Resistance (impedance) the human body
The safety limits currents (or the time current zones Figures 4.1.
Conventional conditions this respect mean situation where the most probable accident is
hand hand hand foot. The curve considered reasonable for the establishment the
disconnecting times function prospective touch voltage for the measure for protection by
automatic disconnection supply. Safety limits current passing through the human body
Nowadays safety limits current are not prescribed Czech standards.3. the designer is
more useful safey requirements are specified terms voltage function time.4. Equipment assigned in
relevant ČSN standard
permanent 3,5 10
3.1 which organic
damage expected.1.3.2) are
inconvenient for direct application the practical design installations. For this
purpose, certain values body impedance must taken into consideration.2.c.1 and 4.2.1 Informative safety limits current passing through the human body according to
new standards
Type equipment The longest duration
of current
(s)
Safety limits current
(mA)
for
alternating current direct current
1.
Table 4. The document
IEC 479 implemented Czech standard ČSN IEC 479 (33 2010).1. All equipment (except
medical equipment)
permanent 0,5 2
2.
For a.1.1. The sign 95%, 50%, the curves mean that the values given
with the relevant curve are not exceeded for percentage 95%, 50% and the human
. The relationship of
current voltage not linear because body impedance varies with the touch voltage. placed with certain margin safety below zone in
which the risk ventricular fibrillation arises, which the main cause death electricity,
the probability which increased with the intensity the current and the duration flow.EFFECTS CURRENT PASSING THROUGH THE HUMAN BODY
26
4. The informative limits
which, according this standard, can used for electrical equipment are shown table 4. the Figure 4.1 the dependence the total body impedance to
the touch voltage can seen.1 Requirements for characteristics protective devices.2. Industrial equipment
according relevant
ČSN, not possible
to fulfill limits for point 2
5
(exceptionally
permanent)
10 30
4. (15 100 Hz), the curve situated zone (Fig.
4
