control system. Field cables are linked and cross-wiring is performed within the marshalling cabinets to organize the signals according to the I/O modules. Prefabricated cables can be used to link the marshalling cabinets to the I/O modules in this manner.

Cabinet Types

  1. System Cabinet,
  2. Marshalling Cabinet,
  3. System cum marshalling cabinets,
  4. Electronic Marshalling

System Cabinet

Controllers, I/O Modules, Communication Modules, Power Supply Modules, Diode Oring, and other essential components of the system cabinet are included.

Marshalling Cabinet

Isolators/Barricades, Relays, Terminal bocks for field home run cables, shield terminals, Terminal board for cross-wiring, Power supply modules, and Diode Oring are the main components of a marshalling cabinet. For big I/O systems, a dedicated marshalling cabinet is used.

When separate marshalling cabinets are employed, they can be delivered to the job site early in the project to terminate field wires. Prefabricated cables are inserted between marshalling and system cabinets later, when system cabinets are available. Separate cabinets offer the benefits of factory acceptance testing and delivery in stages.

However, installing the prefabricated cables necessitates on-site labour. When the FAT for the system and the Marshalling cabinet are completed at the same time, the link between the two cabinets is disconnected before shipping to the job site.

System cum Marshalling Cabinet

Controllers, I/O Modules, Power Supply Modules, Diode Oring, Isolators/ Barrier, Relays, Terminal bocks for field home run cables (main cables), shield terminals, and Terminal board for cross-wiring are the major components of a system cum marshalling cabinet.

For smaller I/O systems, this combination system cum marshalling cabinet is employed. In most cases, packaged control panels with fewer I/Os can be used with the combined system and marshalling cabinets.

The controller, I/O modules, terminals, relays, barriers, and other components are all installed in one cabinet. Prefabricated cables are installed in this situation.

Electronic Marshalling

Field cables are directly attached to I/O modules due to universal I/O ideas. In comparison to traditional marshalling cabinets, this removes terminal blocks, cross-wiring, and premade cables. Software can be used to change the type of I/O.

I/O cards will feature barrier slots for installation or associated adaptors for field cable termination on I/O cards for fundamentally safe design.

Common Mistakes

Common mistakes that can be found during factory acceptance test or site loop checking activities.

  • The incorrect multi-pair/multi-core cable was utilised (individual shield, overall shields)
    Terminals with loose wire connections.
  • lugging, ferrule, and termination are all incorrect.
  • Cable glands were chosen incorrectly.
  • In Junction boxes/marshalling cabinets, the termination is incorrect.
  • MCC interface terminations are incorrect (Common and Signal cable Interchanged)
  • Wrong terminations (in the case of analogue signals, polarity reversal)
  • Shield connection in the Marshalling cabinet is incorrect.
  • Incorrect field instrument configuration (Upper range/lower range/square root/offset, etc.)
  • The Control system’s channel setup is incorrect (Active or passive or 3 wire signals)
  • At the I/O module, the configuration is incorrect (Improper range or tag no mismatch)
  • Blown fuse, no fuse inside terminals, insufficient fuse rating, or open terminals are all possibilities.
  • Incorrect field contact (NO/NC for digital signals)
  • For digital output signals, the wrong contact (dry contact/wet contact) was used.
  • Interrogation In dry contact, voltage was discovered.
  • Incompatible components or incorrect connections in the relay, isolator, and barrier
  • The size of the power supply module is incorrect, as is the MCB rating.
  • Internal wiring colour and wire size aren’t up to snuff.
  • The use of an external power supply is not recommended.

Electronic Marshalling Cabinets

Points to take care during the design stage when using electronic marshalling cabinets:

The grouping of junction boxes should be exact so that the cable can be terminated straight to the I/O card, just like the sequence of junction box pairs. Because the electronic marshalling system does not include cross-wiring, a change in junction box grouping will have an influence on I/O assignment in the DCS. Because some field connections may carry both redundant and non-redundant signals, segregating redundant and non-redundant signals in an I/O card may not be viable. Because the control room side I/O termination is the mirror image of the Junction box, the system vendor may need to deploy redundant I/O modules in such circumstances.

Parallel equipment’s related I/Os should be isolated as much as feasible in distinct cables so that they can be assigned to various I/O cards. If those signals are assigned to a single multi-pair cable that will be terminated in a single I/O card, that equipment will be unavailable for control if that I/O card fails. Channels’ sparse philosophy should be decided upon with the client.

For example, if a 5 Pair field multi-pair cable has 3 I/O signals and 2 spares, 3 Signals are linked directly to the I/O card. The remaining 1 signal is wired as a spare to the I/O card, and the final 1 pair is left unterminated behind the I/O module or in the cable duct. For example, if a 5 Pair field multi-pair cable has 3 I/O signals and 2 spares, 3 Signals are linked directly to the I/O card.

The remaining 1 signal is wired as a spare to the I/O card, and the final 1 pair is left unterminated behind the I/O module or in the cable duct. Because the first four I/O channels (3 I/O signals + 1 wired spare) are already in use, the fifth channel will be assigned to a signal from another multi-pair cable. Philosophy should be discussed with the customer early in the design process; once the I/O assignment has been frozen as indicated above, changing the philosophy will be difficult.

Dedicated Marshalling Cabinets

Points to take care during the design stage when using dedicated marshalling cabinets:

  • In marshalling cabinets, all wires from field multi-pair/core cables should be terminated.
  • The number of terminals inside the marshalling cabinet would rise if the cable type (for example, 16 pair to 24 pair) was changed. Cross-wiring will be unaffected by changes in junction box grouping.
  • It will, however, have no effect on I/O assignment. 2o3 voting-related I/Os should be assigned in different ways on parallel equipment.
  • For ease of maintenance, the quantity of main wires terminated in a single cabinet should be carefully examined.
  • This applies to all types of marshalling and system cabinets. The Controller segregation principle should guide I/O allocation and marshalling cabinet design.
  • This is true of all marshalling/system cabinets.

Dimensions, colour, type of access, spare space, spare components, internal wire/duct colour, size, cable entrance, smoke detection requirement, Ingress protection class, EMC requirement, and other cabinet building aspects should be addressed according to project requirements.

System Cabinet Photo

Marshalling Cabinet Photo

Closure view of marshalling cabinet components

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