Schneider Electric - Electrical installation guide 2009
E
© Schneider Electric - all rights reserved
Chapter E
LV Distribution
Contents
Earthing schemes
E2
1.1 Earthing connections
E2
1.2 Definition of standardised earthing schemes
E3
1.3 Characteristics of TT, TN and IT systems
E6
1.4 Selection criteria for the TT, TN and IT systems
E8
1.5 Choice of earthing method - implementation
E10
1.6 Installation and measurements of earth electrodes
E11
The installation system
E5
2.1 Distribution boards
E15
2.2 Cables and busways
E18
External influences (IEC 60364-5-5)
E25
3.1 Definition and reference standards
E25
3.2 Classification
E25
3.3 List of external influences
E25
3.4 Protection provided for enclosed equipment: codes IP and IK
E28
2
3
Schneider Electric - Electrical installation guide 2009
E - Distribution in low-voltage installations
E2
© Schneider Electric - all rights reserved
Earthing schemes
. Earthing connections
Definitions
National and international standards (IEC 60364) clearly define the various elements
of earthing connections. The following terms are commonly used in industry and in
the literature. Bracketed numbers refer to Figure E :
b Earth electrode (1): A conductor or group of conductors in intimate contact with,
and providing an electrical connection with Earth (cf details in section 1.6 of Chapter E.)
b Earth: The conductive mass of the Earth, whose electric potential at any point is
conventionally taken as zero
b Electrically independent earth electrodes: Earth electrodes located at such a
distance from one another that the maximum current likely to flow through one of
them does not significantly affect the potential of the other(s)
b Earth electrode resistance: The contact resistance of an earth electrode with the
Earth
b Earthing conductor (2): A protective conductor connecting the main earthing
terminal (6) of an installation to an earth electrode (1) or to other means of earthing
(e.g. TN systems);
b Exposed