According to its electrical composition, the cable distribution box can be divided into two categories: one is without any switchgear, and the box only has accessories for processing and connecting the cable ends, which has simple structure, small volume and single function, and can be called ordinary distribution box; The other is that the box contains not only the accessories of ordinary distribution box, but also one or more switch equipment, which has complex structure, large volume, many connectors, difficult manufacturing technology and high cost, so it can be called advanced distribution box.

1. General distribution box

There is no switch equipment in the common distribution box, the incoming line and outgoing line are electrically connected together, and the potential is the same, so it is suitable for tapping or branch connection. Usually, it is customary to add the number of incoming circuits to the number of outgoing circuits, which is called branch number. For example, the three branch cable distribution box has three equipotential connection points on each phase, which can be used as one in two out or two in one out. The cable distribution box contains u, V and W three phases. The three phases have the same circuit structure and are arranged in sequence.

2. Advanced distribution box

The advanced distribution box contains switch equipment, which can not only play the role of common distribution box, but also play the role of power supply circuit control, conversion and change the operation mode. The switch break roughly divides the cable circuit into the incoming side and the outgoing side, and the potential on both sides may be different. The switchgear itself has a large volume, so the overall dimension of the high-grade distribution box is relatively large, the height is generally 1.4 ~ 1.8 m, the depth is about 0.9 ~ 1.0 m, and the length depends on the number of switchgear, mostly between 1.0 m and 2.4 M. The shape of the box is similar to the outdoor box type transformer. There are several movable doors on the box shell. Some doors are set for the operation of the switchgear, and some doors are set for the installation, construction, maintenance and overhaul of the cable connecting devices.

1. Technical requirements

(1) Flame retardancy: V-2 grade flame retardancy, temperature resistance ≥ 130 ℃.

(2) The insulation resistance of the meter box shall not be less than 20 megohm.

(3) Electrical strength: apply voltage of 50 Hz / 1 500 V for 1 minute, no flashover or breakdown lightning.

(4) Acid and alkali resistance: drop 1ml of 3% acid-base solution on the surface of the box, wipe it off after 1 hour, and there is no crack or delamination.

(5) Static pressure resistance: 100kg weight (volume: 10 kg) × 10 cm2) placed at any position of the product for three minutes without cracking or damage.

(6) Static extrusion resistance: 100kg gravity is applied to the flat meter box, and there is no crack, peeling or damage in the meter box after 1 minute.

(7) Sandbag impact resistance: the sandbag in 7kg is dropped freely from 1m height, repeated 5 times, and there is no crack, breakage and other abnormal phenomenon at the connection part of the meter box.

(8) Climate impact: products in the outside world ± 10 ℃, internal 75 ℃ and long-term sunlight, and high temperature: 60 ℃ ± 4 h at 5 ℃; Low temperature: - 30 ± Under the condition of 3 ℃ for 4h, it does not deform, does not crack, and remains transparent.

(9) Impact resistance: the box shall be kept in good condition when the fixed screw is tightened (without package) and free falling test is conducted from 2m height. Resistance to sandbag impact: the sandbag weighing 7kg falls freely from 1m height for 5 times, and there is no crack, breakage and other abnormal phenomenon at the surface box.

Environment of electric meter box

Installation location: outdoor 10kV power supply, high supply low meter measurement and resident measurement.

Ambient temperature: - 25 ℃ ~ + 55 ℃

Air relative humidity: + 40 ℃, not higher than 50%; - 40 ℃ not higher than 60%

The intensity of the earthquake does not exceed magnitude 8

Inclination: not more than 3 °； For electric energy meter, it shall not exceed 1 ° Pollution level: 3

Installation site: the external magnetic field shall not exceed 5 times of the geomagnetic field in any direction