Copper (CU) and aluminium (AL) are the two main materials for the current-carrying parts of the cable, that is, for the core and the screen. The features of AL are as follows:
1️⃣ AL is up to 3-4 times cheaper than CU.
2️⃣ AL is 3 times lighter in weight than CU.
3️⃣ AL resistivity is 1.6 times higher than that of CU.

Factors 1️⃣ and 2️⃣ make AL very attractive, despite 3️⃣. In practice, AL is widely used for cable cores, especially:
✅ For medium voltage cables (the insulation is not very thick / expensive there, and therefore the cost of the cable quite noticeable depends on the cost of metals).
✅ For cables with a core cross-section of up to 1200 mm2.

As for the screen, everything is not so simple in the CU and AL pair, and the choice of material depends on the screen design:
➡️ CU is more often used for a wire screen.
➡️ AL is more often used for a screen made of tape (foil).
➡️ AL is more often used for a corrugated screen/sheath.

Let’s focus on the wire screen. Bending of wires is important when installing cable terminations and joints. The reasons for the widespread use of CU for wire screens are probably related to the fact that CU wires can be bent repeatedly, and this does not lead to their breakage. Despite what has been said, periodically there are ideas to make cables with screens not from CU wires but from AL wires.

Let’s consider an interesting case of a 10 kV line. Initially, the cable had a screen made of AL wires. However, when, due to damage to a section of cable, it was necessary to replace this section with a new cable, it turned out that the supply of a short length of cable with an AL wire screen was a problem (due to the fact that this screen design is not typical for the industry). As a result, a piece of cable with a CU screen was used for repairs. Such a segment having a CU screen was inserted using two cable joints into an existing cable having an AL screen. It was a bad idea.

The fact is that in medium-voltage networks with small cable cross-sections, the screens inside the joints are connected not with “bolt connectors”, but with special “clamping rings”. Thus, in the two new joints of the considered line, rings were used, which compressed the wires of the CU and AL screens together. The results were electrochemical processes, increased resistance of the connection, overheating, and short circuits.

What conclusions can be drawn? If someone wants to use a cable with an AL wire screen, he is recommended to prepare answers for the following questions:
👉 Will it be possible to repair a cable with such a unique AL screen? (repairs by a standard cable with CU screen may be problematic).
👉 Will it be possible to install joints? (when inserting a section with a CU screen, the AL and CU wire screens should not be connected directly to each other; for example, a bimetallic connector may be required there, but it is rarely found for cables of a small cross-section).