Lucent Technologies 555-670-116 User Manual

Issue 1

April 1999

 

90

Power Supply Unit Load Requirements 

Hybrid/PBX,
Modified Key,
or
Behind Switch

6

1

 

1

The 391A1 and 391A2 power supply units generally support 6 modules 

of any type in Hybrid/PBX mode. However, if all 6 carrier slots meet the 
following conditions, the unit load total may exceed 48:

Only MLX or analog multiline station modules are installed.
More than 45 MLX-20L or 34-button analog multiline telephones are 

installed.

The 391C1 and 391A3 power supplies have maximum ratings of 96 and 72 

unit loads respectively. Use these power supplies in place of a 391A1 or 
391A2 on systems where unit loads will exceed 48.

Not required.

Square Key
or
Behind Switch

4 or fewer

2

 

2

The 391A1 power supply unit generally supports 4 modules of any type in 

Square Key mode.

Not required.

Square Key
or
Behind Switch

5 or more

Use the “Unit Load Rating of System 
Modules” table and instructions below to 
determine the estimated unit loads (ULs):

■

If the ULs < 96 and the 391C1power 

supply is used, or the ULs < 72 and the 
391A3 power supply is used, then no 
calculation is required. If a 391A1 or 
391A2 power supply is used and the 
ULs > 48, then replace the power 
supply with a 391C1 power supply.

■

If ULs > 96, reconfigure the system so 

that the total ULs does not exceed 96 
per carrier.

For more information on unit load 
calculation, refer to Appendix F of 

System 

Planning.