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BD2 <strong>System</strong> — <strong>160</strong> ... 1250 A<br />
© Siemens AG 2007<br />
Engineering information<br />
Power distribution systems (grid types) according to<br />
IEC 60364-3 or DIN VDE 0100-300<br />
Determination of the protective measures and selection of the<br />
electrical equipment in accordance with the power distribution<br />
system used.<br />
TN systems<br />
TN-S system<br />
L1<br />
L2<br />
L3<br />
N<br />
PE<br />
Other systems<br />
TT system<br />
L1<br />
L2<br />
L3<br />
N<br />
NSV0_01081<br />
PE<br />
1<br />
1<br />
NSV0_01078<br />
Separated neutral and protective conductors throughout the system.<br />
TN-C system<br />
L1<br />
L2<br />
In a TT system, one point is directly earthed; the chassis of the electrical<br />
system is connected to earth, which has no direct connection to the<br />
power earth.<br />
In the modern TT system, protective measures include protective earthing<br />
as well as current-operated e.l.c.b. systems and voltage-operated<br />
e.l.c.b. systems.<br />
IT system<br />
L1<br />
L2<br />
L3<br />
PEN<br />
L3<br />
2<br />
NSV0_01082<br />
PE<br />
1<br />
1<br />
NSV0_01079<br />
5<br />
Neutral and protective functions are combined throughout the system<br />
in a single conductor.<br />
TN-C-S system<br />
L1<br />
L2<br />
L3<br />
PEN<br />
NSV0_01080<br />
PE<br />
N<br />
1<br />
Combination between neutral pole and protective earth functions. They<br />
are combined in one part of the system to a single conductor and<br />
separated in another part.<br />
$ Chassis<br />
% Impedance<br />
In the IT system there is no direct connection between the live conductors<br />
and earthed components; the chassis of the electrical system is<br />
earthed.<br />
The IT system corresponds with the system where a protective earth<br />
system for protective measures is applied.<br />
Explanations<br />
First letter = earthing condition of the power supply source<br />
• T = direct earthing of a point<br />
• I = either insulation of all live parts from earth or connection of one<br />
point with earth via impedance<br />
Second letter = earthing condition of chassis of the electrical<br />
equipment<br />
• T = chassis directly earthed, independently of any earthing of a point<br />
in the power supply<br />
• N = chassis connected directly with the system earth in AC systems,<br />
the earth point is normally the neutral point<br />
Additional letters = arrangement of the neutral conductor and protective<br />
earth conductor<br />
• S = separate conductors for neutral and protective earth functions<br />
• C = neutral and protective earth functions combined in a single<br />
conductor (PEN)<br />
5/90 Siemens LV 70 · 2006
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