How to calculate the wire size for wiring?

  • Dec 26, 2019
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In the houses of the Soviet construction wiring is outdated and no longer provides the full functions entrusted to it. Due to the conglomeration of household electrical appliances there is a tendency to an increase in electricity consumption, which in turn leads to an increase in load on the wiring. Sooner or later the power reserve is exhausted, and then the accident can not be avoided.

Prevent the possible consequences of a fire or its wiring fault is possible by replacing the old wiring. In order to properly perform upgrades, you must know how to calculate the cross-section of wires for wiring. The fact that the thin wires of the installation does not solve the problem, and the acquisition of the wiring with a large margin will entail additional costs.

A simple method of calculation

There are several ways to calculate the wire:

  1. calculating electric power consumers;
  2. largest input current;
  3. calculations based on undervoltage.

Consider the most simple and accessible method of calculation for each home wiring - of the total capacity of electrical appliances.

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Theory

Electric current passing through the conductor meets resistance, overcoming which it performs the operation: A = U × I × t, where A - work, U - line voltage, I - current intensity, t - time. The result is a heat conductor.

From the well-known Ohm's Law, which holds for the chain portion it follows that U = I × R, then A = U × I2 × R × t, where R - resistance of the conductor. Hence P = A / t = U × I2 × R. The formula shows that the power on the circuit can be reduced by reducing the resistance.

Geometrically conductor resistance is: R = ρ * ( l / S), where ρ - the resistivity of the conductor material, l - the length and S - cross-sectional area. Thus, the resistance (and hence on the output circuit portion) can be reduced by increasing the cross section.

As in practice, define the cross section

Methods of calculating the cross section of the conductor, in practice, consists of two stages:

  1. The calculation of the total power of all consumers of electricity in the house according to the formula: P = (P1 + P2... +... Pn) × K × J, where P1 +... + Pn - the power of each appliance, K - ratio (dimensionless) indicating the percentage of the equipment involved (of the total cash in the home), J - power headroom factor (usually J = 1,5... 2).
  2. Determining the cross-section of the table (Fig. 1).

In the above formulas coefficients determined by practical trials. In particular K typically less than 0.8 (80%). This means that the cash in the house is not used appliances at the same time. In fact, no doubt you would include air-conditioning and heating device at a time.

Power reserve (J) Should also be considered for the future. After all, energy consumption is growing every year. If you do not take into account growth in some years may be required to strengthen the wiring.

By calculating according to the formula total power of all the users in the table readily determine the desired wiring section.

Picture 1. Sizing Table
Picture 1. Sizing Table

Note

The calculated cross section applicable for the circuit portion from the meter to the first junction box. If you want to save money, is evaluated separately for each section of the room. For example, in the kitchen the most energy-consuming devices, respectively, conductor cross-section there will be more.

In other rooms, general can do minimum cross-section, for example, for lighting a bathroom and a toilet. Approximate wire size for different users, see Fig. 2.

It is not necessary to save on wiring to sockets. If today they are little used, not the fact that they will not be involved tomorrow solid load.

Figure 2. Approximate wire size for different customers
Figure 2. Approximate wire size for different customers

In order to save, you can instead use single-core multi-strand wire. (Fig. 3) In the steady state this posting will last a long time, and the price it lower.

Figure 3. solid conductors
Figure 3. solid conductors