Operation With Ungrounded (It) Supplies; Operation With Residual Current Devices (Rcd) - Siemens PM250 Hardware Installation Manual

4.3

Operation with ungrounded (IT) supplies

Operation with ungrounded (IT) supplies
IT supplies are fully isolated from the protective earth system, usually by an isolating
transformer. It should be noted, however, that a protective earth is still provided.
Power Modules with built-in filters or external filters must not be used with IT supplies.
If the Power Module connected to an IT supply is required to remain operational if an input or
output phase is connected to ground, then an output reactor must be fitted to prevent
overcurrent tripping. The probability of overcurrent tripping without output reactor increases
with the size of the IT supply.
Operation of the Power Modules without a protective earth is not permitted under any
circumstances.
4.4

Operation with Residual Current Devices (RCD)

Operation with Residual Current Devices (RCD)
If an RCD (also referred to as an ELCB or a RCCB) is fitted, the Power Module will operate
without nuisance tripping provided that:
● A type B RCD is used.
● The trip limit of the RCD is 300 mA.
● The neutral of the supply is grounded.
● Only one Power Module is supplied from each RCD.
● The output cables are less than 50 m (164 ft) screened or 100 m (328 ft) unscreened.
If no RCD is used, the touch protection can be achieved by double insulation or by
separating the Power Module from the mains system using a transformer.
PM250 Power Module
Hardware Installation Manual, 09/2012, A5E01003502B AD
WARNING
Siemens Parts
4.3 Operation with ungrounded (IT) supplies
Connecting
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