What is a control cabinet?
A control cabinet is a lockable enclosure that houses the electrical and electronic components which operate, monitor and protect an industrial machine or installation, such as PLCs, IO modules, power supplies, relays, protective devices and network equipment. The cabinet is the physical junction where cabling from sensors and actuators in the field meets the control logic and the OT network that leads to SCADA or a DCS. Anyone working on a control cabinet therefore deals with electrical safety, process availability and cyber security at the same time.
🧠 What is inside a control cabinet?
A control cabinet is usually built on a galvanised mounting plate with DIN rails, cable trunking and terminal strips. Its contents fall into five groups:
| Group | Typical components | Function |
|---|---|---|
| Power supply and distribution | Main isolator, miniature circuit breakers, 24 VDC power supplies, transformers, UPS | Distribute energy safely and convert it to control voltage |
| Control | PLC, IO cards, Safety PLC or safety relays, time-delay relays | Execute logic, control loops and safety functions |
| Power switching and drives | Contactors, motor starters, soft starters, frequency converters, thermal overloads | Switch and protect motors and other loads |
| Communication | industrial switches, fieldbus interfaces for ProfiNET, Profibus or Modbus, routers | Exchange data with the HMI, SCADA and other controllers |
| Wiring and termination | Terminal strips, cable trunking, cable glands, earth bar, labels | Connect field cabling in an orderly, traceable way |
The door often carries operator devices as well: an emergency stop, indicator lamps, selector switches and sometimes an operator panel. In larger plants the power section for motors sits in a separate MCC, and the control cabinet holds only the control equipment. Increasingly, I/O is also distributed in the field as Remote IO, which makes the main cabinet smaller and reduces the number of cables it has to receive.
📏 Which standards must a control cabinet meet?
There is no single standard for “the control cabinet”. Which requirements apply depends on what the cabinet does and where it stands:
| Standard or rule | What does it cover? | When is it relevant? |
|---|---|---|
| NEN-EN-IEC 61439 | Low-voltage switchgear and controlgear assemblies up to 1000 V AC / 1500 V DC: design verification and routine verification | Cabinets that distribute power, such as distribution boards and MCCs (part 2) |
| IEC 60204-1 | Electrical equipment of machines: emergency stop, protective conductors, wiring, documentation | Every control cabinet that belongs to a machine |
| IP Code (IEC 60529) | Protection against dust and water | Choice of enclosure, for example IP54 on a factory floor |
| EMC Directive 2014/30/EU | Electromagnetic compatibility | Every cabinet with drives, power supplies and sensitive signals |
| Machinery Regulation (EU) 2023/1230 | Safety of machinery including control systems, with requirements against corruption of the control system | From 20 January 2027; until then the Machinery Directive |
| NEN 1010 and NEN 3140 | Installation, and safe operation and inspection, of low-voltage installations respectively | Installation and maintenance in the Netherlands |
The current editions are IEC 61439-1 and -2 from 2020 (third edition) and IEC 60204-1:2016 with Amendment 1 from 2021; in Europe EN 60204-1:2018 with amendment A1 from 2025 applies. A seventh edition of IEC 60204-1 is in preparation.
Design verification and routine verification. IEC 61439 distinguishes between the original manufacturer, who develops the enclosure system and carries out design verification, and the assembly manufacturer (the panel builder), who assembles the cabinet and performs routine verification on each unit. A panel builder who deviates from the system manufacturer’s instructions becomes the original manufacturer for that deviation. Temperature rise may be verified by calculation for single-compartment assemblies up to 630 A and for multi-compartment assemblies up to 1600 A using IEC/TR 60890; above that, testing or derivation from a tested reference design is required. The US market follows different rules: UL 508A and the short-circuit current rating (SCCR) marking required by NEC Article 409.
🔧 How do you design and build a good control cabinet?
A reliable cabinet starts with the design, not with the assembly. A practical sequence:
- Define the environment - ambient temperature, dust, moisture, cleaning regime and any hazardous areas determine the enclosure, IP rating and material (steel, stainless steel or plastic).
- Schematics and documentation - draw circuit diagrams, terminal plans and a cable list in a CAE package such as EPLAN; IEC 60204-1 requires diagrams, parts lists and test records.
- Zoning on the mounting plate - separate power (drives, power supplies) from signal sections (PLC, analogue I/O) and route power and signal cables in separate trunking. This is the basis of good EMC design.
- Earthing and shielding - a common reference plane, an earth bar and 360° shield terminations with EMC cable glands. See earthing.
- Heat balance - add up the heat dissipation of all components and choose passive cooling, filter fans, an air-to-air heat exchanger or a cooling unit.
- Colour and wire coding - IEC 60204-1 makes green-yellow mandatory for the protective conductor and recommends black for power circuits, red for AC control circuits, blue for DC control circuits and orange for interlocking circuits supplied from an external source.
- Spare capacity and maintainability - many clients demand 20 to 30 percent free space and spare I/O; this is not a requirement of the standards, but it avoids a complete rebuild when the plant is extended.
- Test and handover - routine verification (insulation, protective circuit, wiring, function), a FAT at the panel builder and a SAT on site.
Typical values. IEC 61439-1 assumes, for indoor installation, an ambient temperature of no more than 40 °C, a 24-hour average of no more than 35 °C, and a minimum of −5 °C. Many components, power supplies and drives in particular, lose rated output or service life above their nominal temperature; a widely used rule of thumb is that the life of electronics roughly halves for every additional 10 °C. An IP54 cabinet on a factory floor and IP65 or higher in wet or dusty areas are common choices.
🔍 What is the difference between a control cabinet and an MCC?
| Feature | Control cabinet | MCC |
|---|---|---|
| Contents | PLCs, I/O, relays, power supplies, network | Motor starters, soft starters, frequency converters |
| Purpose | Machine or process control | Supplying and switching motors |
| Location | Close to the machine or installation | Usually a central electrical room |
| Cabling | Control, I/O and data cables | Power and motor cables |
| Main standard | IEC 60204-1, IEC 61439 where it distributes power | IEC 61439-2, including forms of internal separation (form 1 to 4) |
In practice the terms overlap: on a small machine, control and motor supply share one cabinet, while a process plant has PLC cabinets, MCCs and distribution boards side by side in an electrical room.
🏭 Where are control cabinets used?
Control cabinets are found wherever industrial automation takes place:
- Discrete manufacturing - packaging machines, conveyors, robot cells and assembly lines
- Process industry - dosing and mixing systems, batch reactors and utilities
- Water and infrastructure - pumping stations, treatment plants, locks and tunnels, often as outdoor cabinets with climate control
- Buildings and cleanrooms - air handling, cooling and pressure control
The cabinet links field equipment to higher-level systems: locally through an HMI on the door, centrally through SCADA or a DCS, and for maintenance through an engineering station.
🔐 How do you secure a control cabinet physically and digitally?
A control cabinet is also a cybersecurity asset: anyone who can open the door can connect a laptop to the PLC, insert a USB stick or install a wireless router. In 2010 the Stuxnet worm showed that malware on USB media can reach an isolated installation. Key measures:
- Physical access - lockable doors with key or cylinder systems, door contacts that report openings to SCADA, and a record of who has access (access control)
- Ports and media - disable unused switch ports, cover programming ports and apply USB control
- Network - treat the cabinet as a zone under the zones and conduits model of IEC 62443, with network segmentation, VLANs and a firewall between the machine network and the plant network
- External access - allow routers for remote maintenance by the machine builder only through a managed, logged connection
- Safety - thermal monitoring, surge protection and a clearly marked main isolator that can be locked off during maintenance
Periodic maintenance and an audit of cabinets, including a NEN 3140 inspection at a risk-based interval in the Netherlands, keep the installation safe and reliable.
❓ Frequently asked questions
Is a control cabinet the same as a control panel or switchboard?
In everyday language, control cabinet, control panel and electrical cabinet are often used interchangeably. Strictly speaking, a control cabinet mainly contains control equipment such as PLCs and relays, while a switchboard or distribution board primarily distributes power. Many cabinets combine both functions.
Which IP rating does a control cabinet need?
The IP rating of a control cabinet depends on its environment: in a dry, clean electrical room IP20 to IP43 is often sufficient, while IP54 is common on a factory floor. In wet or dusty areas, or where equipment is washed down, you choose IP65 or higher, and IP69 or IP69K for high-pressure cleaning in the food industry.
Does a control cabinet need CE marking?
A control cabinet that is part of a machine is covered by the CE marking of that machine, under the Machinery Directive and, from 20 January 2027, the Machinery Regulation; the machine builder includes the cabinet in the technical file. If the cabinet is supplied as a stand-alone product, the panel builder usually declares conformity with the Low Voltage Directive 2014/35/EU and the EMC Directive itself, backed by routine verification to IEC 61439 or checks against IEC 60204-1.
How do you prevent overheating in a control cabinet?
You prevent overheating in a control cabinet by adding up the heat dissipation of all components and comparing it with the cooling capacity of the enclosure. With little heat, passive dissipation through the cabinet surface is enough; beyond that, filter fans, heat exchangers and cooling units come into play. A temperature sensor that raises an alarm through the PLC prevents faults from going unnoticed.
What does a control cabinet have to do with cybersecurity?
A control cabinet contains PLCs, switches and often a router for remote maintenance, which makes it an entry point into the OT network. Anyone with physical access to the cabinet can change configurations or introduce malware. Lockable doors, covered ports and network segmentation in line with IEC 62443 therefore belong in a well-secured control cabinet.
How often should a control cabinet be inspected?
In the Netherlands, control cabinets are usually inspected under NEN 3140, which gives substance to the employer’s duty of care in Article 3.4 of the Dutch Working Conditions Decree (Arbobesluit). The interval is risk-based and usually lies between one and five years, with shorter intervals in heavy industrial or damp environments. An annual visual check for dust, heat and loose connections is common practice in addition.
📌 In summary
A control cabinet is the lockable enclosure in which PLCs, power supplies, protective devices and network equipment control a machine or installation, and the physical point where electrical safety, availability and OT security meet.
A good cabinet complies with IEC 60204-1 and, where it distributes power, with NEN-EN-IEC 61439; it has a suitable IP rating, a well-considered EMC and thermal design and complete documentation. Treat the cabinet as a security zone as well: restrict physical access, close off unused ports and separate the machine network from the rest of the plant.