3 principle: How to choose wires according to their section and power? Bashny.Net

The choice of wire size is an important design stage of power supply of the house or apartment. With insufficient cross-section of the wire is overheating, which can lead to melting of insulation and short circuit, the consequences of which are unpredictable.

Wire size selected based on the magnitude of currents flowing through them and can be determined from tables or by calculation. Table of sections of conductors Requirements for wiring are indicated in the "Regulations for electrical installation" (PUE). In the same normative document has tables with the maximum permissible currents depending on the conductor cross-sections and operating conditions.

We must note that according to the EMP, the cross section of copper wires for residential buildings shall be not less than 2.5 sq mm to meters and 1.5 sq. mm after them. Before wiring read electrical safety rules relating to houses. Compliance with these requirements will improve the reliability of power supply and avoid claims inspection services.

 





Wires rated load current depends on cooling conditions of the conductors. Wire laid in the walls, ducts and pipes, not blown by air, so slower cooling. Thick wires give off heat worse than thin and sustain a lower current density. The current density is determined by dividing the allowed current conductor cross-section. For aluminum wires, it is within 5 — 10 A/sq. mm for copper — 7 — 15 A/sq. mm. Multiplying the current density at the load current you can determine the required wire size.

Use the wiring for the flat copper wires — they are less oxidized and are not broken at the folds, therefore, have greater reliability.

The use of aluminium in hazardous occupations prohibited for good reason. Calculate the wire size you need to start with determine the total power load on the mains. It is especially important to consider the powerful consumers of the electric energy having the following characteristics: iron — 1 — 2 kW; washing machine — up to 2 kW; vacuum cleaner — 1 — 2 kW; water heater — about 2 kW; furnace — 1 — 2 kW; microwave — 0,6 — 2 kW, electric — 2 kW; air-conditioning — up to 3 kW; the refrigerator is about 1 kW; electric heating boiler — 2 — 5 kW; lighting — the power of one light bulb, multiplied by their number. The power of the electrical devices can be specified in the operating instructions. Calculating the total capacity of consumers and by dividing its value on a voltage of 220 volts, determined by the load current.

Further, the tables or the current density we find the cross section of the conductors.

When calculating the power you need to keep in mind that not all consumers are included at the same time — if the boiler heating, air conditioning nobody uses. This fact can be taken into account by multiplying the total power by a factor of demand. Experiments have shown that for apartments with a total capacity up to 14 kW it is equal to 0.8, up to 20 kW — 0,65 up to 50 kW — 0.5. For example, consider choosing wire size from the junction box to the kitchen outlets. The kitchen has a refrigerator with a capacity of 1 kW, dishwasher — 1 kW, electric — 2 kW microwave oven — 0.8 kW electric oven — 2 kW and air conditioning — 2 kW.

The total capacity of 8.8 kW. Multiply this value by a factor of 0.8 to demand and receive of 7.04 kW. Converting kilowatts to watts (1 kW = 1000 W) and the designated load current: I = 7040/220 = 32 A. the table for hidden wiring selectable copper twisted pair wire of 3 sq. mm aluminium — 5 mm sq. the same section obtained by dividing the current average values of its density. Sometimes there is a wire of the unknown section. Knowing the diameter, it is easy to determine the size according to the formula S =0,785D2, where D is the conductor diameter. For stranded conductor, the result is multiplied by 0,785. published

 

P. S. And remember, only by changing their consumption — together we change the world! ©

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Source: vk.com/p.obrazovanie?w=wall-67888368_28480