Had a few transformers from ToroIDY with two 115V primarys I needed to serialize, unfortunately no markings of the phase.
Hook'ed up one of the secondaries to a function generator, and serialized the two primaries.
Having two free leads and two connected leads (CT)
Measured the voltage V1 from CT to one lead, and V2 from CT to second lead.
Finally measured the voltage V3 from lead to lead.
If V1 + V2 = V3, then the two windings are in phase.
If V1+V2 ≠ V3, the the two windings are out of phase.
Are there an easier way of determine the phase of transformer windings?