transformer nameplate provides information necessary to complete connections. The voltages should be measured when the transformer is energized to ensure that the connections are correct before the load is connected to the transformer.

Single-phase distribution transformers can be connected to obtain three-phase secondary service (fig. 4-20). There are four normal connections: the delta-delta (D/D ). the wye-wye (Y/Y). the delta-wye (D/Y), and the wye-delta (Y/ D). Figure 4-21 shows the proper connections for three single-phase distribution transformers connected to a three-phase three-wire ungrounded delta primary-voltage system to obtain three-phase three-wire delta secondary service. The illustration is for a 2,400-volt primary system and voltages would be connected the same. Single-phase transformers with secondary windings constructed for voltage of 240/480 should be used to obtain 480-volt three-phase secondary service.

Figure 4-22 shows the proper connections for three single-phase distribution transformers connected to a three-phase four-wire grounded neutral wye primary- voltage system to obtain 208Y/l20- or 480Y/277-volt

Figure 4-20. - Cluster-mounted bank of transformers.

Figure 4-21. - Three single-phase distribution transformers connected delta-delta.

Figure 4-22. - Three single-phase distribution transformers connected wye-wye.

secondary service. Figure 4-23 shows the proper connections for three single-phase distribution transformers connected to a three-phase three-wire ungrounded neutral delta primary-voltage system to obtain 208Y/l20-or 480Y/277-volt secondary service.

Transformers must be constructed with the proper windings for the primary-voltage system and the desired secondary voltage. Properly manufactured distribution transformers can be connected wye-delta if it is desired to obtain three-wire three-phase secondary voltages from a three-phase four-wire ground neutral wye primary-voltage system. The