Why are there two rows of circuit breakers in the secondary distribution box?

Generally, there is secondary leakage protection for tertiary power distribution on site, so there is no need to set a leakage breaker (leakage protection switch) in the secondary distribution box, and a leakage breaker is set in the terminal load tertiary distribution box. The Code for Temporary Power Use in Construction Site of Secondary Distribution Box does not require the installation of leakage protection switch. Of course, special circumstances should be adjusted according to the needs of the site. This is not a hard requirement.

I. Configuration in the box

It is suggested to take a look at JGJ46-2005, which is a specification for temporary electricity consumption on the construction site and clearly states the configuration requirements of distribution boxes at all levels. Here is a brief talk;

First-class configuration: bus: total isolation+total circuit breaker or total fuse; Shunt: shunt isolation+shunt leakage protection switch.

Secondary requirements configuration: bus: bus isolation+bus fuse or circuit breaker; Shunt: shunt isolation+shunt fuse or circuit breaker.

Tertiary configuration: isolation+leakage protector. Among them, the product of action current and action time of leakage protection switch in primary distribution is not more than 30mA. The action current of the leakage protection switch in the three-level distribution is not more than 30 mA, and the action time is not more than 0. 1 sec.

Second, the distribution box classification and configuration requirements

The main distribution box refers to the main distribution box. Generally located in the power distribution room. The first-class cabinet adopts downward entry and downward exit, and the front door is opened. The main bus is connected by copper bars with good contact, and there is a metering system inside. It is safe and beautiful, and the roof of the rain box is suitable for field work.

Secondary distribution box, namely distribution box, also known as sub-box, is generally responsible for a power supply area. The auxiliary box adopts the design of inner and outer doors, and the exterior is sprayed with plastic, which is safe and beautiful. The rain-proof box top is suitable for field work.

The third-level distribution box, that is, the switch box, can only be responsible for one device. The so-called "one machine, one brake, one box and one leakage" is aimed at the switch box.

Third, the user's distribution box has leakage experience to choose.

Common household distribution box air switch configuration has three kinds:

(1) The main switch adopts 2p air switch with leakage protection, and the shunt adopts 1P air switch without leakage protection!

(2) The main switch adopts 2P air switch with leakage protection, and the shunt adopts 1P or 2p air switch with leakage protection!

(3) The main switch adopts 2P air switch without leakage protection, and the shunt adopts 1P or 2P air switch with leakage protection!

The shunt with leakage protection usually cannot use leakage protection in kitchen, bathroom, cabinet air conditioner, ordinary socket, lighting and wall-mounted air conditioner socket. Of course, for safety, the shunt can also use all air switches with leakage protection!

First, analyze the first one. The main switch adopts 2p air switch with leakage protection, and the shunt adopts 1P air switch without leakage protection! In this configuration, when there is a leak in the loop, the total opening action is idle and the branch is inactive. When the circuit is short-circuited, both the main switch and the branch may act or act simultaneously! This configuration is not very friendly to leaky circuits. Some people think that you can open one by one to determine which circuit has leakage! But have you ever thought that if a circuit has slight leakage and the leakage current can't reach the open circuit action current, the leakage protector will probably trip every hour or every other day, and it is obviously impossible to open and close one by one to find the leakage circuit! Unless there is a very serious leak, it can be ruled out one by one! If the main brake trips frequently and the reason cannot be found, it is not convenient for domestic electricity consumption at all!

For example, if you are using a computer and the power is suddenly cut off, will your hard-earned data or documents fall short? Or when you are doing something, you suddenly trip all the time, and the room has no electricity. How many times can you stand dark situations? Do you agree with this electric box configuration?

The first configuration was rejected. Let's look at the second configuration: the main switch adopts 2P air switch with leakage protection, and the branch switch adopts 1P or 2p air switch with leakage protection!

The main switch has leakage protection, and so does the circuit. The starting point of this practice is undoubtedly for the safety of life! However, careful people will find that the rated working current of these circuit breakers is 30mA. When the leakage reaches the working current, it will trip regardless of the strength of the open circuit current! When leakage occurs in a certain circuit, the branch protector and the main switch may trip at the same time, or the branch may not trip because the main switch leakage protection is too sensitive. Although this configuration has the meaning of double protection, it is inevitable that the main switch will trip, and its practicability is not high, which is different from the first possible situation! Do you agree with this electric box configuration?

The first two were rejected. Let's look at the third configuration: the main switch adopts 2P air switch without leakage protection, and the shunt adopts 1P or 2P air switch with leakage protection!

This configuration in use, when the circuit leakage and or short circuit, only the branch air switch action, will not affect the main switch action! The power outage range is small, and troubleshooting is simple. This configuration is the most common in building electrical design! At the same time, remind everyone that the air switch with leakage protection should press the experimental button on time every month to test whether the leakage protector trips normally. If it can't run normally, it should be replaced in time to play a safety role!

In the distribution box configuration, don't forget to add self-recovery overvoltage and undervoltage protection appliances. Installing overvoltage and undervoltage protector can protect household appliances from high and low voltage damage! See Code for Electrical Design of Buildings and Code for Electrical Design of Residential Buildings (JGJ 242-20116.3.2+0.6.3.2) for details. Each residence should be equipped with self-recovery overvoltage and undervoltage protection devices.

Four, household distribution box master switch with leakage circuit breaker or air switch.

In home decoration, water and electricity decoration, there are generally two types of air switches:

The first type: use the air switch with leakage protection as the main switch, and use the 1P air switch for lighting/ordinary sockets/kitchen and bathroom sockets/air conditioning sockets!

The second type: use ordinary 2P air switch as the main switch, use 1P air switch except lighting and air conditioning, and use air switch with leakage protection for all sockets!

There are many people who use the second air switch configuration, and seven or eight circuits in a house are relatively normal. Without changing the size of the developer's electric box, the second one is basically enough! The first configuration is rarely used, and it is basically more than ten laps. You don't need so many rings in a house. More than a dozen cycles are basically the practice of decoration companies! Because there are many circuits, an air switch with leakage protection is used!

In theory, of course, it is good to make the main switch by leakage, but in fact, if there is leakage in sockets, toilets and light lines, it is best to let the switches that control them individually trip so as not to make the whole family have no electricity. Moreover, the leakage switch is installed in the socket and toilet respectively, which is conducive to judging the scope of leakage lines and troubleshooting. Therefore, at present, there is no leakage protection for home master brakes. Usually, the leakage protection switch is used for the switch of the socket and the switch of the toilet, and the circuit of the lamp is basically inaccessible to the human body, so the leakage protection switch is not used. I always can't open it, and I feel that I have lost my protective role. No leakage protection. If something goes wrong, only the electric meter will act. In that case, it will be very troublesome for you to go to the property to open the meter box control cabinet for you. If the leakage protection device is always installed, the problem is only the action of always turning on.

General requirements for secondary leakage protection of five-level and three-level distribution

★ Three-level distribution and two-level leakage protection system should be adopted in the power distribution system of the construction site;

★ Electrical equipment must have its own dedicated switch box;

★ The parameters of leakage protector should be matched, sensitive and reliable;

Taken the total distribution box, switch box should be installed leakage protector, distribution box, switch box and electrical equipment distance should comply with the specification requirements;

Reference Legend of Three-stage Distribution and Two-stage Leakage Protection System

Six, distribution box, switch box Settings

★ The box structure, the setting and use of electrical appliances in the box should meet the specification requirements.

Taken the distribution box, switch box electrical reliable in good condition, in and out of the line neatly.

Schematic diagram of switch box

Setting requirements:

1, distribution box and switch box shall be made of cold-rolled steel plate or flame-retardant insulating material, and the thickness of steel plate shall be 1.2 ~ 2.0 mm, in which the thickness of switch box steel plate shall be no less than 1.2mm, and the thickness of distribution box steel plate shall be no less than 1.5mm, and the surface of the box shall be treated with anti-corrosion. (Article 8. 1.7 of JGJ46-2005)

2. The incoming and outgoing lines of the distribution box and switch box shall be equipped with fixed clamps, and the incoming and outgoing lines shall be insulated, bundled and fixed on the box body, and shall not be in direct contact with the box body. Incoming and outgoing lines of mobile distribution box and switch box shall be rubber-sheathed insulated cables, and there shall be no joints (Article 8. 1. 16 of JGJ 46-2005).

3, distribution box, switch box shape structure should be waterproof and dustproof. (Article 8 of JGJ46-2005.1.17)

4. The electrical appliances in the distribution box and switch box must be reliable and intact, and damaged and unqualified electrical appliances are strictly prohibited. (Article 8.2. 1 of JGJ46-2005)

5. The electrical appliances in the main distribution box have the functions of power isolation, normal on/off, short circuit, overload and leakage protection. (Article 8.2.2 of JGJ46-2005)

6. When the bus is equipped with a total leakage protector, it should also be equipped with a total isolating switch, a shunt isolating switch, a total circuit breaker, a shunt circuit breaker or a total fuse and a shunt fuse. When the main leakage protector is equipped with a leakage breaker with short-circuit overload leakage protection function at the same time, there is no need for a main circuit breaker or a main fuse. (Article 8.2.2 of JGJ46-2005)

7. When the shunt leakage protector is set in each branch, the main disconnector, shunt disconnector, main circuit breaker, shunt circuit breaker or main fuse and shunt fuse should also be installed. When the parallel leakage protector is a leakage breaker with short circuit, overload and leakage protection functions at the same time, there is no need to set a parallel circuit breaker or a parallel fuse. (Article 8.2.2 of JGJ46-2005)

8, fuse should choose products with reliable arc extinguishing and breaking function. (Article 8.2.2 of JGJ46-2005)

9. The rating and action setting value of main switchgear should be compatible with the rating and action setting value of parallel switchgear. (Article 8.2.2 of JGJ46-2005)

10, the main distribution box should be equipped with voltmeter, ammeter, watt-hour meter and other necessary instruments. When installing the current transformer, the secondary circuit must be connected with the protection zero line, and it is forbidden to disconnect the circuit. (Article 8.2.3 of JGJ46-2005)

1 1. The distribution box shall be equipped with main disconnector, shunt disconnector, main circuit breaker, shunt circuit breaker or main fuse and shunt fuse. Its setting and selection shall conform to the requirements of the front-mounted general distribution box (Article 8.2.4 of JGJ 46-2005).

12, switch box must be equipped with isolating switch, circuit breaker or fuse, and leakage protector. (Article 8.2.5 of JGJ46-2005)

13. It is forbidden to connect the power inlet terminals of distribution box and switch box with plugs and sockets. (Article 8.2 of JGJ46-2005.15)

14. When the distribution box and switch box are inspected and maintained regularly, the corresponding power disconnector at the next higher level must be turned off and the power-off sign "No switching on, someone is working" should be hung, and live work is strictly prohibited. (Article 8.3.4 of JGJ46-2005)