This part of IEC 62317 specifies the dimensions that are of importance for mechanical interchangeability for a preferred range of EP-cores@ the essential dimensions of coil formers to be used with these cores and the locations of their terminal pins on a 2@50 mm printed wiring grid in relation to the base outlines of the cores@ and the effective parameter values to be used in calculations involving them. The general considerations upon which the design of this range of cores is based are as given in Annex A.