Protection Through Residual Current Protective Devices; Additional Protection With I; (Previously "Protection Against Direct Contact") - Siemens SENTRON Manual

3. Protection through residual current protective devices

The basic prerequisite for use of a residual current protective device in order
to "automatically disconnect the power supply" as a protective measure is that
an appropriately grounded protective conductor is connected to the system
components and equipment to be protected. Current can then pass through
a human body only when two faults occur (interruption of the PE conductor
in addition to a fault in the insulation) or when there is unintentional contact
between live parts.
3.1

Additional protection with I

(previously "Protection against direct contact")

Additional protection is understood to mean protection which takes effect if there
is direct contact of a human body with a part normally live during operation in the
event of basic and/or fault protection failing. If a person directly touches live parts,
two series-connected resistors determine the level of the current – the internal
resistance of the person R
Fig. 1.
≤ 30 mA
Δn
and the transfer resistance of the location R
m
; see
st
9