Overcurrent Protection By Means Of Line Fuses And Circuit Breakers; Using Residual-Current Devices - Siemens S120 Manual

3.3

Overcurrent protection by means of line fuses and circuit breakers

Line fuses or circuit-breakers must be used for cable protection/overcurrent protection. NH,
D, and DO type fuses with a gL characteristic or suitable circuit-breakers according to
IEC 60947 can be used for this purpose.
The appropriate fuses and circuit-breakers are listed in the technical data of the associated
Power Module.
Danger to life due to electric shock and fire hazard caused by overcurrent protective
equipment tripping too late
Overcurrent protective equipment that trips too late or not all can cause electric shock or
fire.
• To protect personnel and for fire protection purposes, at the infeed point, the short-
• In TT systems, besides suitable overcurrent protection equipment, also use residual
For further information: See catalog PM 21.
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 operated circuit-breakers (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.
Note the following conditions when using residual current operated circuit-breakers:
● Only use type B delayed tripping, selective AC/DC residual current operated circuit-
● Ensure that the loop impedance is maintained corresponding to local installation
● It is absolutely imperative that you connect parts of the drive system and the machine that
AC Drive
Manual, (GH6), 04/2014, 6SL3097-4AL00-0BP4
3.3 Overcurrent protection by means of line fuses and circuit breakers
WARNING
circuit rating and loop impedance must match the specifications in the documentation for
the installed overcurrent protection devices to trip within the specified time.
current devices (RCD) and, as of an infeed power of 55 kW or in extensive installations,
also use residual current monitors (RCM).
breakers.
regulations.
can be touched with the protective conductor of the plant or system.
Mains connection and line-side power components
41