How many zones and how many devices fit, and what if I want to extend it?

The criteria for splitting them are given by UNE 23007-14 and they can be checked: a zone should not go beyond about 1,600 m², it should not span more than one storey except in very small buildings, and inside it you should not have to walk more than about 30 m to find the device that has gone off. Vertical shafts —stairs, risers, lifts— are treated as a separate zone. As for the loop, each manufacturer declares how many devices it takes, and in practice it is filled well below that number to leave headroom, spreading short-circuit isolators so that one badly driven screw takes out a section and not the whole storey.

Extending depends on three things: whether there is capacity left in loops and cards, whether the manufacturer is still supplying devices compatible with that version and —the one always forgotten— whether the batteries still give the standby time the documentation says, because every new device draws current. When the control panel can take no more, the alternative is not always to throw it all out: you can add a new panel on the network and replace it in phases.