Hospital intercom system: Do you mean window intercom system or ward intercom system? The former is generally a one-to-one correspondence between the host and the extension (using one audio cable), and sometimes multiple hosts are connected hand in hand (2-core cable) to realize the communication function with the management host (used when there are functions other than intercom).
Ward call intercom system consists of call host, sickbed call extension, waterproof switch, etc. The extension cord is connected hand in hand (3-core wire) and finally connected to the host. The maximum number of extensions connected to each bus depends on the calling host. Take Nippon's products as an example, the pictures are as follows: