In recent years, intra-house electrical networks have become much more complex, the load on them has increased several times. The requirements for protection devices have also increased — the notorious “plugs” (protective circuit breakers for a screw cartridge) are technically outdated and are used less and less in EU. They were replaced by more modern and advanced modular circuit breakers mounted on a DIN rail.
First level of protection — circuit breakers
Devices of the first level of protection — automatic switches — basically protect the intra-apartment wiring and power receivers from the damaging effects of high current, which occurs primarily during a short circuit. Accordingly, it is necessary to choose a device depending on the cross-section of the wire and the way it is laid.
In everyday life, switches are used, designed for a rated current from 6 to 32 A; this figure must be indicated on the product. Simplistically, we can assume that 6 and 10 A machines are used in lighting networks with a small load (less than 1 kW for a single-phase 220 V network). 16 A machines are installed in apartments most often. For particularly powerful equipment (for example, instantaneous water heaters), automatic machines of 32 A or more will also be required.
What happens to the circuit breaker when the load in the network reaches a dangerous value? The wire starts to heat up. The device includes a thermal release with a bimetallic plate. When a certain temperature is reached, it acts on the cocked shutdown mechanism, which breaks the contact. If the load slightly exceeds the nominal, the machine does not turn off soon. But when the load is twice the nominal, the shutdown will follow in a few seconds.
To turn off the network during a short circuit, another release is used — electromagnetic. It cuts off the current almost instantly — in milliseconds. At this moment, a very large short-circuit current passes through the machine — thousands of amperes. Household models of automatic machines are usually designed for a maximum short circuit current of 4500 or 6000 A. If it is higher, then the release will not be able to break the circuit.
When choosing a circuit breaker, in addition to the rated current, pay attention to the type of disconnection. It is denoted by the Latin letters B, C (devices of other types are not found in everyday life) and means the maximum load that the machine can withstand without triggering the electromagnetic release. Type B devices can withstand 3…5 rated loads before disconnecting the circuit, and type C — 6…10 ratings. Type C automata are used in cases where there are powerful electric motors that can create an additional (so-called reactive) load at startup.
Do not try to connect all sockets and appliances through one switch. It is desirable that each group of devices has its own machine.
What do power outages indicate?
Many users do not pay attention to the frequent tripping of circuit breakers, which is one of the most common mistakes in everyday life. Regularly “knocks out traffic jams”?
Perhaps they are weak, can not cope with the load.
This conclusion is made by the homeowner and goes to the store for a more powerful machine — by 20, 25, and preferably by 32 A. Keep in mind: you cannot replace machines without consulting an electrician! Moreover, shutdowns should not be ignored. As a rule, they signal that some section of the wiring is damaged or cannot cope with the load. If you simply replace the machine with a more powerful one, then the damaged wire will heat up and collapse even faster.
How to prevent current leakage?
Circuit breakers are basic protection against short circuits and network overload.
Unfortunately, electricity can also carry other dangers that other devices are used to prevent.
Electric shock protection. Units of the second level — residual current devices (RCDs) — appeared in the 70s. 20th century and has since been widely used in developed countries. By determining the difference in current strength in the live conductor and the neutral conductor, the RCD is able to detect the current that flows along an unintended route (neutral). If the leakage current (differential current) reaches a predetermined value, the RCD trips and opens the circuit. The response time should be as short as possible (for most devices it is a few milliseconds). The main criterion for choosing an RCD for the consumer is the amount of leakage current (it is indicated on the case).
The most sensitive models operate at a current of 10 mA. Such an RCD can be recommended for installation in wet rooms (bathroom, sauna) or, for example, in a nursery. However, a highly sensitive device can even respond to the connection of sufficiently powerful (2–3 kW) equipment. Therefore, in everyday life it is commonly accepted to use an RCD that operates at a leakage current of 30 mA. Its effect is quite noticeable, but it is considered safe for a healthy adult under normal conditions (at room temperature and low humidity). But such a current allows you to connect sufficiently powerful equipment to the network.
How to use RCD correctly?
The residual current device needs regular performance monitoring. The latter, however, will not be difficult — once a month you need to press the button located on the RCD case. A healthy device will turn off and turn off the voltage.
Fire protection. Devices of the third level of protection — fire differential load switches. In fact, they are the same RCDs, but with a higher trip current (hundreds of milliamps). Such switches are designed to protect against the negative effects of hidden wiring damage.
For example, a conductor broke in some area, the screw clamps on the socket terminals loosened (they need to be tightened regularly, but few people do this) — accordingly, the conductive ability worsens, the damaged area begins to warm up. The heat can be strong enough to eventually lead to a large leakage current and a fire. Fire protection differential switches respond to such leakage. These devices can be recommended to owners of old houses with dilapidated wiring.
The first three levels involve protection from problems associated with internal factors. The next two levels are protection from adverse external influences.
Over voltage protection. If instead of 220 V, 250–280 V is suddenly supplied to the network, then household appliances can massively fail. Many manufacturers, knowing about the unpleasant features of domestic networks, supply their equipment with built-in protection, however, special devices of the fourth level — differential switches (RCD with overvoltage protection) — provide effective protection for all house equipment.
SPDs must be installed in all buildings with lightning rods, as well as in houses with overhead power lines located in areas where thunderstorms are frequent (more than 20 hours per year).
Surge protection. Appropriate devices of the fifth level (the so-called SPDs) protect the internal electrical network from the effects of powerful (thousands of volts), but extremely short in time (of the order of microseconds) voltage surges that are detrimental to sensitive electronic equipment.
Circuit breaker selection parameters depending on the type of electrical appliances and the nature of the load
|Electrical appliance (device)
|Rated current of the circuit breaker, A
|Storage type water heater
|Instantaneous water heater
|Kitchen sockets (electric kettle, toaster, bread machine)
Devices of each level of protection solve their own range of tasks and, by and large, do not intersect with devices of other levels. However, some of them can perform the functions of several levels of protection. For example, there are so-called difautomats, which are a combination of automatic switches and differential current switches, that is, devices of the first and second levels. They are recommended to be used, in particular, when there is an increased risk of a short circuit to earth. For example, street segments of the electrical network (garden sockets and lighting elements) are equipped with difavtomatami.
All devices must be connected in strict sequence, in accordance with the recommendations of manufacturers and the requirements of GOST R 51628–2000 “Distribution boards for residential buildings”. Wiring diagrams can be complex, so leave the job to a qualified electrician.
All modern circuit breakers are quite complex devices, when connected, polarity, input and output terminals must be strictly observed, and also not to confuse, say, phase and neutral. Unfortunately, RCDs and other devices are often connected incorrectly. In such cases, the RCD will not work and, most likely, will fail. When properly connected, all devices, as a rule, serve “from repair to repair”.
Breakdowns usually occur due to some external cause. For example, too much short-circuit current when the contacts open causes a powerful spark, similar to a welding arc. In general, each operation of the machine slightly reduces its resource. Therefore, do not use protective devices as mains switches. For power management, it is best to install special circuit breakers. If there is no such switch, then before turning off the protective devices, disconnect the entire load from the network, turn off the equipment and lighting.
One of the most common myths is that RCDs do not work in a two-wire network (without ground). In fact, if there is no earth, then RCDs can not only be installed, but necessary! If, say, something goes wrong in a washing machine without a short circuit (on a 220 V case), its operation without an RCD will be deadly.
Easy9 launch manager, schneider electric