Chapter A General rules of electrical installation design

F - Protection against electric shock
8 Residual current devices (RCDs)
b Type B
RCD for which tripping is ensured:
v as for type A,
v for pure direct residual currents which may result from three-phase rectifying
circuits.
Cold: in the cases of temperatures under - 5 °C, very high sensitivity
electromechanical relays in the RCD may be “welded” by the condensation – freezing
action.
Type “Si” devices can operate under temperatures down to - 25 °C.
Atmospheres with high concentrations of chemicals or dust: the special alloys
used to make the RCDs can be notably damaged by corrosion. Dust can also block
the movement of mechanical parts.
See the measures to be taken according to the levels of severity defined by
standards in Fig. F70.
Regulations define the choice of earth leakage protection and its implementation.
The main reference texts are as follows:
b Standard IEC 60364-3:
v This gives a classification (AFx) for external influences in the presence of corrosive
or polluting substances.
v It defines the choice of materials to be used according to extreme influences.
Disturbed
network
Influence of
the electrical
network
Clean network
Superimmunized
residual current
protections
Type A if: k
Standard
immunized
residual current
protections
Type AC
Fig. F70 : External influence classification according to IEC 60364-3 standard
Schneider Electric - Electrical installation guide 2008
SiE k
residual current
protections
SiE k
residual current
protections
+
Appropriate
additional
protection
(sealed cabinet
or unit)
AF1 AF2 AF3 AF4
b External
influences:
negligible,
b Equipment
characteristics:
normal.
b External
influences:
presence
of corrosive
or polluting
atmospheric
agents,
b Equipment
characteristics:
e.g. conformity
with salt mist
or atmospheric
pollution tests.
b External
influences:
intermittent
or accidental
action of
certain
common
chemicals,
b Equipment
characteristics:
corrosion
protection.
Examples of exposed sites External influences
SiE k
residual current
protections
+
Appropriate
additional
protection
(sealed cabinet
or unit +
overpressure)
b External
influences:
permanent
action of
corrosive
or polluting
chemicals
b Equipment
characteristics:
specifically
studied
according to
the type of
products.
Iron and steel works. Presence of sulfur, sulfur vapor, hydrogen
sulfide.
Marinas, trading ports, boats, sea edges, naval
shipyards.
Salt atmospheres, humid outside, low
temperatures.
Swimming pools, hospitals, food & beverage. Chlorinated compounds.
Petrochemicals. Hydrogen, combustion gases, nitrogen
oxides.
Breeding facilities, tips. Hydrogen sulfide.
F39
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