Why is 24 Volts Mostly used in Industrial PLC Systems?

One of the most important parts of industrial automation and control is the programmable logic controller (PLC). Particularly for control and input/output functions, one common trend in PLC systems is the widespread usage of 24V DC as the standard voltage level. This choice is not random; it results from a succession of technological, safety, and financial factors.

Honoring this decision is about more than just voltage; it’s about the efficiency, dependability, and harmony it offers the industrial automation community. Let us investigate in depth why 24V DC is mostly employed in industrial PLC systems and why it merits the acknowledgment it receives.

Why 24v dc always used in plc?

Safety Considerations

Low Voltage, Low Risk

Under worldwide electrical safety criteria, 24V DC is regarded as a safe voltage level. Though enough to run most industrial control systems efficiently, this level is low enough to prevent the danger of major electric shocks under regular working situations.It provides comfort to engineers and technicians who work near live circuits.

Elimination of Heavy Safety Gear

Working with higher voltages like 120V AC or 230V AC calls for personal safety equipment (PPE), such as insulating gloves and face shields. This requirement is significantly less with 24V DC, hence simplifying maintenance and lowering running expenses.

Compatibility with Industrial Devices

Sensor and Actuator Compatibility

Most industrial sensors including inductive proximity sensors, photoelectric sensors, and pressure transmitters and actuators including solenoids and contactors are built to run on 24V DC. This guarantees smooth integration and eliminates the need for voltage converters.

Reduced Risk of Equipment Damage

A consistent 24V DC system guarantees no possibility of accidentally applying a high AC voltage to a DC-only device, which could permanently harm input modules and sensors.

Technical Advantages of 24V DC

High Switching Speed of Semiconductors

Built on semiconductor electronics, PLC systems naturally function better and more effectively at low DC voltages. Processing quick signals from field devices requires high-speed switching, hence 24V DC is a reasonable option.

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Stable Voltage Supply

Unlike AC voltage, which periodically changes direction and amplitude, DC voltage is continuous and does not fluctuate. Timing issues related to zero crossing in AC are eliminated and sensitive electronics are guaranteed to operate reliably with a steady voltage source.

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Better Noise Immunity

Industrial settings are well known for electromagnetic interference (EMI), particularly from motors and high-power AC devices. Compared to higher voltage AC systems, DC systems at 24V are less sensitive to noise, which lowers signal distortion and enhances the dependability of control signals.

Standardization Across Industry

Global Industrial Norms

In industrial automation, 24V DC has become the accepted norm. This uniformity guarantees compatibility of parts from different makers and streamlines engineering, maintenance, and documentation.

Compatibility with Fieldbus Systems

Modern communication protocols such as Profibus, Profinet, and DeviceNet are built with 24V DC signal levels in mind. Using 24V DC ensures compatibility with fieldbus networks, which are essential for real-time communication in automated systems.

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Economic Benefits

Cost-Effective Components

Widespread availability of 24V DC components pulls prices down because of mass manufacture. Cost-effective options for 24V systems are easily accessible from input/output modules to relays and sensors.

Simplified Wiring and Design

Low-voltage DC systems let for easier wiring and lower insulation needs. Wire sizes can be smaller and routing more flexible, hence reducing installation costs.

Reduced Cooling Requirements

Higher voltage AC systems produce greater heat from power losses and resistive heating. 24V DC systems generate less heat, hence reducing the need for costly cooling solutions and extending the life of the equipment.

Smaller PCBs and Devices

Tend to be smaller and more compact, electronic boards made for low voltage operation. This minimizes the whole PLC system footprint and saves space in control panels.

Adaptability and Power Supply Versatility

SMPS Compatibility

Switch Mode Widely utilized to transform fluctuating AC input voltages into a standard 24V DC output, Switch Mode Power Supplies (SMPS) This lets producers make worldwide compatible PLCs without customizing goods to fit various regional AC standards (110V, 230V, etc.).

Universal Applications

From automotive to pharmaceuticals and from food processing to water treatment, 24V DC systems can be used in many different sectors. Its versatility across industries makes it a perfect candidate for standardization.

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Low Power Consumption and Environmental Impact

Energy Efficiency

Especially at lower power levels, DC circuits are naturally more efficient. Especially in systems with hundreds or thousands of sensors and actuators, 24V DC helps to save total energy.

Sustainable Design

Less energy use helps the system to lower its carbon footprint. This fits with current business objectives to support sustainable automation methods and green production.

Flexibility in Control Logic

PLC Programming Compatibility

Most PLC programming languages and environments including ladder logic, function block diagrams, and structured text are created with 24V DC logic levels in mind. This improves the simplicity of creation and lowers the need for troubleshooting.

Modular Expansion

By enabling scalable control systems that may develop with evolving process needs, 24V DC facilitates the inclusion of expansion modules and extra I/O devices.

In addition to being a historical the past, the use of 24V DC in industrial PLC systems is the consequence of numerous technological, safety, economic, and environmental factors. From safer work conditions and lower costs to improved signal integrity and equipment compatibility, 24V DC stands out as the most economical and practical option for powering and operating industrial control systems.

Though often employed in specialized applications, 12V DC, 48V DC, or even 120V AC, 24V DC is still the industry standard for general-purpose PLC use. This guarantees a harmonic ecosystem of devices, tools, and engineering techniques streamlining automation across sectors.

24V DC Power Supply Architecture and Distribution Overview

The below illustred graphic shows how the 24V DC supply is created and safeguarded prior to distribution. 

It comes from a power supply unit (PS1) and has a 10A rating. It converts AC to 24V DC.. Miniature circuit breakers (MCBs) protect this output to guarantee circuit protection and fault isolation. For orderly distribution, terminal blocks (TBD1) route the power. Safety is ensured by appropriate earthing. Supplying HMI, CPUs, I/O modules, and communication devices as indicated in the following distribution diagram, this configuration guarantees a consistent and noise-free power source for PLC systems.

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PLC System 24V DC Power Supply Wiring Explanation

The above schematic diagram shows a PLC system’s 24V DC power distribution. It shows the corresponding schematic picture is a 24V DC power distribution drawing for PLC system. It illustrates the distribution of the 24V DC power supply from a power source (PS1) via terminal blocks (TBD1) to several PLC components and modules.

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Let’s break it down clearly section-by-section:

Power Supply Source

• The label at the top reads: “24V DC SUPPLY FROM PS1 (TBD1)”.
• A power supply marked 26.1E/TBD1 feeds the 24V DC power (positive) and 0V (ground/negative).
• Fuse terminals with LED indicators (symbol denotes this) direct the power to several outputs. Rated at 2A, the fuses are glass.
  

Terminal Blocks (TBD1)

• Power is being distributed by the terminal blocks marked TBD1:1 to TBD1:12.
• Every terminal produces: +24V (from odd-numbered terminals, e.g., TBD1:1, TBD1:3…) and 0V (from even-numbered terminals, e.g., TBD1:2, TBD1:4…)

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Connected Components

Every power pair (24V & 0V) runs to a particular PLC or automation device. Each set links to the following:

Terminal	Connected To	Description
TBD1:1-2	HMI (2711P-T7C21D8S)	PanelView Plus 7 HMI
TBD1:3-4	P1 (1769-L19ER-QB1B)	CompactLogix PLC CPU
TBD1:5-6	ESW1 (1783-US5T)	Ethernet Switch
TBD1:7-8	A0 (1734-AENT)	POINT I/O Adapter Module
TBD1:9-10	M1 (2080-LC20-20QBB)	Micro820 PLC (maybe secondary controller)
TBD1:11-12	CPU Input, Output, DI Modules	The rest feed power to PLC I/O Modules

Module-wise Distribution

Further down the diagram, specific modules are powered:

• 1P1, 1M1,  CPU Input & Output
• 1M2, 1M3, 1M4, 1M5, 1M6,  DI1, DI2, DI3, DI4 modules
  

Each module receives:

• A +24V from TBD1 odd terminal (e.g., TBD1:11)
• A 0V from TBD1 even terminal (e.g., TBD1:12)
  

Features and Best Practices Highlighted

• Fuse Terminals: Each branch is safeguarded by 2A fuse terminals with LED indicators to indicate blown fuses.
• Clean Labeling: Every wire and terminal is obviously marked (e.g., +1V-MS7-1/TBD1:1).
• Separation of Loads: Safety and troubleshooting are improved by each device/module having a specific fuse-protected power supply line.

A PLC panel’s organized 24V DC power distribution is well illustrated by this drawing:

• Easy to troubleshoot, modular, and safe
• Every important PLC part is separately fused.
• Guarantees quick fault separation and consistent functioning

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FAQ on 24V DC in PLC 

What is common PLC voltage?

24V systems are more efficient than 12V, requiring less current and enabling thinner, more cost-effective wiring. This reduces energy loss and overall system costs, making 24V preferable for industrial and large-scale applications like PLCs.

Why use 24V instead of 12V?

24V DC is widely used in industrial automation for powering sensors, actuators, and control devices. It provides stable and safe voltage, ideal for precise operation in manufacturing, process control, and industrial machinery environments.

Why do we use 24 VDC?

In industrial automation, 24V DC is frequently utilized for the purpose of providing power to control devices, actuators, and sensors. It provides stable and safe voltage, ideal for precise operation in manufacturing, process control, and industrial machinery environments.

Why 24V DC used in PLC?

24V DC is safe, reliable, and compatible with most industrial sensors and actuators. It minimizes noise interference and follows standard industrial practices, making it the preferred voltage level for powering PLC systems and related control components.

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