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BETA Protecting
Residual Current Protective Devices
Residual-current operated circuit breakers
2/37
Siemens ET B1 · 10/2008
2
*
You can order this quantity or a multiple thereof.
Residual current protective devices with rated residual current
I
n
30
mA meet the conditions of additional protection against
electric shock (see illustration):
•
In the case of accidental direct contact with parts that are live
under operating conditions (e.g.: failure of the basic insulation,
improper use, ineffectiveness of the basic protection)
•
In the case of negligence on the part of the user (e.g. use of
defective devices, inexpert repairs to systems and/or
equipment)
•
In the case of contact with faulty live parts (e.g. failure of leakage
protection in the event of interruption of the protective conductor)
The use of residual current protective devices with rated residual
current of up to 30 mA has proven an effective enhanced protection
in the event of failure of basic protection measures (protection
against direct contact) and/or fault protection measures (protection
against indirect contact), as well as in the case of negligence on the
part of the user when handling electrical equipment. However, this
must not be the sole means of protection against electric shock.
This does not replace the need for further protective measures
as required by DIN VDE 0100-410.
The requirement for "enhanced protection" with residual current
protective devices according to sections 411.3.3 and 415.1 of
DIN VDE 0100-410 does not mean that the application of this
protection is optional. Rather, it means that this enhanced pro-
tection may be required in relation to external influences and in
specific areas in coordination with further protective measures.
In several parts of the standards for Groups 4 and 7 of
DIN VDE 0100, this additional protection is required or explicitly
recommended. The following explains some of the key
requirements.
The general building standard for protection against electric
shock, DIN VDE 0100-410:2007-06 requires the use of residual
current protective devices with rated residual current 30 mA
for
•
all socket outlets with a rated current of up to 20 A if they are
intended for use by non-experts and for general use.
•
branch circuits for portable tools and equipment used
outdoors with a rated current up to 32 A.
Note:
While DIN VDE 0100-410:06-2007 specifies two exceptions to
these requirements, these are not generally applicable to the
majority of applications.
The standard does not specify enhanced protection for socket
outlets that are used solely by electrical engineers and persons
with electrical training (e.g. in electrical workshops) or if it is
ensured that the socket outlet is permanently used solely for
"
specific equipment".
The standard DIN VDE 0100-723:2005-06, "Requirements for
special installations or locations – class-rooms with experimental
equipment" stipulates that, for the supply of experimental equipment
and their circuits, the TN or TT systems must be fitted with residual
current protective devices, type B, with rated residual current
30
mA.
Leakage protection (protection against indirect contact)
Indirect contact refers to the electric contact of persons with a
conductive part which is not normally live under operating
conditions but has become live under fault conditions. In such
cases, it is essential that the power supply is automatically
disconnected if a fault means that the size and duration of the
touch voltage could pose a risk.
For this purpose, residual current protective devices with a rated
residual current of over 30 mA are also suitable. Compliance
with the trip conditions is essential in order to ensure sufficient
protection. Taking into account the grounding resistance and the
rated residual current, the dangerous touch voltage must not
persist for a time sufficient to cause a risk of harmful physiological
effect in a person.
Fire protection
DIN VDE 0100-482 requires measures to be taken to prevent
fires in "Locations exposed to fire hazards" that may result from
insulation faults. This stipulates that cables and conductors in
TN and TT systems must be protected by means of residual
current protective devices with a rated residual current of
I
n
= 300 mA. This does not include mineral-insulated cables
and busbar systems.
In the case of applications where resistance-related faults may
cause a fire (e.g. ceiling heating with panel heating elements),
the rated residual current must be
I
n
= 30 mA.
Protection against fires provided by separate residual current
protective devices should not be solely restricted to locations
exposed to fire hazards, but universally implemented.
© Siemens AG 2008