What is the actual voltage reading on a step down transformer 240/3phase per leg ?

Question

what should i be reading ,when putting my volt-meter on a step down transformer and the volts is 240/3phase? shouldn't be getting 120v per leg going straight to ground?i was getting a reading of 40v on two legs and 70 volts on the third?yet the transformer worked? any help ?

Answer 1

It depends on the transformer ratio. But the secondary should have the same voltage on all 3 windings.

But the secondary may not be connected to ground, probably is not. For a Y connection measure from each output to the neutral connection. For a delta connection, check between pairs of output wires.

edit: Thomas's answer is probably the correct one. But check.

Answer 2

I'm not sure about the actual values you're getting.  It depends on the primary and secondary voltage ratings as well as the winding connections (wye, delta, etc.)  Can you furnish a description or photo of the nameplate.  The voltage applied to the primary winding will also affect the secondary voltage.

It sounds like your transformer has a delta secondary winding with a grounded center tap on one winding.  You should measure 80 V phase-to-phase across all three legs.  

However due to the center tap, you are measuring 40 V phase-to-ground on two phases and 70 V phase-to-ground on the "high phase".  (a.k.a. wild phase)