When organizing electrical connections to city apartments or private suburban homes, an input-distribution device must be equipped at their entrance. This component of the power supply system is a separate power cabinet with supply cables and switching equipment located in it. An introductory machine (VA) is an obligatory structural element, without which it is impossible to organize a full-fledged power supply for the apartment, as well as any other residential or non-residential property.
The device and principle of operation of the introductory machine
An input automaton mounted in a control cabinet is primarily necessary to limit the user to the useful power consumed by him. If the current exceeds the value set by this device, it will turn off and completely de-energize the apartment or country house. Given this purpose, it is necessary to consider the device of the input switch, as well as the principle of its operation and location within the cabinet.
It also performs its main function - it turns off the serviced line when the current exceeds the permissible value due to emergency overload or short circuit. But in this purpose it is used as the second stage of group defense. The first thing that should work is a line device installed directly in the damaged circuit.
Like all other circuit breakers (AB), the device mounted at the entrance to the house consists of the following components and parts:
- Enclosures with a set of contact connectors.
- Executive modules that ensure its operation.
- Connecting busbars and fasteners in the control cabinet.
In any devices of this class (including devices used for input), two switching elements, called trip units, are used as executive modules. One of them, related to the mechanisms of thermal action, is designed as a bimetallic plate, and the other as an electromagnetic relay of maximum current. The first disconnecting unit is triggered when the current in the protected line exceeds its nominal value for a long time. The electromagnetic release is activated when a short circuit occurs in this circuit. The values of the tripping currents, as well as the time delays inherent in these devices, are determined by their time-current characteristics.
Often, opening machines in front of the counter perform another function, being a dividing element between the aluminum conductors of the supply cable and the copper wires of the electrical wiring.
Thus, it ensures the compatibility of two metals of heterogeneous structure, the direct connection of which in the form of twisting, for example, is unacceptable. It is fraught with oxidation of both conductive materials and subsequent disturbance of contact. And this usually leads to heating of the junction and its gradual destruction.
The introductory machine is traditionally installed directly in front of the meter, which allows you to take into account all internal consumers, as well as register the lack of connection to the power line cable. The second case is when the apartment is completely de-energized and the meter is completely disconnected from the mains.
The main parameters to consider when choosing
The main parameters taken into account when choosing an input device include:
- Rated current and power.
- Mounting method within the cabinet.
- The number of poles available for this VA model.
As additional characteristics that help to choose the right model of the machine, its time-current indicators are considered.
Rated current and power
The rated current of any machine is indicated in the marking on its case (C40, for example). A digital indicator means the value of the current component at which this device is able to work without disconnecting for a long time.
The nominal value is set at an ambient temperature of 30 degrees.
If it decreases, this indicator increases, and when it increases, it decreases.
Together with the rated current, the power that this device can commute without the threat of failure is estimated. For input machines, its value is not more than 5.5 kW - this indicator is selected for a single-phase circuit. A significantly larger parameter - up to 9.5-16 kW - is allowed when the device is turned on in a three-phase network.
VA power change
There may be situations when the 40 Amp input circuit breaker installed when the system was put into operation is not enough for normal operation - it is knocked out all the time. In this case, you can invite an electrician and order a more "powerful" device. But before setting the VA to 63 Amperes, for example, you need to coordinate this procedure with the management company (cooperative council) and Energosbyt services. Only in this case, no one will have any claims that this consumer takes power more than what is required by the standards and that residents of other apartments suffer from this. Such a situation is possible due to general overload and the constant shutdown of collective entry into the house.
For private households, matching the increase in the three-phase load on the input circuits can be even more difficult. It all depends on the amount of power requested and the capabilities of local substations.
Mounting Methods
According to the design features of circuit breakers, several options for their fastening are allowed:
- in most cases, the input device is mounted on a DIN rail mounted on the switchboard housing;
- if there is no such rail, it is allowed to mount it on special screws that are included in the delivery;
- in older models of automatic machines, it is possible to install several devices of the same type on special guide rods (this method is practically not used now).
Preference is usually given to the first of these techniques, as the simplest and most convenient in execution.
Number of poles and time-current characteristic
According to the provisions of current standards (PUE, in particular), according to the number of simultaneously switched circuits, all input protection devices are divided into the following types:
- Bipolar devices.
- 4 pole circuit breakers.
The first are used in switching circuits of a single-phase input, providing a residential apartment with a typical power supply of 220 volts.
According to the requirements of the PUE, it is strictly forbidden to install two single-pole input automatic machines in the cabinet instead of one bipolar.
In this case, the releases will not be able to operate synchronously, which is a safe condition for switching input power lines. Devices of the second type (with 4 poles) are placed in the line of three-phase power supply voltage of 380 volts. It is not allowed to install three-pole disconnectors in such circuits (according to the PUE), since zero must be switched along with the phase in them.
Under current-time characteristics are understood the magnitudes of the currents at which the input circuit breaker disconnects a specific power circuit, as well as the resulting time delays. These parameters are directly related to the operation of the thermal and electromagnetic releases included in the device.
Introduction circuit breaker
When connecting an input automatic machine, it is important to observe the rule according to which a common cable is connected to the upper terminals, and the bends are made from below. To determine the supply points of the power cable cores, you will need to find the contacts with the designations F1, F2, F3 and neutral wire N. If there is no special marking, the buses are connected to the contacts in ascending order of their number when counting from left to right along the comb. In a 4-pole device, the first three in a row will be phase, and the next one will be an earth one. In a 2-pole analog, the first one from the edge on the left is phase, and the next after it is zero.
The place of inclusion of any input device in the general power supply circuit remains unchanged. It is installed at the entrance of the supply circuit to a sealed electricity meter. After it, it is allowed to install a protective shutdown device of the second stage of operation, which improves the quality of protection against electric shock. It is more convenient to install additional machines and RCDs on a common din rail located in the control cabinet next to the meter.
Installation of an input device in three-phase networks
Installation of an introductory machine in three-phase circuits, used only in the private residential sector, is carried out strictly in accordance with the provisions of current standards. A 4-pole device is installed in the introductory distribution cabinet for a current rating of 63 Amperes permitted for private households. In agreement with the services of Enerosbyt, this figure can always be adjusted upwards.
After obtaining permission for a more powerful introductory machine, the user will only have to replace the old device with a new product, which guarantees normal operation with a significantly increased load.
Calculation of the introductory machine for household power
In order to correctly select the input automaton according to the value of the operating current, first you need to take into account a number of factors that affect its specific value.
- Type of power at this facility (two-phase or three-phase).
- The total power of all loads connected to the line.
- The presence of unaccounted for leaks and the current state of the wiring (its deterioration).
After the calculation, you will need to put a current limiter with well-defined cut-off parameters. If the calculated value of this indicator exceeds the permissible norm, you will have to install a device with a large rating. But before this decision is agreed with the management company (local cooperative) and the services of Energosbyt.
Calculation of AB for an apartment
The calculation of the device for an individual apartment is based on the following generally accepted rules:
- For input into such housing, only two-phase power lines of 220 Volts are used.
- Calculation of the consumed current is made by summing up all consumers connected to sockets plus the power of the simultaneously turned on bulbs (illuminators).
- A correction is made with a margin of approximately 10 percent.
For each individual consumer or apartment, according to the standards, a strictly limited current load is assigned (no more than 40 Amps).
Taking into account the limitations and corrections, the calculation and selection of the cut-off current of the input automatic machine are carried out. If you need to change its value in a big way, this is necessarily consistent with the local energy services and the management company.
Calculation of the machine for a private house 380 and 220 volts
It is possible to correctly calculate which machines to put in a private house only when taking into account the following points:
- What loads are supposed to be used in the farm, and whether there is equipment among them that needs three-phase power.
- The total number of these loads and the power consumed by each of them.
- With the availability of 380 Volt equipment (pumps, heating boilers, motors, etc.), a 4-pole circuit breaker is selected, and in their absence, a two-pole circuit breaker.
For a three-phase network, the permissible current through the releases is calculated separately for each phase.
The choice of a specific value of the rating of the machine is possible only after the exact figure of the total capacities connected to the line from single-phase or three-phase loads is obtained. Having decided on how many amperes the machine is placed in the house, they proceed to the direct installation of this device, which is important for the power supply system.
Correct calculation and proper selection of an introductory automatic device is given special importance for the following reasons:
- The operability of the energy supply system of a residential facility (apartment or private house) depends on the correct selection of VA for current.
- There will be no constant operation at the slightest deviation in the connected loads.
- A good machine, tested in performance, will allow you to quickly turn off an apartment or a house if necessary.
If all these conditions are met, the operation of the apartment electrical network will be significantly simplified and will not turn into a source of constant problems and misunderstandings over time.
