APC Symmetra MW Installation Guide download pdf (Page 46)

Appendix: IT Systems

40 Symmetra MW 800 kW 3 × 400/230 V Installation Guide - 990-1510B

In installations where the neutral is distributed, the following conditions must be fulfilled:

In the condition:

Protective devices in IT systems

The following protective devices are recognized in IT systems:

• Insulation monitoring devices

• Overcurrent protective devices

• Residual current protective devices

The following diagram shows a Symmetra

MW installed in a IT system:

• Earthing arrangements and protective conductors - Symmetra

MW in “IT installation”

is the nominal A

RMS voltage between phase and neutral

is the impedance of the fault loop comprising the phase conductor and the protective conductor of

the circuit

is the impedance of the fault loop comprising the neutral conductor and the protective conductor of

the circuit

is the operating current of the protective device. The disconnecting time is 5 seconds (distribution

circuits)

Z′

---------

----

≤

Z′

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APC Symmetra MW Installation Guide Page 46