Have you ever wondered why some low-voltage (115-V) power-consuming devices burn out too often? It could be because they are wired to a “high” or “wild” power leg of a voltage supply. These devices are actually receiving too high of a voltage to operate for any prolonged period of time. This column will try to explain the voltages associated with the high or wild leg coming from the secondary of a Delta service transformer. The high or wild leg of a service transformer is only associated with a Delta transformer.
Many commercial buildings have electrical power delivered by means of dual-voltage, 60-Hz service. One example would be a 120/240-V, three-phase, 4-wire Delta drop. The secondary of the Delta transformer (Figure 1, page 27) delivers power to a building. Remember, the secondary of these transformers receive their voltage from the primary windings (not shown in Figure 1) of the transformer through induced voltage. Any time a Delta transformer’s secondary winding is center tapped, a high leg is created. Notice that one of the windings of the Delta transformer has been center tapped and connected to earth ground. This center tap is connected to a ground rod driven into the earth, which grounds the neutral wire and the equipment’s chassis.