In the winding of an armature, a given percentage of the turns, it may
be 80 per cent., more or less, is assumed to be active; the other 20 per
cent. or thereabouts, is called dead-turns. This portion represents the
wire on such portions of the armature as comes virtually outside of the
magnetic field. They are termed dead, as not concurring to the
production of electro-motive force.