AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 70

Introduction
NOTE:
The 147A protector is usually not needed with the 391A1 power supply. It
may be needed with the older 391A power supply module in heavy lightning
areas.
Complete installation instructions are provided with the protectors.
Unit Loads
A unit load is a measure of power (1.9 watts) used to determine the electrical
load that the following components have on each carrier's power supply:
Telephones and adjuncts
Only the telephones and adjuncts that connect to the analog and digital
ports on the control unit require unit load calculation. Do not include any
equipment with its own power supply, for example, a fax machine, an
MFM, or an answering machine, in the unit load calculation.
800 DID modules
Before installation, unit load and auxiliary power requirements for a new system
are computed by qualified service personnel or an authorized dealer, and any
necessary auxiliary power equipment is ordered automatically. However, in the
event of maintenance or equipment changes, unit loads should be calculated to
ensure proper operation under all conditions.
The power supply module provides 45 unit loads to each carrier. If the unit load
requirement per carrier exceeds 45, an auxiliary power unit is needed to allow
the carrier to support an additional 27 unit loads.
CAUTION:
Running the system with more than 45 unit loads per carrier may not
appear to do harm. However, this can cause the system to
malfunction, creating "NO Trouble Found" situations.
An auxiliary power uni redirects the power requirements from the last two slots
on the carrier. Any telephone connected to the modules in the last two slots
receives power from the auxiliary power unit instead of from the power supply
module.
Checking Unit Loads
In the event of maintenance or equipment changes, recalculate the unit loads
for each carrier resulting in a different configuration
Use the worksheet in Appendix B of Installation.
1-42 System Capacities and Requirements