AT&T System 75, Wiring Diagram

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CHAPTER 2. HARDWARE (66/110-Type)
Index Strips and Connecting Blocks
The index strips (Figure 2-3) are slotted rows that provide space to
terminate 25-pair cables. The wires are placed in the slots in the index
strip. The standard termination for a 25-pair cable is shown in Table 2-A.
CABLE IS TERMINATED
IN 25-PAIR
INDEX STRIP
110-TYPE WIRING
BLOCK (TOP VIEW)
TERMINATION
POINTS FOR
CROSS-CONNECTIONS
(JUMPERS OR
PATCH CORDS)
4-PAIR
CONNECTING
BLOCK
3-PAIR
CONNECTING
BLOCKS
Figure 2-3. 110-Type Index Strip With Connecting Blocks
The connecting blocks (Figure 2-3) are equipped with clips that slice the
insulation of the wires when the connecting block is pushed onto the
index strip. The top of the connecting blocks are used for
cross-connections. When a wire is punched onto the top of the
connecting block, it makes a connection, through the connecting block,
to the wire in the index strip.
The connecting blocks come in 3-, 4-, and 5-pair blocks. When 3- or
4-pair connecting blocks are used, the last connecting block on each
index strip must be one pair larger to complete the 25-pairs. The
ordering codes determine the type of connecting blocks received with a
terminal block. The 110-type wiring blocks allow for individual 3- and
4-pair connecting blocks to be disconnected for testing without
disturbing adjacent circuits.
2-4