AT&T System 75 Wiring Diagram page 88

Distribution Field (110-Type Hardware Only)
Figure 3-3 shows a typical 300-pair terminal block configuration of
110-type hardware arranged for use in the distribution field. One
300-pair terminal block will terminate 192 three-pair port circuits (purple
field), and either 192 three-pair station circuits (white or blue field) or
144 four-pair station circuits (blue field).
FILL
BLUE OR WHITE
CAPACITY WHITE FIELD = 192 3-PAIR CIRCUITS
CAPACITY BLUE FIELD = 144 4-PAIR CIRCUITS
CAPACITY PURPLE FIELD = 192 3-PAIR CIRCUITS
Figure 3-3. Distribution Field Arrangement of 110-Type
Hardware—Four 300-Pair Terminal Blocks
Figure 3-4 shows a typical 300-pair terminal block configuration of
110-type hardware arranged for use in the distribution field. This
configuration will terminate 384 three-pair port circuits (purple field),
Hardware Equipment Room Applications
188D2
BACKBOARD
PURPLE
OR 192 3-PAIR CIRCUITS
3-5