Transcript AVOP-ELEKTRO-SKA-005

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.
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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
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).
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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 of
environment, in which this contact
occurs (ČSN 33 2000-4-41).
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).
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 the duration 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.
Environment
Normal
Dangerous *)
Extremely
Dangerous
contact with parts
(in operation)
Safe low voltage of animate parts [V]
Alternating
Direct
Animate
50
100
Inanimate
50
120
Animate
25
60
Inanimate
50
120
Animate
12
25
Inanimate
25
60
*) It can be also specified differently in the regulation, if the sum of conditions (determining
or influencing danger of an injury caused by an electric current) demands it
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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
damage and conductive environment. These are those
places, where there is a temporary or permanent danger of
an injury caused by electric current because of external
effects.
Extremely dangerous – wet, with extreme 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
 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
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Protection against a dangerous contact with inanimate parts
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Protection against a dangerous contact with animate and
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.
Voltage in animate parts can never exceed the safe amount
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Inanimate part
Dangerous contact voltage
Allowed contact voltage of inanimate parts
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types of environment
Give examples
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www.wikipedia.cz
www.vosaspsekrizik.cz/cs/download/padesat
ka/ochrana-dotyk.pdf
Elektro v praxi, 1 část, Solid Team