 
 <prompt> Wetin be di design element wey make di elevator isolated? Based on di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: Historically, AC motors dey use for single or double speed elevator machines sake of cost and lower usage applications where car speed and passenger comfort no too important, but for higher speed, larger capacity elevators, the need for infinitely variable speed control over the traction machine dey important. Therefore, DC machines wey dey powered by an AC/DC motor generator na the preferred solution. The MG set also dey typically power the relay controller of the elevator, wey get the added advantage of electrically isolating the elevators from the rest of a building's electrical system, so e dey eliminate the transient power spikes for the building's electrical supply wey dey caused by the motors starting and stopping (wey dey make lighting dey dim every time the elevators dey used for example), as well as interference to other electrical equipment wey dey caused by the arcing of the relay contactors for the control system. 