The standard Clear-Com intercom pin out is 1 chnl over aXLR 3 cable Pin 1 = GND Pin 2 = PWR(30VDC)Pin 3 = Channel A
However Clear-Com  also make a TW (2 chnl over XLR3) PL intercom system
Clear-Com intercom products with TW functionality accepttwo individual channels of intercom from one single 3-pin XLR cable, Clear-Com TW pin out (XLR)Pin 1 = GND Pin 2 = Channel A + PWR(30VDC)Pin 3 = Channel B The TW functionality allows the Channel A intercom audio tobe carried on the same pin as the power. Clear-Com TW products are compatiblewith RTS/Telex Partyline systems which normally use this TW configuration.
If a TW-equipped station (like the RS-603TW beltpack) isconnected to a standard Clear-Com intercom line, then only Chnl-B of the RS-603will only operate. On the RS-603 Channel A will appear to be inactive. While ChannelB intercom audio and “call” signalling will still work.
Clear-Com provides an interface TWC-701 which allows twostandard Clear-Com intercom channels to be combined into a TW circuit therebyproviding 2 intercom channels over XLR3. Example Chnl-A and B of a MS-704 can be combined via aTWC-701 unit to allow it to connect to a number of RS-603 beltpacks
The RS-603 supports both DC and AC call signalling in order for it to becompatible with RTS systems. However because the standard Clear-Com intercom “call”signal function is normally accomplished by applying a DC voltage to theintercom audio line, call signalling is deleted from the Channel A line of theRS-603 unit.This means that a RS-603 beltpack connected to a MS-704unit via a TWC-701 unit will only be able to send and receive call signal onchnl-B. The same is true for the MS-704 unit it will only be able to send and receivecall signal on its chnl-B. However both units will be able to talk/listen on both intercom chnl-A and B
Note: Only TW enabled product should be connected to TWPL systems otherwise non TW beltpacks will load the DC power on pin 2 reducingvolume level and changing sidetone characteristics on that channel.The exception is that the RS-601 beltpack has beenspecifically designed not to load Chnl A of TW systems while still being able totalk and listen to Chnl –B of the TW system.