Relays for household electrical networks: types, purpose and principle of work

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The article discusses the device of modern relays, use in everyday life and connection of a voltage control relay, differential relay, time relay, priority power control relay, light control relay, temperature control relay, power relays or contactors.

Relays for household electrical networks, their types, purpose and principle of work

What is a relay

A relay is a device capable of switching (breaking or connecting) various elements of the electrical network when a condition controlled by it occurs. In the home electrical network, various types of relays are used to organize the automatic execution of operations that require turning on and off electrical appliances, as well as a number of protective functions.

A modern relay used in everyday life usually consists of three elements assembled in one housing:

  1. A sensor that monitors the signal and transmits it to the processing module.
  2. A processing module, usually based on a microcontroller, which analyzes the received signal by comparing it with a preset value. When the controlled signal reaches the response value, the processing module sends a signal to the switching part.
  3. The switching part is an electronic key or an electromagnetic relay that breaks or switches the power supply.

Depending on the type of sensor and evaluation module used, the following relay types are the most common:

  1. Voltage monitoring relay.
  2. Differential relay or RCD.
  3. Time relays and programmable timer relays.
  4. Power control relay.
  5. Light control relay.
  6. Temperature control relay.
  7. Power relays or contactors.

Consider all the above types of relays in more detail.

Description and principle of operation of the voltage monitoring relay

Since the quality of power supply in most Russian cities remains rather low, it is necessary to independently resolve the issue of protecting household appliances from sudden surges in the power supply network. Most voltage monitoring relays are based on a high-speed microcontroller, the function of which is to constantly monitor the magnitude of the supply voltage. When the voltage exceeds the specified minimum or maximum threshold, it produces a protective shutdown of the equipment connected through the relay from the mains.

The standard operating threshold of the voltage monitoring relay is the minimum supply voltage less than 170 V and the maximum – 250 V. After shutdown, the device continues to monitor the supply network, after the voltage stabilizes at a safe level, a time delay is turned on, after which the relay automatically connects the protected power network to the supply power system.

Relays for household electrical networks, their types, purpose and principle of work Block diagram of voltage monitoring relay

These devices are recommended to be installed directly after the input machine and the meter, due to which the entire internal power grid is protected by one relay.

Relays for household electrical networks, their types, purpose and principle of work Voltage Monitoring Relay Connection (DIN Rail Mounted Barrier)

The choice of the power of this relay is made taking into account the occurrence of current surges while simultaneously disconnecting a large number of electrical appliances, especially running motors. The most optimal is a 4 or 5 times excess of the switching current of the voltage monitoring relay on the input circuit breaker.

In the event that it is necessary to protect only a single household appliance or a small group, you can use a voltage monitoring relay, made in a housing for a standard outlet or located in an extension cord housing.

When buying this type of relay, it makes sense to give preference to more expensive models with indication of the value of the mains voltage and the ability to independently change the upper and lower limits of protection operation.

When choosing a voltage control relay, you can focus on various time-tested manufacturers from the CIS. The explanation is simple – we have common problems with electricity supply.

Manufacturer Relay type Mount Current, A Price, rub.
DigiTOP V-protector VP-63A DIN rail 63 1125
ZUBR D32t DIN rail 32 720
ZUBR R116y power socket sixteen 620

Description and principle of operation of the differential relay (RCD)

This relay is used in connection with the need to protect a person from the damaging effects of electric current. When a person comes into contact with bare wiring or an energized body of an electrical appliance, a “leakage” current begins to flow through his body.

As is known, in 220 V, 50 Hz networks, when a current of 8-10 mA flows through the human body, very severe pain and spasms are felt, and 100 mA after 2-3 seconds causes cardiac arrest in an adult. It is for the protection against leakage currents in power grids that the differential protection relay is intended.

In terms of their internal structure, they can be either electronic with the ability to control the protection operation current, or electromechanical. For household purposes, it is advisable to give preference to electronic ones, since they can guarantee a power outage with a leakage current of 2-3 mA, which will save the life of both an adult and a naughty child.

Relays for household electrical networks, their types, purpose and principle of work The fundamental structure of the differential relay

The principle of operation of an electronic single-phase differential relay is quite simple. The electronics monitors the current flowing through the neutral wire (N) and the “phase” (L), in case of a difference between them exceeding the specified value, a command is given to turn off the power supply.

Thermal and overcurrent protection can be built into the differential relay, which makes it possible to use it instead of an input disconnector or circuit breaker. During switching, it is important to correctly connect the “phase” and “zero” to the relay, in case of an error the differential relay or RCD will not work.

Relays for household electrical networks, their types, purpose and principle of work RCD mounted in a junction box

With regard to differential relays or RCDs, there is an important rule – the trip current must be less than fatal to humans. Many manufacturers from the CIS are reliable, as well as such well-known brands as ABB or Siemens.

Manufacturer Relay type Actuation current, mA Interruption current, A Price, rub.
Legrand TX3 thirty 25 1260
Eaton -Moeller PF4-25 / 2 thirty 25 650

Description and principle of operation of time relays, programmable timer relays

Every home has electrical appliances, the use of which could be optimized by automatically switching on or off with a certain time delay..

The simplest example of using a time relay would be the on-off arrangement of a pressure compressor for aquariums. A time relay can be used to automatically turn off the light in a common corridor after it is turned on, a time relay is irreplaceable when organizing automatic watering, as well as in other automation systems.

Commercially available time relays can be either digital or electromechanical. Due to the presence of an informative screen and a microcontroller control system, a number of models can support the simultaneous counting of several tasks, as well as work in a cyclic mode with reference to the time of day, which can be used in various automation systems.

Relays for household electrical networks, their types, purpose and principle of work Functional diagram of the simplest electronic time relay

Relays for household electrical networks, their types, purpose and principle of work Electronic and electromechanical time relay

The price of these relays very much depends on their capabilities, you need to choose for a specific case, taking into account the accuracy of the adjustment, maximum exposure, the required number of channels.

Manufacturer A type Switching current, A Price, rub.
ABB E 234 CT-TGD.12 Gives impulse 3000
ELKOep cyclic CRM-2H / 230V sixteen 1300
Eltimo Electronic, socket 020S ten 2560

Description and principle of operation of the priority power (current) control relay

Increasing the intelligence of household networks has become possible with the use of power control relays. This equipment is used to limit the maximum load in weak power grids..

Functionally, this relay consists of several monitored lines. Each line to the central processor transmits data on the current in the load, when the total power exceeds the protective threshold, one of the output lines is automatically turned off. In this case, one of the lines has priority over all the others; it is disconnected only in the event of an emergency current. After reducing electricity consumption along the main line, the secondary consumers are automatically switched on.

Relays for household electrical networks, their types, purpose and principle of work Functional diagram of the relay of priority control of power consumption

The maximum power of the protection operation can be adjusted using the controller relay located on the front panel.

Manufacturer A type power, kWt Price, rub.
Novatek-Electro OM-110 0-20 1200
F&F PR-615 1-7 2100

Description and principle of operation of the temperature control relay

Many household heating devices already have a built-in temperature control relay, but since it is located at a minimum distance from the heating device, the accuracy of maintaining the required temperature is rather low. The use of a separate temperature control relay allows you to achieve the optimal temperature in the room, it can be used to automatically turn on / off heaters, fans, air conditioners, refrigeration units.

Many of these devices have built-in screens and displays showing the current temperature in the controlled room and the value of the task. These relays can be combined with a time relay, so that an automatic transition to a lower or higher set temperature can be set depending on the time of day or day of the week.

Relays for household electrical networks, their types, purpose and principle of work Connecting the simplest temperature control relay

The temperature sensor can be supplied either separately or built into the relay, while various types of sensors can be used, connected using 2 or 3 wires.

Relays for household electrical networks, their types, purpose and principle of work Temperature control relay in housing for connection to a standard socket

Manufacturer A type Temperature, ° С Current, A Price, rub.
F&F CRT-04 -20 … + 40 sixteen 3600
Ukrrele RT-10 / P01 0 … + 99 ten 400

Description and principle of operation of the light control relay (twilight relay)

Automatic lighting control allows you to significantly save energy, due to the possibility of timely switching on and off light sources. For these purposes, you can use ready-made relays, to which the light sensors located in the controlled room are connected..

Relays for household electrical networks, their types, purpose and principle of work Connecting the simplest light control relay

In some models, the sensitivity of the photocell used can be adjusted for earlier or later lighting on.

Manufacturer A type power, kWt Price, rub.
F&F AZH-106 3.5 750
TENSE FT-04 1.1 1000

Power relays – contactors

Since most of the relays discussed above are designed to switch loads with a power of hundreds of watts to ten kilowatts, additional high-power switching relays – contactors are used to increase the switching power. With their help, it is possible to switch a load of several hundred kilowatts, thereby expanding the capabilities of the previously discussed relays.

Relays for household electrical networks, their types, purpose and principle of work

The use of various types of relays allows you to optimize the operation of many electrical appliances, protect them from accidental failure, and save your own life. On their basis, it is possible to create a large number of small automation systems, such as devices for maintaining an optimal microclimate, irrigation systems, automatic door opening, light on / off, and many others. Compact dimensions and standard dimensions of the case allow you to connect them directly to standard sockets or use ready-made electrical boxes for their installation, which significantly reduces the cost of automation in general.

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