Technical solutions and project implementation plans for metal hose and wire protection sleeves

Metal hose is a new type of material used for wire and cable protection sleeves and is flexible Metal hoses can be used for open and concealed laying in various situations and for concealed laying in cast-in-place concrete. Because the pipe is light in weight, has good strength and insulation, can be bent at will (no tools required), and is equipped with various accessories, it is very convenient to construct and can greatly improve work efficiency, so it has been widely used in electrical installation projects.

1. Composition of metal hoses 1.1 Metal hoses

Can be divided into metal hoses and plastic-coated metal hoses. The outer layer of the metal hose is hot-dip galvanized steel strip (or copper strip), the middle layer is cold-rolled steel strip, and the inner layer is water-resistant electrical paper. It is rolled into a spiral shape, and the outer wall has its own thread; it is plastic-coated and flexible. The metal wire protection sleeve is a metal hose coated with a layer of plastic (PVC). Its specifications range from 10# to 101#, and the inner diameter ranges from 9.2 mm to 100.2 mm, with a maximum of 12 specifications.

1.2 Metal hose accessories

Junction box connection joint: for connecting metal hoses to the junction box (box), with waterproof type; direct head connection joint: for metal hose Connected to each other, there are waterproof types; Threadless connection joints: for connecting metal hoses to steel conduits or steel pipes; Hybrid connection joints: for connecting metal hoses to threaded steel pipes, there are waterproof types of 90 degrees and waterproof types of 45 degrees; grounding Card: used for grounding metal hoses.

2. Characteristics of metal hoses

Convenient construction and superior performance. The tube is light in weight, easy to transport, does not require machinery for bending and cutting, can bend freely, is easy to connect (no need for buckles), and is equipped with various accessories. Because the steel strip adopts a special hot-dip galvanizing process, it has excellent moisture resistance and corrosion resistance. It has good strength and good insulation. It has a wide range of uses and can replace ordinary galvanized steel pipes. There are basic types, anti-corrosion types, explosion-proof types, heat-resistant types, etc. Corresponding pipes and accessories can be selected according to different occasions.

3. Construction and application technology of metal hoses

Before laying the pipeline, the appearance of the metal hose should be carefully checked. The requirement is that the casing coating should not be peeled off, rusted, or spotted; The polyvinyl chloride layer of the plastic-coated metal hose must not have bubbles or damage. There are no protrusions or damage inside and on the surface of the casing, and the cut surface is smooth and free of burrs.

3.1 Bending and cutting

Metal hoses can be bent freely by hand without any tools according to the bending direction requirements during piping. The bending angle should not be less than 90 degrees. The bending radius of exposed pipes should not be less than 3 times the outer diameter of the pipe; when used in places that cannot be disassembled, the bending radius of the pipe should not be less than 6 times the outer diameter of the pipe; when embedded, the bending radius of the pipe should not be less than the pipe 10 times the outer diameter. There is no need for tools such as a bench vise when cutting metal hoses. When cutting the pipe, hold the pipe with your hands or place it on the workbench to press it with your hands. Use the blade of a special casing cutting knife to align the threads of the pipe vertically. The groove should be cut at right angles as much as possible, or it can be cut with a hacksaw. After cutting, the burrs at the pipe mouth should be removed in time to make the cut surface smooth.

3.2 Pipeline connection

Interconnection of metal hoses. When metal hoses need to be connected in the middle, use direct heads with threaded joints for interconnection. First check that there are no burrs at the pipe end, then screw the direct head into the end of the metal casing by hand, and then screw the other end of the metal casing into the other end of the direct head. The counterpart of the metal casing should be at the center of the direct head. . Connection of metal hose and steel pipe. The connection between metal hose and steel pipe can be divided into two types: threaded and unthreaded. If there is a threaded connection, use a hybrid connection joint. Screw the mixing joint into the threaded end of the steel pipe first, so that the opening of the steel pipe matches the threaded inside of the mixing joint, and then screw the metal casing into the threaded end of the casing of the mixing joint; you can also First unscrew and disassemble the hybrid connection joint, and then screw it onto the metal casing and steel pipe respectively. Then screw the mixing joint together. Unthreaded connections use unthreaded connection joints. First screw the metal casing into the threaded end of the casing without threaded joint. After the metal casing pipe end should match the inner opening, then insert the casing end of the non-threaded joint steel pipe into the steel pipe. , after the insertion depth reaches the requirement, use a screwdriver or wrench to tighten the two compression bolts on the joint. The connection between the metal hose and the box. The metal hose is connected to the box (box) using a wire box connection joint. Screw the metal casing into the threaded end of the metal casing of the wire box connection joint. Insert the other end of the connection joint into the knock-out hole of the box (box) and unscrew the connection. The fastening nut of the joint is placed on the inner wall of the box (box), and then the fastening nut of the joint is tightened with a wrench.

3.3 Technical requirements for pipeline laying

When metal hoses pass through equipment or building foundations or are likely to be subject to significant mechanical impact, protective measures such as adding protective pipes should be taken. When passing through settlement joints or expansion joints, compensation devices should be installed. When metal hoses are laid open, they should be arranged neatly and firmly fixed. The distance between the fixed points should be even. The distance between the pipe clamp and the terminal, the center point of the turn, and the edge of the electrical appliance or equipment is 150mm~300mm. The maximum distance between fixed pipe clips in the middle of the road is 0.5~1m. The spacing between the fixed points should be even and the allowable deviation should not be greater than 30mm. The allowable deviation in horizontality or verticality of exposed metal hoses laid horizontally or vertically is 5%, and the total length deviation should not be greater than 1/2 of the inner diameter of the pipe.

When metal hoses are installed concealed, they should be laid along the nearest route and bending should be reduced. The minimum distance between the metal casing buried in the building and the surface of the building should not be less than 15mm; when laying in cast-in-place concrete, it should be in close contact with the steel bars. Fixed, the fixed spacing should not be greater than 500mm. When the metal hose is threaded after piping, the total cross-sectional area of ??the wires in the pipe, including the insulation layer, should not be greater than 40% of the empty cross-sectional area in the pipe. When the metal hose line is long or has a bend, in order to prevent the wire from being damaged due to excessive resistance during threading, the distance between the two junction boxes or cable pull boxes is stipulated: no more than 30m when there is no bend; no more than 20m when there is a bend. ; When there are two bends, it shall not exceed 15m; when there are three bends, it shall not exceed 8m. When the above requirements are exceeded, a cable pull box (junction box) should be installed or the diameter of the wiring pipeline should be enlarged. The metal shell of the metal hose should be reliably grounded, the pipeline and the grounding wire should not be welded together, a special grounding card should be used for grounding, and the metal hose should not be used as an electrical grounding wire.