Glossary · Protective devices and interlocks
Electrical interlock
In machine safety, an electrical interlock is an interlock implemented through electrical contacts, wiring or electronic control logic, for example a guard switch wired to a safety relay that removes power from a drive.
- Machine safety
- Technical documentation
In one sentence
An electrical interlock uses switches, wiring or control logic to stop a hazard; its reliability depends on the whole chain, not just the switch.
Example
The access door of a CNC machine operates a safety switch with positively opening contacts, wired to a safety relay that triggers Safe Torque Off on the spindle drive.
How it applies
- Functional safety: An electrical interlock is part of a safety-related part of a control system. Switches, wiring, safety relay or safety PLC and output devices together determine the achieved Performance Level or SIL.
- Design: Fault exclusion, redundancy and monitoring decide whether a single wire fault or welded contact can defeat the interlock. Series-connected switches can mask faults and limit diagnostic coverage.
- Technical documentation: Circuit diagrams must show the interlock circuit clearly. Label safety circuits in the electrical documentation so that service staff do not modify them by mistake.
- Maintenance: Specify the periodic functional test of the interlock and what to do if it fails.
Electrical interlock vs. mechanical interlock
An electrical interlock acts through the control system. A mechanical interlock, such as a trapped-key system, blocks the hazardous action or the guard physically.