AT&T MERLIN LEGEND Installation & Maintenance Manual page 540

Adapters, Accessories, and Applications
Auxiliary Power Units
When a power demand of over 54 unit loads is placed on one
power supply module, an Auxiliary Power Unit 9024 is generally
needed and increases power by 27 unit loads.
To determine the number of unit loads for each power supply
module on each carrier, see "Unit Loads" in Chapter 2 and
Appendix D.
Note: Only one auxiliary power unit can be connected to the
391A power supply unit. If additional 48-VDC power is needed,
connect some telephones to KS22911 or 329A telephone power
units.
In-Range Out-of-Building (IROB)
Protector
See "IROB Protection" in Chapter 3, "Installation."
Power Failure Transfer
A power failure transfer (PFT) telephone is a single-line
telephone connected to a PFT jack on a 400, 400/GS/LS/TTR,
800,800 GS/LS, 408, or 408 GS/LS module (see Figure 4). In the
event of a power failure, the system shuts off and the PFT
telephone automatically turns onto be used for making and
receiving calls.
Notes:
The PFT jack does not operate unless a power outage
occurs or the power supply units are turned off.
A single-line telephone connected to an MFM cannot be used
as a PFT telephone.
Accessories 6-5