Core rules for underground cable installation: choose proper method (direct-buried / conduit / trench-tunnel), burial depth ≥0.7 m (≥1 m for farmland), use armoured cables, sand bedding + protective slabs, markers and reliable earthing. Comply with GB 50217 & GB 50168.
Main installation options
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Direct-buried: ≤6 cables, low-excavation sites. Armoured cable required. 100 mm fine sand above & below cable, concrete cover slabs. Markers every 50-100 m, at bends, joints and building entrances.
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Conduit / duct bank: heavy-traffic, congested underground or explosive-hazard zones. Conduit inner diameter ≥1.5× cable OD. Add sleeves for road/railway crossings, extend ≥0.5 m past roadbed. Fit manholes for bends, branches and runs >100 m.
- Cable trench / tunnel: high-density cable areas. Flat dry base, layered supports (separate power & control cables). Parallel spacing ≥1 m from heat pipelines; drainage and anti-corrosion required.
Direct-buried key steps
- Route survey & trenching: remove sharp debris, soft trench bottom, avoid corrosion / stray current / heavy crushing.
- Bedding: ≥100 mm soft soil / fine sand.
- Laying: armoured cable (YJV22). No ground dragging. Min bending radius ≥12-15× OD, leave serpentine slack.
- Protection: another ≥100 mm sand layer + concrete slabs (50 mm overhang each side); warning tape for urban sites.
- Backfill: layered compact non-corrosive soil, no stones.
- Earthing & marking: armour both-end earthing ≤10 Ω; permanent markers at joints, bends and every 50-100 m straight run.
- Cross-road / railway: protective conduit, conduit top ≥1 m under road surface, end water-block sealing, ≥1 % drainage slope.
Key notes
- Direct-buried must use armoured cables; non-armoured cables have insufficient mechanical protection.
- Depth: ≥0.7 m non-frozen ground, ≥1 m farmland; lay below frost layer in cold regions.
- Keep minimum clearance (≥0.3 m from underground foundations); do not lay directly above / under pipelines.
- Complete concealed-work inspection before back filling.
- Design and briefing per GB 50217 and GB 50168; no construction without formal scheme.
