In all transformers, the H terminals are always the high voltage terminals and the X terminals are always the low voltage terminals. SIngle phase power transformer leads are generally brought out of the transformer's steel casing through insulating bushings. Polarity is the instantaneous voltage obtained from the primary winding in relation to the secondary winding. They do, however, have relative polarity markings that must be adhered to when connecting them together in different arrangements. Since transformers are basically AC devices, they do not have a fixed polarity like that of a DC source. The availability of primary voltages and the requirements of the load dictate how the transformer will be wired.
For example, distribution transformers are normally wound with the secondary or low-voltage windings that can be connected in series or parallel. Single phase transformers, like other electrical devices, may be connected into series or parallel arrangements.
