I have always had a feeling that "growth through imitation and success through innovation". In fact, in real professional work, most of the work is imitation and repetition, emphasizing work efficiency rather than innovation. For enterprises, excessive innovation will inevitably lead to too many failures and low efficiency.
as follows
I. Number of switch boxes = number of switches and number of sockets
Second, the number of junction boxes = the number of lamp boxes [( 1) roads without elbows shall not exceed 30m；; (2) When there is a bend between two junction boxes, it shall not exceed 20m；; (3) When there are two bends between two junction boxes, it should not exceed15m; ; (4) When there are three bends between two junction boxes, it should not exceed 8m; 5] Four elbows are not allowed between two junction boxes of concealed piping]
Third, the junction box, each surface-mounted distribution box (concealed assembly pipe) is followed by a junction box (piping first).
Junction box Generally, distribution boxes are junction boxes.
Generally, there are only terminals in the junction box, and there are no components, such as branch junction boxes and equipotential junction boxes.
The grounding terminal board is the terminal board of the grounding junction box.
LEB is a local equipotential connection box, which is usually very small, and the terminal board inside is also very small, with few terminals.
Grounding jumper is used for electrical auxiliary communication, such as the disconnection interface between each section of the bridge and the conduit.
It plays the role of conducting potential and does not pass current under normal circumstances.
Disconnect card is used for lightning protection grounding, generally used in the lead-in line of artificial grounding electrode, mainly to disconnect the artificial grounding electrode from the grounding network when measuring the grounding resistance, so as to measure the grounding resistance of this artificial grounding electrode conveniently and accurately.
1. Cable heads can be divided into heat-shrinkable type (the most commonly used one at present), dry-wrapped type and epoxy resin casting type according to the manufacturing and installation materials.
At present, cables over 70mm2 are generally heat shrinkable, which is actually the use of heat shrinkage. A thermal shrinkage ranges from tens to hundreds of yuan, that is, the so-called "glove" is shaped like a glove. Peel off the outer sheath of the cable, cover it with a heat shrinkable layer, then heat it with a blowtorch and stick it on the cable head (I won't go into details about copper nose pressing).
Dry wrapping is to use high-pressure self-adhesive tape and electrical tape as cable head. Generally, there is more temporary electricity consumption.
Dry packing type is used below 70mm2.
Second, the difference between cable head
Power cable heads are divided into terminal heads and intermediate joints, indoor and outdoor according to the installation location, and are divided into dry wrapping, epoxy resin pouring and heat shrinkage according to the materials used for cable heads.
1. Indoor dry-packed power cable head is called "simple packing terminal head" when the dry-packed cable head is not equipped with "junction box", which is suitable for general plastic and rubber insulated low-voltage cables.
2. Indoor pouring type power cable terminal head is mainly used for oil-impregnated paper insulated cables.
3. The indoor heat-shrinkable power cable terminal is suitable for 0.5 ~ 10.0 kV XLPE cables and various cables.
Three, three cable head process difference:
1. Indoor dry-wrapped power cable head: stripping protective layer and insulating layer, cleaning, insulating, crimping pipe and terminal, installation and wiring.
2. Pouring power cable terminal indoors: sawing, wire stripping and cleaning, internal shielding treatment, wrapping insulation, locking the pipe and terminal, assembling the junction box, batching and pouring, and installing the wiring.
3. Terminal head of indoor heat shrinkable power cable: sawing, peeling, cleaning, internal shielding treatment, welding ground wire, locking tube and terminal, installing heat shrinkable tube, thermoforming, installation and wiring.
Fourth,
1) dry packing, in some projects with low requirements or in order to save money, dry packing is more used for low-voltage cable joints, because the low-voltage electric field can be ignored, so especially those installation companies use dry packing to save money. At present, it seems that no one in China makes high-voltage dry-wrapped cables. Foreign 3M companies occasionally have dry cable accessories (usually intermediate connectors).
2) Thermal shrinkage, the cost of thermal shrinkage cable accessories is relatively high, but it is more economical to use thermal shrinkage cable accessories at 10KV and below, which is generally suitable for common power supply systems that do not need fire protection in new projects and buildings.
3) Casting cable accessories, basically eliminated, mainly used in oil-immersed insulated cables, basically eliminated since the advent of heat-shrinkable oil-immersed cables. At present, 3M and other low-voltage cables also have cast cable joints. .
4) Cold-shrinkable cable connector, a cable accessory that is being vigorously promoted at present, is especially suitable for petrochemical industry and other environments where open flame construction is prohibited, which reduces human factors and is safer. The disadvantage is that it is more expensive.