Adding Modules to Your System
When adding additional modules to a MERLIN MAGIX® Integrated System you must determine if the unit loads provided by the current power supply can support new modules you may be adding to the system. A unit load is a measure of power used to determine the electrical load that a component draws from a carrier's power supply. 

General Rules on Adding Modules

● Never have more than two (2) 800 BRI modules,
  two (2) DS1 modules (100D or 100 DCD),
  two (2) INA modules (100R), or more than
  one (1) 100D/100 DCD, and one (1) 100R
  module in a carrier.

● A maximum of two MERLIN® Messaging
  R2.5 modules can be installed per MERLIN MAGIX
  Integrated System R2.2; however, only the first
  module installed (left most slot in system) can
  be programmed for voice messaging and/or delayed
  announcement service. The second MERLIN Messaging
  module installed can only be programmed for delayed
  announcement service. Whether both MERLIN Messaging
  modules can be installed in the same carrier depends
  on how many other -5 volt modules are also installed
  in that carrier.

● Lastly, there can be any combination of the
  following three -5 VDC modules per carrier,
  but do not exceed three per carrier:
         ● MERLIN MAGIX Integrated System processor
         ● MERLIN Messaging module
         ● DS1 module (with or without built-in CSU/DSU)
         ● INA module
         ● 800 BRI module

If you exceed three -5 VDC modules in a single carrier, the system will fail to come online.