ZA stands for Central Off, ZE for Central On and ZI for Central Pulse. By wiring the inputs in parallel, several devices can be conveniently switched on and off via a central control unit. The ZI input acts in the same way as the local input B1 and is therefore ideally suitable for activation by a doorbell system. These inputs are electrically isolated and can be operated with voltages from 8 V to 230 V DC or AC.