Accessories
4.8 Residual current devices
3VA molded case circuit breakers with IEC certificate
386
Manual, 03/2019, A5E03603177010-03
4.8
Residual current devices
Residual current devices afford fault protection (formerly referred to as: protection in case of
indirect contact) and supplementary protection (formerly referred to as: protection in case of
direct contact) in low-voltage systems. In the event of a basic insulation failure or direct
contact with live components, they provide some degree of protection to persons, material
assets and livestock against harm.
Operating principle of a residual current device
In fault-free electrical installation, the vector sum of the load currents of all connected
conductors equals zero. A residual current occurring in the protected circuit as the result of
an insulation fault, for example, induces a voltage in the secondary winding of a summation
current transformer. The evaluation electronics system monitors the induced voltage and
transmits a trip command to the RCD trip unit if the trip criterion is fulfilled. The molded case
circuit breaker with residual current protection combination is designed to ensure that the
molded case circuit breaker contacts open if the residual current exceeds a preset value.
4.8.1
Portfolio
The new portfolio of residual current devices includes different RCD designs so that an
optimum solution is available for every conceivable type of application. The types can be
distinguished as follows:
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Designs:
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Side mounted
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Loadside
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Modular
Because a wide variety of residual current waveforms (e.g. sinusoidal AC residual currents
or smooth DC residual currents) can occur in different applications (depending on the
electronic switch in the circuit), the following types of residual current devices are available:
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Type A
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Type B
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Type B+
