The presence of protective automation at the voltage input to an apartment or a private house is a necessity dictated by security. On the shelves of stores today you can find a variety of devices that can help in solving this issue. But often people do not fully understand what this or that device is intended for, confusing, for example, RCDs with other types of protection. This article will open the veil and explain what a differential machine is, how to connect such a device, what you should pay attention to when choosing.
What is a protective device like this
Differential circuit breakers are installed in water switchboards and protect a person from electric shock in the event of an insulation breakdown on the housing of a household appliance, as well as a short circuit. This is a technically sophisticated device that combinesthe properties of an RCD and a circuit breaker. It is worth dwelling on the mentioned devices in more detail in order to understand the work they perform.
Circuit breaker: device and principle of operation
This device is designed to protect the home or industrial electrical network from overload and short circuit. The machine consists of a solenoid and a movable rod. Under normal load, the voltage on the coil keeps the stem in the neutral position. In the event of a short circuit or network overload, the solenoid pushes out the stem, which opens the contact. As a result, the power supply to the premises is interrupted.
Residual current device: what functions does it perform
RCD operates in a completely different scenario. Both wires pass through it - phase and zero. When voltage is applied, the current on both wires is balanced. In the event of a breakdown of the insulation on the body of a household appliance and a person touches it, the potential difference changes, as a result of which the automation works, turning off the power. The response of the RCD to an emergency situation is instantaneous, it is a fraction of a second, which allows you to protect a person from the onset of the consequences of an electric shock.
The problem with the residual current device is that it does not respond to a short circuit. That is why the RCD is installed in tandem with the circuit breaker. Otherwise, if a short circuit occurs, the device will simply burn out without turning off the power supply to the power network of an apartment or a private house,which can lead to disastrous results.
The issue of comprehensive protection can be solved in another way by installing a differential automaton instead of the “cut-off / RCD” pair. Such a solution has both many advantages and disadvantages, which means that you should understand this in more detail.
Features of differential automata and their principle of operation
Such protective devices are able to turn off the power supply to the power network of the apartment in case of overload or short circuit, but at the same time they also work for current leakage, by analogy with the RCD. Three-phase or single-phase differential circuit breakers provide comprehensive protection aimed at preventing wiring burnout and human injury in contact with live surfaces.
To test the performance and quality of the protection provided, you can conduct a little experience. An evenly cut cable connected to a conventional circuit breaker is lowered into a bucket of ordinary tap water. At the same time, absolutely nothing happens, which is not surprising - there are few s alts in such a liquid, it cannot become a full-fledged conductor. Next, the cable is connected through the installed difavtomat. When lowering the cut edge into the water, an instant cutoff occurs, the device turns off. This experience clearly proves the advantage of a differential automaton over a conventional one.
Advantages and disadvantages of such protective devices
Positive qualities of suchenough equipment. The RCBO (Residual Current Circuit Breaker) saves a lot of space in the switchboard. This is especially important when it is necessary to fit many devices on a DIN rail in a small box. When using RCBOs, installation becomes much easier - there are no extra wires and connections. The quality of device protection is also at a fairly high level. However, it was not without flaws either.
The cost of any type of differential machine (single-phase or three-phase, input or separate) is significant. It exceeds, for example, the price that you have to pay for the RCD. Moreover, if the RCBO is turned off, it can be difficult to understand the reason - it is overload, short circuit or current leakage. Of course, devices with special indications are offered on the Russian market today, but their cost is even higher. Breakdown is also a problem - if one node fails, you will have to change the entire RCBO, while when installing the automatic / RCD pair, it is possible to change only one of the protection elements.
How to connect a differential machine in a shield: nuances and common mistakes
When installing RCBOs, inexperienced home craftsmen quite often go the wrong way. The main reason for this is the lack of knowledge on the topics of protective grounding and zeroing. The result will be an unreasonable periodic shutdown of automation.
Despite the differences between the differential machine and the RCD, the installation essence of these devices is similar. If during operation the neutral comes into contact with earth, the RCBO considers this as a leakage and disconnects the voltage. This is a very important point that should not be overlooked. The differential machine can also work if the wiring of the home electrical network is incorrect, errors in the installation of sockets.
Connection order: step by step instructions
If you fully understand the essence of the work algorithm, then there will be no difficulties in their implementation. Before connecting the differential machine in the shield, the voltage must be removed, this is a prerequisite. After making sure that there is no current with an indicator screwdriver, you can proceed with the installation. AVDT is installed after the electricity meter. Between it and the meter, additional protection, as in the case of an RCD, is not required. After making sure that the markings on the front side are not upside down, you can fix the device on the DIN rail.
Contacts on the body of the difavtomat are marked with the letters N (neutral) and the numbers 1, 2, 3 (if the device is single-phase, then only one). The input is suitable for the upper contacts of the RCBO, the distribution into groups is carried out from the bottom. The ground wire does not come into contact with the contacts, it stretches directly from the busbar in the shield to the main junction box of the apartment. Here is the answer to the question of how to properly connect a differential machine. However, even with error-free installation, RCBOs may malfunction.
Why difavtomat turns off for no apparent reason
Most often the problem is the wrongconnecting sockets. Many "craftsmen" believe that if you put a jumper from zero to ground, an expensive household appliance will be thoroughly protected. This is a pretty dangerous misconception. In order to understand the reason, let's dwell a little more on the theory.
Ideally, three wires are suitable for the outlet - phase, neutral and ground. The last two are disconnected in the switchboard according to all the rules. There is a breakdown of the phase wire on the housing of the household appliance. When a person comes into contact with a metal surface that is energized, the current rushes along the path of least resistance, through the body to the ground. This is what creates the leak, which catches the differential machine, instantly turning off the power supply.
Now it's worth considering what happens when you connect the neutral wire to the ground contact. If there is no load on the outlet, the RCBO does not pick up any changes, however, it is worth turning on any household appliance that has a grounding contact on the plug, as the above described is repeated - a short-term small leak leads to a cut-off, the electricity is turned off. That is why, before connecting the differential machine, it is worth checking the wiring of the sockets if they were not installed by the home master himself.
Installation of RCBOs without ground busbar
In the switchboards of old houses it is rare to find a ground bus. This does not interfere with installation, but significantly increases the risk of injury.electric current. Before connecting a differential machine without grounding, it is worth considering whether it makes sense to purchase an expensive device. Yes, it will protect against short circuits, overloads and sudden power surges, but a regular circuit breaker will also cope with this.
If a private house is purchased and there is no ground loop around it, for the sake of your own safety and to protect household appliances, it makes sense to equip it. It will not take much time, and the he alth of loved ones is more expensive. For apartment buildings, this is also possible, but involves some difficulties in reconciliation.
Conventional and separate installation of RCBOs: differences
Depending on the number of consumers and humidity in the room where the switchboard is installed, different types of connection are used. If the apartment is small and the load on the power grid is small, installation is carried out in the usual way - a differential machine is installed after the electricity meter and is responsible for protecting all groups. However, this is not always enough.
So how to connect differential breakers if the power consumption is high or the humidity in the room is high? In this case, you will have to purchase several protective devices, installing each on a separate group. The connection diagram is as follows. Meals are divided into groups, for example:
- Kitchen appliances.
- Bedroom and hallway.
- Living room and nursery.
With this disconnect3 difautomats are required, the power to which is connected after the counter in parallel. From each of them, in this case, a separate line will depart. Such installation of difavtomatov increases financial costs, but significantly improves the protective characteristics of the entire scheme.
There is quite a lot of debate among specialists about the rationality of using differential automata. But sometimes the master simply has no other choice - there is not always enough space in the distribution cabinets. One thing can be noted - when purchasing such protective equipment, you should not try to buy something cheaper. It is better to give preference to more expensive products of well-known manufacturers that have proven themselves on the Russian market on the positive side.
In conclusion of the topic
The installation of protective automation is necessary, it is pointless to argue with this statement. But it should be understood that all actions must be performed, observing the rules and safety precautions. If you carefully deal with the question of how to connect a differential machine only once, then such work will not cause any difficulties. The main thing is the correct choice of protective device. If the home master did not make a mistake with him, the RCBO will last a long time, eliminating the very possibility of emergency and dangerous situations.
