I recently installed a buck-boost transformer in one of our buildings with 208Y/120v service to support a 1hp submersible well-pump rated for 230v single-phase.
The transformer is a GE 9T51B0158 which is labeled for 208v primary x 240v secondary, up to 500va.
Per the label diagram, I connected 208v nominal (210v measured at the transformer) to X1 & X2, tied H2 to H3, and then took a meter reading at H1 & H4 before connecting to the well-pump control. I measured 259v at H1 & H4, unloaded. Is there some reason to expect this kind of over-voltage? Would you expect the secondary to drop down closer to 240v under some load? Or is it more likely that I have either misunderstood the wiring diagram or acquired a dud unit?
Any thoughts are appreciated.