An elevator overrun (or lift overrun) is the portion of a building's lift shaft that extends above the top landing of the lift.
Understanding Elevator Overrun
In simple terms, the elevator overrun is the vertical space situated directly above the highest floor served by an elevator. It is an essential part of the lift shaft or hoistway structure. This area isn't used by passengers but plays a crucial role in the safe and efficient operation of the elevator system.
The size and dimensions of the overrun are determined by strict building codes and safety standards, such as those found in the [ASME A17.1](placeholder_link_to_asme_standards) in North America or the [European EN 81 series](placeholder_link_to_en_standards) in Europe. These regulations ensure adequate space for safety and maintenance functions.
Why is Elevator Overrun Necessary?
The overrun space serves several critical functions:
- Safety Space: It provides a safety buffer. If the elevator car travels slightly beyond the top landing, the overrun space prevents it from hitting the top of the shaft directly. This area is also designed to ensure there is safe refuge space above the car roof for maintenance personnel.
- Housing Equipment: Depending on the type of elevator system (e.g., traction or machine-room-less), the overrun may house essential equipment. This can include the hoisting machine, control panels, and sheaves (pulleys) that manage the hoist ropes.
- Maintenance Access: It allows technicians safe access to key components for inspection, maintenance, and repairs.
Components Often Found in the Overrun
While this varies by elevator type and design, common components found within or associated with the overrun space include:
- Hoisting Machine: (Often in machine-room-less elevators or machine rooms located above the shaft) The motor and gearbox that lift the elevator car.
- Deflector Sheaves: Pulleys that guide the hoist ropes.
- Final Limit Switches: Safety devices that stop the elevator car if it travels too high.
- Buffers (sometimes): Though more common in the pit, safety buffers might be located in the overrun in specific designs.
Overrun vs. Pit: A Simple Comparison
It's helpful to compare the overrun to the elevator pit. Both are non-passenger areas at the ends of the hoistway, but they serve opposite ends:
| Feature | Elevator Overrun | Elevator Pit |
|---|---|---|
| Location | Above the top landing of the elevator shaft. | Below the bottom landing of the elevator shaft. |
| Purpose | Safety space, housing equipment (sometimes), maintenance access for the top of the car/shaft. | Safety space, housing buffers, drainage, maintenance access for the bottom of the car/shaft. |
Understanding both the overrun and the pit is key to appreciating the safety engineering built into modern elevator systems.
Safety and Regulations
Building codes rigidly define the minimum required dimensions for the elevator overrun. These dimensions ensure there is sufficient vertical clearance above the elevator car when it is at its highest limit, protecting both the equipment and any personnel who might need to access the top of the car for maintenance. Adherence to these codes is mandatory for elevator installation and operation.
