Cable Termination Bottom Treatment: How to Prevent Ground Settlement from Stressing Cable Terminations

1. Introduction

When an underground cable line terminates on a tower or pole, the transition from the buried cable trench to the overhead termination is a critical construction detail. After backfilling, the soil around the tower foundation and the trench will settle to a certain degree. If the cable near the bottom of the termination is laid too tight, this settlement will directly pull on the termination, causing mechanical stress on the termination body, the cable insulation, and the sealing point — in serious cases leading to sheath damage or even termination failure.

Two typical site practices for the cable at the bottom of a termination are shown below. The key question is: which one prevents stress on the termination caused by ground settlement?

2. Method 1 — Direct Rise from the Trench

In the first practice, the cables (protected by corrugated ducts) come out of the cable trench around the tower base and rise along a short, almost vertical path directly into the bottom of each termination. The routing is simple and the trench layout is compact, but almost no slack is reserved in the cable. Any settlement of the backfilled soil or the tower foundation is transmitted almost directly to the termination as a pulling force.

Figure 1 Cables in corrugated protective ducts laid around the tower-base trench before rising to the terminations.

Figure 2 The cables rise almost vertically from the pit directly into the bottom of each termination, with little reserved slack.

3. Method 2 — Curved Trench Routing with Reserved Slack

In the second practice, the cables are first routed through a curved, S-shaped masonry trench around the tower base before rising to the terminations. This serpentine routing deliberately reserves a generous slack section in the cable. When ground settlement occurs, the movement is absorbed by the slack loop, so no significant tensile stress is transferred to the termination or the cable body.

Figure 3 Curved (S-shaped) brick trench under construction around the tower base.

Figure 4 With the slack reserved, the cables rise to the terminations through gentle bends instead of a taut, straight pull.

4. Comparison of the Two Methods

5. Recommended Good Practice

1. Always reserve a slack section near the bottom of every cable termination; never pull the cable taut into the termination.
2. Where backfill settlement is expected (newly filled ground, tower foundations), route the cable through a curved or serpentine path so that settlement movement can be absorbed.
3. Protect the transition section with corrugated ducts or other suitable sleeves to avoid sheath damage during backfilling and settlement.
4. Backfill the trench carefully and compact the soil in layers to minimize future settlement.
5. Check the slack and the fixing points after the first rainy season, when most of the settlement takes place.

6. Conclusion

The difference between the two methods comes down to one simple principle: leave the cable some room to move. A directly rising cable transfers every millimeter of ground settlement into mechanical stress at the termination, while a curved routing with a reserved slack section absorbs the movement safely. When installing or accepting cable terminations, pay special attention to this often-overlooked detail at the bottom of the termination — a small construction detail that protects a major investment.