How to calculate the cable cross-section by power?
Each electrical network, regardless of its purpose, must withstand the electrical load connected to it for a long time. Both household electrical appliances and industrial electrical equipment can be used as a load.
Household and industrial consumers
Household electrical appliances and devices include lamps, electric kettles, vacuum cleaners, boilers, heaters, personal computers, printers, scanners, televisions, washing machines, kitchen appliances, etc.
Industrial electrical equipment includes electric motors, relays, starters, contactors, power transformers, industrial lighting, etc.
Each device, device and equipment consumes a certain amount of electricity during operation. The amount of consumption depends on the rated and operating power of the device, device or equipment.
Rated power of an electrical product
The power unit is specified in watts or kilowatts. The value of the rated power is indicated either in the passport of the electrical product, or on the product itself.
If this is a household appliance, for example, a kettle, then the rated power consumption can be indicated on a special sticker. For a boiler, the power is indicated in the passport. And for an ordinary incandescent lamp, the value of the rated power is printed on the bulb of the lamp and on the cardboard packaging.
If this is an electric motor for industrial use, then the power (and not only power) is indicated on the nameplate (special metal plate) attached to the motor housing. For power transformers, the power is also indicated on the rating plate.
Calculation of the cross section of an electrical cable or wire
For the correct choice of an electrical conductor through which voltage will be supplied to electrical consumers, it is necessary to know the total number of consumers themselves, the rated power of each consumer, as well as the list of consumers that will work simultaneously. Knowing all this, it will be possible to choose such a conductor cross-section at which the electrical network will be able to withstand the load connected to it.
Conductors of the electrical network can be conditionally divided into two groups. The first group is a common (introductory) cable or wire. The second group is outgoing lines.
Initially, the cross section of the input electrical cable is selected. Because the entire load will pass through the input cable, then its cross section should be larger than that of the outgoing conductors. As for the outgoing conductors, the cross section will depend on the power and number of connected consumers.
Section calculation steps
Household consumers
Let's say the following consumers will be in the apartment:
- lighting (5 incandescent lamps of 100 watts each, 5 incandescent lamps of 75 watts each, 2 incandescent lamps of 65 watts each, one 80 watt fluorescent lamp);
- 100 watt TV;
- boiler with a capacity of 2 kilowatts;
- electric fireplace with a capacity of 1.5 kilowatts;
- personal computer with a power of 450 watts;
- refrigerator with a capacity of 100 watts;
- electric kettle with a capacity of 1.5 kilowatts.
We translate the power values โโโโof all consumers into kilowatts and summarize:
5*0.1kW + 5*0.075kW + 2*0.065kW + 0.080kW + 0.1kW + 2kW + 1.5kW + 0.45kW + 0.1kW + 1.5kW = 6.735kW.
It turns out that the total installed power of consumers in the apartment is almost 7 kW. If you look at the table of cross-sections and powers for copper wires in a 220V single-phase network, then for a value of 6.735 kW, you can choose a standard cross-section of the input common wire or cable 4mm 2 or 2.5mm 2. A cross section of 4mm 2 in a single-phase network is 8.3 kW. Those. when using this section, there will be a power margin.
As for the section 2.5 mm 2, then this section corresponds to a power of 5.9 kW. Those. even less than the installed capacity. However, a cross section of 2.5 mm 2 can be selected if, in the future, the power of simultaneously operating electrical consumers will not exceed 5.9 kW.
Industrial users
Suppose the following three-phase consumers are located in the production room:
- three-phase electric motor with a power of 5 kW;
- a three-phase power transformer with a power of 100 kW (although usually the power of a power transformer is indicated in kVA);
- task lighting with three groups with a total power of 3 kW.
We calculate the total power by adding the power of the electric motor, the power transformer and the power of the working lighting. We get 5kW + 100kW + 3kW = 108kW. According to the table, for a load of 108kW, an electric cable with a core cross section of 70mm 2 is suitable. For this section, the maximum three-phase load is 118.8 kW. Those. and in this case, the section of 70mm 2 has a power reserve.
Above were the calculations for a common electrical cable. As for outgoing wires and cables, the calculations are carried out similarly. It should only be borne in mind that there are usually several outgoing conductors and each may have its own separate load.
Sometimes, to select a section, they do not resort to detailed calculations and the selection of a section according to the table. In practice, in a household electrical network (wiring) for outlet circuits, a copper wire with a cross section of 2.5 mm 2 is chosen, and for lighting circuits, a copper wire with a cross section of 1.5 mm 2. As for production, cross-sectional calculations for wires and electric cables are mandatory.
