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Backward Power Transformer

Posted by Triode_Kingdom on September 21, 2017 at 21:05:07:
I experimented with a power transformer this evening by wiring it backwards. It's the first time I've tried this with a small transformer of this type. The transformer is a Hammond 186C120 with dual 115V primaries and a 120V CT secondary. The diagram is below:

I was hoping to use this by applying line voltage across the whole CT secondary. I assumed the two primary windings in series would then develop about 230V, and I would be able to draw 50 mA at that voltage.
For the test, I connected a 5K resistor across the series primary windings, then applied line voltage to the secondary. Line voltage was 123V. Instead of 230V however, all I measured was 182V. Just to be sure the transformer isn't defective, I also connected it in the usual way, with the two primaries in parallel. When I applied 123V to the primaries, the secondary produced about 127V with a 1.15K load (about 110mA). That's the correct voltage, relative to the 115V input that Hammond specifies.
Can someone explain why this transformer doesn't develop the same voltage ratio forward and backward?