Catalog LV 70 2011 - Low & Medium Voltage - Siemens

© Siemens AG 2011
BD2 System — 160 ... 1250 A
Configuration information
Power distribution systems (grid types) according to
IEC 60364-3 or DIN VDE 0100-300
Determination of the protective measures and selection of the
electrical equipment in accordance with the power distribution
system used.
TN systems
TN-S system
L1
L2
L3
N
PE
Other systems
TT system
L1
L2
L3
N
NSV0_01081
PE
1
1
NSV0_01078
Separated neutral and protective conductors throughout the system.
TN-C system
L1
L2
In a TT system, one point is directly earthed; the chassis of the electrical
system is connected to earth which has no direct connection to the
power earth.
In the modern TT system, protective measures include protective
grounding as well as current-operated e.l.c.b. systems and voltageoperated
e.l.c.b. systems.
IT system
L1
L2
L3
PEN
L3
2
NSV0_01082
PE
1
1
NSV0_01079
Neutral and protective functions are combined throughout the system
in a single conductor.
TN-C-S system
L1
L2
L3
PEN
NSV0_01080
PE
N
1
Combination between neutral conductor and protective earth functions.
They are combined in one part of the system to a single conductor and
separated in another part.
$ Chassis
% Impedance
In the IT system there is no direct connection between the live conductors
and earthed components; the chassis of the electrical system is
earthed.
The IT system corresponds with the system where a protective earth
system for protective measures is applied.
Explanations
First character = grounding condition of the power supply source
• T = direct grounding of a point
• I = either insulation of all live parts from earth or connection of one
point with earth via impedance
Second character = grounding condition of chassis of the electrical
equipment
• T = chassis directly earthed, independently of any earthing of a point
in the power supply
• N = chassis connected directly with the system earth in AC systems,
the earth point is normally the neutral point
Additional letters = arrangement of the neutral conductor and protective
earth conductor
•S = separate conductors for neutral and protective earth functions
• C = neutral and protective earth functions combined in a single conductor
(PEN)
5
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