1. isolate electrical equipment
The distribution box used at home or similar places belongs to the combined electrical appliance used by unskilled people, so the main switch should adopt the isolation electrical appliance with obvious isolation fracture or obvious isolation indication. When an electrical fault occurs, as long as the isolated electrical appliance is disconnected, the user will be cut off from the power supply, and even unskilled people can safely repair the electrical equipment at this time.
HK2 plastic shell porcelain bottom knife switch is still used as an isolation appliance in many areas because of its low price. However, this kind of switch is not only bulky, but also the moving and static contacts are prone to heat and corrosion, so it is gradually being eliminated in some fields.
HY 122 recommended by the Ministry of Construction is a modular disconnector with obvious fracture (patent approval number 98224507.6), which has the following advantages:
(1) The connection between the moving contact and the switch socket is welded and soft. The connection between the moving contact (knife) of the rubber porcelain bottom knife switch and the outlet terminal is hinged by rivets, which has large contact resistance and is easy to overheat or even melt the connection point. The movable contact (knife) of HY 122 is connected with the outlet terminal by copper braided flexible wire and welded, so the connection point will not be poor in contact and generate heat.
(2) The static contact (tool holder) adopts springs to ensure the reliability of contact. The static contact (knife seat) of rubber porcelain bottom knife switch is made of elastic copper, which can achieve good contact at first. However, after being put into use for a period of time, due to heating and other reasons, the elasticity gradually disappeared, and the contact began to heat up, resulting in arc melting. The stationary contact (tool holder) of HY 122 is made of pure copper and clamped by a spring to ensure the elastic connection of the switch.
(3) obvious fracture, to prevent false closing. HYl22 not only has obvious fracture, but also has an insulating needle. When the disconnector is off, insert the insulating pin printed with the words "No Closing" into the tool rack, so that the disconnector will not be closed by mistake.
(4) modularization. Modular electrical switches must be used in household distribution boxes for easy operation and maintenance. HY 122 disconnector has been widely used in household distribution box and watt-hour meter box because of the above advantages.
2. Leakage circuit breaker
In order to ensure the safety of household electricity, the power supply of household appliances that can be easily reached by human hands should have the function of leakage protection. Usually, the power supply circuit of fixed lighting equipment can't be protected by leakage because it can't be reached by human hands; In addition to the wall-mounted air conditioning socket, the socket circuit should also be provided with leakage protection.
There are two kinds of leakage circuit breakers (commonly known as leakage switches): electromagnetic and electronic. At present, most of the leakage circuit breakers on the market are electronic, such as ZLl8, DZl33, DLK and DZL30-32.
DZL 18, DZL33 and DLK electronic leakage circuit breakers not only have the function of personal electric shock protection, but also have the function of overvoltage protection, but they do not have the function of overload protection. Therefore, when selecting these leakage circuit breakers, the fuses must be connected in series.
The fuse is usually connected in front of the main switch, for example, when the electromagnetic leakage circuit breaker is used, the fuse is connected between the electric energy meter and the electromagnetic leakage circuit breaker. However, when using the electronic leakage circuit breaker, the fuse should be connected in series after the leakage circuit breaker because the electronic leakage circuit breaker needs auxiliary power supply to work. If the fuse is connected in series before the electronic leakage circuit breaker, when the phase fuse is not blown and the neutral fuse is blown, the leakage circuit breaker will not trip under overload or short circuit. At this time, if people touch the phase line at the load end, they will get an electric shock, but the electronic leakage circuit breaker will not trip because the auxiliary power supply of the leakage circuit breaker cannot work because the N line is disconnected.
If the fuse is installed behind the electronic leakage circuit breaker, even if the fuse is blown, the auxiliary power supply will not be interrupted, so it can still protect against electric shock.
DZL30 series earth leakage circuit breaker is a small molded case modular circuit breaker, which not only has the function of electric shock protection, but also has the function of overload and short circuit protection. When using this leakage circuit breaker, there is no need to install a master fuse. The rated current of DZL 30-32 is 6, lO\ 16, 20, 25, 32A.
Generally, 16-32a is selected according to the loop number and load current controlled by the leakage circuit breaker in the household distribution box.
DZL 18, DZl33 and DLK are fixed on the switchboard with wood screws provided by the manufacturer. DZL30 is fixed in the lighting switch box with special guide rails.
3. Shunt switch and shunt fuse
10 years ago, household appliances were not popular, and household electricity was mainly lighting. In home electrical design, the main switch is often a knife switch with fuse, and several branches are connected to the lower pile head of the knife switch after meeting. Every household also has a flashlight or candle. Once the fuse is blown, it can be replaced by flashlight or candlelight.
With the popularity of household appliances, shunt control is very important, such as dividing the socket and lighting into two shunts and setting fuses as shunt overload protection respectively. When the household appliances connected to the socket are short-circuited, the fuse of the socket branch will be blown, and the fault will not expand, but the lighting branch can still work, and it is not necessary to replace the fuse with flashlight or candlelight. The shunt can be controlled by a modular switch or a modular fuse. If the switch is used, it should have overload and short circuit protection function, and there is no need to install a fuse in the shunt at this time. The shunt switch can be a bipolar molded case circuit breaker, such as DZ30F 1-32, with rated current of 6, 10, 16, 20, 25, 32A. When used as a shunt switch at home, 6A circuit breaker should be used.
The shunt can also be controlled by fuses, such as HG30 fuse isolators. This kind of fuse isolator has four specifications of L-4 pole, and bipolar fuse isolator should be used in household distribution box.
It is cheaper to use fuse for shunt control than to use circuit breaker, but it is more troublesome to replace fuse in case of failure, so it is not introduced at the end of distribution system diagram.
4. Lighting switch
There are many kinds, which should be considered from the aspects of practicality, quality, beauty and price.
(1) cable switch. There are two kinds of hidden and exposed. The concealed type is used for concealed piping, and the exposed type is used where exposed piping or sheathed pipes are laid. In the family performance, the cable switch is limited to the bathroom and kitchen, and its purpose is to ensure the safety when wet hands operate the switch. The pull wire of the pull wire switch is in direct contact with the phase wire in the switch, so the moisture resistance and insulation of the pull wire are good, and nylon rope pull wire is widely used now. Because the pull switch affects the beauty and is inconvenient to maintain, the social demand is decreasing year by year, and it is often replaced by rain switch in wet places.
(2) Flip the switch. There are two types: open type and dark type. This kind of switch is characterized by obvious opening and closing positions, and people will not misoperate if they touch the switch unintentionally. Because the toggle switch is bulky and unsightly, it is rarely used in home decoration.
(3) the seesaw switch. Its volume is smaller than toggle switch and its operation is lighter than toggle switch, so it is widely used in home decoration. Because this kind of switch is popular with users, there are many manufacturers, and the prices and quality of products from different manufacturers vary greatly. First of all, consider the quality, and then consider the price. Quality can be measured by whether the switch activity is light, whether the contact is reliable and whether the panel is smooth. The seesaw switch has two kinds of terminals: exposed and non-exposed. Of course, it is safer to choose a switch with no exposed screws.
(4) toggle the switch. It is characterized by the smallest volume among all kinds of lighting switches, and a panel can be combined with up to five switches and operated by ten squares. Home improvement must choose a reliable button switch. High-grade button switch adopts pure silver contact and silver-copper composite rocker, which can avoid poor contact caused by arc oxidation and has reliable performance.
(5) Rain switch. In the bathroom, because of the humid environment, in order to use electricity safely, the rain switch can be used instead of the cable switch; It is inevitable to operate the switch with wet hands in the kitchen, and it is safer to use the rain switch. The structure of household rain-proof switch is that a waterproof soft plastic cover is added to the toggle switch. At present, there is also a rain-proof switch with novel structure on the market. Its contacts are all sealed in a hard plastic cover, and two movable magnets are used outside the plastic cover to attract the magnets in the cover to drive the contacts to open and close, so the operation is very flexible.
There are also touch switches and voice-activated switches in home decoration, which will not be introduced here. When selecting the switch, every household should choose the same series of products.
5. (power supply) socket
The brand of socket used in home improvement is very important. Although inferior products are cheap, they are often poorly contacted, or they are poorly contacted after a period of use. You must open the panel and clamp the spring piece to work for a period of time. The die design of the socket selected in the project is wrong. Although it is a three-pole socket, the grounding electrode is unreasonable and the electricity consumption is unsafe, so it needs to be purchased again, which leads to an increase in investment. If the home decoration is entrusted to the decoration company, the brand of switch and socket should be indicated in the contract.
6. Insulated conductor
Home decoration. Hard plastic sheath line for bare insulated wire; Hard or soft plastic wire for pipe-penetrating concealed wire; Plastic flexible stranded wire for lamp holder wire. Users can check the quality of insulated wires from two aspects: section size and insulation uniformity.
The conductor section is clearly defined in GB5 3.2-85. However, in the manual published by 1986 and reprinted by 199 1, there are old standards in the hard-wired part, which is very common.
The insulation layer is uneven in thickness, and wires with air holes and bumps on the surface cannot be used. The wires produced by certain brands of manufacturers should be selected, and the certificates are complete. The allowable error of each coil length of100m conductor is 2m.
In China, the vast majority of household electricity consumption is single-phase, and there are three wires entering each household: phase wire, neutral wire and grounding wire. Conductor color: the phase line is yellow (or red or green), the neutral line (also called zero line) is light blue, and the grounding line is green/yellow. After these three wires enter the home distribution box, the color of the outgoing wires should be selected according to the standards in home installation. The grounding wire from the household distribution box must adopt green/yellow double-color wire. The color of personality line must be light blue, the color of phase line and incoming line can be the same, and several color lines can be selected to distinguish different output circuits. For example, the incoming line is yellow, and the outgoing line has four loops, all of which can be yellow lines, yellow lines, green lines and red lines, so that the faulty lines can be quickly detected when patrolling the lines.
7. Wire protection tube
Wires are not allowed to be laid directly in the wall, and must be protected by wire protection tubes. GB50096- 1999 Code for Residential Design does not require the type of wire protection tube. GB 50258-96 "Code for Construction and Acceptance of Electrical Equipment Installation Engineering 10kV and Below Distribution Engineering" has the following provisions: thick-walled steel pipes or liquid-proof flexible metal wire protection pipes should be used in wet places and directly buried; Thin-walled steel pipes or flexible metal wire protection pipes should be used for wire protection pipes in dry places; Plastic pipes should not be laid in places with high temperature and easy mechanical damage. Plastic pipes and accessories for protecting wires must be marked with flame retardant and manufacturer's labels; Metal hoses should be laid in dry places that are not easily damaged by machinery, and should not be directly buried underground or in concrete. Dbj08-20-98 "Design Standard for Residential Buildings" stipulates that power supply, telephone and TV lines should be concealed with flame-retardant plastic pipes.
Flame-retardant plastic pipe is cheaper than metal pipe, which is convenient for construction and won't rust, so the use of plastic pipe in home decoration is welcomed by users.
At present, there are many manufacturers of plastic pipes in China, and the quality of products in most factories is good, but the quality of plastic pipes produced by some factories is extremely poor. This kind of protective tube collapses when it is bent and cracks when it is impacted. This inferior product must not be used for home decoration.
When decorating at home, you can carry out the following effective inspections on the wire protection tube: (1) Check whether there are manufacturer's signs and flame retardant signs on the outer wall of the plastic tube, and the protection tube without the above two signs cannot be used. At present, Gutian and other brands are widely used in Shanghai projects. (2) Make the plastic pipe burn with fire, and the plastic pipe will extinguish itself within 30s after being evacuated from the fire source, and the flame retardant test is qualified. (3) When bending, a special spring should be inserted into the tube. During the test, bend the pipe by 90', the bending radius is 3 times the pipe diameter, and the appearance after bending should be smooth. (4) Knock with a milk hammer until the protective tube is deformed, and those who have no cracks in the impact test are qualified.
In home decoration, in addition to using flame-retardant plastic pipes to protect wires, metal wires can also be used to protect pipes. For example, some residential power lines are protected by flame-retardant plastic pipes, and telephones and cable TVs use galvanized metal thin-walled pipes (which can play a shielding role). There is no need to set jumpers for the metal protective tubes of telephone and CATV transmission lines, because galvanized tubes connected with threads or sleeves can meet the shielding requirements. The steel pipe shall be free from flattening and cracks, and there shall be no burr in the pipe. The outer diameter and wall thickness of steel pipes shall conform to relevant national standards. If there is tooth decay or brittle fracture when the steel pipe is twisted, it means that the quality of the steel pipe does not meet the requirements.
The wires from the junction box to the lamps on the ceiling shall be protected by hoses, including plastic hoses, metal hoses, plastic-coated metal hoses and Pulika hoses. General household installation uses plastic hoses or plastic-coated metal hoses. If a metal hose without plastic coating is used, the hose should be grounded.
Corrugated pipe has both the strength of metal pipe and the flexibility of hose, so it is used in senior residence, but the price is higher.
8. Lightning arrester
When lightning strikes or induces low-voltage overhead lines, the high pulse voltage generated by lightning will enter the room along the overhead lines, damaging the electrical equipment connected with the power lines, so it is necessary to install lightning arresters (also known as surge voltage protectors, SPD for short) at home. Lightning arrester is a kind of low-voltage power supply protection equipment, which can release a large amount of pulse energy generated by lightning stroke on the line in the shortest time and transmit it to the earth through the grounding wire. Lightning arresters have been made into modular products. Installed in the household distribution box, one end is connected to the phase line or N line, and the other end is connected to the ground wire. Under normal circumstances, the arrester is in a state of high resistance. When instantaneous pulse overvoltage occurs in the incoming line of household power supply due to lightning strike or switching operation, the lightning arrester will be quickly short-circuited and turned on in nanosecond time, and the pulse voltage will discharge to the ground, thus protecting household electrical equipment. When the pulse voltage flows through the lightning arrester, the lightning arrester becomes a high resistance state again, so it does not affect the household power supply.
At present, foreign products include V25-B enhanced power arrester produced by German OBO company, LTD/LTM surge limiter produced by Meilan Zhilan company, SP series surge protector produced by Haige company, etc. China has a series of sockets from Zhejiang Wanma, Shandong Longda and Beijing Breakthrough Company.
9. Equipotential bonding
When taking a bath in the bathroom of a house, the impedance of human skin is reduced due to humidity. If there is a low voltage along the metal tube, it will also cause an electric shock accident. Therefore, it is necessary to carry out equipotential connection to the bathroom. GB 50096- 1999 Code for Residential Design (6.5.2) stipulates that the bathroom should be partially equipotential connected. At present, equipotential bonding must be done in the bathrooms of hotels and high-grade houses under construction, and equipotential bonding should also be done in the bathrooms of ordinary houses if they have bathing equipment. The introduction of the finalized product TD22 equipotential bonding terminal box has brought great convenience to the construction and daily inspection of equipotential bonding.
C65N indicates the model, 50 indicates I=50A, 3P indicates a three-pole switch, and +N indicates that the zero line follows or passes through the unbroken switch.
YJV22 Four-Core Unequal Cross-Section Steel Belt Armored Copper Cable
Calculation result: section S = 70 square.
Bending radius r = 720; Cable weight W = 3393/km
Calculated power pjs = 50kw；; Calculated current Ijs = 94.96A
Power factor cos = 0.80 Phase: three-phase correction coefficient = 0.70
Pjs=Pe x Kx Kx demand coefficient, with 1 for branch lines and 0.9 to 0.95 for power supply trunk lines;
Single-phase circuit: ijs = PD * kx (1+@)/v * cos φ;
Three-phase circuit: PJS = PD * KX；; ijs = Pd * Kx( 1+@)/3 * V * Cosφ.
Pe line lamp capacity kw; Pjs-lighting calculation load kw; V-rated voltage kv of line distribution; Ijs-calculate current a; @-rectifier power loss coefficient; Cosφ- power factor.
VIgi 30mA means that the leakage current of the leakage isolating switch is not more than 30mA when it is energized.
Pjs=20kw calculation power
Ljs+30A Calculation current +30A
1P-2P are click and bipolar circuit breakers.
1.44Kw is the total power of circuit electrical equipment, which is the sum of rated power of circuit electrical equipment.