(1) Wiring method of distribution box

1) Generally, the incoming line of power distribution box adopts five wire system, that is, a, B and C three-way phase line (the general color is yellow, green and red), one way zero line (the color is light blue) and one way ground line (the color is yellow with green stripes). Outgoing line according to need.

① The 220 V load usually takes one phase line, one zero line and one ground line.

② 380V load (such as 380V AC motor) three-phase full take, and then add grounding wire（ If the load has local control, it also needs zero line.)

③ There are special two-phase 380V AC welding machine, any two-phase line. Add a ground wire. The grounding wire is generally required to be connected, but it is not connected in many occasions (such as construction site). Generally, the incoming line is a 3pin air switch, circuit breaker, knife switch or other circuit breaker; The zero line is pressed to the neutral terminal block, and the ground line is pressed to the ground terminal block. In addition, the incoming line directly adopts 4Pin circuit breaker, and the three-way phase line and the zero line enter together, and the grounding wire is pressed to the grounding terminal block.

2) According to the load, one phase line + one zero line + one ground line can be used for lighting distribution; Or the above power distribution is 220 v.

(2) Installation method of distribution box

1) When the distribution box is installed on the wall, it should be fixed with split bolts (expansion bolts). The length of the bolts is generally the sum of the embedded depth (75-150 mm), the thickness of the box bottom plate, the thickness of the nuts and washers, plus the "overhanging allowance" of about 5 mm. For smaller distribution boxes, wood bricks can also be embedded at the installation place (according to the installation holes at the four corners of the distribution box or distribution board), and then wood screws can be used to fix the distribution box or distribution board at the wood bricks.

2) The distribution box shall be installed in a concealed way. The distribution box shall be embedded in the wall. When the wall is built, the reserved hole shall be about 20 mm larger than the length and width of the distribution box. The reserved depth is the thickness of the distribution box plus the thickness of the plastering on the inner wall of the hole. When the distribution box is buried, the box can be fixed by filling concrete between the box and the wall.

3) The distribution box shall be installed firmly, horizontally and vertically, and the vertical deviation shall not be greater than 3mm; During concealed installation, there should be no gap around the distribution box, the edge around the panel should be close to the wall, and the contact part between the box and buildings and structures should be coated with anti-corrosion paint.

4) For the spiral fuse installed in the distribution box, the power line shall be connected to the terminal of the middle contact, and the load line shall be connected to the threaded terminal. In this way, there will be no electric shock when loading and unloading the molten core. The porcelain plug-in fuse shall be installed vertically.

5) The power supply of AC, DC or different voltage levels in the distribution box shall have obvious marks. In the lighting distribution box, zero line (N line) and protective zero line (PE line) bus bars shall be set respectively. The zero line and protective zero line shall be connected on the bus bar, and shall not be twisted and numbered.

6) When the wire is led out of the panel, the wire hole of the panel shall be smooth without burr, and the metal panel shall be equipped with insulation protection sleeve. The shell of metal shell distribution box must be reliably grounded.

(3) Classification of distribution box

1) Fixed panel switch cabinet, often called switch board or distribution panel. It is a kind of open type switch cabinet with panel barrier. The front side has protective effect, and the back and side can still touch the live parts. The protection level is low. It can only be used in industrial and mining enterprises with low requirements for continuity and reliability of power supply for centralized power supply in Substation.

2) Protective (i.e. enclosed) switch cabinet refers to a low-voltage switch cabinet with all sides closed except the mounting surface. The switch, protection, monitoring control and other electrical components of the cabinet are all installed in a closed shell made of steel or insulating materials, which can be reliably installed on or off the wall. Each circuit in the cabinet can be isolated without isolation measures, or with grounded metal plate or insulating plate. Generally, the door is mechanically interlocked with the main switch. In addition, there is a protective platform type switch cabinet (i.e. console), which is equipped with control, measurement, signal and other electrical appliances. The protective switch cabinet is mainly used as the power distribution device in the process site.

3) Drawer type switch cabinet. This kind of switch cabinet is made of steel plate with a closed shell, and the electrical components in and out of the line circuit are installed in the extractable drawer, forming a functional unit that can complete a certain type of power supply task. The functional unit and bus or cable are separated by grounded metal plate or plastic functional plate to form three areas: bus, functional unit and cable. There are also isolation measures between each functional unit. Drawer type switch cabinet has high reliability, safety and interchangeability. It is a relatively advanced switch cabinet. At present, most of the switch cabinets produced are drawer type switch cabinets. They are suitable for industrial and mining enterprises and high-rise buildings that require high reliability of power supply, as the distribution center of centralized control.

4) Power and lighting distribution control box. Most of them are closed vertical installation. Due to different use occasions, the degree of protection of the shell is also different. They are mainly used as power distribution devices in the production site of industrial and mining enterprises.

(4) Matters needing attention in setting of distribution box

1) The distribution system shall be equipped with indoor main distribution box and outdoor distribution box, or each distribution box of outdoor main distribution box to implement hierarchical distribution.

2) The power distribution box and lighting distribution box should be set separately. If they are combined in the same distribution box, the power and lighting lines should be set separately.

3) The main distribution box shall be located near the power supply. The distribution box shall be installed in the area where the electric equipment or load is relatively concentrated. The distance between distribution box and switch box shall not exceed 30m. The horizontal distance between the switch box and the fixed electrical equipment controlled by it should not exceed 3M.

4) For the distribution box that needs to be installed on the ground, it should be installed 50 ~ 100 mm away from the ground, and within the range of 0.8 ~ 1.2 m in front of the distribution box, there should be no debris hindering the power supply, and the surrounding environment should be ventilated and dry.

5) Zero line, protective earth line and phase line shall be set for the wiring busbar in the box to ensure that all components, instruments and lines in the distribution box are firmly installed and arranged in order to facilitate maintenance. After the installation, the sundries and dust in the box should be removed in time.

6) The electrical appliances in the distribution box shall be first installed on the non-metal or wood insulation electrical appliance mounting plate, and then fastened in the distribution box as a whole. The metal plate shall be electrically connected with the iron distribution box.

7) Each electrical equipment shall have its own special switch box, and the system of "one machine, one switch and one protection" must be implemented. It is strictly forbidden to use the same switch to directly control more than two electrical equipment.

8) The rated leakage action current and the rated leakage action time of the two-stage leakage protectors in the distribution box and the switch box should be reasonably coordinated to make them have the function of graded and segmented protection.

9) The wood brick and iron parts needed for the installation of the distribution board need to be buried in advance, and the exposed distribution box should be fixed with metal expansion bolts. The wiring should be arranged in order and bound into bundles, and the movable parts need to be fixed.

10) The rated value of various switching devices should be adapted to the rated value of the controlled electrical equipment.

11) When the construction site stops working for more than one hour, the power switch box shall be powered off and locked.

12) During the inspection and maintenance of the distribution box and switch box, the corresponding power switch of the first level must be turned off and the power failure sign must be hung. Live working is strictly prohibited.

(5) Size determination of distribution box

1) When the electric box is only used for lighting the electric box or small power, and the incoming line is less than 10 square meters, if the number of switch bits is less than 20, the width of the switch plus 20 mm on each side is the width of the electric box, the height is the height of the switch plus 40 mm, and the depth is the depth of the switch plus 10 mm.

2) When the electric box is only used for lighting the electric box or small power, and the incoming line is less than 10 square meters, if the number of switches is more than 20, the electric box needs to be arranged with two rows of switches. The width of the switch plus 40mm on each side is the width of the electric box. The height is the height of the switch plus 40mm, and the depth is the depth of the switch plus 10mm.

3) When the electric box is only used for lighting the electric box or small power, and the incoming line is less than 10 square meters, if the incoming line switch needs a separate row, the width of the switch plus 20 mm on each side is the width of the electric box. The height is the height of the switch plus the height of the incoming line switch plus 40 mm, and the depth is the depth of the switch plus 10 mm.

4) When the electric box is a power box or a power lighting box, the algorithm is basically the same as above, but when the incoming line is more than 10 square meters, the bending radius of the incoming line should be considered, and sufficient space should be reserved for the level 1 terminal. When the switches are arranged in two rows, the wiring of the switches should be considered.

Of course, there is no final conclusion on the size of the electric box. We should consider the actual installation, the actual wiring diagram and how to arrange the switch layout and the wiring of level 1 switch. If all miniature circuit breakers are determined according to the number of digits (each 18 mm), PZ series distribution box has a fixed size. If the circuit exceeds 80 digits, it can be identified in the drawing by Party A (words). The equipment control box identifies the equipment itself. If the incoming line is greater than 185 mm ~ 2 and the output line is greater than 2, cabinet type shall be selected as far as possible