What are the precautions for mineral-insulated fire-resistant cables?
Release date:
2022-08-01 11:12
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What are the precautions for mineral-insulated fire-resistant cables?
1. Laying out Mineral-insulated fire-resistant cable Beforehand, check whether the cable is intact and whether the insulation resistance meets the standard requirements.
2. When laying mineral-insulated fire-resistant cables, in addition to support-based installation and fixing at the supports, the distance between fixing points can be determined according to the recommended values listed in the table for exposed locations. If cables of different sizes—small, medium, and large—are arranged in the same direction, for aesthetic and neatness purposes, they may be fixed either according to the standards for small-sized cables or at uniform spacing intervals. When cables are installed at an incline, if the angle between the cable and the vertical direction is 30 degrees or less, they should be fixed at vertical spacing intervals; if the angle exceeds 30 degrees, horizontal spacing intervals should be used instead.
3. When laying mineral-insulated fire-resistant cables, secure them at both sides of corners and intermediate joints wherever possible.
4. When calculating the required length for cable laying, a 1% margin should be taken into account.
5. For parts of the cable that may suffer mechanical damage during operation, appropriate protective measures should be taken.
6. When laying single-core cables, each cable should be installed individually. After straightening each group of cables, arrange and secure them with ties spaced 1 to 1.5 meters apart.
7. When laying copper-sheathed cables in corrosive environments, or when they are partially buried or installed through conduits, a polyethylene outer sheath or a low-smoke, halogen-free outer sheath should be used.
8. During the wiring process, if the cable breaks, the cable end should be temporarily sealed immediately.
9. When cables are laid in a straight line or when the connected electrical appliances may vibrate, expansion loops should be installed wherever permitted.
10. Mineral-insulated fire-resistant cables generally do not require conduit installation; however, they must be installed in conduits under special circumstances (single-core cables are not permitted to be run individually inside metal conduits).
11. You can bury it, but avoid having any intermediate joints. If joints are unavoidable, make sure they are waterproof.
12. For large-section single-core cables, eddy current elimination measures should be implemented when used in AC power grids. Under the influence of alternating current, the copper sheath can generate transverse eddy currents, leading to energy losses. When the line load is heavy and requires two or more cable groups, the cables can be arranged as shown in the diagram below. However, the distance between each group should be twice the outer diameter of the cable, and the connecting leads within each group must be positioned at the same location. Additionally, when cables enter distribution boxes/cabinets, holes should be drilled in the cabinet panels to securely fasten the cables. At the same time, to prevent eddy currents from forming on the cabinet panel surface, the panel should either be perforated as shown in the diagram or fitted with non-magnetic material spacers for cable fixation. Such cable supports are typically made from aluminum or copper busbars, which are pre-drilled accordingly. If flat steel or angle steel is used to fabricate the supports, the same drilling method described above should also be applied to avoid the generation of eddy currents.
13. When laying single-core cables, there must be a clearance of at least 2 times the cable's outer diameter between each cable. If no clearance is left, the current-carrying capacity reduction factor should be taken into account.
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