4 40.6
38 190 33.3
40 200 35.1
25 100 17.2
25 150 26.5
31.2 20.
The size minimum cross-sectional area of
the conductor must therefore gauged in
accordance with these criteria.2
40 160 28.8
31 186 32.2 16.4
50 150 26.2
50 200 35.4 15.6
75 450 79.6 10.3
50 250 44.3
38 228 40.0 25.S.2
30 15.5 6.
19
—
Earth conductors
.4 15.1 12.1 12.
Copper conductor recommended following
BS 7430, aluminium should not installed in
contact with soil, nor damp areas, and should
not used make the final connection to
an earth electrode.4 15.5 5.2 7.4 9.8 5.2
40 120 21.6
25 8.6 3.6 6.2 12.5
50 400 70.
Conductors for earthing systems
For below ground earthing applications offer
a large range bare copper tape, solid circular
and stranded conductors thus offering the
designer the system the correctly rated
conductor without the need oversize.3 3.5 37.3
40 240 42.1 11.
These conductors provide either the connection
to final earth electrode (earth rod plate), or
the earth electrode itself (earth grid ring
earth arrangement).8 30.8
25 13.5 126 22.0
20 10.7 18.2 20.4 19.
An earth conductor must capable carrying
the maximum expected earth fault current and
leakage current likely occur structure.2
31 16.2
30 150 26.9
38 114 20.
(mm2
)
kA for
1 Sec
kA for
3 Sec
20 1.A.2 45.2 24.6 35.1 23.4
50 300 52.5
50 350 61.1
30 120 21.1
25 1.8 9.CONDUCTORS
Conductor Size
(mm)
C.7
These conductor ratings are based upon the recommendations 7430 with initial
conductor temperature 30°C and maximum temperature 250°C.
A good earth conductor must also:
• able withstand mechanical damage
• compatible with the material the
earth electrode
• Resist the corrosive effect local soil
conditions
Furse conductors effectively meet these
requirements and are available range sizes
to meet differing current ratings (see table left)
