When installing electricity meters in private houses, depending on the amount of current in the electrical circuit, a very specific connection diagram for a three-phase meter is used. It is connected directly to the break in the supply line or through a step-down current transformer. The second option for connecting a three-phase electric meter is used at consumption currents of more than 100 Amperes. Both of these methods of connecting an accounting device have their own characteristics, which the owner of the house must understand.
Types of inclusions and their features
Depending on the method of switching the current transformer windings, three-phase meters installed in power grids are connected according to the following schemes:
- direct connection;
- indirect inclusion;
- semi-indirect connection.
Direct inclusion is called direct, and to understand the differences between the second and third types, it is necessary to take into account the scope of their application. Purely indirect connection is the open installation of current transformers (CTs) on high-voltage power cables of a three-phase line (6-10 kV). This method is found only at power substations and at large industrial enterprises with their own distribution networks. In domestic conditions, this type of transformer connection is not used.
Varieties of the semi-indirect method
There are several schemes for connecting meters based on the semi-indirect method, but the most common are the following:
- ten-wire circuit;
- connection by disconnecting on a special block;
- star connection.
Ten-wire switching
Connecting a 3-phase meter in a 10-wire circuit is the easiest and most reliable way. To implement it, you will need to observe the order of connecting ten wires: three for each phase and one neutral. This option has one indisputable advantage, which is the ability to replace the meter while the power is on. The line is allowed to be left energized even when repairing a device disconnected from it. With such a scheme, the current circuits are reliably grounded, therefore, the possibility of the appearance of a dangerous potential on them is excluded.
Another advantage of the 10-wire connection is that each of the three phases is independently connected. If one of them disappears, the remaining two retain the functionality of the device.
Other connection schemes
Connection by means of contact distributors refers to more complex methods, implemented by switching each of the wires coming from the current transformer. Wye connections are also complex, but in this case fewer conductors are used. When installing the converter, first the unipolar outputs of all three secondary windings are assembled into one common point. After that, the three counter ends of the CT windings are connected to the corresponding terminals of the meter.
There is one more circuit of commutation using a semi-indirect method, called 7-wire. When organizing it, one of the ends of the windings are connected by jumpers directly in the current transformer itself. This option is used extremely rarely in private houses, which is explained by a number of shortcomings of the switching circuit.
The choice of metering device
Before connecting a 3-phase meter suitable for a private house, you need to make sure that the use of this brand of device is provided for by the type of supply network. Next, you need to find out what operating current the purchased meter should be designed for. In this case, one should proceed from the value of the power taken into account by the device and the power consumed in the load. As a rule, in this case, they are guided by the nominal value of the input machine, according to which the following options are possible:
- when using a switch with a setting of "40", the operating current of the meter must be 60 Amperes;
- with a machine rating of 40-60 Amperes, an accounting device with a maximum current indicator of 100 Amperes should be purchased.
When choosing the right meter for a private house, it is important to consider the issue of the possibility of saving electricity consumed in a personal household. Therefore, preference is usually given to modern electronic devices that have a "day-night" function and allow you to take into account the consumption at a preferential rate.
A big advantage of a three-phase meter is the ability to fix the load schedule and keep track of the power consumed for any time period. When choosing such a device, it is important to inquire about its accuracy class (from 0.2 to 2.5) and the permissible temperature range. It is desirable that the latter be as wide as possible (-20º C to 50º C).
Inclusion in a single-phase circuit
In a single-phase network, the voltage difference between the phase conductors A, B, C and zero is 220 Volts, and between the phases themselves - 380 Volts. The so-called "linear" voltage is formed due to the fact that the vectors of the effective potentials in each of the phases are shifted relative to each other by 120 degrees.
With an abundance of sales of various models of single-phase current meters on the market, the inclusion of a three-phase meter in a single-phase network is extremely rare. In most cases, such a switching scheme is similar to direct connection. The difference is that lines B and C are not connected to the meter, only one phase must be connected. A significant drawback of such inclusion is the possibility of problems with regulatory organizations, which really do not like all options for connections that do not comply with current regulations and standards.
New connection rules
You can connect electricity meters in private houses in various ways. The choice of one or another circuit for switching on a three-phase meter is determined by the power of the loads being serviced, as well as the type of the meter itself. The new edition of the PUE under number 7 specifically stipulates the procedure for installing and connecting three-phase and single-phase metering devices. The correct approach to solving this issue is reduced to the implementation of the following recommendations:
- 3-phase electricity meters should be connected according to the simplest and most reliable switching scheme;
- the current transformers used in this case must correspond to the conversion factor provided for the selected meter sample;
- when connecting an electronic device, it is imperative to observe the uniformity of the load of each of the phases of the supply line.
The latter requirement assumes that the currents in each of the load circuits A, B and C must be approximately the same. Violation of this rule entails overloading the neutral conductor and its gradual destruction. Experts call this unpleasant phenomenon "zero burning". It is dangerous in that when zero is broken, the combined neutral conductor loses its protective function.In such a situation, the risk of accidental injury from high voltage to the operator working on the electrical equipment increases dramatically.
When considering the methods of fixing the meter in the switchboard, the following approaches are distinguished:
- fixation by means of three fastening screws (this method is suitable for meter housings of type S or Ш);
- installation of the metering device on a DIN-rail specially equipped in the panel (for R or P enclosures).
In the second case, the position of the mounting rail is adjusted in such a way that the holes on the device body and its own slots completely coincide.
Issues related to connecting a three-phase electric meter in the dashboard of a private house are regulated by regulatory documents (PUE, for example). When organizing and carrying out these procedures, the most important thing is to choose a reliable and safe option for connecting the measuring device to the power line.
