Mains connection and line-side power components
3.5 Overvoltage protection
SINAMICS S110
Manual, 07/2015, 6SL3097-4AC10-0BP5
41
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 the entire plant.
• Always install residual current monitors in conjunction with suitable circuit-breakers.
Note the points below when using residual current monitors:
● Use only AC/DC-sensitive RCM type B devices with delayed tripping that guarantee
reliable tripping even for smoothed DC residual currents.
● Connect parts of the power drive system and the machine that can be touched to the PE
conductor of the plant.
● Do not route the PE conductor through the measuring current transformer because this
would remove its protection function.
To protect the units against line-side surge voltages, you should install an overvoltage
protection device directly at the infeed point (on the line side of the main disconnect switch).
To comply with the requirements of CSA C22.2 No. 14-05, a type VZCA7 or VZCA8 surge
arrester is absolutely mandatory. The Raycap company has suitable surge arresters.
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