Contact voltage

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The touch voltage , also touch voltage , is the electrical voltage between conductive parts when they are touched by a person or an animal at the same time. ( International Electrotechnical Dictionary - IEV 195-05-11 ) It is valid for current flow with skin resistance or body resistance. The conductive parts touched can be active parts, bodies, external conductive parts, protective conductors, earth or conductive floor. ( International Electrotechnical Dictionary - IEV 826-12-12 )

General

The touch voltage creates an electrical current , the touch current . Accordingly, the touch current is defined as "electrical current that flows through the body of a person or an animal when this body touches one or more touchable parts of an electrical system or electrical equipment". ( International Electrotechnical Dictionary - IEV 195-05-21 )

Although the current strength per area ( current density ) and the duration of exposure are responsible for the effects of an electrical accident , the voltage is specified as a source of danger, since the current strength that enters the body is, in the simplest case, derived from Ohm's law and thus from voltage and body resistance can be calculated. This electrical current flowing through a person or animal can lead to an electrical accident which can lead to life-threatening injuries or death.

The value of the effective touch voltage can be influenced by the impedance of the person or animal in electrical contact with the touched conductive parts. ( Internationales Elektrotechnical Dictionary - IEV 195-05-11 ) For example, when a computer is supplied by a protective insulated power supply unit, a significant Voltage can be measured at the housing, which, however, drops to a harmless value when touched and causes a possibly noticeable but harmless contact current. (If the low touch current is perceived as unpleasant, the use of a power supply unit of protection class I can help, as this dissipates the corresponding current via the protective conductor.)

In healthy adults, exceeding the low voltage from 50  V alternating voltage (AC) or 120 V direct voltage (DC) is assumed to be a life-threatening situation. For children and larger farm animals, among other things, the contact voltage is only set to a maximum of 25 V AC or 60 V DC, and in damp-proof installations sometimes even to 12 V.

For damp or wet skin, e.g. B. by sweat or hands freshly washed with soap , the skin resistance decreases. Furthermore, the values ​​of the contact voltage are not valid if other internal body parts such as the tongue touch the conductor or conductors involved in the circuit, as these have a much lower resistance. In rooms used for medical purposes, the limit of the contact voltage is set at an alternating voltage of 25 V eff and a direct voltage of 60 V.

Conductive parts that carry a higher voltage than the contact voltage must be secured against contact, i.e. This means that it must not be possible to touch them with the standardized test finger ( International Electrotechnical Dictionary - IEV 442-01-15 ). This is achieved either by basic insulation or by covers or sheaths that correspond at least to protection class IPXXB or IP2X. If the horizontal surfaces of covers or casings are easily accessible, they must comply with protection class IPXXD or IP4X.

literature

  • Gerhard Kiefer, Herbert Schmolke: VDE 0100 and practice, guide for beginners and professionals . 14th edition. VDE Verlag GmbH, Berlin and Offenbach 2011, ISBN 978-3-8007-3190-9 .
  • Klaus Tkotz: Electrical engineering. 28th edition, Verlag - Europa - Lehrmittel, Wuppertal, 2012, ISBN 978-3-8085-3189-1
  • Gottfried Biegelmeier, Dieter Kieback, Gerhard Kiefer, Karl-Heinz Krefter: VDE series 80; "Protection in electrical systems, Volume 1: Dangers from electrical current . 2nd edition. VDE Verlag GmbH, Berlin and Offenbach 2003, ISBN 3-8007-2603-3 .

Individual evidence

  1. ^ Norbert Leitgeb: Safety of medical devices: Law - Risk - Opportunities . Springer-Verlag, 2015, ISBN 978-3-662-44657-7 ( limited preview in Google Book Search [accessed on December 16, 2016]).
  2. ^ Ernst Ahlers: Tingling Notebook. In: c't 9/12. Retrieved June 5, 2013 .
  3. ↑ Wilfried Plaßmann, Detlef Schulz: Handbook of electrical engineering: Basics and applications for electrical engineers . Springer-Verlag, 2008, ISBN 978-3-8348-0470-9 ( limited preview in Google Book Search [accessed on December 16, 2016]).
  4. ↑ http://www.elektro-wissen.de/Elektroinstallation/ Fehlerarten.html
  5. ↑ SR 734.2: Ordinance of March 30, 1994 on Electrical Power Systems ( Heavy Current Ordinance) (PDF; 268 kB)
  6. ↑ DIN VDE 0100-410: 2007-06 Appendix A