Glossary · Automation fundamentals, platforms and components
Control circuit
Also known as: Control circuit (electrical)
German: Steuerstromkreis
In electrical equipment of machines, a control circuit is a circuit used for the operational control of the machine and for the protection of the power circuits, as distinct from the power circuit that supplies motors and other loads.
- Automation components
- Standards
In one sentence
A control circuit carries the signals that operate and protect a machine, separate from the power circuit that supplies motors and loads.
Example
The 24 V DC control circuit of a press powers the contactor coils, push buttons and the safety relay, while the 400 V power circuit feeds the main motor.
How it applies
- Engineering: IEC 60204-1 sets requirements for control circuits, such as supply via a transformer or power supply, protection against overcurrent and measures so that earth faults do not cause unintended operation.
- Maintenance: Control circuits may remain energized from separate sources even when the main power is off. Lockout procedures must consider every supply.
- Documentation: Circuit diagrams should clearly separate power and control circuits and show voltages and protective devices. Maintenance instructions should warn when control voltage remains present after the main switch is turned off.
Control circuit vs. power circuit
The power circuit carries the energy to motors, heaters and other loads. The control circuit carries the logic: commands, interlocks and feedback. Safety-related control circuits are part of the safety-related parts of the control system and are assessed under standards such as ISO 13849-1 or IEC 62061, not just IEC 60204-1.