Medium Voltage Power Cables Catalogue - AEC Online

Annex E: Derating Factors
Cables on horizontal perforated trays (spaced)
Clearance = 2 cable diameter (D e )
Clearance from the wall ≥ 20 mm
Number of trays
Number of three-phase circuits
1 2 3
Laying form
1
2
3
1.00
0.97
0.96
0.98
0.93
0.92
0.96
0.89
0.86
2D
20 mm
e
D
e
Cables on vertical perforated trays (spaced)
Laying form
Clearance = 2 cable diameter (D e )
Clearance betw. trays ≥ 225 mm
Number of three-phase circuits
Number of trays
1
1 2 3
1.00
0.91
0.89
225 mm
2D e
2
1.00
0.90
0.86
D e
3
-
-
-
Cables on ladder supported, cleats, etc. (spaced)
Clearance = 2 cable diameter (D e )
Clearance from the wall ≥ 20 mm
Number of trays
Number of three-phase circuits
1 2 3
Laying form
1
1.00
1.00
1.00
2D
e
D
e
2
3
0.97
0.96
0.95
0.94
0.93
0.90
20 mm
NOTES:
1 . Values given have to be applied to the current carrying capacity for one three-phase circuit of single-core
cables in free air, either in trefoil or horizontal (flat) formation.
2 . Values given are averages for the cable types and range of conductor sizes considered. The spread of values is
generally less than 5 %.
3 . Factors are given for single layer of cables (or trefoil groups) as shown in the table and do not apply when
cables are installed in more than one layer touching each other. Values for such installations may be significantly
lower and should be determined by an appropriate method.
4 . Values are given for vertical spacing between trays of 300 mm. For closer spacing, the factors should be reduced.
5 . Values are given for horizontal spacing between trays of 225 mm with trays mounted back to back. For closer
spacing, the factors should be reduced.
6 . For circuits having more than one cable in parallel per phase, each three phase set of conductors should be
considered as a circuit for the purpose of this table.
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