I have a project of installing an announcer system for a small clinic, the clinic has 6 screening rooms. The announcer system should be connected in such a way that when one microphone is conveying the rest should be blocked or remain off. Please help.

Joshua, September 2015

You leave it slightly vague and unclear where the announcement is coming from and where the announcement is going to.

I imagine a situation with a central admin station needing to communicate to six different places but only on a one place at a time basis.

To achieve that six momentary push button switches might be used to make the connection - the operator holding down the switch when speaking. Just 6 cable runs.

To have it the other way with any one of six places communicating to a central station is much more complicated - again you could use a push switch but it would need to be configured to disable 5 other stations when in use - each room in mutual contact with every other room and each room in contact with the central place - 36 sets of wire run.
A more complex and more expensive switch.

Good Luck..., September 2015