The presence of protective automation at the input of voltage to an apartment or a private house is a necessity dictated by safety. 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 automaton is, how to connect a similar device, which is worth paying attention to when choosing.
What is a similar protective device?
Differential automatic machines are installed in water distribution boards and protect a person from electric shock in case of breakdown of insulation on the housing of the household appliance, as well as a short circuit. This is a technically sophisticated device that combines the properties of an RCD and a circuit breaker. It’s worthwhile to dwell on the mentioned devices in more detail in order to understand the work they are doing.
Circuit breaker: device and principle of operation
Such a device is designed to protect the home or industrial power network from overload and short circuit. The machine consists of a solenoid and a moving rod. Under normal load, coil voltage keeps the stem in neutral. In the event of a short circuit or network overload, the solenoid pushes the stem, which opens the contact. As a result, the supply of voltage to the premises is interrupted.
Residual current device: what functions does it perform
RCD operates according to 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 insulation on the housing of a household appliance and when a person touches it, the potential difference changes, as a result of which the automation is triggered, turning off the power. The response of an RCD to an emergency is instant, it is a split second, which helps protect a person from the onset of the effects of electric shock.
The problem with the residual current circuit breaker is that it does not respond to a short circuit. That is why the RCD is installed in conjunction with a circuit breaker. Otherwise, if a short-circuit occurs, the device simply burns out without turning off the power supply to the power network of the apartment or private house, which can lead to a disastrous result.
The issue of comprehensive protection can be solved in another way by installing a differential machine instead of a pair of "cutoff / RCD". This 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 apartment’s power network during overload or short circuit, but at the same time they also trigger a current leak, similar to RCDs. Three-phase or single-phase differential machines provide comprehensive protection aimed at preventing burnout of the wiring and damage to a person in contact with surfaces that are under voltage.
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. In this case, absolutely nothing happens, which is not surprising - there are few salts in such a liquid, it cannot become a full-fledged conductor. Next, the cable is connected through the installed difavtomat. When lowering the trimmed edge into the water, instantaneous cut-off occurs, the device turns off. This experience clearly proves the advantage of a differential automaton over an ordinary one.
Advantages and disadvantages of such protective devices
The positive qualities of such equipment are enough. AEDT (residual current circuit breaker) significantly saves space in the switchboard. This is especially important when on a DIN rail in a small box you need to fit many devices. When using AVDT, installation becomes much simpler - there are no extra wires and connections. The quality of device protection is also at a fairly high level. However, it was not without drawbacks.
The cost of any type of differential automaton (single-phase or three-phase, introductory or separate) is significant. It exceeds, for example, the price that will have to pay for the RCD. Moreover, if the AEDT is disconnected, it can be difficult to understand the reason - this is an overload, a short circuit or a current leak. Of course, devices with special indications are offered on the Russian market today, but their cost is even higher. Failure is also a problem - in the event of failure of one node, it will be necessary to change the full automatic circuit breaker, 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 the dashboard: nuances and common mistakes
When installing AVDT, inexperienced home masters quite often go the wrong way. The main reason for this is the lack of knowledge on the topics of protective grounding and grounding. The result will be an unreasonable periodic shutdown of automation.
Despite the differences between the differential machine and the RCD, the essence of the installation for these devices is similar. If during operation the neutral contacts the ground, the high voltage circuit breaker considers this a leak and disconnects the voltage. This is a very important point that should not be overlooked. Differential automatic machine can be triggered by improper wiring of the home electrical network, errors in the installation of outlets.
Connection order: step by step instructions
If you fully understand the essence of the algorithm of work, then difficulties in their implementation will not arise. 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 the indicator screwdriver, you can proceed with the installation. AEDT is installed after the meter. Between it and the counter, additional protection, as in the case of RCDs, 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.
The contacts on the difavtomat case 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 AEDT, the bottom is the distribution of the groups. The ground wire does not come into contact with the contacts, it stretches directly from the bus in the shield to the main junction box of the apartment. Here is the answer to the question of how to connect the differential automaton correctly. However, even with an error-free installation, the operation of the high voltage transformer can cause malfunctions.
Why the difavtomat turns off for no apparent reason
Most often, the problem is the incorrect connection of outlets. Many "craftsmen" believe that if you put a jumper from the zero contact to the ground, an expensive household appliance will be thoroughly protected. This is a rather dangerous misconception. In order to understand the reason, let us dwell a little more on theory.
Ideally, three cores are suitable for the outlet - phase, neutral and ground. The last two are turned off in the switchboard according to all the rules. A breakdown of the phase wire occurs 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 precisely what creates the leak, which the differential machine catches, instantly turning off the power supply.
Now it’s worth considering what happens when the neutral wire is connected to the ground terminal. If there is no load on the outlet, the AEDT does not catch any changes, but it is worthwhile to include any household appliance that has a grounding contact on the plug, as the repetition of the above is repeated - a short-term small leak leads to cut-off, the electricity is turned off. That is why before connecting a differential machine, it is worth checking the wiring of outlets if they were not installed by the home master himself.
Installation of high voltage transformer without grounding bus
In the switchboards of old-built houses, it is rarely possible to find a grounding bus. This does not interfere with installation, but significantly increases the risk of electric shock. Before you connect a differential machine without grounding, you should consider whether it makes sense to purchase an expensive device. Yes, it will protect against short circuits, overload and sudden power surges, but an ordinary 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 its own safety and for the protection of household appliances, it makes sense to equip it. It will not take much time, and the health of loved ones is more expensive. For apartment buildings, this is also possible, but involves some difficulties in coordination.
Conventional and separate installation of AVDT: 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 - the differential machine is installed after the meter and is responsible for protecting all groups. However, this is not always enough.
So how to connect differential machines if the power consumption is high or the humidity in the room is increased? In this case, you will have to purchase several protective devices, each installed on a separate group. The connection diagram is as follows. Food is divided into groups, for example:
- Kitchen appliances.
- Bedroom and hallway.
- Living room and nursery.
With this arrangement, 3 difavtomats will be required, the power to which is connected in parallel after the counter. From each of them, in this case, a separate line will depart. Such installation of difavtomats increases financial costs, but significantly improves the protective characteristics of the entire circuit.
Among experts, there is a lot of debate about the rationality of using differential automata. But sometimes the master simply has no other choice - the space in the distribution cabinets is not always enough. One thing can be noted - when acquiring such protective equipment, one should not try to acquire something cheaper. It is better to give preference to more expensive products of well-known manufacturing companies that have established themselves in the Russian market on the positive side.
To conclude the topic
The installation of protective automation is necessary; arguing with this statement is pointless. But it should be understood that all actions must be performed, observing the rules and safety precautions. If you carefully understand the question of how to connect a differential automaton only once, then such work will not cause any difficulties. The main thing is the right choice of protective device. If the home master did not make a mistake with him, the AVDT will last a long time, eliminating the very possibility of emergency and dangerous situations.