IT system - Preliminary conditions

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Scope and content of Wiki EIG
General rules of electrical installation design
Connection to the MV utility distribution network
Connection to the LV utility distribution network
MV & LV architecture selection guide
LV Distribution
Protection against electric shocks
Sizing and protection of conductors
LV switchgear: functions & selection
Protection against voltage surges in LV
Energy Efficiency in electrical distribution
Power factor correction and harmonic filtering
Power harmonics management
Characteristics of particular sources and loads
PhotoVoltaic (PV) installation
Residential electrical installations
ElectroMagnetic Compatibility (EMC)


(see Fig. F51 and Fig. F52 )


Minimum functions required Components and devices Examples
Protection against overvoltages at power frequency (1) Voltage limiter Cardew C
Neutral earthing resistor (for impedance earthing variation) (2) Resistor Impedance Zx
Overall earth-fault monitor with alarm for first fault condition (3) Permanent insulation monitor PIM with alarm feature Vigilohm TR22A
or XM 200
Automatic fault clearance on second fault and protection of the neutral conductor against overcurrent (4) Four-pole circuit-breakers (if the neutral is distributed) all 4 poles trip Compact circuit-breaker or RCD-MS
Location of first fault (5) With device for fault-location on live system, or by successive opening of circuits Vigilohm system

Fig. F51: Essential functions in IT schemes and examples with Merlin Gerin products


FigF52.jpg















Fig. F52: Positions of essential functions in 3-phase 3-wire IT-earthed system
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