B. CABLES INSTALLED IN FREE AIR

B1. Rating Factor for Variation in Air Temperature

B2. Rating Factor for Group in Air for Single-core cables in three-phase systems

Arrangement of Cables	Number of cable trays or cable racks	Installed in one plane Clearance = cable diameter d distance from wall ≥ 2 cm				Installation in bunches Clearance = 2d distance from wall ≥ 2 c
		Number of group				Number of group
		1	2	3		1	2	3
On the floor	-	0.92	0.89	0.88		0.95	0.90	0.88
On Cable trays	1	0.92	0.89	0.88		0.95	0.90	0.88
	2	0.87	0.84	0.83		0.90	0.85	0.83
	3	0.84	0.82	0.81		0.88	0.83	0.81
	6	0.82	0.80	0.79		0.86	0.81	0.79
On cable racks	1	1.00	0.97	0.96		1.00	0.98	0.96
	2	0.97	0.94	0.93		1.00	0.95	0.93
	3	0.96	0.93	0.92		1.00	0.94	0.92
	6	0.94	0.91	0.90		1.00	0.93	0.90
On support or on the wall	-	0.94	0.91	0.89		0.89	0.86	0.84

B3. Rating Factor for Group in Air for Multi-core cables in three-phase systems

EXAMPLE :

Two XLPE three core cables N2XSEY 3x240 cm 6/10 kV are loaded. The cable is laid ground under conditions :
Permissible operating temperature : 90°C
Load Factor : 0.7
Depth of laying : 1 meter
Ground temperature : 35°C
Resistivity of soil : 1.2 °K.m/watt
Clearance between cables : 7 cm
The current-carrying capacity of the cable is calculated as follow :
From brochure N2XSEY 3x240 cm, we get current : 491 Amp.
Rating factor :
Depth of lay : 0.98
Ground temperature 35 °C : 0.96
Resistivity of soil 1.2 °K.m/watt : 0.95
Two group of multi core cables in three-phase system : 0.85
So, current-carrying capacity is :
| load = 491 x 0.98 x 0.96 x 0.95 x 0.85 (Amp.)
| load = 373 (Amp.) (Load factor : 0.7)