The model SSA-324 is a system-to-system adapter (or interface). The SSA-324 is ideal for systems with steady loads. (Amount of user stations are steady like in fixed installations.) It interconnects the voice signals between different intercom systems. In addition, it can optionally interconnect "Calls" or tally signals between systems. Each SSA-324 includes two two-wire to four-wire converters. An SSA-324 can also function as a two-wire to two-wire interface by interconnecting the two individual interfaces at the four-wire level. The SSA-324 does two voice channels when used as a dual two-wire to four-wire interface, and one voice channel when functioning as a two-wire to two-wire interface. In addition, there is a call light option board available for compatibility with RTS Two-Wire Intercom and Telex Audiocom systems.