Wired Party-Line systems are systems in which a number of participants are all involved in the same conversation. Think of the telephone extensions in your home, if each person in your family picks up a telephone in your home, you will all be able to hear each other.  You can talk to one another simultaneously and the person “on the other end of the line” will be a full participant in one “public” conversation. Most people refer to this type of system as “PL” (for “party-line), “TW” or “Two-Wire” from the telephone systems, where on two wires, a full duplex conversation takes place, or “conference” denoting the type of activity taking place in the conversation.  The physical configuration and implementation of “PL” or “TW” does not necessarily need to be on two physical wires, in most cases it is not.  In the case of Clear-Com 3 wires are used for a single channel PL system, commonly this is done with standard 3-pin XLR cable consisting of a shield wire and 2 seperate conductors.  Pin 1 is usually the shieldPin 2 is used for transport of +30 VdcPin 3 is used for unbalanced two way audio