Requirements on the external safety controller

[1]	Safety relay with approval
[2]	DC 24 V voltage supply
[3]	Fuses according to the manufacturer's specifications for the safety relay
[4]	Safety-related DC 24 V voltage supply
[5]	Reset button for manual reset
[6]	Approved EMERGENCY STOP actuating device

A safety relay can be used as an alternative to a safety controller. The following requirements apply mutatis mutandis.

• The safety controller and all other safety-related subsystems must be approved for at least the safety class required in the overall system for the respective application-related safety function.
• The following table shows an example of the required safety class of the safety controller:

• The wiring of the safety controller must be suitable for the endeavored safety class (see manufacturer's documentation).
• In a disconnected state, there must be no test pulses on the supply line.
• The values specified for the safety controller must be strictly adhered to when designing the circuit.
• The switching capacity of the safety relays or the relay outputs of the safety controller must correspond at least to the maximum permitted, limited output current of the 24 V supply voltage.
• Observe the manufacturer's instructions concerning the permitted contact loads and fusing that may be required for the safety contacts. If the manufacturer provides no specific information, the contacts must be protected with 0.6 times the nominal value of the maximum contact rating specified by the manufacturer.
• To ensure protection against an unexpected restart in accordance with EN ISO 14118, the safe control system must be designed and connected in such a way that resetting the command device alone does not lead to a restart. This means that a restart may only be carried out after a manual reset of the safety circuit.

INFORMATION

It is not possible to control the STO inputs via pulsed signals such as self-testing digital outputs of safety controllers, for example.