2023 Author: Philip Bishop | [email protected]. Last modified: 2023-05-24 22:24
- The principle of operation and operation of the RCD
- Motivation for installing an RCD. Electric current hazardous to the human body
- Selection of RCDs depending on leakage currents
- The causes of the leakage current
- Types and types of RCDs; visual and technical designation
- RCD sections
- RCD tripping, main and additional reasons
- The main types of RCD connection
- One protection device and several circuit breakers
- The main types of incorrect connection of the RCD, zero working and protective conductor
- Cotton to ampere converter, online calculator
The main protection of the human body from dangerous voltage and the action of electric current in household and power electrical networks is the installation of a residual current device. In addition, the RCD is used to protect household appliances from emergency operation in household and power networks of direct and alternating sinusoidal current. But very often it works and the household consumer is interested in why the RCD is turned off at the input or the RCD is constantly triggered.
The principle of operation and operation of the RCD
The sum of the currents that enter the section must equal the currents that go out. This is the main principle of operation of this residual current device. The reason for the disconnection of the RCD for power supply is that the currents that leave the section of the electrical network are not equal to the currents that enter this network. This difference is called the magnitude of the leakage current or the differential current. The vector sum of the currents in the phase conductor ( I1 ) must be equal to the currents in the neutral conductor (I2). They are the same in magnitude, but multidirectional in direction and thus compensate each other and EMF (electromotive force) is absent. If these currents are not equal, then there is a difference between them and this is the leakage current. He, in turn, creates an EMF and it, in turn, through the solenoid acts on the disconnecting mechanism and the RCD is turned off.
Motivation for installing an RCD. Electric current hazardous to the human body
In Fig. 1, the normal mode is I 1 = I 2. When a person touches a bare wire, a differential current I∆n occurs. If we calculate the current that will pass through a person, we get I = 230 / R h, A, where 230 V is the voltage of the household electrical network, R h- human resistance. Although this characteristic is individual for each person, it is considered to be about 1 kOhm (1000 Ohm). As a result, we get 230/1000 = 23 mA. It should be noted that the human sensitivity threshold starts from 0.6 - 1.5 mA. With this current, a person has a tangible irritation. At a current of 10 - 15 mA, a person experiences a muscle spasm, and this current is called non-releasing. In this case, a person cannot independently release the bare wire if he has taken it. At a current of 90 - 100 mA, a fibrillation current occurs. With this current, the heart muscles contract chaotically, and after a few seconds the heart stops. A current safe for humans is considered 2 mA when it passes for more than 10 s, and if more than 120 s, then a safe current is 6 mA. These currentsas well as the shutdown time must be remembered when choosing a residual current RCD in order to understand what will happen to you if you fall under a dangerous voltage. For these reasons, remember that if the RCD of a water heater turns off, then it saves you at least from unpleasant sensations.
Selection of RCDs depending on leakage currents
According to SP31-110-2003 p. A.4.15, if the bathroom is powered by a separate line, then it is necessary to provide an RCD for 10 mA, if the line is common with the kitchen and the corridor, then it is necessary to install an RCD for a current of up to 30 mA. For an ordinary household power line (sockets, lighting), a protective device is selected for a current of not more than 30 mA (PUE clause 7.1.79.). RCDs for differential currents of 100 and 500 mA, as seen above, do not protect the human body from dangerous voltages, and the main purpose is to protect against fire. When installing a residual current device, you need to understand that it does not protect against prolonged overload, maximum currents or overvoltage. For these reasons, its installation must be combined with a circuit breaker with an electromagnetic and thermal release, and for overvoltage protection, an overvoltage relay or an SPD (surge voltage protection device) must be installed. For these reasons, if the Termex turns off the RCD and the machine does not work, then the cause of the malfunction is the leakage current.
If the RCD is turned off simultaneously with the circuit breaker, then the cause of the malfunction can be both the differential current and the maximum currents that occur during a short circuit.
The causes of the leakage current
It must be well understood that the presence of a leakage current is an emergency mode of operation or malfunctions in household electrical networks or malfunctions in household appliances. The causes of this current are quite common. The main reasons for the occurrence of a leakage current are a person's contact with a bare wire, its flow through the deformed cable insulation or through a conductive element. For example, the reason for the disconnection of an RCD on a water heater may be the leakage current through the water. The cable insulation was damaged, moisture got on the bare wire and current flowed through it. This current is just not enough for the difference between the incoming and outgoing currents to be equal to 0 (zero) and the protection turns off the emergency section. If this is a Termex water heater, the RCD of this device is turned off. Water can also be the reasonwhy the RCD is turned off on the pump pumping various liquids.
Types and types of RCDs; visual and technical designation
- Household and power supply voltage 220/380 V.
- By the number of poles. If there is a single-phase load in the power network, then the RCD must be installed two-pole, if a three-phase load, then four-pole.
- According to the rated operating current. The value of the rated (operating) currents for the RCD is the same as for the circuit breakers, it is 16, 25, 32, 40, 63, 80 A.
- By the differential current (leakage current), the value of which the residual current device is guided by is 10, 30, 100, 300, 500 mA.
By the type of leakage current, which in turn is subdivided into:
- Alternating electrical sinusoidal and pulsating current. The RCD type for a given current is " AC". The pulsating current is present in dimmable lamps and lamps, in washing machines where the speed is regulated.
- Variable and constant electrical pulsating, type RCD " A". This type of protection device is recommended for use where there is consumer electronics, microwave oven, computer, TV, etc.
- Constant electric and variable, RCD type "B". This type of protection device is mainly installed where there is rectified current. This type is not used in household electrical networks.
- To ensure that selectivity is observed when installing 2 or more protection devices in household and power electrical networks, an RCD with a trip time delay is used, this is the RCD type "S". This type of RCD is used in networks where ATS (automatic transfer switch) is used, and type " G ", in the same networks, but has a shorter time delay.
RCD tripping, main and additional reasons
The most common reasons for the operation of an RCD on an electrolux boiler or water heater is an unscrupulous manufacturer or various types of problems in the electrical network. If the RCD on the water heater turns off, then you must turn it on again. If the appliance works and the RCD does not turn off, then there was a short-term leakage current. Next, you need to use the "Test" button. It simulates emergency operation.
- It is necessary to turn off the machines that are included in the network together with the RCD and determine why the RCD is turned off. At the same time, we disconnect the zero working conductors. After they have been disconnected, turn on the RCD. If it has not turned off, then click on the "Test" button. If after pressing "Test" the RCD worked, then it is working properly. It should be noted that the functional check of the residual current device must be checked at least once a month by pressing the "Test" button.
- If, during connection, an RCD operates without a load, then it is out of order or there are leakage currents in the place of its installation. If it is working properly, then you need to figure out why the RCD works without load. In this case, if several machines are connected from it, then we disconnect all of them at once. Then we determine why the RCD is turned off and turn on the circuit breakers in turn and determine the emergency section of the electrical network.
The main types of RCD connection
Any electrician who has at least the 3rd category of an electrician can connect an RCD. The connection diagram is written on the device itself and there is nothing difficult there. The only thing that needs to be done before installation is to take into account the nuances when connecting to the network and choose the right number of outgoing machines for one RCD. It is possible to install one protection device for the entire apartment in the floor panel if it is an apartment building, as shown in Fig. 3. Can be installed separately on the socket and lighting, if there is enough space for installation. This will be the best option for an apartment. When installing and choosing an RCD, it is necessary to take into account the rated (operating) current, which should be one step higher than the rated current of the machine, which is located after the protective device. For example, if the machine is 25 A,then it is necessary to install an RCD in front of it with an operating current of 32 A, etc. If this is a private house, then it is better to consider the following configuration, one RCD and one automatic machine, if there are not many machines.
One protection device and several circuit breakers
If, for example, there are many machines in a house (one machine = one room, or = one electrical appliance), then in this case the dimensions of the electrical panel can be huge. For these reasons, it is better to complete the electrical panel so that several circuit breakers are installed under one RCD, but no more than 5. In this case, it is necessary to correctly calculate the rated current of the protective device relative to the outgoing circuit breakers so that their sum does not exceed the operating current of the residual current device. For example, the outgoing machines BA1 16 A, VA2 16 A, VA3 32 A, the sum is 16 + 16 + 32 = A. So the RCD should be for a rated current of at least 64 A, and knowing the range of rated currents, the best option is a residual current device for the rated current at 63 A.
As seen in Fig. 4 there is nothing complicated when connecting, but in some cases, it will be interesting to know why the RCD on the Ariston water heater is triggered if the household network and the protection device are in satisfactory and working condition. When an RCD is triggered, the reasons may be in its incorrect connection.
The main types of incorrect connection of the RCD, zero working and protective conductor
- It is impossible to connect the zero working (N) and the phase conductor that has passed through the RCD with other neutral and phase conductors after the RCD.
- It is impossible to make the connection of the neutral working conductor (N) after the RCD with open structures of the electrical installation, and also it cannot be connected to the protective conductor (PE).
- It is strictly forbidden to connect the zero working and protective conductors in the socket.
- If two protective devices are installed in the electrical network, then the combination of neutral working conductors will lead to the appearance of an additional leakage current and, as a consequence, the operation of both.
- If a lot of RCDs are installed in the electrical panel, then it is worth rechecking the connection diagram so that there is no connection of the phase wire and working zero from different protection devices.
Only a properly selected protective shutdown device and its correct connection will protect a person in the event of an accident from the dangerous effects of electric current.
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