Features of 15 kW cable
The product consists of several solid metal cores (the number depends on the number of phases), coated with a layer of protective material. The insulation is characterized by increased elasticity and resistance to external factors. Cables for open wiring are coated with a protective layer that can withstand exposure to ultraviolet light.
The conductors must withstand the rated load without heating and destruction or ignition of the sheath. If SIP category wire is used for switching, then the product design includes a steel load-bearing core.
Single-phase and three-phase underground cables
Most high-voltage underground electrical cables are three-phase. That is, they have three conductors through which balanced currents pass. But some of them are single-phase, with only two conductors, “output” and “back” or “output” and “return”. Today we have a very practical phase measuring apparatus https://electricvdome.ru/montaj-electroprivodki/op which is fast you can determine the current, so it is very easy and convenient to use not only for specialists, but also for just craftsmen. This can happen, for example, with rail transport.
Note: In a three-phase system, the single-phase load is supplied through two of the three phases. So, in terms of voltage, it is two-phase: each conductor has voltage across it, and neither is at ground potential, like the neutral conductor is at low voltages. In modern parlance, current flowing through one conductor flows back through the other, meaning it is more naturally described as "single-phase". Single-phase or two-phase are the same thing in this context, and how you describe it depends on which aspect you approach it from.
We calculate the exact field for a single-phase circuit numerically in exactly the same way as for a three-phase circuit (download a tutorial on how to do this). But when you are far away from the cable compared to the separation of conductors, there are simpler expressions for the field.
Types of cables
Products are divided into categories according to:
- number of phases in the power supply network;
- core material and load power;
- the method of laying a main line from a substation or pole to a house.
Three-phase
The wiring for connection to a three-phase network consists of individually insulated metal cores, additionally covered with an outer protective layer. It is distinguished by a reduced cross-section of the cores, but the voltage of 380 Volts is suitable for switching industrial equipment. There are powerful household appliances (for example, electric kitchen stoves) designed for a three-phase network.
A three-phase wire consists of metal conductors insulated.
Single phase
The cable is distinguished by the use of cores for supplying phase, neutral and equipment grounding. The operation of energy-intensive equipment requires an increased cross-section of conductors. Due to the voltage drop, the current is increased to provide the required power, which causes increased heat generation (in accordance with the Joule-Lenz law). Single-phase wire is used when wiring circuits inside the house. The cross section is selected depending on the power of the equipment.
Which one should you choose?
The use of three-phase power supply requires the installation of special protection equipment and a meter in the panel. In return, the home owner receives increased system reliability and a reduced heat load on the supply line. If it is necessary to ensure switching of equipment with a power of up to 15 kW, then only a three-phase incoming line should be used.
A single-phase connection is suitable for houses consuming no more than 7 kW, or for internal wiring of the power supply system.
Let's first consider a single-phase cable with current, which I leave in one.
Most high-voltage underground electrical cables are three-phase. That is, they have three conductors through which balanced currents pass. But some of them are single-phase, with only two conductors, “out” and “back” or “out” and “return”. This can happen, for example, with rail transport.
Note: In a three-phase system, the single-phase load is supplied through two of the three phases. So, in terms of voltage, it is two-phase: each conductor has voltage across it, and neither is at ground potential, like the neutral conductor is at low voltages. In modern parlance, current flowing through one conductor flows back through the other, meaning it is more naturally described as "single-phase". Single-phase or two-phase are the same thing in this context, and how you describe it depends on which aspect you approach it from.
We calculate the exact field for a single-phase circuit numerically in exactly the same way as for a three-phase circuit (download a tutorial on how to do this). But when you are far away from the cable compared to the separation of conductors, there are simpler expressions for the field. Let's first consider a single-phase cable with current I coming out in one wire and back in the other: diagram of a single-phase cable.
We are interested in the field at a distance r. When r is large compared to the conductor spacing d, the field is given by
B = (μ0 / 2π). Ya (d/r2)
μ0 / 2π is just a constant. So the field is equal to this constant times the current times d/r2.
Now consider a three-phase cable:
Most high-voltage underground electrical cables are three-phase. That is, they have three conductors through which balanced currents pass. But some of them are single-phase, with only two conductors, “out” and “back” or “out” and “return”. This can happen, for example, with rail transport.
Selection of cable cross-section for 15 kW
When selecting the cross-section of the cores, the load, the number of phases and the material of the cable cores are taken into account. To roughly determine the parameter, use the standard values indicated in the tables. To protect the wiring from overheating, it is recommended to provide a larger cross-section margin of 10–15%. If you use cables with a core diameter below the permissible value, then at rated load the metal heats up and destroys the insulation, and if overloaded, the wiring burns out or causes a fire in the house.
Aluminum wires
The use of aluminum makes it possible to reduce the cost of cable production, but the metal is not highly elastic and gradually becomes brittle.
The wiring is not suitable for installation on surfaces that support combustion (regardless of the material of the protective screens). Difficulties also arise when joining aluminum and copper conductors; the resulting electrochemical pair is rapidly destroyed (the problem is solved by using special terminals). The table shows the values of the core cross-section depending on the power and number of phases in the network.
| Standard cross-section, mm² | Current and power for 1-phase network | Current and power with 3-phase network |
| 4 | 28/6,1 | 23/15,1 |
| 6 | 36/7,9 | 30/19,8 |
| 10 | 50/11,0 | 39/25,7 |
| 16 | 60/13,2 | 55/36,3 |
| 25 | 85/18,7 | 70/46,2 |
The table allows you to determine which cable is needed for switching at home. For example, with single-phase power, you will need wiring with an aluminum core cross-section of at least 25 mm²; the previous standard value of 16 mm² will withstand about 13 kW.
With three-phase power, you can get by with a cable with a core cross-section of 4 or 6 mm² (the second option increases the reliability of the network).
Copper wires
The use of copper makes it possible to reduce resistance and reduce the cross-section of the cores while maintaining load power.
Is it possible to calculate the cross section yourself?
The home owner needs to calculate the peak load on the electrical network taking into account the power of the devices. It should be remembered that when switched on, the equipment consumes increased starting current, which loads the wiring. When making your own calculations, there is a risk of error; an incorrect choice of cross-section can lead to additional costs for dismantling and laying a new power line. It is more advisable to order the service from a sales company or a specialized company; the investment will be repaid by the reliability of the power supply system.
Selecting a machine for 15 kW cable
When selecting a machine, take into account the number of phases and the current at which the mechanism operates. It is recommended to purchase equipment manufactured by large factories (for example, Schneider Electric). Budget models use cheaper materials, which reduces the service life and negatively affects the accuracy of work.
An important operating parameter is the PKS, which determines the peak current at which the device opens the network and remains operational. If the current is higher than the PKS, then the moving contacts melt or weld and the device fails.
Functions of slot machines
Automatic fuses located in the distribution panel ensure that the power supply line is disconnected in the event of a short circuit. They provide a total protection of 15 kilowatts and additional devices that cut off power to circuits (for example, for sockets or lighting fixtures in each room).
For powerful equipment, separate fuses are installed, the rating of which cannot be higher than the characteristics of the main protective element.
Necessary calculations
To calculate the circuit breaker, use online calculators; in the dialog box indicate:
- type of equipment connected to the network (household or equipped with asynchronous electric motors);
- power of devices (obtained based on documentation analysis or specified in the contract with the sales company);
- voltage in the power supply network.
For example, when connecting equipment with a power of 15 kW to a 220 V line, you will need a 63 or 80 A circuit breaker (depending on the load metering method used). In the case of switching to a three-phase network, the parameter drops to 20–25 A. The example demonstrates the advantage of a 380 V power supply. With the same power of devices, the current in the circuit drops by 3–4 times. When using 380 V electric motors that consume high current at start, fuses with a rating of 40 A are required.
For household networks, machines with a type C response curve are used, and for electric motors, the installation of modules of category D is required. The devices differ in the value of the currents that cause the contact group to open. Products must comply with the network's rated voltage. For single-phase wiring, fuses with 1 or 2 poles are used; for 380 V lines, units with 3 or 4 poles are required.
What kind of machine for 15 kW 3 phases
Being the owner or owner of non-residential premises is not easy. A wide range of questions immediately arise, which are sometimes very difficult to solve on your own. One of these global challenges is electricity supply. The further operation of the premises will directly depend on the solution to this problem.
Before you begin making technological connections, you should decide which devices will be connected to the electrical network, as well as how often and for how long they will be used. All power-receiving devices will make up the total load of the network, the value of which can either fall within the value of the permitted power or exceed this value.
In order to ensure the safety of your facility in terms of the operation of energy receiving devices, it is necessary to install an appropriate machine. It is quite difficult to choose the right one, as many related questions arise. For example, which machine should I install at 15 kW? For 15 kW 3 phases, how many amperes should the breaker be at the input of the electrical installation? First of all, it must be said that a 15 kW 3-phase machine accepts a voltage of 380V. Therefore, a 15 kW circuit breaker requires a 25 A input circuit breaker. How to take into account all these requirements? Let's figure it out.
Power cable calculation
To determine the cross-section of the power cable you must:
- Calculate the rated load (75–80% of the power of the appliances installed in the house).
- Decide on the number of phases and core material.
- Select the cross-section according to the tables, taking into account the power reserve within 10–15%.
For an accurate calculation, you can use a calculator. The program includes information about the material of the cores, the load and the length of the supply line. Additionally, indicate the voltage and number of phases, enter the power factor and the value of permissible transmission losses. Additionally, the maximum temperature of the outer insulation layer during operation is taken into account.
The obtained value is compared with the table one, but a larger cross-section is selected to increase the reliability of the electrical wiring.
Let me give you an example, for example, we have a cable cross-section of 6 sq. mm:
- with the open method, its long-term permissible current is 50A, therefore the machine must be set to 40A;
- with the hidden method, its long-term permissible current is 34A, in this case the machine is 32A.
Suppose we chose a cable cross-section for an apartment, which are laid in grooves or under plaster (in a closed way). If we mix it up and install 50A circuit breakers for protection, the cable will overheat, because... with a closed method of laying it, In = 34 A, which will lead to the destruction of its insulation, then a short circuit and fire.
!!! TABLES ARE NOT CURRENT. WHEN SELECTING A MACHINE FOR CABLES, USE THE TABLE ABOVE.
Safety precautions
Basic safety rules when connecting electrical wiring:
- installation work should be carried out on a de-energized line;
- when connecting cables, do not rely on random objects;
- do not touch bare sections of wires with your hands without protective gloves;
- use tools with handles made of dielectric material without damage;
- do not install cables with a torn, melted or cut protective layer;
- use metal sleeves for switching, ensuring reliable contact;
- Do not connect cores made of dissimilar materials without using separating terminals.
Connection diagram
The power cable is inserted into the distribution board through holes located on several sides and closed with technological plugs. The design allows you to quickly dismantle the cover; the direction of installation depends on the location of the box. For example, for switchboards located outdoors or installed in rooms with high humidity, the cable is inserted from the bottom plane (in accordance with the requirements of the PUE). The technique protects the internal cavity of the box from water penetration.
A layer of insulation of 200–250 mm is cut off from the power wire, the cores are spread apart and marked using nozzles (if necessary). When switching, a length reserve of 500 mm is provided, allowing adjustments to be made to the arrangement of elements inside the panel. Inside the box there are holders for the correct positioning of the power line, which is held in a given position by clamps.
Regardless of the number of phases, the cable is divided into cores led to machines or buses. Metal tips, crimped with pliers or a press, are placed on the bare ends. The terminal has a plane with a hole for bolts that press the plate to the contacts. If fuses with clips are used in the panel design, then installation of the tip is not required. The core with the insulator removed is inserted into the contact socket and secured with a bolt.
When switching, it is important to ensure maximum contact area between the wire and terminals.
Three-phase connection
The scheme provides for phase separation into 3 lines with individual circuit breakers and a common zero circuit. It is necessary to ensure a uniform load on the resulting single-phase sections. If the use of devices designed for 380 V is intended, then separate fuses designed for three-phase power should be provided.
According to a single-phase scheme
The cores are inserted into the distribution board, the neutral wire is distributed among the working areas. The phase is connected to fuses, selecting the rating according to the load. Voltage relays and residual current devices (RCDs) are introduced into the distribution box circuit, increasing the safety of operation of electrical equipment.
Cable laying for 15 kW
The standard power of equipment connected to the home electrical network varies from 4 to 6 kW. If there is a construction permit, the owner of the property has the right to lay a main line designed for a load of up to 15 kW. Increased power is necessary for connecting and stable operation of energy-intensive equipment (for example, an electric boiler or oil heating radiators). Switching is carried out via overhead or underground lines, each method has its own advantages and disadvantages.
By air
AVVG, AVK and SIP cables are suitable for entry into the house via an overhead line. The products are designed for a maximum voltage of up to 1 kV and are distinguished by durable insulation that can withstand cooling down to -50°C without the risk of mechanical destruction.
An inlet pipe is provided in the wall of the house, located at an angle to the street surface of the wall (to protect against precipitation and rapid drainage of condensate). The line must be located at a height of at least 2.75 m from the ground surface; additional racks are installed to prevent the cable from sagging.
Why is one phase missing?
In fact, options with two phases also occur, but this is a rather rare occurrence. As a rule, these are consumers that were connected in the late nineties - early 2000s, when powerful consumers appeared and one phase with a cross section of 1.5 mm2 was no longer enough. However, more often we still encounter 1 or 3 phases. One phase is enough to operate most electrical appliances (with sufficient wiring cross-section). There are several reasons for having three phases.
The first is the need to power three-phase consumers, for example, an electric heating boiler. Accordingly, in this case, a three-phase meter is installed (not to be confused with a multi-tariff meter), a general input machine and several linear machines.
The second reason is the same as in the case of two phases - the ability to unload the phases in the presence of a large number of powerful single-phase consumers. This is especially necessary when you have a welding machine. Or you need to connect a hob, water heater or underfloor heating system to a separate phase. Thanks to such a clear distribution, there is no phase imbalance and the voltage on each is approximately the same and within normal limits.
Assembling a 15 kW three-phase switchboard with your own hands
The number and range of elements in the distribution board depend on the number and list of consumers. It is necessary to install a grounding bus in the panel with a connection to the protective line of the sockets. An introductory switch is installed at the entrance, allowing the house to be de-energized during repair work. A power outlet should be provided for switching powerful equipment. To fasten the elements, standard DIN rails installed in the panel are used.
In a box designed for 380 V, a separate line of fuses and additional devices is provided for each phase. Provides a programmable surge protection relay. To connect the contacts, use pieces of PuGV wire with a cross-section of 6 mm² with tips crimped with metal sleeves. If it is intended to use 380 V devices, then provide an area for mounting the appropriate voltage relay and differential fuses.
