AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 130

Hardware Components
Also, if the network interface is greater than 25 feet (7.6 meters) from the control
unit, connect the control unit to the network interface using an OPRE.
See the documentation packaged with the OPRE for complete installation
instructions.
146A and 147A Surge Protectors
Protection from lightning and power surges is needed to safeguard system
functioning.
It is the responsibility of the local telephone company to provide primary
protection on the outside lines at the network interface and to ensure that these
protectors are properly grounded. If the telephone company line protector is
properly grounded and bonded to the AC power ground, most lightning
damage will be prevented.
The 391A1 power supply has built-in AC line protection. This built-in protection
handles almost all situations.
Occasionally, additional AC line protection maybe needed if the customer is
located in a heavy lightning area. A 147A protector an be connected to the
system to limit surges from the AC lines and outside lines. One 147A protector
provides protection for four outside lines. Up to three 146A protectors can be
added to the 147A to provide protection for a maximum of sixteen outside lines.
For more than sixteen lines, additional 147A protectors are required (see Figure
2-22).
NOTE:
The 147A protector is usually not needed with the 391A I power supply. It
may be needed with the older 391A power supply in high-risk lightning
areas.
Installation instructions are provided with the protectors. See Figure 2-22.
2-56 Power-Related Hardware