Distribution box (panel) installation project
This chapter applies to the installation of building electrical distribution boxes (panels).
I. Material Requirements
1. Metal distribution box (panel): The box body should have a certain mechanical strength, the perimeter should be flat and undamaged, the paint should not be peeling off, the thickness of the second-layer base plate should not be less than 1.5mm, flame-retardant plastic board should not be used as the second-layer base plate, all kinds of appliances inside the box should be firmly installed, the wires should be neatly arranged and firmly crimped, and there should be a product certificate of conformity.
2. Flame-retardant plastic distribution boxes (panels): The box body should have a certain mechanical strength, the perimeter should be flat and undamaged, the thickness of the double-layer insulating base plate should not be less than 8mm, and there should be a product certificate of conformity.
3. Galvanized materials: angle steel, flat iron, sheet metal, machine screws, wood screws, bolts, washers, round nails, etc.
4. Insulated wires: The specifications and models of the wires must meet the design requirements and have a product certificate or "CCC" certification.
5 Other materials: electrical instruments, fuses (or fuse sheets), terminal blocks, insulating nozzles, card frames, soft plastic tubes, plastic tape, black tape, anti-rust paint, solder, flux, welding rods, cement, and sand.
II. Main Equipment
1. Pencils, measuring tapes, squares, spirit levels, steel rulers, plumb bobs, buckets, brushes, shovels, high stools, etc.
2. Hand hammers, chisels, hacksaws, saw blades, wood chips, flat files, round files, wire strippers, needle-nose pliers, crimping pliers, adjustable wrenches, socket wrenches, Allen wrenches, tin pots, tin spoons, etc.
3. Bench drills, electric drills, drill bits, wood drills, bench vises, workbenches, electric furnaces, welding tools, insulating gloves, iron shears, punches, megohmmeters, tool bags, toolboxes, high stools, etc.
III. Working Conditions
1. Reserve the installation location of the concealed electrical box in the civil engineering structure.
2. When assembling the electrical box panel, plastering, spraying, and painting should all be completed.
IV. Operating Procedures
(I) Process Flow:
(II) Installation requirements for distribution boxes (panels):
1. Distribution boxes (panels) should be installed in safe, dry and easy-to-operate locations. When installing distribution boxes, the bottom opening should generally be 1.5m from the ground. Within the same building, the height of similar panels should be consistent, with an allowable deviation of 10mm.
2. All wooden blocks and iron parts required for installing the distribution box (panel) should be pre-embedded. All pre-embedded iron parts should be painted with anti-rust paint and properly grounded. Wall-mounted distribution boxes (panels) should be fixed with metal expansion bolts.
3. All doors of metal distribution boxes (panels) with appliances should have a clearly visible and reliable bare soft copper wire grounding.
4. Wiring on the distribution box (panel) must be neatly arranged and bundled, with clips securing both ends of moving parts. Sufficient slack should be left for both incoming and outgoing wires from the panel to facilitate maintenance.
5. The stripped part of the wire should not damage the wire core or make the wire core too long. The wire crimping head should be firm and reliable. Multi-strand wires should not be coiled and crimped. When using crimping terminals and set screws, multi-strand wires should be tinned before crimping. The number of wire strands should not be reduced.
6. All manual and electrical control devices installed on the panel of the distribution box (panel) should not have any moving parts energized when the circuit is open (except in special circumstances).
7. For vertically mounted electrical appliances, the power supply should generally be connected to the top and the load to the bottom; for horizontally mounted appliances, the load should be connected to the left side (facing the panel) and the right side.
8. The power indicator lights on the distribution box (panel) should be connected to the outside of the main switch and should be equipped with a separate fuse (power supply side). The switch on the panel should correspond to the branch circuit, and a card frame should be installed below it to indicate the circuit type and capacity.
The neutral wire in 9TN-C should be repeatedly grounded at the incoming π junction box.
10. The distribution box (panel) is equipped with neutral (N) and protective earth (PE) busbars respectively. The neutral and protective earth wires are distributed through the busbars, and the crimping points are made with hex socket screws.
11. The exposed screw hole in the center of the base of a magnetic plug fuse should be filled with insulation to prevent discharge to ground. Magnetic plug fuses must not have exposed metal screws; they should be filled with sealing wax or silicone rubber.
12. When there are no design requirements, and the material used for the PE line is the same as that for the phase line, the cross-section should be selected according to the thermal stability requirements and should not be less than the values listed in the table below.
13. The busbars on the distribution box (panel) should be painted with yellow A phase (L1), green B phase (L2), red C phase (L3), and light blue (N neutral wire). The yellow-green bicolor wire is the PE wire.
14. Electrical appliances and instruments on distribution boxes (panels) should be secure, level, clean, evenly spaced, with no loose terminals, flexible opening and closing, and complete parts.
15. The installation of distribution boxes (panels) should be firm and level, and the allowable deviation of their verticality is 1.5‰.
16. Vertical cabinets should be installed in a dedicated room or with a fence, and the iron fence should be grounded; the back should be at least 800mm from the wall (special cases should be handled according to the design); the foundation steel should be straightened and fixed before installation, and its horizontal error should not exceed 1mm per meter, and the total error over the entire length should not exceed 5mm. The bottom of the panel should be at least 500mm from the ground.
(III) Marking and positioning: Locate the distribution box (panel) according to the design requirements, and mark the positioning according to the external dimensions of the box (panel); the purpose of marking and positioning is to more accurately locate the embedded parts, or to locate the position of the metal expansion bolts, in the case of pre-embedded wooden blocks or iron parts.
(iv) Surface-mounted electrical control boxes (panels):
1. Fixing the distribution box (panel) with an iron frame: Straighten the angle steel, measure the dimensions, draw the sawing line, cut and bend it, drill holes, and weld. Use a square to align the bends, then use electric (gas) welding to weld the joints firmly. Make the embedded end into a dovetail shape, remove rust, and apply anti-rust paint. According to the elevation, use high-grade cement mortar to firmly embed the dovetail end of the iron frame. When embedding, pay attention to the straightness of the iron frame and the distance between holes. Use a plumb line and level to measure accurately before stabilizing the iron frame. The distribution box (panel) can only be installed after the cement mortar has solidified.
2. Fixing the distribution box (panel) with metal expansion bolts: The distribution box (panel) can be fixed to a concrete wall or brick wall using metal expansion bolts. The method is to locate the precise fixing point according to the chalk line positioning in Section 9.4.3, and drill a hole at the fixing point using an electric drill or impact drill. The diameter of the hole should be just enough to embed the expansion tube of the metal expansion bolt into the wall, and the hole should be straight and not crooked.
(v) Fixing of distribution boxes (panels):
1. When fixing surface-mounted electrical boxes (panels) to concrete or brick walls, two methods can be used: concealed conduit and concealed junction boxes, or surface-mounted conduit. If there is a junction box, first clean out any debris inside the box, then straighten the wires, distinguish the branches and phase sequence, and bundle them together according to the branches. After the box (panel) is in the correct position, lead the wire ends into the box, strip the wire ends, and then crimp them one by one to the device.
Simultaneously, press the protective ground wire and neutral wire onto the PE busbar and N busbar, and fix the box (panel) after adjusting it to be straight. After the panel with many electrical appliances and instruments is installed, use instruments to check for any errors. After adjusting and confirming that there are no errors, test power on the panel and fill in the location and number on the cards in the card frame.
2. When fixing distribution boxes (panels) on wooden or light steel keel wall panels, reinforcement measures should be taken. If the piping is concealed within the wall panel and there are concealed junction boxes, the box opening should be flush with the wall surface. Fireproofing treatment should be applied to wooden wall panels; fire-retardant paint can be used for protection. Except for the above requirements, the fixing methods are the same as described above.
3. Fixing the concealed electrical box. First, determine the elevation and horizontal dimensions of the box according to the pre-drilled holes. Fix the box securely, then fill the surrounding area with cement mortar and smooth it. After the cement mortar has hardened, install the panel and mounting plate. If the bottom of the box is flush with the exterior wall, a metal mesh should be fixed to the exterior wall before plastering. Do not plaster the bottom plate of the box. The installed panel must be flat, with uniform and symmetrical gaps around it. The mounting plate (door) must be straight and not crooked, and the screws must be vertical and evenly stressed.
(vi) Insulation resistance test:
After the distribution box (panel) is installed, use a 1kV megohmmeter to perform insulation resistance tests on the lines. The tests include tests between phase wires, between a phase wire and the neutral wire, between a phase wire and the ground wire, and between the neutral wire and the ground wire. Two people should perform the tests, record the results, and include them in the technical documentation archive.
V. Quality Standards
(I) Key Controlled Items:
1. The grounding (neutral) protection measures and other safety requirements of the equipment must comply with the provisions of national construction specifications.
The cross-sectional area of the wires on both sides of the internal pressure plate crimping point is the same; no more than 2 wires are connected on the same terminal, and anti-loosening washers and other parts are complete.
3. The leakage current switch is flexible and reliable, with an operating current not exceeding 30 mA and an operating time not exceeding 0.1 S.
4. Set up N-line and PE-line busbars. The neutral and protective wires are distributed through the busbars. The wire clamping points should use internal hex screws.
Inspection method: Observe and check the installation records.
(II) General Items:
1. The location is correct, all parts are complete, the openings in the box are appropriate, the cuts are neat, the concealed distribution box is flush against the wall (box cover), the paint is intact, and the inside and outside are clean.
The wiring inside the two boxes (panels) is neat, the circuit numbers are complete, the labels are correct, and the PE line is installed securely and clearly.
There are no flammable materials inside or outside the 3 boxes (panels).
Test method: visual inspection.
(III) Allowable deviation items: The allowable deviation for the verticality of the distribution box (panel) installation is 1.5‰.
Inspection method: Use a plumb line and measure with a ruler.
VI. Finished Product Protection
1. After the distribution box (panel) is installed, protective measures should be taken to avoid damaging or soiling electrical appliances and instruments.
2. When installing the box (panel) panel (or faceplate), be sure to keep the wall surface clean.
VII. Issues to be noted
1. The elevation or verticality of the distribution box (panel) exceeds the allowable deviation: This is caused by inaccurate measurement and positioning or uneven ground, and should be corrected in time.
2. Incorrect installation method of iron frame: This is caused by failure to straighten and align the iron frame before installation, or by the offset position of the fixing point during installation. A plumb line should be used to re-align the iron frame before fixing it.
3. The electrical appliances and instruments on the panel are not secure, flat or unevenly spaced, the pressure head is not secure, the pressure head damages the wire core, the pressure head of multi-strand wires is not equipped with pressure terminals, and the card frame is not installed below the switch: screws that are not tight should be tightened, the spacing should be adjusted evenly as required, and the surface should be leveled; the damaged part of the wire core should be cut off and reconnected, multi-strand wires should be equipped with pressure terminals, and the card frame should be installed.
4. Insufficient protective grounding wire cross-section, or series connection of protective grounding wires: This should be corrected according to the specifications.
5. Untidy wiring: Wiring should be bundled together according to branch lines and fixed neatly.
6. Distribution box (panel) lacks parts: All necessary parts for installation should be provided.
7. For iron boxes, long holes should be made by electric or gas welding: one pipe per hole. Holes should not be made by electric welding. The pipes should be neatly inserted into the box, and lock nuts and protective covers should be complete.
8. Excessive gaps around the box: Use cement mortar to fill the box and pipes firmly and securely.
9. Rust on the weld points on the inner wall of the iron box: Rust-preventive paint should be applied.
