From Design To Factory Acceptance: How Industrial Control Cabinets Are Built.

Designing and building an industrial control cabinet is a structured, multi-stage process combining engineering, compliance, fabrication, and verification. From the initial specification meeting to final Factory Acceptance Testing (FAT), every step influences how reliable, maintainable and safe the final system will be.

In this article we'll walk through the full lifecycle of a typical control cabinet project — from design to FAT — and highlight the practical details that automation engineers, technicians and project managers need to understand.

This article covers three main stages:

• Designing the cabinet and creating the documentation.
• Building and wiring the cabinet in the factory.
• Testing, FAT and resolving issues before the cabinet ships.

1. Designing The Cabinet

1.1 Gathering Design Specifications

The design process starts with clearly defining the project requirements from the client, process, and instrumentation teams.

• Process description and P&IDs.
• Control philosophy and cause-and-effect charts.
• I/O count, redundancy strategy and network architecture.
• Site standards (preferred vendors, drawing standards, colours).
• Environmental conditions and certifications required.

These inputs drive every design decision: enclosure rating, PLC/DCS hardware selection, power distribution, marshalling strategy and cable entry layout.

1.2 Creating The Electrical Design

Once the requirements are defined, the detailed engineering begins.

• Single-line diagrams and power distribution.
• I/O & instrument lists linked to PLC/DCS tags.
• Panel layouts showing all devices and clearances.
• Terminal strip layouts and cable schedules.
• Bill of materials for procurement and manufacturing.

2. Building The Control Cabinet In The Factory

2.1 Preparing The Panel

Before wiring starts, the enclosure and backplate are prepared for mounting components and routing cables.

• Marking and drilling gland plates for cable entries.
• Marking and drilling backplates for DIN rail and equipment.
• Installing mounting rails, trunking and earth bars.
• Labeling equipment positions to match the layout drawings.

2.2 Wiring & Assembly

The cabinet is populated and wired according to the approved drawings.

• Mounting PLC/DCS hardware, power supplies and relays.
• Installing terminal blocks and marshalling strips.
• Routing and dressing wiring in trunking.
• Ferruling, crimping and labeling all conductors.
• Performing in-process checks for torque, polarity and continuity.

3. Quality Checks & Factory Acceptance Testing (FAT)

The FAT is where the finished cabinet is tested against the functional specification and drawings, usually witnessed by the client.

3.1 Pre-FAT Checks

• Visual inspection: wiring, labels, clearances, workmanship.
• Earth continuity and insulation resistance tests.
• Verification of component ratings and certificates.
• Updating as-built drawings for any late modifications.

3.2 FAT Execution

• Power-up tests and basic health checks.
• I/O simulation, loop checks and interlock testing.
• Testing alarms, permissives and trip sequences.
• Verifying HMI / SCADA graphics and navigation.
• Documenting all findings, punch-list items and fixes.

4. FAT Handover To Client

After the Factory Acceptance Test is completed, the cabinet moves into the final handover stage. This step ensures the client receives a fully verified system along with the correct documentation for installation and commissioning.

4.1 FAT Documentation Pack

• FAT checklists and test results
• Updated as-built drawings
• Resolved punch-list items
• Component certificates and manuals

4.2 Engineering Handover

• Panel layout & schematic drawings
• Updated I/O lists and cable schedules
• PLC/DCS backups and network settings

4.3 Release for Shipment

• Cabinet cleaned and sealed
• Transport protection added
• Shipment labels and checklists completed

4.4 Client Sign-Off

The FAT concludes with a review of results, confirmation of documentation, and a final client signature releasing the cabinet to site.

A clear and complete FAT handover ensures the cabinet arrives on site ready for efficient installation and commissioning.