Thank you Mark for your valued contribution. I wrote my little missive in a bit of a rush. And yes, the important thing to do with any transformer with multiple secondaries that you intend to join in some configuration is to determine the phase relationships amongst those windings first. In the absence of a 'scope, an a.c. voltmeter is ideal. The important point is this: it is only safe to determine what those phase relationships are when there is zero - or very little - current flowing from those windings. For the transformer in question in this Thread, even if the two windings are rated as having equal voltages and current ratings, it is still worthwhile checking that the voltages from each winding are equal and that the currents that can be safely drawn are equal too.
Picking up on the point Mark raised about windings in parallel that are connected the wrong way round, phase-wise, what will happen in that situation is that each winding will effectively present a virtual short-circuit to the other winding. Hence, the resultant current will be huge - and hopefully, the resultant primary current will also be large enough to blow the fuse in the primary. Hence, determine phase relationships with no secondary currents first.
Al.
Picking up on the point Mark raised about windings in parallel that are connected the wrong way round, phase-wise, what will happen in that situation is that each winding will effectively present a virtual short-circuit to the other winding. Hence, the resultant current will be huge - and hopefully, the resultant primary current will also be large enough to blow the fuse in the primary. Hence, determine phase relationships with no secondary currents first.
Al.
