AT&T System 75 Wiring Diagram page 238

The following voice terminals/telephones cannot be installed in an exposed
environment:
7300-type voice terminals connected to TN762 hybrid line circuit
packs
MET sets connected to TN735 MET line circuit packs
analog telephones connected TN746 analog line circuit packs.
PROTECTOR ORDERING INFORMATION
Description
361A (Carbon Block)
361E-W (Wide Gap Gas Tube)
3C1S (Solid State)
4B1C (Carbon Block with Heat Coil)
4B1E-W (Wide Gap Gas Tube with Heat Coil)
4C1S (Solid State with Heat Coil)
SCP-1 Sneak Current Protector
79A Fuse (sneak current protector)
Digital Out-of-Building Voice Terminals
Protection is required at both building entrances for digital out-of-building
voice terminals. There are 6 different primary protectors that can be used
with the required secondary (data link) protector to protect digital voice
terminals in an out-of-building environment.
Primary protectors have a surge breakdown voltage range of 200 to 800 volts
at 100 volts per microsecond depending on the type of device. Sneak current
protection is also required. It can be provided by a 4-type protector or a 3-
type protector plus a separate sneak current protector. The 4-type primary
protector is equipped with a heat coil for sneak current protection. The 4-
type primary protector is the preferred device because it eliminates the need
to evaluate the interbuilding cable runs and its vulnerability to power cross
faults. When the 3-type primary protector is used, a separate sneak current
protector is required.
The secondary (data link) protector is required in addition to the primary
protector and is installed on the equipment side of the primary protector.
Table 4-B shows the recommended protectors.
Miscellaneous Wiring Installation
Comcode
102 381 779
104 410 147
105 514 756
102 904 893
104 401 856
104 386 545
403 617 632
103 351 610
4-41