In connection with the massive use of electrical devices in everyday life and at work, there is a need to protect a person from electric shock. A three-phase RCD is a special device that implements this function. The specified unit must be connected using special circuits, which will guarantee its efficiency.
- Purpose and principle of operation
- Selection criteria for a three-phase RCD
- Sensitivity
- Differential current
- Number of terminals
- Amperes
- Preparing to connect
- Connection diagrams to a three-phase network
- The need for grounding
- Connecting the residual current device
- Phase zero search
- Phase connection
- Connecting output devices
- Errors when installing the RCD
Purpose and principle of operation
A 3-phase RCD is designed to equalize the current that flows through the phase and neutral wires. In the absence of emergency situations, the indicated values are equal. Stable operation of electrical devices is possible, since the counter currents in the windings cancel each other out. In the event of an emergency, the protection device switches off the power supply to electrical appliances. This is observed when the insulation of the wires is broken, which provokes the leakage of charged particles. As a result, the currents flowing through the neutral and the phase conductor will have different values.
In every home, a situation can happen when an electric current breaks through to the body of a washing machine or water heater. When the potential begins to flow to the floor, a 3-phase RCD will react and turn off the power to the devices. Therefore, when using this circuit breaker, you can be sure of your safety.
Connecting an RCD is important for powerful electrical appliances in the kitchen and bathroom. Condensation collects on their metal case, which together forms a potential conductor of electricity.
It is good when a protective shutdown is present on outlets, lamps and low-power household appliances. In the event of emergency situations, these consumers are no less dangerous to humans.
Selection criteria for a three-phase RCD
The principle of operation of all RCDs in a three-phase network is the same, but these devices differ in design and operational characteristics. Therefore, when buying a specific model, you need to take into account many nuances.
Sensitivity
The RCD can work with or without an additional power supply. In the first case, he directly takes part in the process of opening the electrical circuit. The presence of this mechanism increases the cost of the device, but also increases its sensitivity.
In the absence of an additional power source, the RCD is triggered in response to the differential of the magnetic field.
Differential current
RCDs designed for 3 phases are able to regulate the value of the differential current at which it is triggered. In the absence of this function, the devices respond to 5 mA as standard. Such a current indicator clearly indicates the presence of an emergency and the need to turn off the electricity supply.
Number of terminals
For a three-phase network, be sure to buy a 4-pole RCD. They are equipped with 8 terminals for connecting input and output cables.Three pairs are intended for connecting the working phase, one for zero.
Amperes
In order for the residual current device to function at any current, it is necessary to choose a model where the number of amperes is significantly higher than that of the machine.
There are universal models on the market. They provide the ability to connect multiple networks at the same time. Despite this advantage, such units have many disadvantages. They are less sensitive, are characterized by a complex wiring diagram, and are more expensive. Such models are suitable for enterprises, but not for private use.
Preparing to connect
Correctly performed preparatory and installation work will ensure the stable operation of the RCD.
Connection diagrams to a three-phase network
When installing an RCD, the following working diagrams are used:
- Complete disconnection of the electrical circuit. One unit has the ability to de-energize all electricity consumers in the event of an emergency.
- Partial shutdown of devices. When emergencies occur, only some consumers are de-energized.
The first connection diagram is used in apartment buildings. Installation of the device is carried out near the electricity meter. If the RCD trips, the whole house is de-energized.
When using the second scheme, the protective mechanism is installed on a piece of electrical wiring going to a specific room. Since all devices are connected in series to the circuit, when the RCD is triggered, only the “problematic” consumer will turn off, while others will continue to function.
The second variant of the scheme can be implemented in a different way. The point of installation of the RCD is the beginning of the serial connection to the wiring, which makes it possible to realize the selective operation of the unit for certain groups of consumers. Also, the protective mechanism can be installed directly in front of the exit device.
The need for grounding
Old power grids belong to the tn-c system, where there is no neutral conductor to connect to the ground. In this case, protection must be provided separately for the house or equipment, which ensures safe drainage of currents. In the absence of grounding, it is prohibited to install a 4-pole RCD.
The correct connection diagram to the electrical network provides for the observance of the following rules:
- The grounding conductor is connected to the output cable only. Direct connection of an RCD is not allowed.
- In the presence of a single-phase network, a four-pole device cannot be used.
- Connection to the B3 network is prohibited.
The grounding conductor is a separate item. The absence of additional terminals in the RCD for its connection only indicates this.
Connecting the residual current device
It is not difficult to install an RCD, having basic information about the operation of electrical equipment. The manufacturer encloses a technical data sheet for each device. It specifies the recommended wiring diagrams to be used during installation.
Phase zero search
Determining the zero phase is very simple empirically. You need to take two wires and connect them to the ends of the bulb holder. Its ignition is observed if it is connected to a phase. Otherwise, nothing will happen.
Connecting a light bulb to two phases at the same time is allowed to be carried out for a short period of time. It is also possible to close such a circuit only for a short period. Otherwise, there is a high probability that the circuit breaker will trip.
Phase connection
If it was possible to find zero, you must immediately connect it to the corresponding terminals. The remaining three wires are working phases. They are connected in any convenient way, which does not in any way affect the functioning of the RCD.
After completing the installation, it is necessary to check the functionality of the system.For this, the tester is launched, which is included in the standard equipment of the device.
Connecting output devices
Connecting several sockets to one RCD occurs only in a parallel way. To accomplish this, each core is divided into the required number of wires. If you do not adhere to this installation scheme, the device will not be able to fully work and be triggered in the event of an emergency.
Errors when installing the RCD
To ensure the stable and safe operation of the power grid, the following mistakes must be avoided:
- The input terminals of the RCD are connected to the network after a special machine. Direct connection is strictly prohibited.
- It is necessary to connect correctly and not to confuse zero and phase contacts. To facilitate this task, there are special designations on the body of the devices.
- In the absence of a grounding conductor, it is strictly forbidden to replace it with a wire draped over a water pipe or radiator.
- When buying devices, pay attention to their main performance characteristics, the magnitude of the currents. If the line is rated for 50 A, the instrument must have a minimum of 63 A.
When performing installation, it is extremely important to comply with electrical safety rules. Before starting the installation, the RCDs de-energize the network. Before starting the device, check the correct installation of the system elements.
