The overspeed governor is a mechanical safety device that monitors the speed of the elevator car by means of a tensioned governor rope connected to the car. If the car speed exceeds the set threshold (typically 115% of rated speed for the first overspeed trip), the governor triggers the safety gear clamps on the guide rails to stop the car. The governor rope forms a closed loop running from the governor sheave (in the machine room or top of shaft) down to a tension sheave in the pit.