Elevator with safety chain overlay control unit with a safety PLC separately monitoring various safety switches for increasing a safety integrity level

A safety chain overlay control unit for an elevator, the elevator including a drive unit for displacing an elevator car in an elevator hoistway, an elevator controller for controlling an operation of components of the drive unit, multiple safety switches being switchable upon occurrence of safety relevant events related to the elevator, the safety chain overlay control unit comprising:

• a safety PLC;
• wherein the safety PLC includes first connectors connectable to contacts of at least one first safety switch of the safety switches being one of a single first safety switch and a plurality of first safety switches connected in series to form a first safety chain;
• wherein the safety PLC includes second connectors connectable to contacts of at least one second safety switch of the safety switches being one of a single second safety switch and a plurality of second safety switches connected in series to form a second safety chain;
• wherein the safety PLC is adapted to monitoring a current safety status of the elevator and identifying a safety critical status of the elevator based on detecting when at least one of the at least one first safety switch and the at least one second safety switch changes its switching state and based on comparing a current switching state of the at least one first safety switch with a current switching state of the at least one second safety switch;
• and
• wherein the safety PLC is adapted to cause interruption of a main energy supply to the drive unit upon identifying the safety critical status of the elevator.