1. Wiring of fire emergency lighting
Generally, the flame retardant wire is used to wear the metal pipe and the protective layer thickness is ≥ 30mm, in the decoration project, when the emergency lighting line can only be applied in the ceiling, the heat-resistant or fire-resistant wire should be selected and the fire-resistant and heat-resistant wiring method should be considered.
Second, the wiring of the fire elevator
The fire elevator is generally distributed by the substation on the ground floor of the high-rise building to the elevator machine room on the top floor, because the line is longer and the route is more complex, the fire elevator distribution line should be selected fire-resistant cable; When there are special requirements for reliability, one of the two distribution lines can choose mineral insulated cables.
3. Wiring of fire shutter doors
The power supply of the fire shutter door is generally drawn from the floor distribution box with dual power switching, and the power supply is supplied to the control box by radial or ring power supply through the special distribution box of the fire shutter door. When the horizontal distribution line of the fire shutter door is long, it is advisable to choose fire-resistant cables and use fire-resistant cable trays in the ceiling.
Fourth, the wiring of smoke prevention and exhaust equipment
For the distribution line of smoke prevention and exhaust equipment, fire-resistant cross-linked low-voltage cable or mineral insulated cable is selected when it is laid open, and general fire-resistant cable can be used when it is concealed. The linkage and control lines of smoke prevention and exhaust equipment are made of fire-resistant cables. The length of the line of smoke prevention and exhaust equipment should be shortened as much as possible when laying to avoid crossing different fire zones.
5. Wiring of fire hydrant pumps, sprinkler pumps, etc
The distribution line of the pump motor often uses flame-retardant wire to pass through the metal pipe and bury it in the non-combustible structure, or the fire-resistant cable is selected and equipped with a fire-resistant cable tray, or the mineral insulated cable is selected. The power supply of the pump room is generally directly supplied by the substation of the high-rise building; When the substation is adjacent to the pump room and belongs to the same fireproof partition, the fire-resistant cable or fire-resistant bus is selected to be laid along the fireproof cable tray; When the substation is far away from the pump room and passes through different fire partitions, mineral insulated cables can be used.
6. Causes of overheating of electrical equipment
1) Short circuit: The formation of a metallic touch between the phase wire and the neutral line or between the phase wire is a short circuit. When the temperature rises sharply during a short circuit, the insulating material burns and a fire occurs.
2) Overload: The current value of the electrical line or equipment exceeds the value of its promise, it is overload. Overload can cause insulation burnout.
3) Poor touch: The electrical connection part is commonly welded or bolted, once loosened, the touch resistance of the connection part increases, and the joint is overheated, resulting in disasters.
4) Core heating: The core insulation is damaged due to the increase in heat generation, which will produce high temperatures.
5) Poor heat dissipation: The heat dissipation method of electrical appliances is damaged, which will form overheating.
7. What are the causes of electrical fire blasting?
Electrical circuits, motors, oil-immersed power transformers, switchgear, electric lights, electric heating equipment, etc., have different risks and causes of fire and explosion due to different structures and operating characteristics. However, in general, in addition to equipment defects, improper equipment and other reasons, in operation, the heat of the current and the spark or arc of the current are the direct causes of fire blasting.
8. What are the fundamental methods for electrical fire and explosion protection?
According to the characteristics of the place, the fundamental methods adopted for electrical fire and explosion prevention are:
1) Correct selection of electrical equipment. Explosion-proof electrical equipment should be selected according to the standard for places with blasting risk.
2) Selecting a reasonable equipment location according to the standard and insisting on the necessary safety distance is an important method for fire and explosion prevention.
3) Strengthen maintenance and maintenance, and insist on the normal operation of electrical equipment: including insisting that the voltage, current, temperature rise and other parameters of electrical equipment do not exceed the promised value, insisting on sufficient insulation ability of electrical equipment, and insisting on excellent electrical connection.
4) Ventilation: in blasting risk places. If there is excellent ventilation, it can reduce the thick bottom of the explosive mixture. Technical training is worth your attention!
5) The selection of fire-resistant equipment plays a very important role in on-site fire prevention. For example, in order to improve the fire resistance, the inner surface of the wooden switch box is lined with white iron sheet.
6) Grounding: The grounding (or zeroing) of blasting risk places is higher than that of general places. It must be grounded as specified.
9. What is a zero-sequence current transformer?
The primary loop of the transformer of the zero-sequence current of the exploration power supply line is the phase line (La, Lb, Lc). That is, all phase lines pass through the window at the same time and in the same direction. If used for a single phase, the effect is the same as that of a normal current transformer (C.T).
10. What is a residual current transformer?
The primary circuit of the transformer that explores the remaining current of the power supply line is the phase wire (La, Lb, Lc) and the neutral line N. That is, the phase line and the neutral line pass through the window at the same time and in the same direction. The primary requirements for the remaining current transformers are high accuracy in the mA class and overload resistance of more than 40A.
11. What is the grounding current?
The current flowing into the ground due to insulation defects or unexpected loads. It is commonly known as "leakage current". This current is generated by an arcing short circuit between the phase line and the ground. It is generally accepted that in a non-combustible environment, less than 100 mA does not pose a fire risk.
12. What is normal leakage current?
In the absence of insulation problems, the current flowing into the ground from the live parts of the device. This current is often caused by a non-pure impedance, which is determined by the intrinsic operating characteristics of some devices and promised within a certain range.
13. What is zero-sequence current?
Vector sum of currents communicating the phase wires (La, Lb, Lc) of the power supply line. When no grounding problem occurs, the theoretical value of this vector sum is equal to the value of the neutral N current. When a grounding fault occurs, the zero-sequence current is the vector sum of the current of the phase wire (La, Lb, Lc), the grounding fault current and the normal leakage current; At this time, it is not equal to the neutral N current.
14. What is residual current?
Vector sum of currents of the phase wires (La, Lb, Lc) and neutral lines N of the communication supply line. When there is no single-phase grounding problem, regardless of whether the three-phase load is balanced or not, the theoretical value of this vector sum is zero (in fact, there is still the normal leakage current of the line and equipment); When a grounding fault occurs, the remaining current is the vector sum of the grounding fault current and the normal leakage current.
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