In fire engineering, the construction of distribution pipelines is the largest and most demanding task in the fire alarm system, and it involves a wide range of aspects. To ensure the good operational performance of the system, scientific and reasonable construction must be carried out.

1、 The problem of laying wires and pipelines in fire alarm systems

In fire engineering, the construction of distribution pipelines is the largest and most demanding task in the fire alarm system, and it involves a wide range of aspects. To ensure the good operational performance of the system, scientific and reasonable construction must be carried out.

In the design specifications of fire alarm systems, regulations are made for the wiring requirements of transmission lines: "Metal pipes, flame-retardant treated hard plastic pipes, or enclosed wire trunking protection methods should be used for wiring." This means that metal pipes do not necessarily need to be used for wire conduits.

This only considers the protection of wires from mechanical damage, as well as the functions of flame retardancy and moisture prevention, but neglects the role of wire conduits in shielding and discharging strong electricity, leakage, static electricity, and electromagnetic interference. Therefore, in the current construction, although metal conduit is used, plastic junction boxes are used at the junction of pipelines. Even if metal junction boxes are used, locking nuts are not added at the interface of the junction box for connection and mouth protection. There is no conductor connected at the junction of two conduit or conduit, resulting in the pipeline not forming a complete connection. This construction method and wiring, even if grounded at the entrance of the alarm controller, cannot provide the necessary lightning protection and electromagnetic interference resistance. In the event of lightning strikes or leakage of strong electrical circuits, the electrical wiring cannot be effectively shielded and discharged to the ground, which will inevitably cause equipment damage or malfunction, especially in explosion-proof areas. This wiring method will leave a hidden danger of serious consequences.

To ensure the reliable operation of the system, the metal conduit and cable shielding layer entering the fire control center must be connected to the controller casing and ensure reliable grounding. The grounding resistance must meet the requirements of fire protection regulations. Meanwhile, during construction, metal junction boxes must be selected for the junction box. When the wire conduit is inserted into the box, a metal locking nut should be set on the outer side to lock the conduit, and a protective opening should be installed on the inner side of the junction box. If metal wire trunking is used for wiring, U-shaped galvanized metal trunking should be used at the junction of the trunking, and both sides should be fixed with metal screws. In short, it is necessary to ensure that the metal pipeline is fully connected in order to have the function of shielding and discharging strong electricity.

2、 Selection of Signal Lines for Fire Alarm Systems

In the specifications, only the minimum cross-sectional area of the wire core for the transmission line of the fire alarm system is specified, and there is no clear requirement for the wire type. Equipment manufacturers only provide recommendations for the wire specifications used in their own products. For example, in the product design manual of a certain brand, it is recommended to use BVR type twisted pair for signal lines, even for ordinary parallel lines. A certain brand manufacturer recommends using ZBN-BV line for alarm bus. Due to the chaotic guiding ideology, in fire engineering construction, only flame retardant requirements are considered when selecting wires. As long as the price is cheap and the construction is convenient, the selection of signal wires is arbitrary and blind, and some use a single (BV) copper wire.

With the widespread application of advanced fire alarm technology, intelligent fire alarm controllers have been widely used, and signal transmission has evolved from switch quantity in the past to digital. When digital communication is transmitted on the second bus (the alarm bus is the second bus), the smaller the distributed capacitance between the two wires, the better. If the capacitance is larger, it will cause more severe distortion of the transmission waveform, increase the probability of false alarms, and have a negative impact on the reliability of the system's operation.