AT&T System 75, Wiring Diagram

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CHAPTER 2. HARDWARE (66/110-Type)
Network Interfaces
RJ21X Network Interface
The RJ21X network interface is the connection point between the local
telephone company lines (1-pair trunks) and the switch. The interface is
supplied and installed by the local telephone company. See Table 3-G
for network interface pin assignments on CO and DID trunk circuit
packs.
RJ2GX Network Interface
The RJ2GX network interface is the connection point between the local
telephone company tie-trunks and the switch three-pair tie-trunks. The
interface is supplied and installed by the local telephone company. See
Table 3-G for network interface pin assignments on tie trunk circuit
packs.
1.544 Mbps Digital Service Interface
The 1.544 Mbps (megabits per second) digital service interface is the
connection point between the local telephone company T1 carrier lines
and the switch DS1 trunks. The interface is supplied and installed by the
local telephone company.
Sneak Fuse Panels
575-4 Sneak Current Fuse Panel
Sneak current protection is required between the RJ21X or RJ2GX
network interface and the switch for both trunk and off-premises circuit
packs. See Installing Off-Premises Voice Terminal Wiring in Chapter 4.
The Model 575-4 sneak current fuse panel (Figure 2-18), or equivalent,
is recommended for sneak current protection. The panel is
connectorized with incoming and outgoing connectors and equipped
with 25 two-pair fuse modules. Connector cables (B25A) connect the
network interface to the sneak fuse panel. Also, 157B connecting
blocks equipped with SCP-1 protectors can be used for sneak current
protection.
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