Primenenie UZO in various systems of networks

Application UZO has the features depending on type of system of grounding. Schemes of inclusion UZO in various systems of networks (fig. 1-3) are more low resulted.

Fig. 1. Application UZO in system TN-S:
1 - power supply grounding; 2 - protective grounding of electroinstallation of a building; 3 - open conducting parts
Fig. 2. Application UZO in TT system:
1 - power supply grounding; 2 - protective grounding of electroinstallation of a building; 3 - open conducting parts
b>Fig. 3. Application UZO in system IT:
1 - protective grounding of electroinstallation of a building; 2 - open conducting parts; UKI - an isolation control unit

In TT system all open conducting parts of electroinstallation are attached to grounding, elektricheski independent from zazemlitelya power supply neutral.
Till now PUE forbade application of system of a TT in electroinstallations of buildings.
GOST R 50669-94 «Electrosupply and an electrosecurity of mobile (inventory) buildings from metal or with a metal skeleton for street trade and population consumer services. Specifications» application of system of a TT as orders the basic in case of connection of the indicated electroinstallations to vvodno-switching centres of the next (capital) building.
In the standard of GOST R 50571 items 413.1.4 it is indicated, that in system of a TT of the system of protection can be used for protection against an indirect touch only in the electroinstallations having earthing systems with very small resistance. Thus guaranteed switching-off of a food of electroinstallation should be made at occurrence on open conducting parts of electroinstallation of pressure no more than 50 Century
In real conditions to carry out automatic switching-off of a food of electroinstallation of system of a TT by means of automatic switches for some reasons (necessities of maintenance of the big frequency rate of a current of short circuit, low resistance of the earthing system, etc.) it is rather problematic.
The effective decision of a problem of automatic switching-off of a food gives application sensitive UZO.
In electroinstallations of individual apartment houses, cottages, country (garden) houses and other private structures where not always probably to execute zazemlitel with necessary parametres, it is necessary to apply system of a TT with obligatory installation UZO. In this case requests to significance of resistance zazemlitelya considerably decrease.

l Δn, mA 10 30 100 300 500

R3Om 5000 1650 500 165 100

Admissible significances of resistance of grounding Rz depending on a nominal disconnecting differential current I n applied UZO are resulted in the table.
In system IT significance of a current of short circuit on the earth is defined by a condition of isolation of a network concerning the earth. At a good condition of isolation (high resistance concerning the earth) the short circuit current on the earth is very small. In case of a direct touch of the person to current carrying parts of electroinstallation current passage through a body of the person also is defined by resistance of isolation and at its parametres above certain significance does not represent danger to a life. Thus, level of resistance of isolation in networks IT supplies both reliability, and an electrosecurity of their operation. In this connection management the automatic constant control of isolation is obligatory electroprotective action.
In electroinstallations of system IT of a control unit of isolation give a signal at the first short circuit on the earth. If before its removal there is a second short circuit on the earth, works UZO (fig. 3 see).
At application UZO in electroinstallation of a building of system TN-C-S ReN-provodnik it is divided on N - and PE - conductors not for all electroinstallation of a building, but only for its part. The first electroreceiver is established in that part of electroinstallation of a building in which is available REN-provodnik. The second is used regarding building electroinstallation where the zero protective conductor is applied.
In system TN-S the systems of protection reacting to a differential current should not be applied.
When the system of protection reacting to a differential current, apply to automatic switching-off in system TN-C-S, REN-provodnik it should not be used on the load party. Joining of a protective conductor to REN-provodniku should be carried out on the power supply party in relation to the system of protection reacting to a differential current.
Thus, according to the indicated standard, is admissible to use UZO in those parts of electroinstallation of a building where electric chains with REN-provodnikami are possessed to source conclusions UZO.
As an exception for protection of separate electroreceivers of PUE suppose application UZO in system TN-C, at observance of certain conditions - connection of open conducting parts of electroreceivers to REN-provodniku from the power supply in relation to UZO.
Till now the large part of electroinstallations in our country works with the system of grounding similar TN-C.
In such electroinstallation at isolation breakdown on the electroreceiver case in case this case is not earthed (for example, a refrigerator or a washing machine on the isolating basis), UZO, included in an electroreceiver feed circuit, will not work, as there is no chain of course of a current of leak - is absent raznostnyiy (differential) current. Thus on the electroreceiver case there will be a dangerous potential concerning the earth.
In this case at a touch of the person to the case of the electroreceiver and course through its body of a current on the earth, exceeding nominal disconnecting differential current UZO (the current ustavki) - I n, UZO will react and will disconnect electroinstallation from a network, as a result human life will be rescued.
In the considered case from the moment of infringement of isolation and occurrence on the case of the electroreceiver of electric potential and till the moment of switching-off of a defective chain from a network there is a period of potential danger of defeat.
From the above-stated follows, as in electroinstallations with system of grounding TN-C application UZO also is defensible, as this system and in such electroinstallations supplies effective protection against electrodefeat.
(On materials of seminar NTS «Stroyinform» «Energosberegayuschie systems and light sources. New specifications, materials, the equipment. The house - garden continuation. Kinds of winter gardens in an interior. Pools, baths, saunas») Source: "the Newspaper Building" #7 (2003) heading “Stroyinform”

It is introduced: on March, 06th, 2003

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