Inrush current is not possible to calculate since it is heavily dependent on your source impedance, source wiring and other factors beyond the transformer. With larger hardwired units a separate breaker or fused disconnect should be installed for the transformer. The recommended breaker or fuse supplying the transformer should have an amperage rating somewhere between 100 & 125% of the full load rating of the transformer (or according to your local electrical codes). The breaker or fuse should be rated for use with inductive loads. This will assure that the source will be able to energize the transformer in most situations.