Let's start with the analysis of concepts. By UZO today it is generally accepted to imply a differential circuit breaker. The device measures the current flowing into the device and outgoing, and when a difference occurs between them, the circuit is cut off. Actually, the differential indicates the finding of leaks. It is assumed that there is a ground at the facility. But often this part is missing. Consider how the connection of the RCD without grounding.
Briefly about the concepts of home electrical protection
Today it is customary to divide equipment to protect the electrical network of a house from various excesses into items:
- The distribution box is a box that is embedded in a wall or hanging where protective devices are placed. Inside there are metal brackets where, according to the plan of electrification of the apartment, various modules are hung, like the designer. Do not confuse the concept with a junction box representing a box with rubber tear-off cuffs on the ends, where the pads of simple electrical connections are embedded. The switchboard is needed so that the installation of the RCD is extremely simple, understandable and convenient. When the equipment is gathered together and signed, the owner is happy. Suppose you need to turn off the sockets in the hall - pressing a finger, and the trick is in the hat.
- Before considering the RCD, we will discuss a circuit breaker. In the simplest case, it is a device with two terminals to which the phase is hooked( brown or red wire).With a sharp increase in current, the internal relays of the switch automatically break the circuit. Depending on the type of device, the time of the operation varies. There is no simple rule - the sooner the better. If the load is an induction motor of a refrigerator or air conditioner, the starting current can be briefly high, and a false positive will not please the owners with the inability to start the climate system or freezer. Remember, the circuit breaker is selected based on the type of load. The specified device is capable of breaking the circuit if the current exceeds the value indicated on the housing. With an overload factor of 1.15, this usually happens in an hour, with 1.45 - twice as long. This does not allow the wiring to overheat and cause a fire or lose insulation as a result of cycles of increase and decrease in temperature.
- Circuit breaker protects the circuit from overheating, the equipment from short circuit, but there is no question of safety. The RCD enters the scene. At occurrence of the slightest leakage current there is a difference of the currents entering and proceeding. Recall one law Kirchhoff. In a series circuit, the current detects a constant value. At the consumer, a source in the form of a transformer, household appliances and a neutral wire, usually grounded in the vicinity of the substation, are connected. When a person takes a hand for the current-carrying part with one hand, and rinses the other under the tap, a leakage current through the electrolytes in the body occurs: blood, lymph, various organelles. Due to this, in the series circuit described above, in the area of the accident localization, electrons begin to be lost, going down the drain through the hands of the victim. UZO immediately fixes the phenomenon and breaks the circuit. In the described case, the response speed is extremely important. And it is characterized by a minimum leakage current. Note the pitfall. With too sensitive characteristics, false positives are possible. It is useful at the entrance to the apartment to put a decent voltage filter, for example, filtering higher harmonics.
So, the conclusion: connecting an RCD without earthing is possible, but there is still a chance that the case under voltage sags for an extremely long time, and a man will undertake it. If done according to the rules, immediately after the breakdown of insulation, a differentiation of currents would occur. As a result, people will avoid unpleasant shock. The RCD will continue to operate, but the result of the contact of electricity and a person depends solely on the physical state of the latter. For example, a pensioner with a weak heart may die from such a shock therapy. Case of life: an accumulative water heater with a broken insulation of heating elements. If the pipes are plastic, and the valves are closed, chances are great to include a person in the ground loop by simply running water from the tap.
RCD in an apartment without grounding
A special standard has been allocated for the connection of household appliances in potentially dangerous areas of the apartment. These include primarily sanitary unit. The areas for the installation of washing machines and security measures in the whirlpool backlight circuit are specified( GOST R 50571.11-96).
In the lines of a smart document it is written that in hazardous areas( according to standard terminology) it is allowed to install electrical equipment only in three cases:
- If the connection is made through an individual separating transformer according to GOST 3 / GOST R 50571.3 according to clause 413.5.1.The meaning of the written: the separating transformer does not convert the voltage. At the output of its secondary winding, the former is 220 V, and the current is equal to the input one minus losses( efficiency & lt; 1).If the first hand to take up the bare wire, and the second for the tap water, a closed circuit is not formed and will not kill the person. Of course, if you take on both ends of the secondary coil at the same time, troubles cannot be avoided, but in practice it is extremely difficult to do. And if insulation breaks through on its own, the transformer will go into short-circuit mode and the plugs will burn( or the circuit breakers will work).But! The end of the secondary winding cannot be planted on the ground. In this case, the meaning of the device installation is lost. And do not forget about the word "individual": it is allowed to apply to a single device from a home set of home appliances.
- Safe is powered by BSNN or CHNN.This is the so-called safe extra low voltage. For example, on a similar principle, all portable shavers and epilators work without exception: the supply voltage does not exceed the 50 V considered safe. In electric shavers, usually 9 or 12 V( up to 15 V).For washing machines - not an option, as well as for dishwashers. Therefore, we again return to the RCD without grounding.
- It is allowed to protect household appliances through a UZO reacting to a differential current. We remind you, this is the name of the difference between input and output power consumption. In connection with what has been written previously, it is prohibited to ground the instrument case through a neutral wire. Otherwise, the RCD reacting to the differential current will not be able to perform protective functions. The housing of the washing machine will bite the shower taker - usually 60 V comes from the input voltage filter. If you do not believe, take a tester and make sure. Place the second dipstick on the water supply tap. The current from the case is usually small, lower than from the casing of the system unit of a personal computer. There is an additional requirement - the differential reaction current of the device is expected to be no more than 30 mA.
According to the standard, the bathroom is divided into three zones:
- The first includes the volume of the bath, the area is called zero. The use of BSNN devices with a voltage not exceeding 12 V is allowed.
- The first zone is limited by the walls of the bath and the plane at a distance of 2.25 meters from the floor. It is allowed to install water heaters only.
- In zone 2, extending to a plane 60 cm from the bath, it is allowed to install( in addition to water heaters) class II luminaires. Roman numerals refer to the degree of electrical safety, meaning that the insulation is reinforced or double.
- Finally, in the third zone, no closer than 60 cm from the bath, it is allowed to put the first sockets. Requirements described above. This is a separating transformer, BSNN or UZO discussed by us. The washing machine is connected according to the rules and is 60 or more cm from the bath. It is ridiculous, given the size of the rooms of the native bathrooms, but the realities are unequivocal.
Connection of an RCD without grounding
The standard clearly states that the use of local potential equalization systems without grounding is not allowed. To make it clearer, let's say that the case of any device is under some kind of voltage. Even when powered from a single network, the difference between the devices is not zero. It is easy to get an electric shock, holding at once for two representatives of household appliances.
To avoid an accident, an electrical connection of all device housings with a single conductor bus( copper, thick steel) is carried out. According to the safety precautions, all( !) Devices in zones 0, 1, 2 and 3 are connected to the potential equalization system. And the latter ends at a distance of about 2.4 meters from the bathroom walls. It turns out, you will not manage with UZO without grounding. And it is right.
How will an RCD operate without grounding if there is a sensitivity to differential current? During insulation breakdown, the current will begin to wait for a leak. But there is no grounding, there will be silence before the storm, until any person decides to pass a leakage current through his own body, for example, into a sewer drain( through a stream of water from the tap).In principle, the restriction of houses connected by the TN-C system( without protective grounding) is permissible to be circumvented. You will need to put the body on the zero wire, but( !) Taken from the entrance to the apartment. RCD continues to operate independently, and the leakage current will pass by. And order.
We enclose an example RCD connection diagram without grounding. Consider this deviation from the standard. According to the rules, it is required by the entrance to order a project of reconstruction of the electrical supply system in accordance with the requirements of ПУЭ 7. The diagram shows:
- Single-phase AC supply voltage 220 V without ground loop. The letter N denotes the neutral wire, called neutral in electrical engineering. We took into account that the supply of the house is always three-phase, it is logical to designate the vein as follows.
- Below, on the left branch, where the potential goes, there is an automatic switch. Please note designated as a device with a break contact. The device’s task is to open the circuit when the current reaches the limit value( a square on the inclined line records the fact of current control).
- RCD is represented by a double breaker operating on open circuit. The composition usually includes a test button, never neglect it.
- At the bottom of the marked outlet protected by the device( for example, RCD ABB).Its side terminal is supplied with a neutral from the entrance to the circuit. This will be filtered leakage current, the value of which in the amount of 30 mA will trigger the RCD.
- At the bottom, Kirchhoff's law is given, explaining how the circuit works. The meaning of the axiom: with branching the sum of the currents in both directions is equal to the original, input. And the difference, characterized by leakage, is intended to cause the operation of the RCD without grounding.
A similar connection circuit RCD is needed exclusively for the bathroom and other wet places. We believe that readers now know how the RCD operates without grounding.