Trumpy,
That's another good question. I can only speak from my own experience as I've only done work in 2 states. In RI, we are required to install the cables for the entire fire alarm cables system in metallic raceway (conduit, MC cable, or flexible metal conduit). For simple analog type systems, #14 THHN wire (I guess you would call in "single core" in your terminology) is used. For modern digital systems, twisted-pair shielded cable with a red jacket is used. Once installed, the system must be tested and approved by the electrician, electrical inspector, and the fire marshall.
Other states that I've been to don't require raceway for the cables, and the twisted-pair cable can be installed out in the open without protection. Of course, these cables still must be protected from damage per the NEC requirements.
As far as connection to the fire department goes, this is dictated by law, and again, this tends to vary state by state. It depends on the type of occupancy, that is, how many people can occupy the building and its use (ie-restaurant, club, theatre, etc.) We have a "local" system, that is, no direct connection to the FD. Systems that are connected to the FD are connected via a dedicated set of lines, or through radio boxes.
I have worked on about the same amount of local and FD connected alarms. The wiring is exactly the same, the only diffence is that we install a radio box and antenna for the connected systems.
I hope that helps.
Peter
