Safe / non safe Coupling Relays

In the process industry safe coupling relays are often used for coupling safety related signals, for example output signals of a safe control system to the periphery. The use of simple relays would result in the interruption of the safety chain and therefore a safe shutdown in case of failure could not be guaranteed.

This problem can be solved by using safe coupling relays. Redundantly built, self-monitoring coupling relays allow the standardized coupling of safety related signals up to SIL 3 / PL e.

Typical fields of application:

  • Galvanically isolated coupling of digital 24V and 230V signals
  • Safe coupling of sensor signals, e.g. pressure switch to control unit
  • Contact multiplication with limited output power of the used contoller
  • Filtering of test pulses sent by the safety controller

Safety contacts /outputs


Auxilliary contacts / outputs


1 / 2 channel wiring Width in mm Approvals

Safe coupling relay


(Variant SR7D for application with EN50156-1 and E746-2)

7 6 1 45


1 1 1 6,8







3 1 1 22,5

Coupling relay with forcibly guided contacts


3 1 1 17,5


Coupling relay with forcibly guided contacts



5 1 1 22,5


Non safe coupling relays


  2 1 17,5


  4 1 22,5


This is a classic, 22.5 mm wide safe coupling relay. It has 3 safe relays contacts which, in addition to the actual coupling function, also offer a contact multiplication.

The SK3D is available for DC 24 V, AC 115 V and AC 230 V. With the SK3D safe digital 24 V output signals can be coupled to the periphery, as well as e.g. 230 V signals of pressure switch contacts safely to the control level.


This safe coupling relay impresses with its ultra compact form. With a width of just 6.8 mm the SD1K meets all relevant standards for the safe coupling of safety-oriented signals in particular according to IEC 61508, IEC 61511, EN 50156-1 and EN 746-2.

When coupling safe PLC outputs a great number of coupling relays is often needed. This may lead to considerable space problems, which are solved up to now with a lot of money by increasing the installation area.

In comparision with standard coupling relays of 22.5 mm width the ultra compact SD1K requires just a third of the space in the control cabinet.

By considering the SD1K early on during the development or also during retrofit, space and costs can be saved.


This safety relay can also be used as a safe coupling relay. Due to the antivalent logic of the inputs, faults in the control lines (cross-fault, short to ground) are detected, so that, in contrast to the above-mentioned coupling relays, the wiring does not have to be carried out in a protected wiring space to reach PL e / SIL 3. Additionally certified according to IEC 61508, IEC 61511, EN 50156-1 and EN 746-2.


The safety relay / coupling relay with 7 safe relay contacts, 4 signalling contacts, 2 semiconductor signalling outputs

The safe coupling relays SK3D and SD1K are especially designed for this application and enable the coupling of safety-related signals up to SIL 3 / PL e applications with a minimum width of 6.8 mm or 22.5 mm.

Aside from the use according to IEC61508 and IEC 61511, the recognised standards for furnaces were also taken into account. Both relays are type approved for the use in furnaces in continous operation according to EN 50156-1 and EN 746-2.

More Safety Relay Series