The MS-2002 is a complete two-channel master station and system power supply (24 VDC, 2 amps total power) in a single unit. You simply plug it into any AC power outlet from 100 to 240 volts, add a microphone or headset, connect intercom stations to the back panel, and you are ready to communicate. It even has both single-channel and two-channel connectors, so you do not have to add a separate breakout box if you want to mix single-channel and two-channel intercom stations. The MS-2002 fits in a standard 19" equipment rack and is 1 rack unit high. The basic MS-2002 can communicate with two intercom channels. Connecting optional EMS-4001 expansion stations can increase this number. Each EMS-4001 adds four additional channels, and up to four of these expansion stations can be connected for a total of eighteen channels.