2024 January 20

Read time : 10 m


The standard for MRL elevators or those without a machine room is one of the issues many elevator companies consistently have trouble calculating, and its significance becomes apparent when there is also a space limitation in the overhead part.

Overhead Calculation

Overhead, also known as the clearance at the top, refers to the distance from the floor of the highest stop to the underside of the shaft’s ceiling. To calculate this measurement, we need an important prerequisite:

Initially, there must be an air gap between the counterweight frame and the buffer, followed by buffer compression, which if our buffer is polyurethane, is compressed to 90% of the buffer’s height, and if our buffer is hydraulic, it compresses to the stroke noted on its plate.

What is Shadow Casting in Elevators?

It means that if we shine a light from above onto any component inside the shaft, its shadow must not fall on the cabin. In this instructional video, the wire rope sockets on the right are colliding with the cabin, hence their shadow is cast onto our cabin. The shadow cast cannot be more than 15 cm, because at the shadowed area, we can separate it from our cabin with a guardrail on the cabin, and the guardrail cannot protrude more than 15 cm over the cabin. When our cabin is positioned on the level of the top floor, we must account for the additional length of its rail.

Our cabin rail casts a shadow with our motor chassis, so our motor chassis must be positioned higher than our rail. In this section, we calculate the distance from the cabin floor to the top of the shoe, which plus our compression plus the air gap, then adding 0.1 + 0.035 v^2, equals the required rail length for our project.

Therefore, we must place the motor chassis at a distance above this measurement from the rail. After the motor is chassis-mounted, we bring up the cabin until our counterweight frame is positioned on the compressed buffer. We then must check the four conditions at the top of the shaft:

  1. Additional rail which after the cabin shoe up to the end of our rail must be spaced at 0.1 + 0.035 v^2.
  2. Standing place. Anywhere on the cabin that is 12 square centimeters with the smallest edge being 25 centimeters up to the ceiling overhead must be spaced at 1m + 0.035v^2.
  3. Equipment. Our tallest equipment is usually the railing, which must be spaced at 0.3 + 0.035v^2 from the shaft ceiling. Note in this part is that since our wire rope socket casts a shadow on our cabin, the ceiling overhead for our cabin right now is considered the wire rope socket plate, so 0.3 + 0.035v^2 should be measured here.
  4. Cube condition. We must have space for a refuge cube measuring 50 by 60 by 80 centimeters on one of its sides on the cabin.

After we have reviewed the four conditions above, we need to determine where our service and maintenance area is on the cabin. This space must be 50 by 60 cm on top of the cabin. This space should be on the side of the motor brake. After we have identified this, we now need to review the MRL (Machine Room-Less) conditions together.

The first point to consider is where we need to activate our parking plate. The parking plate is activated in a space where there is a minimum distance of 2 meters from our service and maintenance area to the underside of the ceiling.


The next point is that when standing in this location, we must have full access to the motor brake, and also nothing in our path should be less than 1820 cm in height to reach this location.

In this section, we want to examine the methods of exit together. We have two types of exits:

  1. Exit through the top floor door: For this purpose, we activate our parking plate where there is at least 60 cm of space between the cabin and the top floor door. One of the greatest advantages of this method is that it requires less overhead space. Considering that the cabin rail now casts a shadow with our motor chassis, and also our cabin with the wire rope end socket, we cannot use this method.
  2. Exit through the hatch: If building conditions allow us to have a hatch above the back of the cabin, it is one of the best methods of exit. This hatch must be at least 60 by 60 cm. It should have a door without any openings, a lock that can easily be opened from the inside, and a key from the outside.

It must also be equipped with a safety switch. When we activate the parking plate, we must not have a height greater than 50 cm from our standing location to the hatch; if we do, we must provide a ladder. Moreover, there should be no more than 30 cm of space from the cabin to the hatch.

Now that we have explained the hatch, we must be able to move to this location. The best scenario is that our entire route has a minimum width of 50 cm.

It is also preferable to provide this route through a staircase. If it is not possible to install a staircase, we must have a ladder.

This ladder cannot be used for heights above 4 meters, and it must be installed in such a way that it cannot be removed. When the height of the ladder exceeds 1.5 meters, it must have an angle of between 65 to 75 degrees.

The useful width of the ladder must be at least 35 cm and the depth of each step must not be less than 25 mm. If a vertical ladder is used, there must be a minimum distance of 15 cm from the wall, and each step must be able to bear a load of 1500 N. The ladder must be at least 1.5 meters away from the nearest edge.

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