A slip ring includes a spindle and a plurality of insulating rings and conductive rings alternately fitted to the spindle. Each conductive ring is connected with a wire, and the wire extends out of the slip ring through a wire hole of the spindle. The insulating rings engage the spindle so that the insulating rings are unable to rotate relative to the spindle. The conductive rings engage the spindle or the neighboring insulating ring so that conductive rings are unable to rotate relative to the insulating ring. The number and size of the insulating rings and conductive rings are selectable to be fitted to the spindle.