The DBC4S is a 4 way distributor unit that will allow you to connect a maximum of 4 door panels to the system you have, it can also be used to connect 4 video monitors as well if you are using a typical "Star Connection" for the cabling
For example, If each video monitor cable has been installed to a central point (Star connection) then you will need a DBC4S 4 way distributor. If the video monitor cables are "looped" from one to the other then you will NOT require a DBC4S 4 way distributor. Please download the specification that will show you
You can have a total of 4 door panels for each system and you WILL require a DBC4S 4 way distributor