Anglicky v odborných předmětech "Support of teaching technical subjects in English “

1. Anglicky v odborných předmětech"Support of teaching technical subjects in English“ Tutorial: Mechanic - electrician Topic: Basics of electrical engineering the 2nd. year Protection in electric networks Prepared by: Škarka Miloš Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

2. Basic terminology • Injury by electric current – physiological effect of electric current coming through a body of a person or an animal • Basic protection – protection against an injury by electric current in a failure-free state • Protection in the case of a malfunction – protection against an injury by electric current during one malfunction • Dangerous animate part – an animate part, which could cause an injury by electric current in certain conditions • Basic insulation – insulation of dangerous animate parts providing basic protection • Additional insulation – separate insulation used for basic insulation, to provide protection in case of a malfunction • Double insulation – insulation containing basic and additional insulation • Links – electric connections between conductive parts for potential balancing

3. Animate and inanimate part • Animate part – conductor of conductive parts designed for voltage in normal operation including the central conductor • Inanimate part is conductive part of an electric device, which can be touched and where there is usually no voltage, but where can a dangerous contact voltage occur because of a malfunction (for example metal casing of a distributor).

4. Dangerous contact voltage • Dangerous contact voltage is voltage (or a variance of potentials), which can cause an injury by electric current to a person or an animal contacting an inanimate part during a malfunction. Its size depends on the type ofenvironment, in which this contact occurs(ČSN 33 2000-4-41).

5. Allowed safe low voltage (contact) Allowed contact voltage is a part of grounding system voltage opposite to the ground, which can be crossed over by a human in distance from hands to feet (horizontally 1m).

6. Allowed contact voltage chart Amount of the allowed contact voltage depends not only on a purpose of its use and on an environment, but even on a duration of a malfunction. The shorter theduration of the contact voltage is, the higher the contact voltage can be. Allowable values of the permanently allowed contact voltage at the device up to 1000V are mentioned in the following chart.

7. Types of the environment • Normal – ordinary; cold; dusty (if dust is not conductive and not flammable). Its character prevents an injury by electric current. • Dangerous – hot, wet (even temporarily), dusty (if dust is conductive and not flammable with increased corrosive aggression), with shocks, outdoor places with mechanical damageand conductive environment. These are those places, where there is a temporary or permanent danger of an injury caused byelectric current because of external effects. • Extremely dangerous – wet, withextreme corrosive aggression, places, where there is danger of an injury greatly increased by adverse conditions (water, kettles and metal tanks, narrow spaces with metal materials, healthcare facilities or special regulations for specific protection). The danger of an injury is even more increased because of special conditions and outer effects

8. Means of protection against the injury caused by the electric current • Protection against a dangerous contact with animate parts Prevents passing of electric current through a body of a person or an animal, or the current is reduced to the safe amount • Protection against a dangerous contact with inanimate parts Prevents passing of electric current through a body of a person or an animal, or the current is reduced to the safe amount or the device in case of a malfunction automatically disconnects from the source. • Protection against a dangerous contact with animate and inanimate parts Voltage in animate parts can never exceed the safe amount • -

9. Describe and explain • Inanimate part • Dangerous contact voltage • Allowed contact voltage of inanimate parts

10. Describe and explain • types of environment • Give examples

11. Literature • www.wikipedia.cz • www.vosaspsekrizik.cz/cs/download/padesatka/ochrana-dotyk.pdf • Elektro v praxi, 1 část, Solid Team