Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Electrical engineering and control panels

Control relay

Also known as: Auxiliary relay, Contactor relay

German: Steuerrelais

In control engineering, a control relay is an electromechanical switching device used in control circuits to switch signals and small loads, to multiply contacts or to provide isolation between circuits, operated by a coil at control voltage.

  • Control panels

In one sentence

A control relay switches signals and small loads in control circuits, multiplies contacts and isolates circuits.

Example

A PLC transistor output drives a control relay whose contact switches the 230 V coil of a solenoid valve.

How it applies

  • Engineering: Control relays interface PLC outputs to loads with different voltages, provide Galvanic isolation and extend contact numbers. Plug-in relays on sockets simplify replacement; suppression diodes or RC elements on coils protect the driving outputs.
  • Maintenance: Relay contacts wear with switching cycles and load. Relays with LED indication speed up troubleshooting.
  • Documentation: Show relay coils and contacts with cross-references in the circuit diagram. The maintenance manual should list relay types for replacement.

Control relay vs. safety relay

A control relay is a standard switching device. A Safety relay is a safety-rated module with monitoring, redundancy and defined behavior on faults, used in safety functions. Replacing a safety relay with a control relay removes the safety properties.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: IEC 60947-5-1, Low-voltage switchgear and controlgear — Part 5-1: Control circuit devices and switching elements — Electromechanical control circuit devices

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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