Brief introduction: Construction projects include factories, theaters, hotels, shops, schools, hospitals and residences. , its new construction, reconstruction or expansion must be realized through construction activities; ? Subsidiary structures and facilities? Refers to water towers, bicycle sheds, pools, etc. Supporting the building. ? Installation of lines, pipelines and equipment? Refers to the installation activities of electrical, water supply and drainage, heating and ventilation, communication, intelligence, elevators and other lines, pipelines and equipment supporting the building and its ancillary facilities.
In recent years, the sustained development of the national economy has brought great vitality to the development of the construction industry, but at the same time, some new problems have emerged, which has brought a lot of inconvenience to people's lives. On the basis of many years of engineering practice, the author puts forward some preventive measures for the quality problems related to electrical installation engineering, and discusses them with colleagues.
1. Qualification of electrical construction unit and scope of contracted projects
1. 1 has a problem.
Some projects (especially small projects) hire unqualified designers and construction units (or self-employed) to design or contract projects without following the construction procedures. Due to the limited technical level of design and construction personnel, some installation projects can not meet the requirements of the specified indicators.
Cause analysis of 1.2
The leader of the unit is not strict, and relatives and friends say hello to introduce the team; The amount of work is small, the profit is small, and qualified teams are unwilling to contract or subcontract.
1.3 preventive measures
Electrical installation is a highly professional job. Generally speaking, the power transmission, transformation and power supply projects of 10KV and above are contracted by the local power supply bureau after being contracted by the construction unit. The power supply project below 10KV is subcontracted to the hydropower installation unit. In order to ensure the construction quality, the supervision department should assist the construction unit to carefully examine the qualifications of contractors and subcontractors, put forward examination opinions, and select the construction unit according to the principle of fair competition.
2. Commonly used main electrical equipment and materials
2. 1 quality problem
(1) No product certificate, production license, technical specification, test report and other documents;
(2) The conductor has high resistivity, low melting point, poor mechanical properties, poor insulation, large temperature coefficient and insufficient size (the length of each coil);
(3) The cable has low withstand voltage, low insulation resistance, poor corrosion resistance and low temperature resistance. There are many internal joints, and the tightness between insulation layer and wire core is poor;
(4) The appearance of power, lighting and socket box is poor, the geometric dimensions can not meet the requirements, and the thickness of steel plate and plastic shell is not enough, which affects the strength of the box and the corrosion resistance can not meet the requirements;
(5) The conductive values of switches and sockets are inconsistent with the nominal values, conductive metal sheets are inelastic, poor in contact, prone to heat, and do not meet the safety requirements, and plastic products have low flame retardancy and temperature resistance and poor safety performance;
(6) Lamps and light sources are shoddy, with poor mechanical strength, poor rust and corrosion resistance and short service life;
(7) Various wires and tubes have thin walls, poor strength, unqualified galvanized coating quality and poor folding resistance.
2.2 Cause analysis
The electrical appliance market is chaotic, and there are many fake and shoddy products and unlicensed products. Procurement personnel have poor ability to distinguish between true and false, and the control is not strict.
2.3 Preventive measures
(1) Leaders attach importance to it, and supervisors and purchasing personnel should ensure good quality. Through investigation, we can directly purchase goods from manufacturers with certain production scale, good reputation and excellent products, reducing intermediate links;
(2) After the electrical equipment and materials enter the site, the storekeeper shall cooperate with the supervision engineer, first check whether the freight yard meets the specification requirements, and check whether the model, specification and performance parameters of the equipment and materials are consistent with the design. Check the instructions, certificates and spare parts, conduct visual inspection, make unpacking records and keep them properly;
(3) The main materials shall have factory certificate or quality certificate, etc. In case of doubt about the quality of materials, samples should be sealed on site and handed over to local qualified testing departments for inspection in time. Only after passing the test can they enter the site and put into use.
3 laying wire and tube problems
3. 1 quality problem
(1) Thin-walled tube replaces thick-walled tube, black iron tube replaces galvanized tube and PVC tube replaces metal tube;
(2) The bending radius of the threading pipe is too small, and it is bent, shriveled and wrinkled, even in severe cases? Dead bend? . Transition box is not set as required for pipeline turning;
(3) The burr of the metal nozzle is not treated, but directly butt welded. When the threaded joint and the intermediate junction box pass through, the jumper bar is not welded or the welding length is not enough. Spot welding? Through-pipe welding is a serious phenomenon. Galvanized pipe and thin-walled steel pipe are welded instead of threaded connection;
(4) The steel pipe is not grounded or the grounding is not firm;
(5) The buried depth of the pipeline wall is not enough, and the pipeline on the precast slab crosses too much, which affects the civil construction. The pipes in the cast-in-place slab are concentrated into bundles, which affects the structural safety;
(6) The pipeline passes through the structural expansion joints and settlement joints without passing through the box body, leaving hidden dangers;
(7) The exposed and concealed pipes are not straight into the box and squeezed into bundles, the outcrop length is inappropriate, the steel pipes are not jacketed, and the PVC pipes are not locked. Nazi? .
3.2 Cause analysis
Construction personnel are not familiar with construction specifications, or have not received professional training, and their skills are not very good; The operation is not serious and responsible, which saves trouble and is convenient. The requirements for supervision engineers and site management personnel are not strict, and the supervision is not enough.
3.3 Preventive measures
(1) The pipeline shall be laid in strict accordance with the design and specifications, and strictly controlled by the professional supervision engineer. The pipeline shall not be constructed if it does not meet the requirements;
(2) When processing pipelines, you must master:
There is only one 90? When bending, the bending radius? 4 times the outside diameter of the pipeline;
2 two or three 90 s? When bending, the bending radius? 6 times the outside diameter of the pipeline;
(3) The bending radius of concealed piping? 6 times the outside diameter of the pipeline;
(4) the bending radius of the pipeline buried in the ground and concrete? 10 times of the outside diameter of the pipeline;
(3) What are the inner diameters of galvanized pipes and thin-walled steel pipes? 25mm can choose different specifications of manual pipe bender, inner diameter? 32mm hydraulic pipe bender for steel pipe. Choose different specifications of spring elbows according to the inner diameter of PVC pipes. What is the inner diameter? 32mm pipe is simmered and bent. If it is processed in large quantities, any elbow can be heated in the oven. After the pipe is bent, the pipe skin will not wrinkle, crack or deteriorate. When PVC is butted, it is recommended to adopt the butt joint method of full material sleeve and stick it firmly;
(4) If the pipe exceeds the following length, a wire box can be added at a proper position (this box is convenient for threading, but wiring is not allowed).
① Straight line 50m
②30m, without bending;
③20m, a 90? Bending;
④ 15m, two 90? Bending;
⑤8m, three 90s? Bending;
(5) It is forbidden to cut the steel pipe with a pipe cutter, and the pipe mouth shall be sawed flat with a hacksaw (do not tilt), and the burr at the pipe mouth shall be cleaned with a circular file. Diameter? When 40mm thick-walled pipes are butted, welding is adopted, and direct butt welding of nozzle is not allowed. Diameter? 32mm pipe should be connected with a set of wires or with casing fixing screws, and should not be welded. The connector and the intermediate junction box are bridged by a special grounding card;
(6) Exposed pipes and concealed pipes must be reliably grounded according to the specification requirements, and galvanized pipes and thin-walled pipes entering the distribution box should be blocked by professional grounding wires. 2.5mm bicolor BV conductor is firmly connected with the box. Diameter? 40mm pipe can be fixed on the box by spot welding when it enters the distribution box, and pay attention to rust prevention and corrosion protection;
(7) When the pipeline is buried in the wall or underground, what is the depth from the outer surface of the pipeline to the wall and the ground? 20mm, ensure the metope, ground along the pipeline gap. When laying pipes on precast slabs, try to avoid crossing. When the number of 20mm pipes exceeds the specified number, 1 16mm pipes can be laid side by side. Pipe laying in cast-in-place floor slab is forbidden to be laid in bundles, and should be laid in rows at intervals to reduce the impact on floor slab structure;
(8) Pipes passing through expansion joints and settlement joints shall be constructed according to design requirements, and transition boxes (boxes) shall be placed flat and firm, as shown in figure 1.
(9) Open pipes and concealed pipes should be straight when they are put into boxes and boxes. If the outer diameter of the pipe is consistent with the reserved hole of the box, it should be used as much as possible. If the diameter of the pipe is smaller than the hole of the box, a drill should be used to open the hole. If the pipe diameter is larger than the box hole, it should be enlarged on the basis of the box hole. It is forbidden to drill holes by gas cutting or electric welding. More pipes should be discharged into the box at appropriate intervals. Tube into the box length 3 ~ 5 mm, neatly arranged. Open pipes entering the distribution box shall be constructed according to Figure 2.
4. Distribution of pipes in the ceiling floor
4. Problems in1
(1) piping is irregular, with skewed lines and fluctuating. The welding quality of steel pipe jumper grounding wire is poor, including virtual welding, slag inclusion, penetration and? Spot welding? . The metal hose is not connected with the grounding protection wire; The length of the tube is not suitable, exposing the conductor; Junction box without cover plate; Rust prevention and corrosion prevention are not in place;
(2) The hanger is set asymmetrically and the distance is too large. Some put the pipe directly on the keel and fix it with iron wire or iron wire.
4.2 Cause analysis
Construction workers think that the pipeline on the ceiling floor is invisible, so they are careless and irresponsible. The supervisor signed the acceptance without careful inspection.
4.3 Preventive measures
(1) Require the construction personnel to lay pipes in the ceiling according to the technical requirements of open piping, and try their best to do so? Horizontal and vertical? Take less ramps and cross less roads;
(2) Galvanized pipe or black iron pipe jumper grounding line is still carried out in accordance with the provisions of the exposed pipe and concealed pipe. Black iron pipes and all welds shall be derusted and deslagging, and painted with antirust paint and topcoat;
(3) Hangers, supports and pipe clamps shall be constructed as specified in Table 2, and derusting, antirust paint and topcoat shall be applied.
5 distribution box, junction box, ceiling fan hook embedded problem
5. Problems in1
(1) The distribution box, junction box and hook are not set according to the drawing, and the coordinate deviation is obvious, and the deviation of rows of lamps and ceiling fan hook boxes is large;
(2) The box and box in the cast-in-place concrete wall and column are deeply bent and sunken, and too many pipes enter the box and box. If the boxes are not firmly fixed, moved by vibration or concrete slurry enters the boxes, the boxes are not treated with rust prevention and corrosion protection.
5.2 Cause analysis
The construction is sloppy, the sense of responsibility is not strong, and the civil engineering and electrician do not cooperate properly.
5.3 Preventive measures
(1) When the hooks of lamps, switches, sockets and ceiling fans are embedded, they shall meet the requirements of the drawings. When positioning, what is the allowable deviation between the left and right slots and the front and rear slots? 50mm, the same indoor rows of lamps and ceiling fans center allowable deviation? 5mm, the distance between the switch box and the door frame is generally 150 ~ 200 mm, and the height should be as shown in the figure. Unless otherwise specified, it should not be less than 1.3m in general occasions and 1.5m in nurseries, kindergartens, houses and primary schools.
(2) The embedded box in cast-in-place concrete should be close to the template, fixed firmly and sealed well. When pouring concrete, electricians should keep an eye on PVC pipes and boxes for 24 hours and solve problems in time. After the template is removed, the sundries and rust spots in the box should be cleaned in time, and antirust and anticorrosive paint should be brushed;
(3) In the embedded construction, according to the thickness of the cast-in-place slab, what is the hook of the ceiling fan? 10 round steel first bends a circle with an inner diameter of 35 ~ 40 mm, and then slowly folds the circle and the steel bar into 90? , insert it into the middle of the bottom of the junction box, and then fold the remaining steel bar head into 90 according to the plate thickness. , welding on the plate reinforcement. After the formwork is removed, fold the lifting ring, adjust the round steel to be vertical and located in the center of the box, clean the hook and metal box, and brush it for rust prevention and corrosion protection.
6 Wire threading, connection and dressing
6. Problems in1
(1) The wire is pulled into the conduit by bending and twisting, and the wire connector in the conduit is mixed with wire color code;
(2) The wires are connected in various ways, instead of pressing multiple strands, multiple single strands are pressed together, and the joints are not tinned. The wire stripping tool cuts the wire, and the bolt lacks washer and spring leaf.
(3) The dressing is not tight, the technology is not in place, only plastic tape or black tape is used for dressing, and the used tape and tape are not sticky after expiration.
6.2 Cause analysis
Operators don't pay attention to ideas and don't understand norms. The demand statistics of wires of various colors are inaccurate, so replace them at will. I am not familiar with the connection process of electric wires, and I am not clear about the wiring process of electric wires.
6.3 Preventive measures
(1) Check the nozzle of the steel pipe before the conductor passes through the pipe. Nazi? And a protective sleeve. PVC nozzle? Nazi? Whether it is in good condition, check whether there are sundries in the tube. If there are sundries in the tube, blow them off with compressed air (0.25Mpa), or tie a piece of cloth with iron wire and pull them out of the tube;
(2) Pay-off should be done slowly with a pay-off reel, and the line should be wrapped straight with cotton yarn. Generally, the conductor colors are yellow, green and red where there are three-phase conductors (A, B and C). Single-phase line is red, zero line is blue, and PE protection line is yellow-green double-color line;
(3) Exposed wires should be tinned to prevent oxidation. No more than two wires shall be connected on each connecting bolt or terminal. When two wires are connected by bolts, a flat pad shall be added in the middle. For multi-strand wire connection, galvanized copper joints should be used for crimping. The down lead of the chandelier should be woven with a flexible cord, and cross with the catenary to enter the lampshade. Both ends of the flexible cord should be buckled to prevent stress. For single-core conductor, the connection mode of safety pressure cap can be adopted. All tinned wires shall be cleaned of welding oil residue (wiped with industrial alcohol) to prevent the welding oil from oxidizing the conductor. It is forbidden to connect wires in the pipe;
(4) Tie the wire joint, first tie the two layers with rubber belt or yellow wax belt (plastic belt can also be used), and then tie the two layers with black adhesive tape or self-adhesive plastic belt, so that the insulating belt can be firmly stuck together to prevent moisture-proof gas from invading.
7 Install switches, sockets, lamps and ceiling fans.
7. Problems in1
(1) The installation positions of switches, sockets, lamps and ceiling fans are deviated. In the same room and corridor, the deviation of levelness and straightness of rows of lamps and ceiling fans exceeds the specified value;
(2) Fluorescent lamps use wires instead of hanging chains, hard wires are used for down leads, soft wires are directly connected to the lamps without hanging chains, and the wires are laid on the fluorescent lamp cover;
(3) The distance between the embedded ceiling fan hook and the junction box is too large, the ceiling fan can't cover the junction box hole, the wires are exposed, and the round steel of the ceiling fan hook is less than? 10, the hook is not embedded and the ceiling fan is fixed on the keel;
(4) The ceiling lamp directly installed on the roof is not equipped with a wooden table (square table) or the quality of the wooden table is poor. The ceiling lamp installed on the ceiling is fixed on the top plate directly with self-tapping screws without fixing the frame;
(5) The lamp shell that needs grounding is not grounded.
7.2 Cause analysis
The installation of switches, sockets, lamps and ceiling fans is deviated due to the deviation of embedded junction boxes, and there is no stay wire for positioning when installing lamps and ceiling fans in rows. I am not familiar with the operation procedures of wiring, wiring and binding of lamps and lanterns, and I have not mastered the installation method. It is more convenient to hook.
7.3 Preventive measures
(1) electrical embedded construction should be accurately positioned, especially the embedded positioning of rows of lamps and ceiling fan junction boxes (ceiling fan hooks), because after the junction boxes are buried, there is little room for adjustment before and after installing ceiling fans. See Table 4 for allowable installation deviation of switches, sockets, lamps and ceiling fans;
(2) According to the specifications and models required by the drawings, the position of the embedded junction box should be set at one side of the hanging chain, not at the center of the lamp, so that the down lead of the fluorescent lamp can be woven with the hanging chain to enter the lamp. If there is no ready-made hole near the chain hanging ring, you can drill another hole to let the wire enter the lamp, instead of laying the wire along the lampshade and entering the lamp from the middle hole;
(3) The hook penetrates into the junction box and is embedded in the concrete floor, so that the ceiling fan upper cover can completely cover the junction box hole and avoid the exposed wires. When the ceiling fan is installed through the ceiling, the fixing device must be embedded in the top plate, and the suspender should be absolutely vertical. If it is not vertical, the ceiling fan will swing when it rotates, vibrating the ceiling and sometimes making noise.
(4) For large ceiling lamps or large chandeliers, fixed frames or embedded hooks must be installed. If the lamp shell requires grounding, it must be firmly connected to ensure safety.
8 Lightning protection and grounding problems
8. Problems in1
(1) The designer set it on the light color steel roof panel? When 10 galvanized steel bar is used as lightning protection net, the test point of lightning protection grounding electrode is not described properly;
(2) During the construction of lightning protection grounding electrode and lightning protection network, the welding does not meet the requirements;
(3) The setting of grounding electrode resistance test points does not meet the requirements.
8.2 Cause analysis
Designers are not familiar with the construction of color steel plates, and constructors do not attach importance to lightning protection safety, or have not participated in training, do not know how to construct or are vague about the concept of lightning protection.
8.3 Preventive measures
(1) When designing the lightning protection net belt of light color steel roof panel, if it is fixed, how to use the color steel plate should be considered;
(2) At present, lightning protection grounding electrode is generally welded with pile foundation reinforcement and foundation reinforcement, and connected with lightning protection network through column reinforcement. In design again? Disconnect card? The test point is not suitable, so the grounding electrode test point should be set instead. Use 2.5 for the test center? Brief introduction of galvanized flat iron;
(3) When the foundation reinforcement is used as the grounding electrode, generally, two main reinforcements are used to weld the overlap of the two main reinforcements inside and outside the whole foundation, and then the main reinforcements on both sides of the vertical and horizontal foundation in the circle are welded with the two main reinforcements outside. If there is a pile foundation, connect two pile reinforcements to the main reinforcement of the foundation according to the design requirements, and then weld the column reinforcement specified in the drawing (generally using two outer reinforcements) to the main reinforcement of the foundation as the down lead. For the sake of welding quality, it is often required to reuse the lap joints of steel bars? 10 round steel jumper. Each welding point shall be welded on both sides as required, and the welding length shall be 6 times of the diameter of each steel bar. Spot welding is not allowed. Lightning protection net belt? 10 galvanized round steel. When the steel bars are butted, they should be welded on both sides. The welding length is 60mm, and the butt joint should be straight.
(4) In the lightning protection construction of high-rise residential buildings, the metal door and window frames with more than 9 floors should be 2.5? 25 galvanized flat iron shall be welded with grounding rod to prevent the side of door frame and window from being struck by lightning. From the first floor to the top floor, the lap joint of the main reinforcement around the ring beam is welded firmly, and then connected with the column reinforcement of the lightning protection downlead as the equalizing ring.
In building engineering, the above phenomenon exists more or less in the construction of fire fighting, communication, broadcasting, lighting, cable laying and other projects. To improve the project quality, we must first improve the quality of construction personnel, strengthen the sense of responsibility of management personnel and improve construction technology. Only in this way can the quality of the project be guaranteed.
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