Residual-Current Monitors (Rcm) - Siemens Sinamics S120 Manual

3.4.2

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
Residual currents in the power supply that are not detected can cause fires and failures in
the entire system.
• Always install residual-current monitors in conjunction with suitable circuit breakers.
Note the points below when using residual-current monitors:
● Only use AC/DC-sensitive RCM type B devices with delayed tripping that guarantee
● Connect parts of the power drive system and the machine that can be touched to the
● Do not route the protective conductor through the measuring current transformer, as this
Booksize Power Units
Manual, (GH2), 04/2014, 6SL3097-4AC00-0BP6
WARNING
reliable tripping even for smoothed DC residual currents.
system's protective conductor.
would cancel its protection function.
Line connection and line-side power components
3.4 Line supply connection via residual-current devices
55