AT&T 75 Wiring Manual page 526

66-TYPE HARDWARE
Figure 4-65. 574-5 Power Transfer Unit Option Switches
Requirements—Optional DID Make-Busy Trunk
Figure 4-68 shows the connections at the Trunk Auxiliary Field for an optional Direct
Inward Dialing (DID) make-busy trunk. This option prevents DID trunks from being taken
out of service by the serving central office during emergency transfer. This trunk is used for
this function only and should be specified to appear on the twenty-fifth pair of a network
interface jack.
Installation—Emergency Transfer Units
1 . Mount emergency transfer unit on the wall to the left of the Trunk/Auxiliary
Field. Additional units should be mounted below the first one in a column.
2. Connect A25B cable from the emergency transfer unit to a 66-type connecting block
in the yellow Trunk/Auxiliary Field associated with emergency transfer.
Installation—Terminals
Trunk/Auxiliary Field Connections—Terminals Used Only for Emergency Failure Transfer
1 . At Trunk/Auxiliary Field, run and connect pair of wires between PWR terminals
on the yellow emergency transfer connecting block to EM TRANS RELAY PWR
terminal (see Figure 4-66).
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