Each qualified electrician, having learned the magnitude of the expected load on the wiring, can immediately make a choice of the cable cross section for current. The task is simple, it is taught to solve in any educational institution with a technical profile, from primary to higher. It should be remembered that, when choosing a cable, it is preferable to make a mistake in a greater than in a smaller direction.
At industrial enterprises, all the necessary calculations are carried out by professionals with a special electrical education, therefore, the network parameters are determined not by the principle of “lay what we have,” but optimally, taking into account the minimization of costs while observing technical regulations. There are standard rules for the installation of electrical installations, so they are guided by engineers, making a choice of cable cross-section for current. PUE (Radio Installation Rules) are the handbook of every electrician-designer.
Difficulties arise when people who are not qualified enough try to independently install or replace wiring in their home or cottage. The selection of the cable section is a responsible matter. Having done it wrong, in the best case you may encounter 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 an error when choosing a cable, you need to familiarize yourself with fairly simple rules based on a school physics course.
So:
The magnitude of the electrical resistance of the conductor is directly proportional to its length and resistivity. The section, on the contrary, 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 a conductor of this material with a length of 1 m and a cross section of 1 mm 2 ;
- L is the 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 about 0.016 Ohm x mm 2 / m 2 , in platinum it is 0.1, and in gold it is 0.02. However, the choice of cable cross-section for current does not imply the use of precious metals (the reason is clear).
Now about the load. In order not to make a mistake in the magnitude of the 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 is the power measured in watts;
- U is the network voltage (we have 220 Volts);
- I is the current value (Ampere).
In fact, Volt-Amps are different from Watts, but in living conditions, in which active loads prevail (incandescent lamps, electric heaters, etc.), this difference can be neglected.
Adding the power of all electrical appliances, you can set the load value in Watts, which will allow you to make a choice of cable cross-section for current.
Then everything is simple. Since Abramovich is unlikely to use gold or platinum wiring, other metals that are 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 say “square”) is able to pass up to 10 Amps. Aluminum has more modest properties, 8 amperes, but it is also cheaper.
As a rule, the choice of the cable cross section for current in apartments is made in favor of an aluminum wire with a cross section of one and a half square (sockets) and half square (lighting). Electric stoves and other energy-intensive consumers require separate cable entries with a cross-section of a core of 2.5 mm 2 .
It is important to remember that you cannot connect a copper wire to an aluminum wire. Such a twist over time loses its conductive properties.