AT&T MERLIN LEGEND Release 3.0 Installation Manual page 346

Unit Loads
Auxiliary Power Units
The power supply provides 54 unit loads (102.6 watts) to each carrier.
If the unit load requirement for a carrier exceeds 54 (102.6 watts), an auxiliary
power unit is needed to allow that carrier to support an additional 27 unit
loads (51.3 watts).
CAUTION:
Running the system with more than 54 unit loads (102.6 watts) per
carrier may not appear to do harm. However, this can cause the system
to malfunction, creating "No Trouble Found" conditions.
An auxiliary power unit redirects the power requirements from the last
two slots on the carrier. Any extension 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
installation instructions are provided in Installation.
1–28 Introduction