4-way cross-block for power supplies. The input voltage is 9-28 V. When using wires of long length and small cross section at the output of the line, we get a real voltage that may be unsuitable for powering certain devices, a situation may arise when, for example, during a short circuit (short circuit) at the end such a long power cable will not blow the output fuse of the power source. In this case, the source will work mainly to heat the wire. These reasons explain the inappropriateness of the wiring of the power of detectors and other devices of the fire alarm system using individual long wires of small cross section. Moreover, if a branched power bus departs from the IWEPR, it is very difficult to determine which branch of the bus the short circuit occurred in. To avoid such troubles, especially in objects with high saturation of the OPS equipment, the use of so-called protective switching devices (ZKU) is recommended. ZKU it is expedient to place in places of concentration of announcers. For example, a redundant power supply can be located at the entrance to the floor, or in a specially allocated room, and at the entrances to separate groups of rooms are ZKU.