Cascade of safety switches with additional voltage source connection

A cascade of safety switches having safety switches for the monitoring of

• accesses of an automation system;
• at least one connection unit for the arrangement between two safety switches;
• and
• a terminator for the termination of the cascade of safety switches,
• wherein each safety switch has a first conductor and a second conductor, the first conductor comprises conductor cores for transmitting signals and for receiving voltage, the second conductor comprises conductor cores for receiving signals and for forwarding the voltage along the cascade, and
• the connection unit comprises a first circuit and a second circuit;
• and
• wherein the first circuit is provided for receiving the signals of a subsequent safety switch and for forwarding the signals of the subsequent safety switch to an upstream safety switch and the second circuit is arranged for transmitting a voltage from the subsequent safety switch to the upstream safety switch by a conductor core;
• and
• the connection unit providing an external voltage source to feed additional voltage into the cascade by the second circuit and conduct the additional voltage to the upstream safety switch.