0
20 10.7 18.
19
—
Earth conductors
.2
31 16.CONDUCTORS
Conductor Size
(mm)
C.1
25 1.
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.2 24.A.
An earth conductor must capable carrying
the maximum expected earth fault current and
leakage current likely occur structure.4 19.3
40 240 42.2
30 150 26.4 15.4 9.3
40 200 35.5 5.1 23.6 35.4 15.2 16.5 126 22.
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.8 30.6 6.8 5.
(mm2
)
kA for
1 Sec
kA for
3 Sec
20 1.7
These conductor ratings are based upon the recommendations 7430 with initial
conductor temperature 30°C and maximum temperature 250°C.3
50 250 44.2
40 160 28.1 11.2 12.5
50 400 70.4
50 300 52.2
25 150 26.
The size minimum cross-sectional area of
the conductor must therefore gauged in
accordance with these criteria.3 3.5
31.S.6
75 450 79.6
25 8.5 6.2
30 15.2 20.5
50 350 61.6 3.6 10.
These conductors provide either the connection
to final earth electrode (earth rod plate), or
the earth electrode itself (earth grid ring
earth arrangement).
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).6
38 190 33.1
30 120 21.1 12.4 40.5 37.1
25 100 17.2 20.8
31 186 32.2
50 200 35.8
25 13.8 9.2 45.2
40 120 21.1 12.4
50 150 26.4 15.9
38 114 20.3
38 228 40.2 7.0 25
