ELECTRICAL PROTECTION: SYSTEM 85 AND DEFINITY GENERIC 2 WITH TRADITIONAL MODULES
3-5
Sneak-Current Device: Fuse
A sneak-current fuse is a fuse that melts when currents of .35A (for 4 hours) to 5.25A (for more than 10
seconds) reach it. Sneak-current fuses may be installed before or after the network interface (NI) in
series with the primary protector.
Sneak-current fuses operate independently of the primary protector
and must be installed after it.
NOTE:
AT&T protector units that start with the number 4 are equipped with a heat coil to provide
both sneak-current and overvoltage protection.
ENHANCED PRIMARY PROTECTION
Enhanced primary protectors are protectors that operate at lower voltage or current levels than primary
protectors.
SECONDARY PROTECTION
Secondary protection, such as a data-link protector (DLP), provides additional protection for equipment
with a specific vulnerability.
A DLP is an isolation transformer that provides protection for digital
terminals by isolating the low-impedance, phantom-powered circuit from an exposed loop. Local power
must be provided if the digital terminals are to be port-powered.
RECOMMENDED PROTECTORS
Following are recommended electrical protectors that can be used for primary, enhanced primary, and
secondary applications.
With the exception of the 79A sneak-current fuses, all of the following primary
and enhanced primary protector units plug into 188 panels.
PRIMARY PROTECTORS
The following AT&T primary protector units are recommended for the protection of analog circuits.
●
3B1A —
carbon block protector unit
● 3B1E-W
— gas tube protector unit
● 3C1S —
solid-state, overvoltage protector unit for analog circuits
● 4B1C —
carbon-block and heat-coil protector unit
● 4B1E-W
— gas-tube and heat-coil protector unit
● 4C1S —
solid-state, overvoltage protector unit for analog circuits and heat-coil protector unit
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