AT&T System 75 Wiring Diagram page 249

CHAPTER 4. STATION WIRING
Installation
Connect the DID make-busy trunk as follows:
1.
At the trunk/auxiliary cross-connect field, connect a jumper from
one DID make-busy lead to terminal COM3 on the yellow emergency
transfer row/connecting block (Figure 4-30).
2.
Connect a jumper from the other DID make-busy lead to terminal
NC3 on the yellow emergency transfer row/connecting block.
Installing the Power Transfer Unit
Install the 574-5 power transfer unit as follows:
1 .
Mount the power transfer unit on the wall to the left of the
trunk/auxiliary cross-connect field. Mount additional units on the
wall below the first one in a vertical column.
2 .
Connect a B25A (for 110-type hardware) or A25B (for 66-type
hardware) cable from the power transfer unit to the connector
associated with the yellow emergency transfer row/connecting
block in the trunk/auxiliary cross-connect field.
Installing Telephone Associated with 574-5 Power Transfer Unit
Trunk/Auxiliary Field Connections—Telephone Used Only for Emergency
Transfer
Install telephone as follows:
1.
At trunk/auxiliary cross-connect field, connect a pair of wires
between the -48V and GRD terminals on the yellow emergency
transfer row/connecting block and the EM TRANS RELAY PWR
terminal (Figures 4-28 and 4-29, respectively for 110-type and
66-type hardware).
2.
Connect CO trunk leads from the purple field to TC terminals on the
yellow emergency transfer row/connecting block for each trunk.
3.
Connect CO trunk leads from the green field to TK terminals on the
yellow emergency transfer row/connecting block for each trunk.
4.
Connect ST leads on the yellow emergency transfer row/connecting
block for each emergency transfer telephone to the ST terminal
appearance in the yellow trunk/auxiliary field (see Note).
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