Glossary · Electrical engineering and control panels
24 V DC control voltage
Also known as: 24 VDC control power, 24 V control supply
German: 24-V-DC-Steuerspannung
In control panel engineering, 24 V DC control voltage is the direct voltage of nominally 24 V commonly used to supply controllers, I/O modules, sensors, relays and other control circuits in industrial machines and plants.
- Control panels
In one sentence
24 V DC is the standard control voltage for PLCs, I/O, sensors and relays in industrial control cabinets.
Example
The control cabinet has a 24 V DC power supply with electronic circuit protection that feeds the PLC, the I/O modules and the sensors in separate branches.
How it applies
- Engineering: 24 V DC circuits are usually built as PELV circuits according to IEC 60204-1, with one side connected to protective earth. Tolerances for PLC inputs and outputs are defined in IEC 61131-2. Distribute the supply in protected branches so a short circuit in one sensor line doesn't stop the whole controller.
- Commissioning: Measure the voltage at the far end of long lines under load; voltage drop can push devices below their minimum input voltage.
- Documentation: Show the 24 V distribution, branch protection and the grounding point clearly in the circuit diagram. Maintenance manuals should explain how to find and reset tripped branches.
24 V DC vs. mains voltage
24 V DC is extra-low voltage and in PELV or SELV form doesn't present a shock hazard under normal conditions. Mains-voltage circuits in the same cabinet still do, so warnings and isolation procedures remain necessary.