Thunder won’t strike…

Rapid progress in the field of electrical equipment of modern housing and the conservatism of its inhabitants— what a contradiction between the achievements of engineering and those to whom they are addressed!

Since the time of Peter the Great, novelties of technological progress, whether it be a Dutch-style stove or city sewerage, have been introduced into the life of Russians by the highest decrees and the method of coercion. Over the past centuries, we, apparently, have not been able to overcome the inertia of thinking. This paradox was also expressed in relation to the problem of introducing RCDs. Despite all the evidence of the enormous benefits of this device— guaranteed protection against electric shock, a radical reduction in the likelihood of fires, is established by its citizens by no means voluntarily, but on instructions from above. By order of the Moscow government since 1995years, neither housing under construction nor reconstructed can be put into operation without the installation of RCDs and circuit breakers that provide protection against overcurrents— overload and short circuit currents. ATIn the catalogs of foreign companies, RCDs are often called differential protection devices, differential relays, differential modules, etc.P.

So, the use of RCDs in combination with circuit breakers minimizes the risk of electric shock to a person and practically eliminates the possibility of ignition of electrical appliances and electrical wiring in cases of overload or short circuit in the network.

Meanwhile, to explain to people the need to equip homes and institutions with new generation protective devices— an occupation as ungrateful as lecturing on the dangers of smoking. Everyone agrees with you, but they don’t quit smoking. In the same way, until someone is shocked, until the iron, hair dryer, food processor and the wires leading to them catch fire, no one is in a hurry to install an RCD. Truly, a saying is wise, explaining the phenomenon of the mysterious Russian soul: «Thunder will not strike— the man will not cross himself.

However, the abundance of calls to the editorial office and written responses to the article about the RCD «Do not fit,— kill!» («Ideas of Your House», 1998, N1) testifies that the word of a journalist still hits the target from time to time. For a more detailed conversation, let us briefly explain the principle of operation of the RCD, which, as it turned out during the preparation of this article, is far from clear to every electrician.

Functionally, an RCD can be defined as a high-speed protective switch that responds to differential current in conductors supplying electricity to the protected electrical installation.

The structure of the RCD is formed from the following main functional blocks (cm.rice.«The structure of the RCD»):

• In RCDs, a differential current transformer is used as a current sensor (one).
• Threshold element (2) is performed on a sensitive magnetoelectric relay.
• Actuating mechanism (3) consists of a spring drive with a high-current contact group.
• The testing circuit, which artificially creates a differential current, is designed to periodically monitor the health of the device by pressing the «TEST» button (four).

In normal mode— in the absence of leakage current— operating current of the load, flowing in the forward and reverse conductors, forming the oppositely connected primary windings of the differential current transformer(one), induces in the magnetic core of the current transformer equal, but vectorially oppositely directed magnetic fluxes Ф1 and Ф2, compensating each other. ATAs a result, the current in the secondary winding is zero and does not trigger the threshold element(2).

When a current leaks to the ground or a person touches the current-carrying parts, the balance of currents in the forward and reverse conductors, and hence the magnetic fluxes, is disturbed, a transformed differential current (unbalance current) appears in the secondary winding, which causes the threshold element to operate(2) acting on the actuator(3). Acting on the principle of a latch, the actuator actuates the spring drive of the contact group and the protected circuit is de-energized.

In electronic RCDs, the functions of a threshold element and a partial actuator are performed by an electronic circuit.

According to the estimates of energy specialists, the current need of Russians for RCD is 100millionthings. It is no coincidence that electrical protective devices are already becoming the most liquid product in electrical stores. ATBasically, these are foreign-made products. However, it does not at all follow from this that domestic protective devices are unreliable or uncompetitive in comparison with Western counterparts. The advertising opportunities of our manufacturers are significantly more modest than those of such electrical giants as «SIEMENS”, “ABB”, “SCHNEIDER”, “LEGRAND”. Not always in favor of domestic products and their design. Clearly, there are still not enough regulatory and instructive materials on the use of RCDs.

A serious problem is the lack of guidelines for a potential RCD buyer (andthis is usually a person who has a thorough knowledge of electrical engineering). RCD— a very complex precision instrument. Give a qualified assessment of the compliance of the parameters of a particular device with the requirements of the RCD standard— GOST R 50807-95 — only a few specialized laboratories can. The duration of operation of RCDs already installed in Russia is still too short to draw conclusions about reliability indicators. Basic device parameters— rated load current— In, rated residual current (leakage current)— IDn, rated residual current— IDno, switch-off time— Tn, operating voltage— Un and some other indicators for most RCDs are approximately the same. Therefore, when buying, you have to be guided, first of all, by information about the reputation of the manufacturer in the market. The quality of the product of a defense plant is traditionally higher than that produced by an enterprise that produces consumer goods. Abroad, these are, as a rule, large electrotechnical concerns, with which suppliers from Indochina are not able to compete in terms of quality and reliability.

Another important criterion when choosing a device— availability of a certificate. And not «export», which is usually issued for a small batch of imported devices, but a certificate of the established form with a direct indication of the compliance of products with the specified GOST. This is important, since recently there has been an influx of dubious products: stale in the warehouses of firms produced by companies that have ceased to exist from the GDR, Poland, China, Korea, India, etc.d.

With regard to foreign products, the cost of the device is commensurate with their quality.

When choosing an RCD, be sure to take into account the principle of operation of the device. There are two main categories of RCDs:

• supply voltage dependent— «electronic»,
• supply voltage independent— Electromechanical.

Electromechanical RCDs are more expensive than electronic ones. ATEuropean countries— Germany, France, Austria, Belgium, Italy, etc.— the vast majority of RCDs— electromechanical. According to the electrical regulations of these countries, electronic devices are installed only in addition to the already existing electromechanical ones.

The advantage of electromechanical RCDs— their complete independence from fluctuations and even the presence of voltage in the network. This is especially important, since a break in the neutral wire often occurs in electrical networks, as a result of which the danger of electric shock increases: after all, a person assumes that there is no voltage in the network and calmly touches live parts. The use of electronic RCDs is advisable when insurance is needed for safety purposes, for example, in especially dangerous, wet areas. ATIn the United States, you cannot buy a hair dryer that does not have an RCD built into the plug, where this is determined by law. In fairness, we note that the letter of Glavgosenergonadzor in the Russian Federation recommended for use both electronic and electromechanical RCDs that meet the requirements of current standards and have a certificate of conformity.

When choosing an RCD, the following factors are most important:

• RCD installation site;
• RCD parameters: rated load current, rated differential breaking current, thermal resistance;
• circuit solutions for various grounding systems of supply networks;
• choice of RCD type.

RCDs must only be installed by qualified personnel licensed to perform electrical work.

In connection with the introduction of a power supply system with a third neutral protective wire and the use of RCDs, in old (two-wire) systems, when installing these devices, it is necessary to clearly separate the zero working and neutral protective wires in the RCD coverage area, i.e.e. The zero working wire must not be connected to grounded elements of the installation.

Before commissioning an electrical installation with an RCD, it is recommended to measure the background leakage currents to earth with simultaneous or sequential switching on of all electrical receivers. Of course, for this you need to contact a specialized organization. Damage to the insulation is possible both in the phase and in the neutral wires (while the RCD responds to leakage in both cases), however, when using single- and three-phase circuit breakers in an electrical installation without dismantling the circuit, it is impossible to find leakage from the neutral wire by the method of serial disconnection. Therefore, in network diagrams with a zero protective conductor, it is advisable to use two- and four-pole circuit breakers that switch both phase and neutral wires.

For the readers of our magazine, we are doing a selective review of RCDs on the Russian market that meet the requirements of Gosstandart and Glavgosenergonadzor.

Stavropol plant «SIGNAL» produces electronic «UZO-20». According to MNIITEP at the beginning of 1997inMoscow was installed about 45000devices of this model. It should be borne in mind that they received numerous complaints from specialists and users due to numerous failures in their work. Price UZO-20 — one of the lowest for electrical protective products of this type.

OJSC «TECHNOPARK-CENTER» produces an electromechanical device under an Austrian license ASTRO*UZO. It is approved for use in residential, public and industrial buildings, has a certificate of conformity. ASTRO*RCD maintains its performance in case of any fluctuations and even in the absence of voltage in the network, for example, in the event of a break in the neutral or phase conductors.

The ASTRO*RCD family includes 9modifications that differ from each other in the number of poles (two- and four-pole), rated current parameters (16, 25, 40 and 63A) and rated breaking current (30 and 100mA). Life time ASTRO*RCD — at least 10years, resource— four000electrical and 10000mechanical cycles.

The cost of bipolar ASTRO*RCD modifications F1111— 372rub., F2211, F3211— 306rub., F3311— 356rub., four-pole F3212, F3312, F4212 and F4312— from 450 to 560rub.

In OJSC «NII PROEKTELEKTROMONTAZH», based on a generalization of more than 25 year old experience of the institute in the field of electrical safety, an electronic UZO-2000. Available in combination with a circuit breaker.

Feature of this RCD— its ability to maintain performance during short-term (up to5seconds) voltage dips up to 50% of the nominal. This mode is possible in case of short circuits for the time of operation of the system ATS (automatic transfer device). Electrical durability UZO-2000 — twenty000cycles. Price— 210rub.

As for imported RCDs, in this review we will only note the products of companies that have long and seriously cooperated with Russian power engineers. They are designed to ensure the electrical safety of people and fire protection of residential and office premises.

The well-established company «ABB» offers devices F360 F370, D.S.640/DS650, D.S.652 and DS654. The average cost of these products in the stores of the group of firms «TFS»— 90y.e.

The French company «MERLIN-GERIN», which is part of the industrial group «SCHNEIDER», produces RCDsDPNNVigi, VigiC60 VigiNC100,C60,NC100 or NC125. Their average cost according to the TFS price list— 85y.e.

A wide range of RCDs is offered by the concern «SIEMENS«. ATits catalogs include dozens of devices, the variety of which can satisfy any requirements of buyers. Most popular model— bipolar RCDNFI5SZ3227. Cost of products «SIEMENS» almost does not differ from analogues of the above-mentioned firms.

The French company «LEGRAND» supplies RCDs of the type DX/D40, two- and four-pole. Their cost in the stores of the group of companies «TFS»— before90y.e.

Here is the time to remind once again that it is just as impossible to give a comparative description of the residual current devices supplied to the Russian market as it is to compile a «table of ranks» of manufacturers and suppliers of these devices to Russia. Do you want to see the compliance of the purchased RCD or differential machine with the required parameters? Compare the characteristics of your device with those for UZO-2000 and for ASTRO*UZO. If imported analogues are inferior to them, buy domestic products. If possible, consult with experts. As for the quality and reliability of devices, you can rely on the reputation of their manufacturers and sellers. Preference should be given to specialized stores and electrical trading houses.

The editors of the magazine thank the employees of the technical department of JSC «TECHNOPARK-CENTER», the general director of JSC «NII PROEKTELEKTROMONTAZH» E.M.Feskov and the leading manager of the electrical trading house «TFS-ELECTROTECHNIKA» S.BUT.Ptashkin for help in preparing the article.

• Source: Ideas for Your Home Magazine#8