Figure 15 shows a typical arrangement of bringing leads out of a single-phase distribution transformer. To provide flexibility for connection, the secondary winding is arranged in two sections. Each section has the same number of turns and, consequently, the same voltage. Two primary leads (H1, H2) are brought out from the top through porcelain bushings. Three secondary leads (X1, X2, X3) are brought out through insulating bushings on the side of the tank, one lead from the center tap (neutral) (X2) and one from each end of the secondary coil (X1 and X3). Connections, as shown, are typical of services to homes and small businesses. This connection provides a three-wire service that permits adequate capacity at minimum cost.
The neutral wire (X2) (center tap) is grounded. A 120-volt circuit is between the neutral and each of the other leads, and a 240-volt circuit is between the two ungrounded leads.
Figure 15 – Single-Phase Transformer