Instrumentation

Marshalling Cabinet drawing and its significance

What is a Marshalling cabinet diagram?

A Marshalling cabinet drawing is an Engineering drawing developed by Instrumentation Hardware design engineers with the help of draftsman to outline the specific details of a cabinet.

A typical Marshalling cabinet diagram will contain the details about Marshalling cabinet’s General layout, Internal layout, Power Wiring, Earthing wiring, Termination, Alarm Wiring and Name plate.

In the diagram, the terminal blocks are shown as squares, and the field wiring is shown as lines connecting the terminal blocks. The terminal blocks may be labeled to indicate their function or the device they are connected to.

The marshalling cabinet drawing may also include other components such as fuses, circuit breakers, and protective covers.

Why Marshalling cabinet diagram is required?

Marshalling cabinet diagram will aid an Instrumentation Engineer or technician to install, commission and troubleshoot the interface between field devices and control system IO cards.

This diagram helps to identify the terminal block or Field Terminal Assembly location.

This diagram will enable an Instrumentation Maintenance Engineer or technician to troubleshoot any failure in the control loop like open loop or signal short or blown fuse and so on.

Marshalling panel wiring diagram:

A marshalling panel wiring diagram can also be referred as Marshalling panel termination diagram. This drawing is critical document for marshalling panel design.

A marshalling panel wiring drawing can be developed based on the design inputs from below mentioned documents

  • I/O Database
  • I/O Sizing
  • Loop Drawing

Typical Marshalling cabinet diagram:

A typical marshalling cabinet drawing contains various drawing sheets which contain details about

  • Cabinet general layout
  • Cabinet Plinth fixing layout
  • Cabinet internal layout
  • Cabinet power wiring detail
  • Cabinet alarm wiring detail
  • Cabinet earthing detail.
  • Cabinet name plate detail.

Various sections in a Marshalling diagram:

1. General Arrangement/Layout:

Marshalling Cabinet 1

Details covered in marshalling cabinet general arrangement layout sheet are

  • Cabinet dimensions
  • Cabinet Make
  • Cabinet Model
  • Cabinet IP rating details
  • Cabinet external view
  • Cabinet Dust filter arrangement detail
  • Cabinet Fan arrangement detail
  • Cabinet door opening detail

This drawing is required to understand whether the manufactured cabinet diagram is meeting all the project specific requirements mentioned by the client or end user.

2. Cabinet Plinth Fixing Hole layout:

Marshalling Cabinet 2

Details covered in marshalling cabinet plinth fixing hole layout sheet are

  • Cabinet plinth dimensions
  • Cabinet plinth hole dimensions

This drawing is required for the Instrumentation technicians/foreman while fixing the marshalling cabinet in its desired location in the rack room or Local Equipment room.

3.Internal Arrangement/Layout:

Marshalling Cabinet 3
Marshalling Cabinet 4

A conventional marshalling cabinet contains six locations inside it as mentioned below

a. Front:

  • Left Hand side – LHS
  • Front Side
  • Right Hand side – RHS

b. Rear:

  • Left Hand side – LHS
  • Rear Side
  • Right Hand side – RHS

Details covered in marshalling cabinet internal arrangement layout sheet are

  • TB location details inside the cabinet
  • Incoming Field signal cable TB details
  • Earthing/Grounding strip details
  • Fan and light details
  • Utility power socket details
  •  Thermostat details

This drawing is mainly required for Instrumentation Engineers and Technicians during initial plant commissioning and also during plant maintenance phases.

This drawing will be helpful to identify the location of the TB’s while troubleshooting any issue between field devices and the control system to trace the signal fault in the loop.

4. Power Distribution details:

a. 230V/240V AC Power distribution

Marshalling Cabinet 5

In a conventional marshalling cabinet there will be always redundant power connections one from primary power source and another one from secondary power source. This is required to run the control system without any risk of losing any signal conditioning component in case of a power failure in one power source.

These marshalling cabinets also have Uninterrupted Power supply (UPS) and Non-UPS power supply.

  • UPS power supply is used for critical components like signal conditioning boards and Isolators/barriers.
  • Non-UPS power supply is used for less critical equipment like cabinet fan and Tube light.

Details covered in marshalling cabinet 230V/240V AC Power distribution sheet are

  • Incoming Power cable TB details (Both UPS & Non-UPS).
  • Incoming power cable size details.
  • Incoming power cable color coding details.
  • Incoming power MCB details.
  • Incoming power distribution details to critical and Non-critical equipment.
  • Internal 230V/240V AC power cable size details.
  • Internal 230V/240V AC power cable color coding details.

b. 24V DC Power distribution

Marshalling Cabinet 6

Details covered in marshalling cabinet 24V DC Power distribution sheet are

  • 24V DC TB details.
  • 24V DC MCB details.
  • Internal 24V DC power cable size details.
  • Internal 24V DC power cable color coding details.
  • Internal power distribution details of 24V DC to required component.

This drawing is required for the Instrumentation Engineers/technicians while fabricating the cabinet at system staging location.

5. Cabinet Alarm wiring detail:

Marshalling Cabinet 7

Details covered in marshalling cabinet alarm wiring sheet are

  • Alarm TB details
  • Alarm signal connection details
  • Cabinet Fan and Thermostat side alarm terminal details.
  • NO/NC contact details.
  • Alarm cable size details.
  • Alarm cable color coding details.

The Marshalling cabinet Fan and Thermostat Alarms are wired to one of the Digital input of DCS/PLC system, to indicate any heat built up in the cabinet due to failure of fan or due to congestion of air circulation path with dust particles.

Once the alarm is sensed Instrumentation Engineer/Technician can be informed to address the issue.

6. Grounding/Earthing details:

Marshalling Cabinet 8

Details covered in marshalling cabinet Grounding/Earthing drawing sheet are

  • Instrument Earth strip detail.
  • Safety Earth Strip detail.
  • Earthing TB detail.
  • Earthing distribution detail.
  • Earthing cable size details.
  • Earthing cable color coding detail.

7. Name Plate details:

Marshalling Cabinet 9

Details covered in marshalling cabinet Name plate drawing sheet are

  • Cabinet Name detail.
  • Cabinet type detail.
  • Cabinet Name Font size detail.
  • Cabinet specifications like Material, Make, Model, and Color so on.

The marshalling cabinet name is required to identify particular cabinet inside a rack room.

8.Marshalling Panel information in a typical loop diagram:

Below drawing illustrates a typical loop drawing of a pressure transmitter where a section of Marshalling panel drawing is covered.

Marshalling Cabinet 10

In this drawing we can find

  • Assigned terminal block details for a multi pair incoming cable from field junction box.
Marshalling Cabinet 11
  • Cross wiring detail from the terminal block to the Isolator/Barrier, in this case the signal is IS signal. For Non-IS signal the barrier will not be required.
Marshalling Cabinet 12
  • Pre-fabricated cable detail from the Isolator/Barrier to the assigned I/O card on the system cabinet.
Marshalling Cabinet 14

Key Questions:

What is a Terminal Block?

Terminal blocks are connectors used to terminate and join a single wire to a circuit or other system.

What is a Terminal Block?

What is Field Terminal Assembly (FTA)?

A Field terminal assembly (FTA) is a device that is used to connect field wiring to a control panel or other electrical control system. It typically consists of a terminal block and a set of connectors or terminals that are used to terminate the field wiring. The FTA is used to connect sensors, switches, and other input devices to the control system, as well as to connect actuators, motors, and other output devices to the control system.

Field terminal assemblies are typically used in industrial control systems and automation applications to provide a convenient and secure connection point for field wiring. They are designed to be mounted on a Marshalling panel and are often used in conjunction with programmable logic controllers (PLCs) or other control devices. Some field terminal assemblies also include features such as protective covers, terminal strip labeling, and grounding provisions to enhance their functionality and reliability.

What is signal conditioner?

A signal conditioner is a piece of equipment that changes the raw analog signals that sensors send out, these adjustments transform the original signals into signals usable by process monitoring and control equipment.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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