Chapter A General rules of electrical installation design

G - Sizing and protection of conductors
2 Practical method for determining
the smallest allowable crosssectional
area of circuit conductors
Figure G1 gives the values of correction factor k 4 for different configurations of
unburied cables or conductors, for groups of more than one circuit of single-core
cables in free air.
Method of installation Number Number of three-phase Use as a
of tray circuits multiplier to
rating for
1 2 3
Perforated 31 Touching 1 0.98 0.91 0.87 Three cables in
trays horizontal
2 0.96 0.87 0.81 formation
20 mm
3 0.95 0.85 0.78
Vertical 31 Touching 1 0.96 0.86 Three cables in
perforated vertical
trays
225 mm
2 0.95 0.84 formation
Ladder 32 1 1.00 0.97 0.96 Three cables in
supports, Touching
horizontal
cleats, etc... 33 2 0.98 0.93 0.89 formation
34 3 0.97 0.90 0.86
20 mm
Perforated
trays
31
2De
De 1 1.00 0.98 0.96 Three cables in
trefoil formation
2 0.97 0.93 0.89
20 mm
3 0.96 0.92 0.86
Vertical
perforated
31 De
Spaced 1 1.00 0.91 0.89
trays
225 mm
2 1.00 0.90 0.86
2De
Ladder
supports,
32 2De
De
1 1.00 1.00 1.00
cleats, etc... 33 2 0.97 0.95 0.93
34 20 mm 3 0.96 0.94 0.90
Fig. G17 : Reduction factors for groups of more than one circuit of single-core cables to be applied to reference rating for one circuit of single-core cables in free air
- Method of installation F. (table A.52.21 of IEC 60364-5-52)
Schneider Electric - Electrical installation guide 2008
G13
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