Compensating cablesgreenspun.com : LUSENET : Elevator Problem Discussion : One Thread
Regarding traction elevators, why do some have compensating cables while others do not?
-- Paul Jung (firstname.lastname@example.org), November 26, 2000
It is primarily a matter of the length of the hoist ropes (cables). Compensating ropes compensate for the weight of the hoist ropes by adding an approximately equal amount to the counterweight.
When the car is at the lowest floor, the weight of the ropes between the hitch point on top of the car must be lifted by the hoisting machine.
If, as an example, the car has six 5/8" diameter hoist ropes, these weigh .57 pounds per foot, so six would weigh 3.42#/foot.
If the rope length mentioned above was, say, 250 feet, that is 855#. This would generally be enough to significantly affect the horsepower required and one would need either more horsepower or compensating ropes.
There are other considerations as well. Rule of thumb - comp. ropes typically not required up to 100 feet of rise, above that, may be needed.
-- John Brannon (akaelevman@AOL.com), November 26, 2000.