Chapter A General rules of electrical installation design

D12
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D - MV & LV architecture selection guide
Service rating Protection index
IP
4 Technological characteristics
The types of electrical connections of functional units can be denoted by a threeletter
code:
b The first letter denotes the type of electrical connection of the main incoming
circuit,
b The second letter denotes the type of electrical connection of the main outgoing
circuit,
b The third letter denotes the type of electrical connection of the auxiliary circuits.
The following letters are used:
b F for fixed connections,
b D for disconnectable connections,
b W for withdrawable connections.
Service ratings are related to other mechanical parameters, such as the Protection
Index (IP), form of internal separations, the type of connection of functional units or
switchgear (Fig. D6):
Form Functional Unit
Withdrawability
1 1 1 2 X X 1 F F F
2 1 1 2 X B 1 F F F
2 2 3 2 X B 3b W F D
2 3 2 2 X B 3b W F W
2 3 3 2 X B 3b W W W
3 3 2 2 X B 3b W W W
3 3 3 2 X B 3b W W W
Fig. D6 : Correspondence between service index and other mechanical parameters
Technological examples are given in chapter E2.
b Definition of the protection index: see IEC 60529: “Degree of protection given by
enclosures (IP code)”,
b Definitions of the form and withdrawability: see IEC 60439-1: “Low-voltage
switchgear and controlgear assemblies; part 1: type-tested and partially type-tested
assemblies”.
4.3 Other considerations
Other considerations have an impact on the choice of technological solutions:
b Designer experience,
b Consistency with past designs or the partial use of past designs,
b Standardization of sub-assemblies,
b The existence of an installed equipment base,
b Utilities requirements,
b Technical criteria: target power factor, backed-up load power, presence of harmonic
generators…
These considerations should be taken into account during the detailed electrical
definition phase following the draft design stage.
Schneider Electric - Electrical installation guide 2008