Planning for the power supply of your own home begins long before the purchase of the first outlet. The foundation of the whole system is lead-inwhich takes on the load from all simultaneously switched on devices. An error in the calculations at this stage can lead to permanent shutdowns of the machines or, much worse, to overheating of the wiring and fire.
Many property owners mistakenly rely on the opinion of builders, who often put the minimum permissible values "by eye". However, the modern apartment is saturated with energy-intensive equipment: from air conditioners and electric ovens to smart home systems and charging stations for electric vehicles. Section lived It should be selected with a margin, taking into account the prospects for the development of the electric power industry.
In this article, we will discuss the technical nuances that will help you avoid fatal mistakes. You'll find out why. aluminum wire with a cross section of less than 16 mm2 is prohibited for entering residential buildings according to current standards, and how to calculate the required power. Competent approach to the choice of conductor will ensure the safety of your family and preserve expensive equipment.
Normative requirements and standards of ISPs
The main document regulating the device of electrical installations is PUE (Rules of electrical installations). It is here that strict requirements for the material and cross-section of conductors are prescribed. For inputs to residential buildings and apartments, priority is given to copper cables with better conductivity and mechanical strength.
According to the current editions of the rules, the use of aluminum cables for laying inside residential premises is prohibited. Aluminum is allowed only for backbone networks or inlets if the cross-section of the vein is not less than 16 mm2. This is due to the physical properties of the metal, which is prone to oxidation and flow under load.
β οΈ Attention: The regulatory framework may be updated. Before starting work, be sure to check with the latest edition of the PPU and local technical specifications (TU), issued by your energy supply organization.
It is also important to consider the type of insulation. Entrances that can pass down the street or in unheated basements require a double-insulated cable with UV protection, such as stamps. VVGG or SIP (for overhead lines). Choosing the wrong type of insulation will lead to cracking and short circuit.
Calculation of the cross-section by power and current
The choice of cross-section is based on two main parameters: the total power of electrical appliances and the strength of the current flowing through the conductor. First, the total load must be calculated. This is done by all consumers who can theoretically work simultaneously.
In real life, however, all devices are not immediately turned on. Therefore, it applies demand (usually 0.7-0.8). The resulting power is translated by current according to the formula I = P / (U Γ cos Ο), where U is voltage (220V), and cos Ο is cosine phi (for household networks 0.95 are taken). It is from the strength of the current that the heating of the vein depends.
To simplify calculations, electricians use ready-made tables, where the methods of laying (open or hidden) and the material of the vein are taken into account. Below are the approximate data for copper cables with a hidden pad in the wall (string), which is the most common scenario.
| Copper vein cross-section (mm2) | Current (A), 220B | Power (kW), 220V | Score of the machine (A) |
|---|---|---|---|
| 1.5 | 19 | 4.1 | 10 |
| 2.5 | 27 | 5.9 | 16 |
| 4.0 | 38 | 8.3 | 25 |
| 6.0 | 46 | 10.1 | 32 |
| 10.0 | 70 | 15.4 | 50 |
Please note that the section of the introductory cable into the apartment is rarely less than 6 mm2 for copper. If you have three-phase input (380V), the load is distributed into three phases, which allows you to use a smaller cable for the same total power, but the calculation is different.
When calculating power, always add a 15-20% margin for future appliances, such as a dishwasher or flowing water heater.
Copper or Aluminum: Comparison of Materials
The eternal dispute between the supporters of copper and aluminum in the context of apartment building has long been over with the victory of the first option. Copper. It has a lower resistivity, which means less heating when passing current. In addition, copper veins are more flexible and convenient for installation in a limited space of the shield.
Aluminum is cheaper, but it requires regular maintenance. Over time, the contacts on aluminum weaken due to the effect of βfluidityβ of the metal, which leads to sparkling and heating. For entry into an apartment where access to the cable after installation will be limited, reliability is more important than savings.
If you still have to connect aluminum input (for example, in an old house), use special transition sleeves or terminals with quartz vaseline paste. Direct connection of copper and aluminum twist is strictly prohibited and leads to electrochemical corrosion.
- π Conduction: Copper conducts current 1.6 times better than aluminum of the same cross section.
- π₯ Safety: Copper can withstand higher temperatures without losing its insulation properties.
- π οΈ Editing: Copper veins are easier to bend and stack in narrow channels without the risk of breaking them.
Effect of track length on voltage loss
Often, the owners of apartments in new buildings or private houses are faced with a situation where the meter is far from the switchboard inside the room. In this case, the physical law comes into force: the longer the conductor, the greater its resistance and, consequently, the drop in voltage at its ends.
Norms allow voltage deviation of no more than 5% of the nominal value. For a 220V network, this is 11 volts. If the entrance to the house is 220V, then the outlet in the back room should be at least 209V. At lower values, sensitive equipment (refrigerators, boilers) may work incorrectly or burn.
How to compensate for the drop in tension?
If the calculations show a critical voltage drop, it is necessary to increase the cross section of the inlet cable one or two steps above the calculated. For example, use 10 mm2 instead of 6 mm2. This will reduce resistance and level the tension.
For long runs (more than 50 meters), the cross-section is calculated not only by current, but also by voltage loss. Sometimes it is more cost-effective to lay a thicker and more expensive cable than to fight the unstable operation of electrical appliances.
Mistakes in the selection and installation of the introductory cable
The most common mistake is to choose a cable for the power of only one device (for example, electric stoves), ignoring the rest of the load of the apartment. The introductory cable must withstand the sum of currents of all group lines protected by the input automatic.
The second mistake is to use a cable with an under-section "in the hope that the machine will protect." The circuit breaker protects the cable from overload, but it is triggered with a delay. During this time, a thin cable can already heat up to dangerous temperatures, damaging the insulation.
β οΈ Attention: Do not use cables of PUNP or PUGNP brands for inputs. They have long been banned for production due to thin insulation and under-section of the veins, not corresponding to the declared.
The third mistake is the violation of the conditions of the gasket. A cable designed for hidden laying in concrete cannot be used outdoors without additional protection. Conversely, the use of combustible insulation cables in wooden houses requires laying in metal pipes.
βοΈ Checking before buying the cable
Methods of laying and protection of cable
The method of laying directly affects the permissible current load. A cable lying in the air cools better than one walled in or laid in a bundle with other wires. For inputs, a combination of methods is often used: from a pole to a house - an overhead line or an underground entry, inside a house - hidden or open wiring.
With a hidden gasket in the stroves under the plaster, the heat sink deteriorates. In such cases cable-section It is recommended to choose with a margin. It is also important to avoid sharp angles when bending so as not to damage the veins and insulation. The bend radius shall be at least 10 outer diameters of the cable.
To protect against mechanical damage when passing through walls and foundations, be sure to use shells or pipe segments. This will prevent the cable from squeezing when the building shrinks and will allow the input to be replaced if necessary without destroying the structures.
A properly selected inlet cable cross section is a one-time investment that guarantees safety and no electrical problems for decades to come.
Can I use a smaller cable if I don't turn all the devices on at once?
Theoretically, it is possible, but it is a violation of safety rules. You cannot guarantee that in the future another tenant or you yourself will not accidentally create an overload. The machine may not work instantly, and the cable will warm up. Always focus on the denomination of the introductory machine.
What to do if the old aluminum inlet is heated?
Warming means there is bad contact or overload. First, check the plugging. If the contact is normal, then the cable cross section cannot cope with the load. The only correct solution is to replace the input on the copper cable of the corresponding section.
Do I need to ground in the introductory cable?
Yes, the current standard implies a three- or five-wire system (zero and ground). Even if the house is old riser without grounding, lay a fifth vein (PE) in your shield is worth in the future, when upgrading the home network, to be ready to switch to the TN-C-S system.