Cable lines - ampacity / 28.08.2025

Ampacity of cable line in duct

In medium voltage networks of 6-35 kV, at least the following methods of laying single-core cables in the ground are known:1️⃣ Directly in the ground;2️⃣ In the ground in a common pipe;3️⃣ In three different pipes arranged in a bundle. In 110-500 kV high voltage networks, option 2️⃣ is missing, and only options 1️⃣ and

Read More
Cable lines - screen bonding / 07.08.2025

Cable ampacity calculation mistake

For medium voltage (MV) line, usually, screens of single-core cables are grounded at both sides. Let us assume that we have two separate MV lines, differing in the mutual arrangement of three single-core cables:Line 1️⃣ – trefoil;Line 2️⃣ – in row. In the conditions of the example, according to the book, we get the following

Read More
Cable lines - ampacity / 11.07.2025

Cable line selection

It is not enough to have money to buy a good cable. It is also important to find the time and knowledge to make the necessary calculations and select the best way to lay a cable line, taking into account the screen bonding type. Today, let’s look at a simple calculation example of a double-circuit

Read More
Cable lines - ampacity / 03.07.2025

The system of correction factors

In cable catalogues, in addition to the main types of cables, there are simplified recommendations on cable selection. They are given as a table with capacity currents for basic laying conditions (Ib), as well as a series of 5-8 additional tables with various correction factors (K). It is important to note that the system of

Read More
Cable lines - ampacity / 09.05.2025

Cable current selection

Our industry has excellent international standards (IEC) and excellent software. Both provide us with high accuracy calculations. However, despite the precise methods, can we be sure of the results of the calculations? Of course not! At least because we don’t always understand which source data to use in calculations. If we do not have accurate

Read More
Cable lines - ampacity / 20.03.2025

Cable block optimisation

Numerous cable lines running next to each other are usually assembled together into so-called pipe blocks. For example, this happens in areas near the switchgear, where up to several dozen parallel lines can be located in one place. Usually, the number of pipes exceeds the number of cables that need to be laid. Such a

Read More
Cable lines - ampacity / 29.11.2024

Cable overheating

Single-core cables of medium voltage 6-35 kV often have simple grounding of the screens on both sides (“solid bonding”). As a result, the cable screens form closed contours, and the magnetic field of the core current induces currents in these contours, that is screen currents. Induced currents (Is) in the screens pass through the screens

Read More
Cable lines - ampacity / 07.10.2024

Three cables arrangement

In 6-35 kV networks, single-core cables are most often arranged in a closed triangle (1), and cable screens have a small cross-section of up to 50 mm2 and a simple solid grounding. Let us figure out what happens if the cables, contrary to the project, are laid not in a closed triangle, but otherwise. Three

Read More
Cable lines - ampacity / 03.09.2024

Selection of double-circuit cable line

The vast majority of cable lines (CL) are double-circuit. Two circuits are needed not only to increase the transmitted power, but also for reliability reasons. If one circuit turns out to be disconnected (for testing, damage locating, repair, replacement), then the second circuit can provide power supply to consumers (to load). Two modes are possible

Read More