This part of IEC 60424 gives guidance on allowable limits of surface irregularities applicable to planar-cores in accordance with the relevant generic specification defined in IEC 60424-1.The relations between the main dimensions of planar E-, ER- and EL-cores differ from those of standard cores. For example, the width of planar cores is larger while the total height is much smaller. Also the thickness of the legs is in most cases smaller than compared to standard cores. Therefore the concept of fixed reference dimensions to determine the length of crack limits yield crack lengths which are not acceptable for this type of core. This part of IEC 60424 follows another concept which relates the crack length to dimensions of the surface on which the crack occurs. Also the concept to determine the maximum area of chips based on the total mating surface fails in the case of planar cores. The outer legs of planar cores are much thinner than those of standard cores which makes overlapping and gluing much more difficult. A single chip of maximum size on the outer leg may risk the functionality of the core set. Therefore this standard uses as a reference the mating surface on which the chip occurs. Windings of planar cores are often PCBs which are glued to the inner surfaces of the planar core. For this reason the inner surfaces of the planar cores need to have a better quality than the inner surfaces of standard cores. This was taken into account by reducing the maximum allowable area of pull outs in the inner surfaces. This standard is considered as a sectional specification useful in the negotiation between ferrite core manufacturers and users about surface irregularities.