Using Residual-Current Devices - Siemens SINAMICS S120 Manual

3.4

Using residual-current devices

Selectively tripping, AC/DC-sensitive residual current devices (type B) can be used in
addition to the overcurrent protection devices.
Residual current devices have to be installed if the power supply conditions in terms of short-
circuit power and loop impedance at the infeed point are not such that the installed
overcurrent protection devices will trip within the prescribed period if a fault occurs.
Residual current device (RCD)
Residual current operated circuit-breakers (RCD) can be used in addition to the overcurrent
protection devices provided. They prevent excessively high touch currents being maintained.
They are the preferred solution for TT systems.
Conditions when using residual-current operated circuit breakers
● Only use type B delayed tripping, selective AC/DC residual current operated circuit-
breakers.
● Ensure that the loop impedance is maintained corresponding to local installation
regulations.
● It is absolutely imperative that you connect parts of the drive system and the machine that
can be touched with the PE conductor of the plant or system.
● The shielded motor cable must not be longer than 50 m.
● Use a separate residual current operated circuit-breaker for each Power Module.
● Ensure that the switching elements (disconnector unit, contactors) for connecting and
disconnecting the drive line-up have max. 35 ms delay time time between the
closing/opening of the individual main contacts.
If no residual current device is used, touch protection can be ensured by means of double
insulation or by isolating the Power Module from the supply system through a transformer.
Residual current monitors (RCM)
Used in conjunction with appropriate circuit-breakers, residual current monitors (RCMs)
provide fire and system protection even at high levels of grounding resistance (in TT
systems, for example). When operating on TT systems for infeed powers exceeding 55 kW,
and with systems that extend across a large area, residual current monitors must be installed
in addition to the appropriate circuit breakers.
Fire hazard and danger of a plant standstill when residual currents occur
Undetected fault currents in the power supply can result in fires with smoke and therefore
pose a hazard for persons or at least result in failures of the entire plant.
• Always install residual current monitors in conjunction with suitable circuit-breakers.
AC Drive
Manual, (GH6), 07/2016, 6SL3097-4AL00-0BP5
WARNING
Mains connection and line-side power components
3.4 Using residual-current devices
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