5 options for three-phase distribution board diagram.

All distribution boards must perform 3 main tasks:

• cable protection against overloads and short circuits

For this purpose, automatic switches are installed in switchboards. They are primarily designed to protect the cable, and not the equipment connected to it, as many still think.

In case of overloads or overheating, the thermal release is activated and protects the wiring insulation from melting. In the event of an obvious short circuit, it is no longer the thermal, but the electromagnetic release that is triggered.

• protecting people from electric shock

This is ensured by installing RCDs or differential circuit breakers.

• protection of equipment from voltage surges

Unfortunately, power surges often occur in our networks. The machines do not react to this, since they are simply not designed for such protection.

The RCD is also not designed to be triggered by overvoltage. To do this, you will need modular voltage relays or UZM - multifunctional protection devices.

They set certain upper and lower voltage limits. As soon as there is a jump, or, conversely, a sharp decrease in the parameters of the electrical network, this relay (UZM) is triggered and turns off the power.

The need for three-phase connection

In a single-phase network, often the only phase is overloaded due to the use of powerful units , which are becoming more and more common in modern homes. As a result, connected electrical appliances fail, creating an emergency situation that threatens a fire.

At the entrance to the house there are always three phases, which are distributed in a phase-zero set. Pairs power groups of loads of equal power. If a residential building is allocated 15 kW of power, then each group receives no more than 5 kW. If the rule is not followed, the circuit breakers will trip if the line is overloaded.

If consumers in the house require a total of more than 15 kW, a three-phase connection is needed

Equipment requiring a three-phase line connection:

• an electric heating boiler in a large house can take about 9 kW;
• water pump operating in a deep well;
• electric stove for baths, high-power saunas (from 5 kW);
• hob, oven;
• equipment for a private workshop at home, for example, milling and lathes, a circular saw, a welding machine, a jackhammer.

Such units can be found with a 220V connection, but 380V is more reliable, more powerful, and more economical . Modern devices for everyday use can be designed specifically for 380V, for example, a motor on a garage door or entrance to a yard.

Three phases are needed if there are three-phase motors on the site that are not designed to operate in single-phase regulation. Alternatively, the organization of such input is necessary when many electrical appliances are used at the same time, for example, a household has been developed, private production has been established.

They try to supply a three-phase power line to every private building, and the user can use it or not as he wishes.

Pros and cons of three-phase connection

Economical use of electricity

Low material consumption of transformers and power cables

Even load distribution

Synchronous and asynchronous current motors show high efficiency

It is possible to obtain simultaneously linear and phase voltage in one installation

Probability of reducing lamp flicker and stroboscopic effect of fluorescent lamps

In the event of an accident, one or two phases burn out, but for power supply there is the possibility of a temporary backup connection

Three phases are required if there is not enough single phase line, but in this case it is easier to request an increase in the limit

It is necessary to distribute the load evenly between phases

A new switchboard and accessories are required

The danger of electric shock increases, since the network contains not only single-phase voltage, but also linear

Calculation of energy consumers

Before distributing the load across phases, it is recommended to perform a preliminary calculation of consumers. This can be easily done by making a list of potential sources that will be assigned to a particular phase. For example, list the main household appliances and their power as stated by the manufacturer:

• Electric hob 6.5-7.5 kW.
• Washing machine 1.5-1.8 kW.
• Dishwasher 1.5-1.8 kW.
• Microwave oven 0.9-1.2 kW.
• Oven 2.0-2.6 kW.
• Vacuum cleaner 1.9-2.2 kW.
• Iron 1.9-2.2 kW.

How to properly divide energy consumers into several groups Source uk-parkovaya.ru

Important! If necessary, the list can be supplemented with other electrical appliances on the balance sheet.

Requirements for connecting 380 volts

The rules for connecting the site are prescribed in the text of Federal Law No. 35 “On Electric Power Industry” dated March 26, 2003 (Articles 20 – 26), edited on December 27, 2019. The work of electric grid companies is regulated by Federal Law No. 135 “On the Protection of Competition” dated July 26, 2006.

Example specifications

Basic Rules:

• the user cannot independently connect electricity to the house; an energy supply organization is needed;
• connection is possible after fulfilling the requirements of the technical specifications;
• use cables with aluminum (not less than 16 mm²) or copper (not less than 10 mm²) conductors; armored cables are laid underground;
• with an aerial connection, the cable does not sag below the road below 6 m, above the sidewalks - below 3.5 m;
• the underground line is buried 0.7 - 1 m or lower;
• entry into the dwelling - not lower than 2.75 m from the ground;
• devices installed upstream of the electricity meter must be sealable.

In a 380V network, it is allowed to connect a three-phase meter in a private house with a maximum current strength of 50A, accuracy class - 2, last check - no more than 1 year ago. It is fixed on the DIN rail of the distribution panel, but it can be located outside the switchboard. The house must have a grounding system.

How to apply for a permit

The consumer has the right to connect to any electrical facility within 300 m from the site (power line supports, transformer substations, cable lines). The contract is concluded for a new connection, increasing power or moving the entry point.

List of project documents:

• site plan in the general layout of the development;
• connection diagram for power receivers;
• internal wiring diagram;
• PPR for connection.

The application is written at the company’s office, or submitted in your personal account through the website.

Information to be submitted with the application:

• Full name of the applicant;
• address of the connected site and the actual location of the user;
• project development period and commissioning time;
• power separation between phases;
• highest required power;
• type of load.

The company must meet deadlines for making decisions on the application. For individuals with a required power of up to 15 kW, this period is equal to 15 days, with other indicators or for a temporary connection - up to 30 days. After signing the contract, the specifications are given, which the user must exactly carry out on his site.

The owner notifies the company about the completion of preparation; in response, the electrical network checks the compliance of the specifications and the actual work in the presence of a representative of the supplier’s supply organization. A certificate of compliance is drawn up (within 3 days), the owner of the site signs the document within 5 days. This is followed by: an agreement on technological connection, an agreement on the supply of electricity. After this, 380V is supplied to the site.

Power distribution system

Initially, the voltage is always three-phase. By “initially” I mean a generator at a power plant (thermal, gas, nuclear), from which a voltage of many thousands of volts is supplied to step-down transformers, which form several voltage stages. The last transformer lowers the voltage to a level of 0.4 kV and supplies it to end consumers - you and me, apartment buildings and the private residential sector.

Large enterprises with power consumption of more than 100 kW usually have their own 10/0.4 kV substations.

Visually:

Three-phase power supply – stages from generator to consumer

The figure shows in a simplified way how from generator G a voltage (everywhere we are talking about three-phase) 110 kV (can be 220 kV, 330 kV or another) is supplied to the first transformer substation TP1, which lowers the voltage for the first time to 10 kV. One such transformer substation is installed to power a city or region and can have a capacity of the order of a few to hundreds of megawatts (MW).

Next, the voltage is supplied to the second stage transformer TP2, at the output of which the end-user voltage is 0.4 kV (380V). The power of transformers TP2 is from hundreds to thousands of kW. From TP2, voltage is supplied to us - to several apartment buildings, to the private sector, etc.

Such voltage level conversion stages are necessary in order to reduce losses during the transportation of electricity. Read more about losses in cable lines in my other article.

The circuit is simplified, there may be several steps, the voltage and power may be different, but the essence does not change. There is only one final voltage of consumers - 380 V.

Selection of materials and equipment

Input components and the meter are placed on the distribution panel, the dimensions of which are determined by the number of connection points. Metal boxes with protection from moisture are placed outside, steel and plastic cabinets are used inside.

Set of components for connection:

• corrugated tubes, self-extinguishing or non-flammable cable ducts;
• copper cable VVGng;
• three-phase meter;
• connecting switches: combs, buses, terminals;
• protective and safety fittings;
• automatic circuit breakers complete with RCDs or combined automatic circuit breakers;
• a relay that protects against voltage surges in the circuit.

A DIN rail is prepared for high-quality fastening of automatic machines and protective devices; mounting spaces for these devices are provided on the bar.

To carry out internal wiring , you need wires, boxes for changing the direction of wiring, socket boxes and for switches. You will need alabaster or plaster to fix the cables in the wall grooves, clamps, electrical tape, and adapters.

AV circuit breaker

A circuit breaker is a device that allows you to close and open electrical network contacts in both normal and abnormal conditions. The main purpose of the AV is protection against short circuits and overloads of electrical installations.

Depending on how many phases of the supply voltage are used in the electrical network of a private home, one-, two- and three-pole circuit breakers are used. It is advisable to use single-pole and three-pole switches for connecting phase wires, two-pole switches for switching neutral and phase wires. Two-pole circuit breakers provide one-time disconnection of these wires.

Input of three phases into the building and outgoing lines

Electricity from the pole is connected to the building through the air or underground.
All conductors are connected to the electrical panel, then the electric current enters the meter and passes to the distribution unit. Here the working zero and the grounding wire are separated, they are connected to the grounding bus, which is connected to the repeated grounding branch. Formation of outgoing lines :

• additional circuits come from the input switchboard (VRS);
• an introductory switch is installed in it, all phases are connected to it;
• circuit breakers are installed for each group circuit in the home, each of them is powered from different phases;
• groups are formed according to the power of units and devices so that each phase has approximately equal value;
• three phase conductors and a neutral conductor from the grounding bus are connected to the meter contacts;
• the meter output is connected to a common circuit breaker for the entire house.

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For connection, use the triangle or star method. The first method is to connect the phases sequentially: the end of the first to the beginning of the second, the end of the second to the beginning of the third, and so on. Star - when the ends of the phases are joined at a common point and the ends of the phases of consumer windings - also in one place.

How are three phases different from one?

In both types of power there is a working neutral conductor (ZERO). I talked in detail about protective grounding here; it is a broad topic. In relation to zero in all three phases - the voltage is 220 Volts. But in relation to these three phases to each other, they have 380 Volts.

Voltages in a three-phase system

This happens because the voltages (with active load, and current) on the three phase wires differ by a third of the cycle, i.e. at 120°.

You can read more in the electrical engineering textbook - about voltage and current in a three-phase network, and also see vector diagrams.

It turns out that if we have three-phase voltage, then we have three phase voltages of 220 V each. And single-phase consumers (and there are almost 100% of them in our homes) can be connected to any phase and zero. You just need to do this in such a way that the consumption in each phase is approximately the same, otherwise phase imbalance is possible.

Electrical panel assembly

The input switch and meter are sealed by power grid workers, so they are located at the beginning of the switchboard so as to provide this opportunity.

Step by step assembly:

• fastening of automatic devices and RCDs on the rail according to the drawn up diagram;
• connecting elements to the input switch using a comb;
• connecting phase wires with wires with lugs;
• installation and connection of the zero bus;
• checking (tightening) joints with a screwdriver;
• turning on the power, checking the operation of the machines;
• determining network parameters using a multimeter.

Before starting to operate the 380V network, make sure that all elements of the internal system (sockets, sockets, switches) are installed and connected.

Photo

Finally, a few more photos with comments.

Electrical panel with three-phase input, but all consumers are single-phase.

Three-phase input. Switch to a smaller cross-section of wires to connect them to the meter.

Friends, that’s all for today, good luck to everyone!

I look forward to your feedback and questions in the comments!

Connecting sockets

The peculiarity of 380V sockets is that they block from asymmetrical connection to avoid short circuit. The contacts are placed at an angle, they are different in size, with guide elements.

Stationary 380V sockets are produced in the following types:

• 2P+PE has two power (phase) terminals and a grounding terminal;
• 3P+PE or 3P+N is characterized by three phase terminals and one for grounding connection;
• 3P+PE+N - there are places for connecting three phases, one for zero, one more for grounding.

The sockets are interlocked to prevent switching off under load. The current strength (25, 63, 125A) for which these sockets are made is significant, and the products do not have an arc-extinguishing effect. Removing plugs under such a load is dangerous in terms of burns or burnt out sockets. The lock can be of an electronic or mechanical type.

Sockets are connected to the power cable in series, parallel or in a mixed way.

The emergence of the three-phase voltage concept

Dolivo-Dobrovolsky is considered the father of three-phase voltage in Russia and Nikola Tesla in the rest of the world. Events relating to the era of the emergence of the subject of the dispute took place in the 80s of the 19th century. Nikola Tesla demonstrated the first two-phase motor while working for a company where he set up electrical installations for various purposes. Interest in the phenomenon of electrification of domestic cat fur led the scientist to great discoveries. While walking in the park with a friend, Nikola Tesla realized that he would be able to put into practice Arago’s theory of a rotating magnetic field, and he would need:

1. Two phases.
2. The shift between them is at an angle of 90 degrees.

To show the great significance of the discovery, we note that Yablochkov’s transformer did not gain mass popularity at the indicated time, and Faraday’s experiments on magnetic induction were safely forgotten, only the formula of the law was written down. The world didn't want to know about:

• alternating current;
• phase;
• reactive power.

Generators (alternators) and dynamos rectified the voltage using a mechanical commutator. The entire electricity industry, which was meager at that time, languished in a similar way. Edison was just beginning to invent; no one really knew about the incandescent light bulb yet. By the way, in the Russian Federation they believe that the device was invented by Lodygin.

Tesla's idea looked revolutionary; it remained unknown how to obtain two phases with a given interphase shift. The young scientist had little interest in the question. He read about the reversibility of electric machines and radiated confidence that he could easily build a generator by arranging the windings accordingly. There were no difficulties with the drive. At the beginning of the 80s, steam was actively used, the demonstration model was supposed to be powered by a dynamo.

3 phase image

Tesla did not set out to obtain a certain frequency. No research was carried out; it was simply necessary to make the rotor rotate. The idea was realized through slip rings. At that time, brushed DC motors were equipped with similar contacts; Tesla’s conclusion is not surprising. It is more interesting to explain the choice of the number of phases.

Electrician's recommendations

For hidden wiring, built-in electrical panels are chosen, and exposed wires are connected in overhead distribution panels. The shield body is placed so that it can be easily reached.

Electricians advise observing the following conditions:

• horizontal sections of wires from the panel to the sockets are made at a height of 2.5 m from the floor;
• wiring in the walls is placed vertically or horizontally; it is prohibited to install it along an oblique line;
• connect the wires with adapters in installation boxes;
• the underground connection to the power pole is made with a single piece of wire without connections;
• Do not connect the switch to the neutral wire;
• When laying on wooden walls, insulating hoses with asbestos linings are used.

The distribution housing is selected according to the type of room, taking into account the characteristics of the microclimate - in aggressive environments, boxes with maximum protection from direct water jets and dust are used.

Peculiarities

To reduce the likelihood of phase overload, the load is distributed evenly across phases. Failure to comply with this condition, as well as burnout of the “zero” conductor or its poor contact, will lead to a difference in voltage on the phase conductors, up or down.

Thus, converted single-phase power (220 V) will lead to malfunction of electrical consumers connected to it. This will happen due to the fact that some devices will receive an increased voltage (240-270 V), while others will receive a reduced voltage (160-200 V).

Important! If the load is unevenly distributed across phases, on meters that are not sensitive to distortions, there will be an increased consumption of electricity.

Electrical 380V electricity metering panel for a private house with a 220V socket

In this electrical panel diagram, there is additionally a modular 220V socket (number 7) with an individual protection device - difavtomat (number 8), which combines a circuit breaker and a residual current device. The rating of the RCD must be higher than that of the circuit breaker, for example 40A, leakage current 100 or 300 mA.

Electrical metering panel 380V, with modular socket, TN-CS grounding

Using an electric motor

You probably know that the rotor of a conventional three-phase motor, after starting, continues to rotate after one phase is disconnected. It turns out that there is an EMF between the terminal of the disconnected winding and the activated terminals.

The phase shift between the stator windings depends only on their location. In a three-phase motor, these coils are located at an angle of 120º, which means they provide the same phase shift angle. This circumstance suggests that an asynchronous three-phase motor can be used to obtain 380 volts from a conventional single-phase network. A simple diagram for connecting an electric motor is shown in Figure 3. The capacitor in the diagram is needed only to start the engine. Once launched, you can disable it. We take the capacitor type MBGO, MBGP, MBGT or K42-4, the operating voltage of which must be at least 600 V. You can use the capacitor K42-19, with an operating voltage of at least 250 V.