Motors, Starters, and Elevator Duty

[noel0589]

For a typical AC-3 Application, a certain sized starter, or more specifically, the contacts of the starter are tested to be good for 1,000,000 electrical operations under its rated application. And tests are done at a high frequency, almost 20-30 make/breaks per minute.
However, for elevator duty, CSA and UL will almost specify that you largely overcompensate the size of the starter to be used. Does anybody know why? Whether or not that motor is being used on an elevator, to drive a conveyor belt, or to drive another hydraulic machine, what is the difference if it is elevator duty that it requires such overcompensation? Can anyone shed any light on this?
Thanks!!!

 

[buzzp]

Just a guess but probably because of the safety issues. You are transporting people. Also, how often is an elevator overloaded? Quite often in our building so it would make sense to have more cushion built-in to the starter.

 

[mc5w]

See NEC table 430.22(E). For motors that are periodically or occasionally overloaded or frequently started, you need oversize wires and contacts so that you have reasonable heating. Repetitive overloads also tend to spot weld contacts which will turn a motor controller or circuit breaker into something that isn't.

An example of a varying duty application that requires 200% conductors is a rubbish compactor or the hoist chain motor for a roller coaster. In these applications it is acceptable to the motor to deliver 200% of full load torque because the overload is very short in duration. In the case of a roller coaster you also need a 200% rated gearbox so as not to have lubrication failure ( metal to metal contact between gears ) when there are a bunch of fat people on the train.