Table 4.3 Correction factors to current rating for ambient temperature
-------------- (Ca)
(from [Tables 4C1 and 4C2] of BS 7671: 1992)
Ambient temperature
Type of insulation
(°C)
70°C p.v.c
85°C rubber
70°C m.i
105°C m.i
25
1.03 (1.03)
1.02 (1.02)
1.03 (1.03)
1.02 (1.02)
30
1.00 (1.00)
1.00 (1.00)
1.00 (1.00)
1.00 (1.00)
35
0.94 (0.97)
0.95 (0.97)
0.93 (0.96)
0.96 (0.98)
40
0.87 (0.94)
0.90 (0.95)
0.85 (0.93)
0.92 (0.96)
45
0.79 (0.91)
0.85 (0.93)
0.77 (0.89)
0.88 (0.93)
50
0.71 (0.97)
0.80 (0.91)
0.67 (0.86)
0.84 (0.91)
55
0.61 (0.84)
0.74 (0.88)
0.57 (0.79)
0.80 (0.89)
Figures in brackets apply to semi-enclosed fuses
used for overload protection

Extracted from The Electricians Guide Fifth Edition
by John Whitfield

Published by EPA Press
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