Potential control

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In the field of electrical installations, potential control is a structural measure with the help of which electrical voltages (potential differences) in the area of ​​electrically conductive building materials can be minimized and thus dangerous step voltages can be reduced or completely avoided in the case of high currents through the earth electrode . It can be "controlled" during the planning phase and before the construction work begins. After completion of the electrical installation, it is no longer possible to “dynamically” control the spatial potential distribution in the building structures. For safety reasons, potential control is recommended for certain areas of application such as swimming pools.

Basics

The potential control (voltage grading, potential grading) is a measure that serves to change the potential of the earth's surface or another accessible area. The potential control should either bring the dangerously high step voltages to zero or at least reduce them to harmless values by means of suitable technical measures .

There are three options for carrying out potential control, which can be used individually or simultaneously, depending on the application.

Measures for controlling potential are:

  • Control earth
  • Potential control grid
  • insulation

Control earth electrodes are earth electrodes that are placed around a main earth electrode in a special arrangement.

Potential control grids are metal parts with a specific structure and specific dimensions that are inserted into the screed in special room types.

By introducing an insulating layer, the electrically conductive layers should be separated from one another. Special plastic films are used for insulation . This measure is very complex and is therefore only rarely used in practice. If necessary, electrically insulating layers are applied to the accessible surfaces.

In the DIN-VDE standards, a potential control is mandatory for agricultural premises in certain areas. It is recommended by experts in swimming pools and bathrooms.

In the case of electrical systems outdoors, e.g. B.

to carry out a potential control by control earth.

Potential control for electrical systems outdoors

In the vicinity of service earths, a voltage funnel forms around the earth due to the currents introduced. If a person moves in this tension funnel, he grabs the so-called step tension with his feet . The step voltage is that part of the ground voltage that can be tapped by humans with a step of 1 m. The level of the step voltage depends on the earth resistance and the current introduced. In the worst case, step voltages of several hundred volts can arise.

Plant earth z. B. in substations are usually created as a deep earth rod. Rods or pipes (rod earth rods) up to 40 m long are driven into the ground. This rod earth has the advantage of a low earthing resistance . Their unfavorable potential distribution is disadvantageous. In order to minimize the step voltages, additional ring or mesh earth electrodes are buried in the ground as control earths immediately around the main earth electrode. The control earths are distributed around the main earth in such a way that they are laid from the inside to the outside with increasingly greater depth. This measure achieves good potential control.

Ring earth electrodes or mesh earth electrodes have a much flatter earth potential profile than rod earth electrodes. This means that they can also be used in combination with rod earthing, as protective earth or as lightning protective earth. They have a controlling effect on the earth potential profile of the earthing system. Another area of ​​application for control earths is the area around high or medium voltage masts. A ring earth electrode is laid around the masts to control the potential. Ring earthers are also used in high-voltage switchgear and transformer stations for potential control.

Potential control in agricultural establishments

According to the DIN-VDE standard, potential control for new systems in certain areas is mandatory in agricultural facilities .

Farm animals such as B. Horses, cattle, goats, pigs, etc. access, due to their larger step size, higher step voltages than humans. In addition, animals are more sensitive to electrical current than humans and can be killed with voltages that are still harmless to humans. But even small leakage currents can cause the animals pain and stressful situations . An inadequate earthing system e.g. B. in a pigsty can lead to painful irritation in the animals, whereby the occurring stress can even be fatal.

For the reasons mentioned, it is necessary to take additional measures on farms in order to protect the animals from contact voltages. The power supply for the stables etc. can either be provided with protective extra-low voltage with a maximum of 25 volts alternating voltage or, if a higher voltage is used, must be monitored with a special residual current circuit breaker (error voltage 25 volts AC or 60 volts DC, residual current maximum 30 mA). Suitable measures are to be taken to ensure that no higher fault voltages than 25 volts alternating voltage or 60 volts direct voltage to earth occur. It makes sense to use a separate residual current circuit breaker for each individual circuit so that the entire system is not switched off in the event of a fault.

There are also increased demands on the earthing system and equipotential bonding. If the company is supplied via a TN-C network , the PEN conductor must not be connected to the equipotential bonding rail. In the event of a fault, this can lead to the introduction of fault voltage. Additional local equipotential bonding and potential control must be carried out in all areas of the stables (e.g. stalls, outdoor cubicles, milking parlor, etc.). The potential control is to be installed in new stables to be built as well as when the cattle stands are renewed.

In the area of ​​the standing and lying areas, the potential control is usually carried out using potential control grids made of welded wire mesh with a maximum mesh size of 150 mm. In milking parlors and milking pits a smaller mesh size of z. B. 50 mm - 100 mm advantageous. The wire thickness of the potential control grid must be at least 3 mm. The mats must be connected to one another in a permanently electrically conductive manner (clamping or welding ). The potential control grids must be connected to the additional local potential equalization at at least 2 points per area. The connection line to the additional local equipotential bonding should be made of hot-dip galvanized round steel with a diameter of at least 8 mm or hot-dip galvanized steel strip 30 mm × 3.5 mm.

The control grids should be installed in the screed at a depth of at least 50 mm. In addition, control earths introduced into the screed, which are connected to the additional local equipotential bonding, also have a positive effect on the potential control. The potential control and the additional local potential equalization are effective against corrosion, e.g. B. by hot-dip galvanized materials or stainless steel to protect. Since several residual current circuit breakers are connected to the earthing system, special requirements are placed on the earthing system. The use of additional control earths is recommended so that a favorable earth potential profile is achieved for the earthing system.

Even if the potential control is only mandatory for new systems or converted systems, it should be installed in older systems as quickly as possible.

Only the potential control in connection with the additional local potential equalization and a carefully executed earthing system offers the animals effective protection against dangerous contact voltages, high step voltages and leakage currents due to potential carryover and voltage funnel.

Potential control in swimming pools

Swimming pools are associated with an increased risk potential due to the swimming pool and its partially wet and humid environment. In this humid environment , the human skin resistance decreases and the sensitivity of the human body to electrical contact voltages increases. In addition to the protective measures prescribed by the DIN VDE standard, additional measures must be taken to ensure that no dangerous contact voltages occur. Potential control is not required for insulating floors.

The current installation standard for swimming pools (covered and outdoors) provides for additional local equipotential bonding for protection areas 0 - 2 in swimming pools (covered and outdoors). A potential control, as prescribed in the previous standard, is not mandatory in the new standard . Nevertheless, experts consider a potential control in swimming pools in the protection areas 1 and 2, as well as wherever the inclusion of electrically conductive standing surfaces in the potential equalization is very recommendable.

By controlling the potential, the base can be made of poorly conductive material (no insulating material), e.g. B. concrete, stoneware, soil, can be brought to approximately the same potential. This allows you to specifically change the potential of a stand area. Thus, the effectiveness of the additional local equipotential bonding can be considerably improved by the potential control.

The potential control in swimming pools can be implemented in two ways:

  • With a ladder running parallel to the edge of the pool
  • Using welded wire mesh

The following applies to potential control grids:

The individual parts of the steel reinforcement for the potential control are to be connected to one another in a permanently electrically conductive manner when they are introduced and to be connected to the additional local potential equalization. The connection line for additional local equipotential bonding must correspond to half the cross-section of the main protective conductor , at least a 6 mm² copper line must be used. If the connecting lines are made of copper, the terminal point must be protected against the ingress of moisture.

We recommend using hot-dip galvanized steel strip with a minimum cross-section of 30 mm × 3.5 mm or hot-dip galvanized round steel with a minimum diameter of 10 mm as connecting lines between the potential control and the additional local potential equalization. This must either be welded to the steel reinforcement or screwed with special clamp connectors. The clamp connections are to be preferred to welding, since further DIN standards have to be observed for welding and only a specially trained welder is allowed to carry out this welding work.

Permanently electrically conductive connections are only made by welding or clamping. The tying of the mats or round bars, which is common on construction sites, is not considered a permanent electrically conductive connection, but only serves to fix the position of the mats or round bars.

The potential control grid should be installed as close as possible under the floor surface. In the case of large-area potential control grids, it is advantageous to place the potential control grid in several places, e.g. B. beginning - middle - end, to be connected with the additional local equipotential bonding.

A foundation earth electrode also has a positive influence on the potential curve in pools made of masonry or concrete , both inside and outside the pool. Additionally introduced control earths can also have a favorable effect on the potential curve. The earth electrodes are to be included in the additional local equipotential bonding.

Potential control through conductors running parallel to the edge of the pool

The distance between the conductors must not exceed 600 mm. It must round bars are used with a minimum diameter of 10 mm.

Cross connections must be made between the conductors at at least 2 points.

The ladder should be laid without gaps in the areas already mentioned. The round bars are to overlap about 150 mm at the clamping points. An overlap of 50 mm - 80 mm is sufficient for welding the round bars.

Potential control by means of welded wire mesh

The usual welded wire mesh with a mesh size of 150 mm can be used. The mats should be laid without gaps in the areas already mentioned.

For screwing , the mats are to be overlapped by a mesh size at the transition points and connected to at least 3 points with special screw terminals. For welding, the ends of the mats must be overlapped by 50 mm - 80 mm.

Potential control in bathrooms

Potential control is not compulsory in bathrooms . If the water pipes are made of non-electrically conductive plastic and the bathtub or shower tray is also made of plastic, the installation of additional local equipotential bonding can even be dispensed with in accordance with the new DIN-VDE standard.

However, it is advisable not to forego the additional local equipotential bonding and the potential control, because if the tub is replaced by a steel tub , the installation of the safety measures is only possible with greater effort.

The potential control in bathrooms is by means of a metal mesh mat, z. B. reinforcement mat with 150 mm mesh size. This should be laid in the screed as close as possible to the floor . The metal mesh mat must be connected to the additional local equipotential bonding with a 4 mm² copper line. The copper line should be continuous, protected against damage and, if possible, clamped in the middle of the mat. The terminal point must be permanently protected against the ingress of moisture.

If several individual metal mesh mats are used for the potential control grid, they must be clamped together so that they overlap. It is also possible to weld the mats. The same rules must be observed here as for potential controls in swimming pools.

Statutory provisions and other regulations

  • DIN VDE 0100 Construction of high voltage systems with nominal voltages up to 1000 V.
in particular:
  • Part 410 "Protection against electric shock"
  • Part 540 "Additional local equipotential bonding"
  • Part 702 "Covered swimming pools (indoor swimming pools) and outdoor swimming pools"
  • Part 705 "Agricultural and horticultural properties"
  • Part 737 “Damp and wet areas and rooms; Outdoor systems "
  • DIN VDE 0101-2 "Earthing of high-voltage systems with nominal voltage above 1 kV"
  • DIN VDE 0105 Part 115 “Operation of high-voltage systems; Special stipulations for agricultural establishments "
  • Accident prevention regulation VSG 1.4 "Electrical systems and equipment"
  • Safety regulations and information sheets from the Association of Property Insurers, in particular:
  • "Power systems in agricultural businesses, safety regulations" (VdS No. 2057, 7/1998)
  • DIN 4099 welding of reinforcing steel, execution and testing.

Individual evidence

  1. ↑ Johann Frei: Measurement of the impedance of extensive Eder systems and their calculation with the help of approximate, analytical and numerical methods online (accessed on February 6, 2012; PDF file; 2.76 MB).
  2. ↑ a b c Wilfried Knies, Klaus Schierack: Electrical systems technology; Power plants, networks, switchgear, protective devices . 5th edition, Hanser Fachbuchverlag, 2006, ISBN 978-3-446-40574-5 .
  3. ^ Dieter Vogt, Herbert Schmolke: Electrical installation in residential buildings . Installation Practice Guide; VDE-Verlag GmbH ISBN 978-3-8007-2820-6 .
  4. ↑ Peter Gredler: Analysis of technical measures in extensive grounding systems to reduce touch and step voltages, taking into account zeroed low-voltage networks. Diploma thesis ( PDF online , accessed on February 7, 2012.)
  5. ↑ a b Requirements for earthing and equipotential bonding measures; Dipl.-Ing. Jürgen Wettingfeld ( memento from January 23, 2016 in the Internet Archive ) (accessed on July 21, 2016).
  6. ↑ a b Equipotential bonding measures for swimming pools; DEHN + SÖHNE ( Memento from November 9, 2007 in the Internet Archive ) (accessed on February 7, 2012; PDF file; 858 kB)
  7. ↑ Walter Castor: Basics of the power supply for non-sector specialists ( online ( memento from June 10, 2014 in the Internet Archive ), accessed on February 10, 2012).
  8. ^ A b Walther Koch: Earthing in AC systems above 1 kV. Second completely revised edition, Springer Verlag, Berlin Heidelberg 1955, pp. 48–71.
  9. ↑ Association of Electricity Companies (Ed.): Implementing provisions for the TAEV for the distribution networks of the network operators in the federal state of Carinthia, 2009 edition online ( Memento from July 21, 2016 in the Internet Archive ) (accessed on July 21, 2016; PDF file; 1.96 MB).
  10. ^ Gerhard Kiefer: VDE 0100 and the practice. 1st edition, VDE-Verlag GmbH, Berlin and Offenbach, 1984, ISBN 3-8007-1359-4 .
  11. ^ Paul Waldner: Fundamentals of electrotechnical and electronic building equipment . Werner-Verlag 1998, ISBN 978-3-8041-3983-1 .
  12. ^ Federal Institute for Occupational Safety and Health: Electrical Safety in Agriculture .
  13. ^ Herbert Bernstein: Workbook Mechatronik. Franzis Verlag GmbH, Poing 2007, ISBN 978-3-7723-4319-3 .
  14. ^ Günter Springer: Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .
  15. ↑ ÖVE-EN Part 4: § 56 Electrical systems in agricultural and horticultural properties. Online (accessed February 7, 2012; PDF file; 234 kB).
  16. ↑ ÖVE / ÖNORM E 8001-4-56 Construction of electrical systems with nominal voltages up to 51000 V and 41500 V Part 4-56: Electrical systems in agricultural and horticultural facilities ( online ).
  17. ↑ Electrical systems in agriculture (accessed on July 21, 2016).
  18. ↑ Hochbaum: Damage prevention in electrical systems in agriculture ( Memento from July 21, 2006 in the Internet Archive ) (PDF file; 1.24 MB)
  19. ↑ Damage prevention in electrical systems in agriculture, guidelines for damage prevention. Online (PDF file; 418 kB).
  20. ↑ a b c Hans-Günter Boy, Uwe Dunkhase: The master's examination in electrical installation technology. 12th edition, Vogel Buchverlag, Oldenburg and Würzburg, 2007, ISBN 978-3-8343-3079-6 .
  21. ↑ DIN EN 62305-3 supplement 2 (VDE 0185-305-3 supplement 2): 2009-10 ( Memento from January 5, 2011 in the Internet Archive ) (accessed on February 6, 2012; PDF file; 394 kB).
  22. ^ Klaus Tkotz: Electrical engineering ; 25th edition, Verlag - Europa - Lehrmittel , 2006, ISBN 978-3-8085-3159-4 .