Repost Standardized construction requirements for cable trays and piping in low-voltage engineering

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This post was last edited by Sake Girl on 2020-10-19 at 14:29. In the construction of low-voltage electrical systems, it is necessary to install pipes and cable trays, and this is a very important aspect. What are the standard guidelines for carrying out these tasks? Let’s summarize it together. Firstly, the key aspects of the construction process are comprehensively explained in the following areas, which are very useful for guiding construction: (1) Construction process for strong and weak current compartments; (2) Construction process for connecting cable trays at bends; (3) Metal wire troughs; (4) Construction process for grounding cable trays; (5) JDG connection process; (6) Construction process for installing JDG pipes exposed indoors. 1. Construction process for strong and weak current compartments · Connection process for distribution box wire troughs. Schematic diagram: Cables leading out of the distribution box. Key points of the process: ① Process flow: Preparing and embedding components → Installing the distribution box → Installing piping → Installing devices inside the box → Wiring → Grounding. ② The distribution boxes are installed in the correct locations, all components are present, and the installation elevation of the boxes in a row ensures that their bottoms are at the same level ； There is a locking nut for the catheter to enter the box ； The cover of the concealed distribution box is flush against the wall. ③ The wiring inside the tray/case is neatly arranged; the cross-sectional areas of the wires compressed on both sides of the screws under the washers are identical. No more than 2 wires are connected to each terminal, and components such as anti-loosening washers are all present ； Inside the lighting panel (box), separate busbars are provided for the neutral wire (N) and the protective earth wire (PE wire); the neutral wire and the protective earth wire are distributed via these busbars. ④ The switches inside the panel (cabinet) operate smoothly and reliably; the circuits are equipped with leakage protection, and the operating current of the leakage protection device is not greater than 30mA, with a response time of no more than 0.1s. The company needs multiple engineering qualification certificates related to electrical engineering in order to meet regulatory requirements; those who have unused certificates are welcome to contact Engineer Chen at 150-0759-9549. Lighting enclosures, brackets, and conduits must be properly grounded. · Construction technique for grounding main lines in electrical shafts – Detail drawings. Bridging of cable trays in electrical shafts with grounding main lines. Key points of the technique: ① Process flow: Positioning → Preparing brackets → Installing brackets → Laying the grounding main lines → Bridging → Marking. ② The materials are selected in accordance with the design requirements: hot-dip galvanized materials are used for the grounding main lines and metal fittings ； Secondly, the minimum allowable cross-sectional area of the cable must meet the specified requirements: ③ When laid horizontally along the wall of a building, it should be at a height of 250–300 mm above the ground ； The gap between the building wall and the structure is 10-15 mm. ④ Along the length of the ground wire, each section measuring 15–100 mm is painted with alternating yellow and green stripes. ⑤ Along the vertical strong and weak cable trays, grounding main lines must be installed, and the cable trays must be effectively bonded to these grounding main lines; anti-loosening fittings should be used for the bonding fasteners. ⑥ The connection must be reliable; during welding, the welds should be complete with no gaps, and the anti-corrosion protection of the welded areas must be adequate. The requirements regarding overlap length and welding methods are specified in the table below: ⑦ The grounding conductors should be labeled. ⑧ It is easy to inspect, and the installation location does not hinder the disassembly and maintenance of the equipment. Construction technique for connecting cable trays at turning points – Detailed drawings. Expansion joints for cable trays; Key points for connecting conduit arrays to cable trays: ① Finished accessories should be used. If the supplier does not provide clear specifications for the accessories or the available dimension data is insufficient, these standard specifications shall be followed. ② When bending the cable tray, if the maximum cable diameter is less than 70 mm, the bending angle of the tray should not exceed 30 degrees; when the maximum cable diameter is 50 mm or less, the bending angle should not exceed 45 degrees. ③ To ensure that large-cross-section cables meet the requirements regarding the bending radius when installed in small cable trays, L must satisfy the condition L≥10D-W/2. ④ When metal cable trays are installed horizontally, their height above the ground should generally not be less than 2.5 meters; when installed vertically, a metal cover plate should be used for protection at a height of 1.8 meters above the ground (except in dedicated areas such as distribution rooms, electrical shafts, and technical floors). ⑤ Expansion joints are provided for steel cable trays with a length of over 30 meters, and for aluminum alloy or fiberglass cable trays with a length of over 15 meters ； Compensation devices are installed at the locations where the cable tray crosses the building’s deformation joints. ⑥ When no specific requirements are specified in the design, the spacing between horizontally installed brackets should be 1.5–3 meters, while the spacing between vertically installed brackets should not exceed 2 meters. It is important to maintain a uniform spacing. Brackets should be installed every 0.5 meters at points such as the entrances and exits of wire boxes, cabinets, corners, turns, both ends of expansion joints, and at T-joints, with the height of these brackets adjusted accordingly. ⑦ The bolts between the cable trays and brackets, as well as the bolts securing the cable tray connection plates, are all tightly fixed without any omissions; the nuts are located on the outside of the cable trays ； When aluminum alloy cable trays are fixed to steel supports, there are anti-electrochemical corrosion measures to ensure insulation between them. ⑧ Cable trays shall be installed below flammable and explosive gas pipelines as well as thermal pipelines; when there are no specific requirements in the design, the minimum clear distance from such pipelines shall comply with the relevant regulations. ⑨ When wiring cables, the bending radius of cable trays, trunking, and pipes should not be less than the minimum bending radius of the cables. 3 Construction techniques for grounding metal wire trays and cable trays; Detailed diagram of tray bridging; Sprayed-paint tray bridging; Key points of zinc-plated tray connection: ① Process flow: Install wire trays → Make grounding connections → Label them. ② Copper core grounding wires are strung across both ends of the connection plates between ungalvanized cable trays; the minimum allowable cross-sectional area of such grounding wires is 4 mm2 ； At both ends of the connection plate between galvanized cable trays, no grounding wire is bridged, but there are at least 2 connection bolts with locknuts or lockwashers at each end of the connection plate. ③ The connection is reliable; the fasteners come with anti-loosening measures during crimping ； Claw pads should be added for the bridging of the powder coating tank frame. ④ When the total length of the cable tray is not more than 30 m, it should be connected to the grounding main at no fewer than 2 points ； When the total length is greater than 30 m, connection points to the grounding main should be added every 20 m to 30 m. Construction technique for 4JDG connections – Detail drawings. Key points of the technique: ① Process flow: Marking positions with lines → Prefabrication (cutting and bending pipes) → Pipe connection. ② For straight pipe connections and bent pipe connections, special straight sleeves and bent sleeves are used; in straight pipe connections, the two pipe ends should be located at the center of the conduit. ③ When using a hand pipe bender, move it moderately and avoid applying excessive force. The bending radius of the pipe shall be no less than 10 times the pipe diameter. ④ Set screws should be tightened using specialized tools. ⑤ For pipe diameters of 32 MM and above, there should be no fewer than 2 set screws at each end of the coupling sleeve. ⑥ The conduit body should be grounded, while the connection points do not need to be grounded; the piping shall not be used as a grounding wire for the equipment. 5 Construction techniques for exposed JDG pipes indoors: Layout of bent pipes and installation of supports; Key points for laying and fixing exposed pipes along walls: ① Process flow: Comprehensive layout → Marking and positioning → Prefabrication → Installation of supports → Pipe laying → Grounding. ② It is recommended to use piping for installations with three pipes or fewer, while conduit should be used for installations with more than three pipes. ③ Before installation, a comprehensive layout should be prepared: the pipes should be arranged neatly, the spacing between supports should meet the requirements, the spacing between fixing points should be uniform, and the installation must be secure ； Pipe clamps shall be installed within a range of 150–500 mm from the terminals, the midpoint of elbows, or the edges of cabinets, benches, boxes, panels, etc. The maximum spacing between pipe clamps on the straight sections in between shall comply with the following requirements: ④ Fittings should be prefabricated components; connections between pipes and boxes shall use prefabricated joints, which must be secured with locking nuts. ⑤ Principle for overly long pipelines and junction boxes: when exceeding 30 meters with no bends ； When there is 1 bend at over 20 meters ； When there are 2 bends over 15 meters ； There are 3 bends when it’s over 8 meters. ⑥ The conduit connections are properly grounded, with at least 2 connections at each end of the circuit to the grounding main.