Temporary Power Use 013: Summary of Distribution Box Issues Found at the Construction Site

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This post was last edited by Shutong on 2024-7-7 09:56. A summary of the issues found with distribution boxes at chemical plant construction sites: First, distribution boxes are installed without verifying their model or conducting inspections/acceptance procedures. After installation, the following problems often occur: 1. The electrical circuit diagrams are missing, and the parameters of the components do not meet the required standards. 2. The distribution panel lacks dedicated grounding bolts, and the cross-sectional area of the protective wire is small. 3. The doors that can be opened are not securely connected to the metal frame using bare copper wires; the wires are not firmly attached to the appliances, their diameter does not meet the requirements, and there is no color coding for the wires. 4. The layout and spacing of the devices are unreasonable, and there are no N and PE terminal rows, etc. Further modifications that delay the schedule also affect quality. Measures: Verify, inspect, and accept each item in accordance with the drawings and technical documents; only after confirmation of compliance should proper installation be carried out. II. Irregular pipelines entering and leaving the distribution box – The pipelines connecting to and coming from the distribution box are arranged haphazardly, and the openings made cause damage to the box body ； The openings of the wire conduits installed inside the floor-mounted distribution box are too low, allowing water and debris to enter the conduits easily. Measures: (1) Before installation, arrange and sequence the inlet and outlet pipelines properly; the openings and damaged areas of metal distribution boxes must be treated to prevent corrosion. Electrical welding shall not be used to create holes for the inlet and outlet wires – one hole should be made for each pipe, and a protective sleeve should be installed at the pipe end. (2) The wire protection tubes in the floor-mounted distribution box should have their openings at a height of 50–80 mm above the base surface of the box. The pipes should be arranged neatly, with flared ends; the openings of the pipes should be sealed off from cables to prevent water, dust, and pests. (3) The inlet tube should not extend more than 2–3 mm into the box; it is prohibited for the second layer of panels inside the box to press against the tube opening, as this can prevent wires from entering the box. Thirdly, the circuit names are not clearly marked – the switch circuits in the distribution box lack names, or the markings are unclear or missing. There are also no labels on the incoming and outgoing cables, which poses many difficulties in use and maintenance, and increases the risk of accidental switching on of circuits, leading to accidents. Measure: In accordance with the relevant standards, complete the nameplates on the distribution boxes; a circuit diagram should be attached inside the box door, and it is advisable to indicate the name of each circuit on the switches as well. Durable labels can be used for this purpose ； Clear labels should be attached to the incoming and outgoing cables and wires. IV. The wiring inside the box is messy, and the reserved wires are too short. The wiring is disorganized and unplanned, with wires running in random directions, which can easily lead to accidents ； The sizes of the wires reserved inside the box vary, which makes maintenance inconvenient and repairs difficult, affecting both the appearance and functionality. Measures: (1) The wiring inside the box should be arranged in a planned and organized manner, in a neat and attractive style that facilitates maintenance; wires should be bent using molds, and it is strictly prohibited to bend them too sharply ； The wires are coiled straight around the perimeter of the box and tied into bundles. (2) The size of the reserved wires should be approximately half the perimeter of the enclosure, with consistent bending radii for wires in the same row or column; it is prohibited for the wires inside the enclosure to run in straight lines or take shortcuts. V. No N and PE busbars are installed in the lighting box; lighting distribution boxes do not have N and PE busbars either. The neutral wire and the ground wire are connected separately, which prevents safe operation of the electrical circuit. Measure: Inside the lighting distribution box, a busbar equipped with insulated posts should be installed for the dedicated neutral wire (N wire), as well as a busbar for the protective earth wire (PE wire). The neutral wire and the protective earth wire should be connected to these busbars; they must not be twisted together. Each terminal should accommodate a maximum of 2 wires, and they should be numbered to facilitate maintenance.