AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 127

Hardware Components
CAUTION:
Running the system with more than 54 unit loads per carrier may not
appear to do harm. However, this can cause the system to
malfunction, thereby creating "no trouble found" situations, such as
malfunctioning LEDs on multiline telephones, or power unit failure.
Any station connected to the modules in the last two slots receives power from
the auxiliary power unit instead of from the power supply.
If an auxiliary power unit is required, complete instructions are provided in
Installation.
To determine the number of unit loads for each power supply module on each
carrier, see Unit Loads in Chapter 1.
NOTE:
Only one auxiliary power unit can be connected to the 391A power unit. If
additional 48-VDC power is needed, connect some telephones to KS-22911
or 329A telephone power units.
Protection Accessories
Certain accessories are used for grounding and protecting special telephone
connections from power surges, electromagnetic interference, and electrostatic
discharge.
IROB Protection
Equipment connected to the analog multiline telephone station jacks (on the
008, 408, 408 GS/LS-MLX (Release 2.0 only), and 408 GS/LS/TTR modules) or
to the MLX telephone jacks (on the 008 MLX or 408 GS/LS-MLX module) that is
located in a different building but within 1000 feet (305 meters) of the control
unit requires in-range out-of-building (lROB) protection units. These units
protect the equipment and the control unit from lightning strikes and power
surges. Two units are required for each piece of equipment—one for the
control unit end of the wire run, the other for the equipment end.
NOTE:
012 basic telephone ports may not be used for out-of-building or off-
premises telephones.
Use the following IROB protectors:
TII Model 343 for analog multiline telephones and equipment
Model 505A for MLX telephones and equipment
Power-Related Hardware 2-53