The car door restrictor limits door opening to _______ if the car is more than _______ from the floor.

In elevator systems, a car door restrictor is a safety feature designed to prevent the doors from opening too far when the car is not at floor level. This is crucial for passenger safety, as it minimizes the risk of accidents that can occur if a door opens at an inappropriate height.

In the context of the question, the correct parameters state that the door opening is restricted to 4 inches if the car is more than 18 inches from the floor. This specific limitation helps ensure that passengers can safely enter and exit the elevator only when it is properly aligned with the landing. The 4-inch maximum allows a minimal gap for the passengers to be aware of the car's position relative to the floor without exposing them to a hazardous situation.

The choice of 18 inches also provides a buffer that ensures that if the elevator car is significantly misaligned, the doors won't open wide enough to pose a risk. This design feature aligns with safety standards in the elevator industry, which prioritize reducing the potential for accidents caused by misalignment.