Grouping Derating Factors

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Above Ground

Single Layer

Installation Above Ground Grouping on a Single Layer Derating Factor Reference Method
Number of Grouped Cables
1 2 3 4 5 6 7 8 9 12 16 20
Bunched in air, on a surface, embedded or enclosed 1.0 0.8 0.7 0.65 0.6 0.57 0.54 0.52 0.5 0.45 0.41 0.38 A to F
Single layer on wall, floor or unperforated cable tray systems 1.0 0.85 0.79 0.75 0.73 0.72 0.72 0.71 0.7 0.7 0.7 0.7 C
Single layer fixed directly under a wooden ceiling 0.95 0.81 0.72 0.68 0.66 0.64 0.63 0.62 0.61 0.61 0.61 0.61 C
Single layer on a perforated horizontal or vertical cable tray systems 1.0 0.88 0.82 0.77 0.75 0.73 0.73 0.72 0.72 0.72 0.72 0.72 E, F
Single layer on cable ladder systems or cleats etc. 1.0 0.87 0.82 0.8 0.8 0.79 0.79 0.78 0.78 0.78 0.78 0.78 E, F

Multiple Layers

Installation Above Ground Grouping on Multiple Layers Derating Factor
No. of Layers No. of Multicore Cables per Layer No. of Single Core Three-Phase Circuits per Layer
Cables Laid Flat Cables in Trefoil
1 2 3 4 6 9 1 2 3 1 2 3
Horizontal perforated cable tray systems (1) Touching
1 1.0 0.88 0.82 0.79 0.76 0.73 0.98 0.91 0.87 1.0 0.98 0.96
2 1.0 0.87 0.8 0.77 0.73 0.68 0.96 0.87 0.81 0.97 0.93 0.89
3 1.0 0.86 0.79 0.76 0.71 0.66 0.95 0.85 0.78 0.96 0.92 0.86
6 1.0 0.84 0.77 0.73 0.68 0.64
Spaced (3)
1 1.0 1.0 0.98 0.95 0.91
2 1.0 0.99 0.96 0.92 0.87
3 1.0 0.98 0.95 0.91 0.85
Vertical perforated cable tray systems (2) Touching
1 1.0 0.88 0.82 0.78 0.73 0.72 0.96 0.86 1.0 0.91 0.89
2 1.0 0.88 0.81 0.76 0.71 0.7 0.95 0.84 1.0 0.9 0.86
Spaced (1)
1 1.0 0.91 0.89 0.88 0.87
2 1.0 0.91 0.88 0.87 0.85
Horizontal unperforated cable tray systems (1) Touching
1 0.97 0.84 0.78 0.75 0.71 0.68
2 0.97 0.83 0.76 0.72 0.68 0.63
3 0.97 0.82 0.75 0.71 0.66 0.61
6 0.97 0.81 0.73 0.69 0.63 0.58
Cable ladder systems. cleats. etc Touching
1 1.0 0.87 0.82 0.8 0.79 0.78 1 0.97 0.96 1.0 1.0 1.0
2 1.0 0.86 0.8 0.78 0.76 0.73 0.98 0.93 0.89 0.97 0.95 0.93
3 1.0 0.85 0.79 0.76 0.73 0.7 0.97 0.9 0.86 0.96 0.94 0.9
6 1.0 0.84 0.77 0.73 0.68 0.64
Spaced (1)
1 1.0 1.0 1.0 1.0 1.0
2 1.0 0.99 0.98 0.97 0.96
3 1.0 0.98 0.97 0.96 0.93

Notes

(1) Vertical spacing between layers is at least 300mm and there is at least 20mm horizontal clearance between the layer and wall
(2) Horizontal spacing between layers is at least 225mm with layers mounted back to back
(3) Cables are spaced at least one overall cable diameter apart

Below Ground

The below ground grouping factors apply to an installation depth of 0.7m and a soil thermal resistivity of 2.5 K·m/W. If a circuit comprises n parallel conductors per phase, then for the purpose of the derating factor, this circuit shall be considered as n circuits.

Buried Direct

No. of Circuits Below Ground Grouping (Buried Direct) Derating Factor
Cable to Cable Clearance
Touching One OD (1) 0.125m 0.25m 0.5m
2 0.75 0.8 0.85 0.9 0.9
3 0.65 0.7 0.75 0.8 0.85
4 0.6 0.6 0.7 0.75 0.8
5 0.55 0.55 0.65 0.7 0.8
6 0.5 0.55 0.6 0.7 0.8
7 0.45 0.51 0.59 0.67 0.76
8 0.43 0.48 0.57 0.65 0.75
9 0.41 0.46 0.55 0.63 0.74
12 0.36 0.42 0.51 0.59 0.71
16 0.32 0.38 0.47 0.56 0.38
20 0.29 0.35 0.44 0.53 0.66

Note (1): A clearance of one cable overall diameter

Buried in Conduit

No. of Cables Below Ground Grouping (Buried in Conduit) Derating Factor
Conduit to Conduit Clearance (Multicore) Conduit to Conduit Clearance (Single Core)
Touching 0.25m 0.5m 1.0m Touching 0.25m 0.5m 1.0m
2 0.85 0.9 0.95 0.95 0.8 0.9 0.9 0.95
3 0.75 0.85 0.9 0.95 0.7 0.8 0.85 0.9
4 0.7 0.8 0.85 0.9 0.65 0.75 0.8 0.9
5 0.65 0.8 0.85 0.9 0.6 0.7 0.8 0.9
6 0.6 0.8 0.8 0.9 0.6 0.7 0.8 0.9
7 0.57 0.76 0.8 0.88 0.53 0.66 0.76 0.87
8 0.54 0.74 0.78 0.88 0.5 0.63 0.74 0.87
9 0.52 0.73 0.77 0.87 0.47 0.61 0.73 0.86
10 0.49 0.72 0.76 0.86 0.45 0.59 0.72 0.85
11 0.47 0.7 0.75 0.86 0.43 0.57 0.7 0.85
12 0.45 0.69 0.74 0.85 0.41 0.56 0.69 0.84
13 0.44 0.68 0.73 0.85 0.39 0.54 0.68 0.84
14 0.42 0.68 0.72 0.84 0.37 0.53 0.68 0.83
15 0.41 0.67 0.72 0.84 0.35 0.52 0.67 0.83
16 0.39 0.66 0.71 0.83 0.34 0.51 0.66 0.83
17 0.38 0.65 0.7 0.83 0.33 0.5 0.65 0.82
18 0.37 0.65 0.7 0.83 0.31 0.49 0.65 0.82
19 0.35 0.64 0.69 0.82 0.3 0.48 0.64 0.82
20 0.34 0.63 0.68 0.82 0.29 0.47 0.63 0.81

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