Since the school curriculum does not include study of the topic "how to calculate the wire size," then into adulthood, many have no idea how to do it.If the future is related to the specialty in electrical engineering, then a teacher at school will talk about the relationship of electric current and the cross section of the conductor.Otherwise, a person still remains in the dark.Although, at first glance, it may seem that in everyday life there is no need to understand how to calculate the wire size, it is not so.Every person at least once in your life begins to overhaul, including the replacement of household electrical wiring.Of course, you can use the services of repair crews.At the same time, not knowing how to calculate the wire size and simply trusting employees can either overpay for a completely unnecessary cable cross sections (some electrics are mounted with a stock - just to be sure), or subsequently to carry out re-replacement due to incorrectly selected section.It is not necessary to study thoroughly all.It is enough to have only a general idea of how to calculate the wire section to understand why workers choose precisely this section, and not any other.
Let's see what all is necessary to choose the cross section?As is well known, transmission of electrical energy is carried out by metal conductors of steel (LEP), copper, aluminum.The greater the number of electrons passed per unit time per unit length of the wire (a so-called current density), the greater its heat.Thus, when too high a current value and a small cross section will experience a temperature rise of the conductor, which could provoke a fire situation.Heat is always there, but if the current wire size is correct, the temperature remains within acceptable limits.In all of the above as formulas can be expressed as follows.
cross section of conductive material:
S = 2 * 3.14 * (R * R)
magnitude of linear expansion for a solid:
L = L1 * (1 + k * T),
where L1 - lengthat zero degrees Celsius;
T - heating temperature;
k - coefficient of expansion (table value).
value section by heating:
S = 3.14 * ((L1 * (1 + k * T) * (L1 * (1 + k * T))
current density, as already mentioned:
J = I/ S
If we now substitute in the value of S when heated, it becomes obvious that all three values are interconnected, the temperature plays a significant role.
One of the simplest of questions, which are often "stumble" newcomers - a "how to define the cross-sectionWire ". First, using calipers or ruler (accuracy below) determined by the diameter. Then, raising it to the square and multiply by 0.78 (the area of the circle). This is so simple.
But in practice, more important relationship section and electric current.That is, you need to know, for example, what kind of conductor for the house wiring. The current value is determined by knowing the power consumption of the device or the group. For example, if a wall outlet is connected Kettle capacity of 2 kW, its current is 2000 W / 220 V 9A. Now, at a special table in the electrical codes, you can find the desired section.Taken into account the total number of cores in the cable;conductor material (aluminum, copper);laying method (open, pipe cutting grooves);voltage and an allowable current value.For example, copper wire 1 mm sq., Being bricked into a wall, capable of long-term pass a current of 14 amperes, which corresponds to 3 kW (for mains with 220 volts).
dependence of current, power and voltage output from a simple formula:
P = U * I,
where P - is electric power in watts;
U - mains voltage in volts;
I - current in amperes.
Note the units of measurement!The result will be invalid if, for example, instead of the value in watts in the formula to substitute the number of kilowatts.
