Overhead Line Construction
Domain 6 - Overhead Line Construction. This domain covers survey, pit digging, pole erection, stays and fittings - the physical work on which later stringing depends.
Sequence and rules
- Survey the route, verify clearances and check for underground services at every proposed pit, then peg pole positions with offsets.
- Excavation depth is commonly one-sixth of pole length plus about 0.3 m: roughly 1.5 m for an 8 m pole, 1.8 m for 9 m, 2.0 m for 11 m in ordinary soil, deeper in loose ground.
- Erect with plumb and line, checking verticality in two directions; backfill in 150–200 mm layers with soil and stones, ramming each layer, and add concrete at the base in soft soil.
- Fit cross-arms, insulators, pole-top brackets, danger plates and anti-climbing devices before stringing; number the pole and update the asset register.
- Stays go opposite the resultant pull, at about 45°, with a stay insulator and a buried anchor block or rock anchor.
Worked example
A 9 m PSC pole: embedment = 9/6 + 0.3 = 1.8 m, leaving 7.2 m above ground. With a 0.6 m cross-arm and 0.2 m pin insulator the pin sits at 6.4 m; even with 1 m sag the conductor is at 5.4 m, only just above the 5.2 m minimum. A road crossing at this location therefore needs a taller pole or a stay-supported section, not a tighter conductor.
Traps
- Setting a stay in the direction of the pull instead of against it.
- Shallow pits, no ramming, or concrete placed only at the top.
- Erecting poles before checking underground services.
- Omitting anti-climbing devices or danger plates near habitation, which breaches statutory requirements.