Space factor, Slot fill factor

An index that indicates the effective ratio of the sum of the cross-sectional areas of metal parts of the wire (usually copper magnet wire) to the slot cross-sectional area when inserting and installing an armature winding in a slot-type core. It is expressed as a percentage. Figure (a) is an illustration of the arrangement of the groove and the conductor, and figure (b) is a cross section of the actual motor. In all of these, the insulating layer cannot be seen, due to the insulating film (slot liner) or epoxy. Apart from these insulating layers and those of the conductor wire, the space occupied by the wires is surprisingly small, usually about 30% for a manually operated wire with a circular cross section. For a high space factor, a rectangular wire and machine to wind it are used.