PLC Control Cabinet Explained: How to Design, Wire, and Choose the Right Components

A PLC control cabinet is essential in order to protect your automation systems from damage in industrial environments. Would you like to know what’s the best way to design and wire such a cabinet? This guide concerns fundamental techniques, starting with part selection, and effective management of panel ventilation, cooling and safety in order to achieve optimal performance and long life of your systems.

1) What’s a PLC control cabinet?

In an industrial setting a PLC control cabinet plays an important role in safeguarding your automation devices as it protects your PLC and other devices from dust, humidity and physical abuse, which guarantees their constant functionality. Considering the fact that nearly 90% of automation malfunctions are due to the environment, having a proper cabinet design is really sensible.

Inside the cabinet, there are power supplies, I/O modules and wiring terminals for interconnection between your devices. Because of cooling and ventilation overheating can be avoided which could reduce lifetime of components by half. For that reason, an appropriate cabinet for PLC’s makes it easier to manage and protect your automation system in any industrial environment.

2) How do you design a PLC control cabinet that fits your needs?

Designing & wiring a PLC control cabinet is a very complicated process, but you can follow our guide below to get an idea of what you should look for;

i) Define Requirements

ii) Select Components

iii) Cabinet Size and Layout

iv) Cooling and Ventilation

v) Wiring of PLC control Cabinets

vi) Safety and Compliance

vii) Testing and Documentation

i) Define Requirements

Before you start the design work, it’s very important to make sure you have clearly stated your requirements. For instance, think about what specific machines or processes will be controlled by your PLC. Also, think about the climate conditions, such as temperature and humidity, where you intend to install the cabinet.

These facts have a great impact on the design of a cabinet, as statistics suggest that roughly 90% of failures in automation have an environment-based origin. So, by setting these limits, you would be able to determine what components and design characteristics are appropriate for smooth functioning.

ii) Select Components

Select PLC: Once you have finalised your parameters, the next stage of the design process is to carefully choose the components of your PLC control cabinet. First off, you need to zero in on a PLC that aligns with your operational requirements. So, look into bus communication protocols like Modbus RTU, Ethernet/IP, or even Profibus. On the other hand, if you have somewhat high requirements for the system, you would need to use a high-end processing power PLC with a wide range of scaling options so that control logic can be well executed.

Power Supply: The next point is the selection of power supplies. It is necessary to be convinced that the power supply satisfies the voltage and current specifications of the relays, PLC and peripheral devices. Choose supplies that are able to provide a stable output in a proper manner, cope with transient loads, and have some means of basic protection against over-voltage and short circuits for your equipment.

I/O modules: Now let us proceed to I/O modules! These Input/Output modules are critical for interfacing the PLC with your field devices. They enable data swapping, such that signals can come from sensors to the PLC and commands may be sent out to actuators and relays. So with whatever application you have in mind make sure to choose appropriately between using analogue or digital I/O modules.

For example, if you’re going to have temperature sensors, find a way to use analogue inputs because they are capable getting & processing varying voltage signals. Last but not least, always choose compatible components, because the mismatch of such components consumes a lot of money in terms of down time – roughly 25% of automation breakdowns are due to that.

iii) Cabinet Size and Layout

When planning the dimensions and arrangements of your PLC panels, take into consideration the following parameters:

• Component Dimensions: Measure the height, width and depth of all the components, including the PLC, I/O modules, power supply and any additional hardware. Also, take into account support brackets and connectors that might increase the size.

• Wiring Space: Provide adequate allowance for wiring and cable management. For ease of routing of cables, devote not less than 20~ 30% of the volume of a cabinet to the wiring.

• Ventilation: Make sure that adequate space is left around the components for ventilation. Atleast, allow 1-2 inches extra space on all sides of each component in order to allow for sufficient cooling.

• Future Expansion: Plan ahead for growth by providing extra room for more parts or I/O modules in the future. This may mean providing 10-20% more space than the currently required space.

• Accessibility: Mount the PLC and the components that need maintenance towards the front of the cabinet. In addition, the handles of the doors and the panels should be set in such a way as to allow a full swing open without obstruction making future maintenance easy.

• Organization: Components can be neatly organised through the use of mounting rails and DIN rails. This is beneficial not only in installation but also in ease of making it during troubleshooting later.

• Evaluate the working environment of the cabinet to see if it’s necessary for it to be weather proof or sealed against dust. If this is the case, make sure that the design and materials used comply with the stated IP ( Ingress Protection ) ratings.

iv) Cooling and Ventilation

To ensure that the PLC control panel operates efficiently, proper cooling and ventilation arrangements need to be in place. Here is everything you should know:

• Heat Load Calculation: The first step would be estimating the total heat produced by all the components including the PLC and the I/O modules by referring to each component’s wattage.

• Ambient Temperature: Consider the installation’s area’s maximum ambient temperature. Then figure out how to keep the internal temperature of the cabinet within 50 °C (122 °F).

• Cooling Methods: Choose the cooling method appropriate for your application.

• Passive Cooling: For low heat generating applications, vents or louvres can be installed to allow free circulation of cooler air.

• Active Cooling: On the other hand, for medium to high heat generating applications, fans, blowers and/or air conditioning should be used.

• Heat Exchangers: Then again in extremely hot conditions, fluid heat exchangers could be employed.

• Air circulation: As a first step, designate intake and exhaust points so as to achieve air circulation. Try to ensure an airflow that satisfies your heat load requirement.

• Temperature Monitoring: The use of sensors is recommended so that the temperature of the inner cabinet is measured constantly enabling self adjusting mechanisms to cool off the cabinet as needed.

• Filters and Maintenance: To minimize the accumulation of dirt, fit your fans with filters and carry out maintenance processes to avoid airflow obstruction.

• Emergency Cooling Solutions: Considering cooling failures especially on critical applications, it is good to have backup cooling methods such as having portable fans.

v) Wiring of PLC control Cabinets

Excited to start with the PLC wiring of the control cabinet? Worry not because there is a sequence that you need to follow, which will help you ensure that everything is done properly and there is no risk of damage. Here’s how you should connect each component:

Step 1) Power Supply to PLC: The first thing that you will be dealing with is the wiring of the power supply to your PLC, enabling the required voltage. You may note that these power cables need to be kept away from any signal wires so as to eliminate disturbances of any kind.

Step 2) Wiring PLC to I/O Modules: Moving forward, one must go ahead to joining the PLC to I/O modules which in turn communicates the signal to your sensor and actuators. However, one must take special care and tag each and every wire during this process. This action can help in quickly tracing the signals in case of a malfunction or a fault.

Step 3) Wiring I/O Modules to Relays/Contactors: Other than that, wire your I/O modules to relays or contactors if you are dealing with a high-power application. Such a connection allows your PLC to drive motors without high-voltage exposure.

Step 4) Protection with Circuit Breakers and Fuses:  Before arriving at integral parts such as the PLC and relays, your power line must pass through circuit breakers and fuse switches. This guarantees that your setup can avoid electrical overload and damage.

Step 5) Terminal Blocks for Distribution: A terminal block can be used as a wiring centre for the interconnections from the PLC, I/O modules or any other power devices. For structural neatness, group together power, signal, and control wires according to their functions.

Step 6) Grounding Connections: It is necessary to connect all the parts to a singular ground point. This also helps in reducing electromagnetic interference and voltage spikes to ensure that your equipment is not damaged.

Step 7) Networking Modules and Communication Ports: Communication ports and networking modules should be wired to the PLC, but avoid laying them alongside power lines as they might interfere with the communication signal. This allows for communication between systems.

Step 8) HMI Connection to PLC: Lastly, connect the HMI to the PLC so as the user is able to control and monitor the operation of the various functions of the systems. HMI wiring should be placed in such a way that is easily accessible.

vi) Safety and Compliance

Security is very important when setting up your PLC cabinet. It is necessary to follow NEMA, IEC, ITA and ATEX (for safety in hazardous environments) standards. For instance, if you are present in an explosible gas or dust-containing environment, then ATEX certification is mandatory.

Since nearly half of industrial accidents are attributed to equipment malfunctioning or damage one must include things like emergency stop switches, circuit breakers, appropriate earthing, and surge protection devices. Also making regular safety audits gives you the opportunity of identifying and mitigating any risks that may come up and ensures your cabinet remains compliant and safe.

vii) Testing and Documentation

Once the assemblage of the cabinet is over, check the wiring, the function of the system, and the performance of the system when under load. After that, prepare understandable documentation such as wiring schematisation, specifications of parts included, and general procedures of repair and maintenance.

It is reported that the availability of such documents can occasionally decrease the repair time during troubles of the equipment by as much as 40% and they are very useful for preventive maintenance targets, which would enable efficient and effective operation of the PLC control cabinet.

➔ Conclusion

Ultimately, understanding how to properly design and wire a PLC control cabinet is important for the safety and security of your automation systems. It is advisable that the procedures outlined in this manual are applied so that the smooth operation of equipment is enhanced and its life is increased. A clear focus on these factors; components screening, ventilation and safety will give the ideal result.

Saipwell is your answer to quality components and sound solutions. We can assist you manufacture a solid PLC control cabinet with its vast selection combined with exceptional quality. Let us work together and enhance the quality of your automation systems!