1 Lighting distribution box use
Lighting distribution box is widely used in various buildings, squares, stations, industrial and mining enterprises and other places, as the terminal electrical equipment of the distribution system.
2 box structure
The lighting distribution box structure is divided into two types: closed hanging type (surface mounted) and embedded (concealed) according to the installation method. The main structure is divided into box, panel, mounting bracket, neutral busbar, grounding busbar and other components. There are opening holes for operating the main switch and the shunt switch on the panel. If it is not necessary to install the full shunt switch, the sealing plate can be used to close the opening hole. The entry and exit line knockout holes are placed on the upper and lower sides of the case. There is also a long circular knockout on the back, which can be used after tapping according to the user's needs.
The lighting distribution box can be divided into steel box, stainless steel box, iron box and plastic box according to the material of the box.
3 main electrical components in the box and their protection
3.1 Miniature Circuit Breaker (MCB)
It is used as the main switch or outlet switch to provide overload and short circuit protection for the distribution line.
3.2 Isolation switch
Usually used as a line switch for power supply separation and isolation.
3.3 Leakage protector
Generally, the leakage current is 30mA for personal electric shock safety protection.
3.4 Surge Protector (SPD)
Used to limit the lightning overvoltage that is conducted from the power line.
4 Lighting distribution box application and safety reliability issues
As the terminal distribution equipment, the lighting distribution box is used in a large amount, and its safety and reliability issues are related to thousands of households, so it should be very cautious when selecting.
4.1 Selection of qualified products
There are a lot of fake and inferior products in the lighting distribution box market. The short-circuit explosion of the cabinet line or other electrical faults directly affects life and work.
Therefore, qualified products that meet the national standards should be selected. The electrical components in the box should be compatible with the controlled electrical equipment and have perfect protection functions. This is an important part.
4.2 Correct design of distribution box electrical system according to national regulations
For example, the national standard "Residential Design Code" (GB50096-1999) clearly stipulates: "Each set of houses should be equipped with a power supply main circuit breaker, and the switchgear that disconnects the phase line and the neutral line when available should be used." Outside the power socket, other power outlet circuits should be equipped with leakage protection devices" and "the total power supply line breaker of each house should have leakage protection function"... and the national standard "Building Lightning Protection Design Code" (GB50057-94) There are also specific provisions for the installation of surge protectors. These regulations must be implemented because they are an important means of preventing personal and equipment safety and preventing and reducing electrical accidents.
4.3 Heating, temperature rise and derating considerations of electrical components
4.3.1 Fever and temperature rise
Electrical switches (including miniature circuit breakers) generate heat sources mainly from three parts: current-carrying parts, electromagnetic system and dielectric loss. In addition, the arc generated when the switch load is opened and closed can also generate a large amount of heat energy in a very short time, but since the switch splitting is generally not very frequent, the influence is negligible and negligible.
It can be seen that the normal working electrical switch is hot, and the temperature rise is an objective fact.
4.3.2 Consideration of derating
The miniature circuit breakers and leakage switches installed in the general lighting distribution box are closely installed side by side. Due to the sealing of the cabinet and the mutual influence of the heating temperature between the switches, it is difficult to dissipate heat. The rated current is used for derating. Otherwise, the switch will be overloaded and heated, and the temperature rise will be too high and trip. Serious or even cause damage to the insulation of the wire, causing short-circuit faults and fire accidents (see Table 1 for derating factor)
Derating factor reference table 1
Side-by-side installation switch number
1
2
3
4
5
6
7
8
9
Derating factor
1
0.94
0.89
0.85
0.82
0.8
0.78
0.77
0.76
5 Application of miniature circuit breaker (MCB)
5.1 See Table 2 for the main technical parameters.
Miniature circuit breaker technical parameters summary table 2
Model and tripping characteristics
parameter name
S250S
S270
S280
S9
S250-DC
S280UC
C, D
K
C
K
C
C
B
C
K