See Fluke 87V specs in:

http://media.fluke.com/documents/8xv_____cmeng0100.pdfFor Model 87 in the 4 ½-digit mode, multiply the number of least significant digits (counts) by 10. AC conversions are ac-coupled and valid from 3 % to 100 % of range. Model 87 is true rms responding. AC crest factor can be up to 3 at full scale, 6 at half scale. For non-sinusoidal wave forms add -(2 % Rdg + 2 % full scale) typical, for a crest factor up to 3.

Taking measurements at a higher

Crest Factor than specified.is not likely to give a useful result as your meter's true RMS converter circuit is probably clipping or distorting the current peak.

As the load on a bridge rectifier tends to zero, the conduction angle becomes vanishingly small and as the current tends to zero, its crest factor tends to infinity.

As I said earlier, you need a *VERY* good True RMS bench meter (preferably using a thermo-resistive true power measurement RMS converter), or a scope that does waveform arithmetic + a calibrated current probe to take meaningful measurements of the current into a lightly loaded bridge rectifier + reservoir cap.

As such, small differences in terminal voltage of the two halves of the secondary, or variations in DC resistance will cause an imbalance at low load currents. If the winding is wound with a tap midway, the increased diameter of the outer half of the winding means it has more resistance for the same number of turns, thus the peak current will be lower even if its unloaded voltage is identical. If the transformer is bifilar wound two matched secondaries are possible, but they will usually be brought out to four terminals so they can be connected in series or parallel.

Another possible cause of imbalance is differences in diode Vf in the bridge rectifier.