Choosing the cable cross-section by current is a simple task, but a responsible one

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Each qualified electrician, having learned the magnitude of the expected load on the wiring, can immediately make a choice of the current section of the cable. The task is not difficult, it is taught in any educational institution of a technical profile, from elementary to higher. At the same time, it should be remembered that when choosing a cable, it is preferable to make a mistake up more than down.

In industrial enterprises, all the necessary calculations are made by professionals with a special electrical engineering education, so the network parameters are determined not on the principle of “lay what we have”, but in an optimized way, taking into account cost minimization while observing technical regulations. There are standard rules for electrical installations, and engineers are guided by them when choosing a cable cross-section for current. PUE (Rules for the design of radio installations) are a reference book for every electrician-designer.

Difficulties arise when people who do not have sufficient qualifications try to independently install or replace wiring in their homeor at the cottage. The selection of the cable section is a responsible matter. Having done it wrong, at best, you may be faced with the need to violate the integrity of the plaster and change the burnt wire. I don't even want to mention the worst options like a fire.

To understand the consequences of a mistake when choosing a cable, you need to familiarize yourself with fairly simple rules based on a school physics course.

So:

The electrical resistance of a conductor is directly proportional to its length and resistivity. The cross section, on the contrary, affects it in the reverse order:

R=(ρ x L)/S, where:

• R – resistance value measured in Ohms;
• ρ - resistivity, that is, the resistance of a conductor made of a given material with a length of 1 m and a cross section of 1 mm2;
• L – wiring length, m;
• S – cross-sectional area of the conductor, mm2.

Resistivity is different for different metals. For example, for silver it is approximately 0.016 Ohm x mm²/m^{2, for platinum it is 0.1, and for gold it is 0, 02. However, the choice of current cable section does not imply the use of precious metals (the reason is clear).}

Now about the load. In order not to be mistaken in the amount of current that will flow in the wires, it is enough to know the simple formula of Ohm's law for a circuit with an active load:

W=U x I, where:

• W - power measured in Watts;
• U- mains voltage (we have it is 220 Volts);
• I – current value (Amps).

Actually, Volt-Amps are different from Watts, but in a residential environment dominated by active loads (incandescent lamps, electric heaters, etc.), this difference can be neglected.

By adding the power of all electrical appliances, you can set the load value in Watts, which will allow you to choose the cable section for current.

Then everything is simple. Since even Abramovich is unlikely to use gold or platinum wiring, other metals, more common, are of interest. If the choice is made in favor of an expensive copper cable, then each square millimeter (or as electricians say “square”) is able to pass up to 10 amperes. Aluminum has more modest properties, 8 Amps, but it is also cheaper.

As a rule, the choice of cable cross-section for current in apartments is made in favor of an aluminum wire with a cross section of one and a half squares (sockets) and half a square (lighting). Electric stoves and other energy-intensive consumers require separate cable entries with a core cross section of 2.5 mm2.

It is important to remember that you cannot connect copper wire to aluminum. Such twisting loses its conductive properties over time.