Lead Sheathed Cables/ Current Ratings/Rating factors for Air, Ground and Duct


Rating factors for Air, Ground and Duct

RATING FACTORS FOR VARIATION IN
AMPIENT TEMPERATURE FOR CABLES LAID IN AIR
Ambient temperature °C 25 30 35 40 45 50 52 55 60
XLPE insulated cables 1.37 1.30 1.24 1.17 1.09 1.03 1.00 0.95 0.88

RATING FACTORS FOR VARIATION IN GROUND TEMPERATURE
FOR CABLES LAID DIRECT IN GROUND OR IN DUCTS
Ground Temperature °C 15 20 25 30 35 40 45
XLPE insulated cables 1.16 1.13 1.08 1.03 1.00 0.95 0.90

RATING FACTORS FOR DEPTHS OF LAYING FOR
CABLES LAID DIRECT IN GROUND OR IN DUCTS

Depth of Laying

Metre

 

 

     600/1000 V Cables                                                          1.9/3.3 KV to 19/33 KV Cables

 

Cables Laid in Ground Cables Laid in Ducts Cables Laid in Ground
upto 50 Sqmm 70 Sqmm to
300 Sqmm
Above
300 Sqmm
Multicore Upto
300 Sqmm
Above
300 Sqmm
0.50 1.026 1.036 1.055 1.026 - -
0.60 1.015 1.016 1.023 1.015 - -
0.75 1.000 1.000 1.000 1.000 - -
 
0.80 0.995 0.995 0.992 0.995 1.020 1.031
1.00 0.974 0.975 0.970 0.985 1.000 1.000
1.25 0.964 0.953 0.949 0.974 0.980 0.979
 
1.50 0.954 0.943 0.939 0.964 0.969 0.969
1.75 0.944 0.922 0.918 0.964 0.959 0.948
2.00 0.933 0.912 0.907 0.954 0.939 0.928
 
2.50 0.923 0.902 0.897 0.954 0.929 0.918
3.00 0.913 0.891 0.876 0.944 0.918 0.907
or more            

Depth of laying is measured from surface of ground to the centre of a Cable/Duct or to the centre of a trefoil group of Cables/ducts as the case may be.