Transformer Core Joint Gaps and Magnetizing Current

Two cores can use the same steel and still draw different magnetizing current. Look at the joints. Air presents much higher magnetic reluctance than grain oriented steel. A step lap lets flux transfer into overlapping sheets and bypass a gap. Wider or uneven gaps restrict that transfer and can concentrate flux locally. Check both mating sheet lengths and the mitre angle. Burrs or debris can hold the joint open. Stack against fixed guides, then preserve the same lacing pattern when the top yoke is rebuilt. Compare the assembled joint with its drawing, and review magnetizing current alongside no load loss. A material certificate alone does not describe the finished joint.