When laying cable lines in the ground, there are several different ways to provide mechanical protection for cables. The following options are known:
1️⃣ Covering the cable with bricks on top.
2️⃣ Covering the cable with polymer tiles/covers.
3️⃣ Laying cable in pipe/duct/conduit.
4️⃣ Laying cable in tray/trough.
5️⃣ Laying cable in concrete tunnel.
Another way of protection is to lay armored cable instead of ordinary cable.

In 6-20 kV networks, options 1-3 are usually used, whereas in 35-500 kV networks – options 3-5. Thus, laying in pipes (3) is the most universal method used in networks of any voltage class. However, today let’s talk only about 6-20 kV networks and discuss options 1 and 2.

The top photo shows a two-circuit cable line. The two circuits are separated from each other by a vertically mounted brick (protection against the effects of a short circuit). Also, each of the circuits is covered with bricks from above. However, you can see that the bricks were laid away from the cables and do not provide protection. This could happen for one of the following reasons:
✅ At first, the cables were covered with sand, and only then bricks were placed on top. That is, the bricks were laid when the cable was no longer visible. As a result, a number of bricks were laid with a shift in the relative location of the cables.
✅ The displacement of cables and bricks could be facilitated by the fact that the sand around the cables was not mechanically compacted after cable laying.
✅ There is groundwater that has displaced cables and bricks from each other.

One way or another, the bricks were displaced relative to the cables. A similar situation happens in cases where the cables were covered with tiles (left photo). The only protection option that is guaranteed not to shift relative to the cable is laying cables in pipes (right photo).

It’s time to point out that not every pipe is suitable for cables. Cables are not allowed to be laid in pipes from recycled materials and in cold water pipes, since such pipes are designed for 40°C, and the cable can be up to 80-90°C. The requirements for pipes are justified in Chapter 12 of the book.