574-5 Power Transfer Unit - AT&T 75 Wiring Manual

The following two types of transfer units are available:
Z1A Emergency Transfer Unit—Each unit serves up to six Power Failure Tansfer
terminals. A ground-start switch is required at each preselected voice terminal when
ground start trunks are used.
574-5 Power Transfer Unit—Each unit serves up to five Power Failure Transfer
terminals. The unit provides automatic ground start.
The units are connected to a yellow connecting block in the Trunk/Auxiliary Field. The
units are powered (-48 V dc) from the EM TRANS RELAY PWR terminals. There are seven
EM TRANS RELAY PWR terminal pairs. This simplifies powering of up to seven
emergency transfer units.

574-5 Power Transfer Unit

The 574-5 Power Transfer Unit has connection for 5 emergency transfer terminals and is
compatible with both loop start and ground start trunks. Ten slide switches in the center of
the unit (Figure 4-65) are set for the trunk type (two per trunk). The switches are set at the
factory for ground start trunks as shown in Figure 4-65.
When ground start trunks are used, the transfer unit will automatically provide ground start
for each trunk without the need for special wiring at the terminal used for emergency
transfer service.
Figure 4-66 shows wiring required at the Trunk/Auxiliary Field for a voice terminal used
only for emergency transfer. Figure 4-67 shows wiring required at the Trunk/Auxiliary
Field for a voice terminal used for emergency transfer as well as a normal extension.
66-TYPE HARDWARE
4-99