In the process of building a house, wiring will be installed in any case. During this period, you need to be especially careful to choose the cross-section of the wires and the maximum required power that they can withstand. For this, approximate data on all consumers of electricity, appliances (from kitchen and household appliances to electric heating) are taken into account. For these purposes, they rely on the long-term permissible currents of the PUE cables.
Content
- general information
- Formula calculation
- Allowable density
- Arrangement recommendations
general information
The inner part of the cable, through which the current is transported, is made of metal. This part is also called the cable cross-section. Square millimeters are used as units of measurement. Depending on the cross-section of the cable, it will be able to transmit a voltage of a certain power. The current is known to generate heat.
These temperatures can be divided into three types:
- the insulation will remain intact when the current flows through the cable;
- the insulation will melt, but the inside (metal) will remain intact;
- the metal will melt at this temperature.
The cable can only be approved in the first version. If the insulation melts at a certain current level, such wires cannot be used. It is also worth noting that with a decrease in the cross-section of the wire, its resistance will increase, and therefore the voltage in the cable will drop. But on the other hand, an increase in the cross-section leads to a large mass of the wire itself and its cost.
If we talk about the materials from which the inner part of the cable is made, then mainly copper or aluminum is used. Copper is of higher quality and more expensive due to the fact that it has a higher level of current carrying capacity. Copper and aluminum have different characteristics and physical properties. This is important to take into account, since with the same wire diameter, materials will withstand different loads.
Formula calculation
Knowing the necessary formula, even a novice craftsman without appropriate work experience will be able to determine the required cable cross-section. It is this value that needs to be calculated, since there are cables with one core, two or more. That is, if the product is two-core, then the total cross-sectional area of the two cores must be taken into account. The advantage of multicore cables is that they are more durable and flexible. They are not "afraid" of kinks during installation work. Basically, manufacturers use copper to make this option.
To determine the permissible current for copper wires or aluminum single-core type, you can use the following formula: S = number pi * d 2 / 4 = 0.785 d 2 . Moreover, S is the area in square millimeters, and d is the diameter.
In order to calculate the permissible current for aluminum wires or using any other material, the formula is applied: S = 0.785 * n * d 2 . S - area, d - diameter, n - number of cores.
The diameter of the wire can be determined using a micrometer or vernier caliper, after removing the insulation. Thus, you can make a choice of the cable cross-section for current. Such calculations will correspond to the table of PUE.
Allowable density
The density is even easier to determine. To do this, it is enough to divide the number of amperes by the section. A lot will also depend on this indicator. Density is primarily responsible for the stability of the power grid. The wiring can be divided into two types:
- open;
- closed.
The characteristic feature of the open one is the best current density due to the high heat transfer. It is necessary to buy a closed one with a correction to the lower side, since this can cause overheating, a short circuit and even a fire.
Calculating heat is a rather complicated process. In practice, the maximum permissible temperature of the weakest structural element is assumed. Thus, the maximum permissible current density is the value, in which it will be safe to use the wiring. In this case, it is worth considering the maximum ambient temperature.
The density of copper in open wiring is 5 A / mm2, and in closed wiring 4 A / mm2. The density of aluminum in an open wiring is 3.5 A / mm2, and in a closed one 3 A / mm2. Most modern wires are insulated with PVC or polyethylene. They allow heating up to a maximum of 90 degrees.
It is also worth understanding the definition of the terms open and closed wiring. The first option is always located in an open space. It is attached to the wall with clamps, can be fastened with a cable or be stretched through the air from wall to wall. Closed can be in trays, pipes, walled up in the wall or under plaster. Closed wiring will be considered if it is located in junction boxes or shields. Its disadvantage can be considered a lower degree of cooling.
Arrangement recommendations
Arrangement and wiring, in addition to other skills, requires skills and a general understanding of design. At the same time, if you have fairly good wiring skills, you cannot make a good power grid. There are times when people confuse design with the registration of any permissive documentation in government agencies.
The simplest project can be done with a pencil and a piece of paper. To begin with, you should draw a rough plan of the entire room. It does not have to be proportional as this is only a sample. Next, you should estimate the location of all future outlets. You also need to find out the power of all electricity consumers in the house.: irons, kettles, any other kitchen appliances, various household appliances, light bulbs and the like.
Then you need to determine in which rooms there will be a large load on the power grid, and in which ones it will be small. Typically, the largest consumer of electricity in a home is the kitchen, as there are many different appliances available. In addition, a washing machine is sometimes placed in the kitchen, which creates an even higher degree of stress. Such a plan will allow you to select the optimal cable section for each room.
With the correct calculations, you can significantly save money on the cross-section of the wiring. Having calculated the required cross-section, it is necessary to add up the entire required footage and get the total cost of such equipment. Each room should have its own line and a circuit breaker. In the dashboard, they can be labeled “kitchen”, “bedroom” and so on. If there is a voltage drop, the automatic fuse will work and turn off the electricity supply on its own.
In addition, this approach allows, for example, to repair the outlet in the bedroom, having previously turned off line, and in the kitchen you can do your usual business, since there the electricity supply will be be carried out.
In damp areas, double-insulated wiring should be used. It is recommended to buy modern sockets and switches based on the European safety standard with the use of grounding. Moreover, it still needs to be connected correctly. It is better not to bend single-core copper wires too much (a small angle is acceptable), as this can lead to a kink. Covered wires in shafts and channels must lie flat. But it is worth noting that they cannot be clamped, and they must be placed freely in the channel.
When installing sockets and switches, you should leave a few extra centimeters for insurance. When calculating the permissible cable size, this parameter is also taken into account. When installing the cable, you need to pay attention to sharp corners that can damage the insulation of the wire, and remove them. It is necessary to tighten the terminals especially carefully when connecting. Single-strand options need to be tightened twice. This is due to their peculiarity of precipitation, due to which, over time, the connections weaken by themselves.
Copper and aluminum wires are incompatible with each other in their chemical characteristics, that is, they cannot be connected together. If there is a special need for this, then you need to use special connectors, galvanized washers or clamps. The place where they will dock must be dry.
According to generally accepted rules, the phase wires (plus) should be white or brown. Minus (ground) - yellow-green color. Compliance with the colors will increase the safety of the electrical network several times.
In the project of any room, from the kitchen to the bedroom, it is very important to choose the right cable cross-section for current. PUE - the main norms to which you should pay attention. The correct choice of equipment will provide a good level of fire safety.
