What is a Safety Relay?
A safety relay is a specially designed relay that monitors and switches safety functions within industrial machines and installations. It forms a critical link in functional safety and ensures that machines stop immediately and reliably in a hazardous situation.
Safety relays are used to comply with standards such as NEN-EN-ISO 13849 and SIL (IEC 62061) within the context of the Machinery Directive.
🧠 How does a safety relay work?
- Receive input signals
- From safety sensors, emergency stop buttons, light curtains, door contacts
- Check the circuit
- Detects faults such as short-circuit, broken wires or tampering
- Carries out self-diagnostics
- Perform safe shutdown
- Drives actuators: the relay breaks the supply to motors or drives
- Restart is only possible after recovery and reset
Many safety relays have force-guided contacts (mechanically linked), which guarantees that the contact status is reliably safe.
🏭 Application in industrial automation
- Control cabinets and MCC for machines, conveyors and robots
- Machines with emergency stops, gate switches or light curtains
- Alternative for simple Safety PLC applications
- A solution for stand-alone safety applications (e.g. in retrofits)
Examples:
- Stopping a press when a guard gate is opened
- Preventing restart without manual confirmation
- Redundant monitoring of emergency stop circuits
🔍 Safety relay vs. standard relay
| Characteristic | Safety relay | Standard relay |
|---|---|---|
| Fault detection | Yes (short-circuit, broken wire) | No |
| Force-guided contacts | Yes | No |
| Application | Safety functions (PL/SIL) | General switching |
| Reset required | Yes – manual or automatic | No |
| Standards compliance | ISO 13849, SIL, Machinery Directive | Not applicable |
🔐 Safety aspects
- Part of a safety function in line with PL or SIL
- Redundancy and fault tolerance through internal logic and hardware
- Reset and test capabilities prevent uncontrolled restart
- Periodic validation required within RI&E, work permit or Audit
- Can be combined with Lock-out Tag-out during maintenance work
With incorrect wiring or improper use, the safety function is no longer ensured.
📌 In summary
A safety relay is an essential and reliable component for safely switching machines in emergency situations. It safeguards the integrity of safety functions and supports compliance with standards such as ISO 13849.