The standard Clear-Com PL intercom, uses one channel over a 3pin XLR (for use with the RS-601 beltpack)
Clear-Com also provides TW beltpacks which use 2 PL intercom channels over 3pin XLR (example the RS-603 beltpack)
To connect a RS-603 beltpack into a standard Clear-Com PL system a combiner is required.
The TWC-70x unit combines two Clear-Com standard PL channels onto a single 3pin XLR cable
The TWC-701 is a single 2-Channel active combiner
The TWC-704 is four TWC-701's in a single rack space... but the TWC-704 has been discontinued and is no longer available.