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23Symmetra MW II 1200 kW 3 × 400/230 V Installation - 990-1979E-001
Appendix
System and Protective Earthing
The purpose of this appendix is to describe the system- and protective earthing principles of the
Symmetra
®
MW.
Caution: All wiring to be in accordance with applicable national and/or local electrical
wiring rules.
TN Systems
Characteristics
TN systems have one point connected directly to ground. All exposed conductive parts must be
connected to that point by protective conductors.
Depending on the way the neutral and protective conductors are fed, there are three types of TN systems:
• TN-S system: a separate protective conductor is used in the system
• TN-C-S system: the neutral and protective conductors are combined to one single conductor in a
part of the system
• TN-C system: the neutral and protective conductors are combined to one single conductor in the
whole system
Reference to IEC 60364-4-41 413.1.3
All exposed conductive parts of the installation must be connected to the earthed point of the power
system by protective conductors which must be earthed at or near to each relevant transformer or
generator.
Exposed conductive parts that are accessible at the same time must be connected to the same earthing
system, either individually, in groups or collectively.
Normally the earthed point of the power system is the neutral point. If a neutral point is not available or
accessible, a phase conductor must be earthed. The phase conductor must not serve as a PEN conductor.
In fixed installations a single conductor may serve both as a protective conductor and a neutral conductor
(PEN conductor).
Reference to IEC 60364-5-54 546.2.3
If from any point in the installation the neutral and protective functions are provided by separate
conductors, it is inadmissible to connect these conductors to each other from that point. At the point of
separation, separate terminals or bars must be provided for the protective and neutral conductors. The
PEN conductor must be connected to the terminal or bar intended for the protective conductor.