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

Each qualified electrician, having learned the value of the expected load on the wiring, can immediately make a choice of the cross-section of the current cable. The task is not difficult, it is decided to solve it in any educational institution of a technical profile, from elementary to higher. In doing so, it should be remembered that when choosing a cable, it is preferable to make a mistake more than the smaller side.

At industrial enterprises, all necessary calculations are made by professionals who have a special electrical engineering education, so the network parameters are determined not by the principle "we build what we have", but optimized, taking into account the minimization of costs while observing technical regulations. There are standard rules for the installation of electrical installations, here they are guided by engineers, making a choice of the cross-section of the current cable. PUE (Rules for the installation of radio installations) are the reference book of each electrician-designer.

Difficulties arise when people who do not have sufficient qualifications, try to independently install or replace the wiring in their home or at the dacha. Selection of the cable section is a responsible business. Doing it wrong, at best, you can face the need to break the integrity of the plaster and change the burnt wire. On the worst options like a fire do not even want to mention.

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

So:

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

R = (ρ x L) / S,

Where:

• R is the resistance value measured in Ohms;
• Ρ is the resistivity, that is, the resistance of the conductor from a given material 1 m long and 1 mm ² in cross section;
• L - length of the wiring, m;
• S is the cross-sectional area of the conductor, mm ² .

The resistivity is different for different metals. For example, in silver it is approximately 0.016 ohm x mm ² / m ² , in platinum 0.1 and in gold 0.02. However, the choice of cable cross-section for current does not involve the use of precious metals (the reason is clear).

Now about the load. In order not to err in the magnitude of the current that is to 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 is the power measured in Watts;
• U is the voltage of the network (we have 220 volts);
• I is the current value (Ampere).

In fact, the Volt-Amperes differ from watts, but in conditions of living rooms, in which the active loads predominate (incandescent lamps, electric heaters, etc.), this difference can be neglected.

By adding the power of all electrical appliances, you can set the value of the load in Watts, which will make the choice of the cross-section of the cable by current.

Then everything is simple. Since gold or platinum wire is unlikely to be used even by Abramovich, other metals, more common, are of interest. If the choice is made in favor of an expensive cable, copper, then every square millimeter (or as the electricians express the "square") is able to pass up to 10 amperes. Aluminum properties are more modest, 8 amperes, but it is cheaper.

As a rule, the choice of the current cable cross-section 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-consuming consumers require separate cable entries with a conductor cross-section of 2.5 mm ² .

It is important to remember that it is impossible to connect a copper wire with an aluminum wire. Such twisting with time loses conductive properties.