Partyline intercom systems are frequently referred to as 2-wire. This term can be misleading since the stations are connected together using 2-conductor shielded microphone cable and the shield is a conductor. This connection is typically used to carry the partyline voice on one wire and the station operating power on another wire.
The interconnecting cable for most intercoms is standard microphone cable with 3-pin XLR type connectors. In any system, pin 1 and the shell of the XLR connector should NOT be connected together. Clear-Com's 2-wire Partyline system (Clear-Com Encore) uses a single audio pair to connect user stations to an intercom master station/power supply via daisy-chain wiring. Splitter boxes can also be used to expand the system.
The power supply generates DC power for the entire system. The power supply usually includes the system termination.
Clear-Com's Encore Partyline systems are the distributed amplifier kind, allowing each user to adjust their own listening level. The distributed amplifier is built into the user station. The user connects to the user station via a headset or loudspeaker and microphone or some combination.
Each main and remote station contains its own mic preamplifier, headset or speaker power amplifier, volume control(s), talk switch(es) and signaling circuitry. Stations bridge the intercom line at a very high impedance and place a minimum load on the line. The audio level remains constant and does not fluctuate as stations leave and join the network. Some user stations have "loop-thru" connectors that allow "daisy-chaining" stations using a single connection to the power supply.