Earthing (grounding) system
according to IEC, BS-EN and IEEE standards
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Legal regulations being applied when designing
earthing (grounding) systems
1.
Good earthing (grounding) system according to IEC/BS EN 62305-3:2011 standard
E.5.4 Earth-termination system
E.5.4.1 General
(...) The LPS designer and the LPS installer should select suitable types of earth electrodes and
should locate them at safe distances from entrances and exits of a structure and from the external
conductive parts in the soil, such as cables, metal ducts, etc. Hence the LPS designer and the LPS
installer should make special provisions for protection against dangerous step voltages in the vicinity of the
earth-termination networks if they are installed in areas accessible to the public (see Clause 8).
The recommended value of the overall earth resistance of 10 Ω is fairly conservative in the case of
structures in which direct equipotential bonding is applied. The resistance value should be as low as
possible in every case but especially in the case of structures endangered by explosive material. Still
the most important measure is equipotential bonding.
E.5.4.2.2 Type B arrangement
(...) The type B earth-termination system is preferred for meshed air-termination systems and for LPS
with several down-conductors.
This type of arrangement comprises either a ring earth electrode external to the structure, in contact
with the soil for at least 80% of its total length, or a foundation earth electrode.
E.5.4.3.2 Foundation earth electrodes
(...) A further problem arises from electrochemical corrosion due to galvanic currents. Steel in concrete
has approximately the same galvanic potential in the electrochemical series as copper in soil. Therefore,
when steel in concrete is connected to steel in soil, a driving galvanic voltage of approximately 1 V
causes a corrosion current to flow through the soil and the wet concrete and dissolve steel in soil.
Earth electrodes in soil should use copper, copper coated steel or stainless steel conductors
2.
where these are connected to steel in concrete.
Good conductors and rods for earthing (grounding) system according to
IEC/BS EN 62561-2:2012
Material, configuration and cross sectional area of earth electrodes
Material ConfiguCross sectional area a
Recommended dimensions
ration
Earth rod Earth conductor
mm2
mm2
Copper
coated
steel c
Solid
round
Solid
round
Solid
round
Solid
tape
≥ 150 h
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≥ 50
≥ 78
≥ 90
14 mm diameter, if 250 µm minimum radial
copper coating, with 99.9% copper content
8 mm diameter, if 250 µm minimum radial
copper coating, with 99.9% copper content
10 mm diameter, if 70 µm minimum radial
copper coating, with 99.9% copper content
3 mm thickness, if 70 µm minimum radial
copper coating, with 99.9% copper content
a Manufacturing tolerance
‒ 3%
c The copper shall be intrinsically bonded to the
steel. The coating can be
measured using an electronic coating measuring
thickness instrument
h In some countries, the
cross sectional area may
be reduced to 125 mm2
1
3.
Good cross section of earthing conductors according to IEEE Std 80-2000
11.2.2 Copper-clad steel
(...) Copper-clad steel is usually used for underground rods and occasionally for grounding grids, especially
where theft is a problem. Use of copper, or to a lesser degree copper-clad steel, therefore assures that
the integrity of an underground network will be maintained for years, so long as the conductors are of
an adequate size and not damaged and the soil conditions are not corrosive to the material used.
Calculation of the cross section of earthing conductors based on IEEE standards 80-2000
A – earthing conductor cross section in mm2
I – rms current in kA
TCAP – thermal capacity per unit volume in J/ (cm3 oC)
tc – duration of current in s
r – thermal coefficient of resistivity in 1/oC
r – resistivity of the ground conductor in Ω-cm
Ko – 1/o or (1/r) – Tr in oC
Tm – maximum allowable temperature in oC
Ta – ambient temperature in oC
Samples cross section for copper clad conductors with different rms current in kA (I) and duration of current in s (tc)
tc \ l
0.11 s
10 kA
20 kA
mm2
25
mm2
50
0.5 s
mm2
53
1s
mm2
75
2s
mm2
105
3s
mm2
129
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A or C
A or C
D
F
H
mm2
105
mm2
149
mm2
210
mm2
257
30.5 kA
A or C
F
H
2xF
H
mm2
74
mm2
158
mm2
223
mm2
315
mm2
386
B or D
H
2xG
2xH
2xI
A) Ø 8 mm ‒ 50 mm2
B) Ø 10 mm ‒ 78 mm2
C) 20 x 3 mm ‒ 60 mm2
D) 25 x 3 mm ‒ 75 mm2
E) 30 x 3 mm ‒ 90 mm2
F) 30.5 x 3 mm ‒ 105 mm2
G) 30 x 4 mm ‒ 120 mm2
H) 40 x 4 mm ‒ 160 mm2
I) 40 x 5 mm ‒ 200 mm2
2
4.
4A
In the points from 4A to 4D there are the guidelines to design earthing
(grounding) systems to the particular building facilities and structures
according to the standards for these facilities.
GROUNDING SYSTEM
OF TRANSMISSION LINE TOWER (HV AND MV)
BS EN 50522:2010
Applied products:
G100 11
G104 12
G100 14
G110 73(40M)
G100 12
G100 22
G103 10
G103 80
G103 82
G103 97
G104 02
G104 03
G104 13
G110 74(30M)
G110 75(30M)
G110 81(20M)
G110 83
G111 50
G114 01
G114 02
Resistance of the tower ground ring
Resistance of the grounding rod with depth h
D = L/π – diameter of the ring in m
L – length of the grounding rod in m
d – half the width of the tape in m
ρE – soil resistivity in Ωm
L – length of the ring tape in m
ρE – soil resistivity in Ωm
d – diameter of the grounding rod in m
Resistance of the grounding system
As the tapes and vertical rods of the external rods’ system are connected with the steel immersed
in the stop footing concrete of the antenna tower, they have to made of precious metals, such as
copper-bonded steel, stainless steel or solid copper. Copper-bonded steel materials were applied
in the presented installation. This allowed to decrease the grounding (earthing) costs by 45%
comparing to the stainless steel or solid copper.
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3
4B
GROUNDING SYSTEM OF LV TRANSMISSION
LINE
TELECOMMUNICATION TOWERS
HD 60364-5-54
Resistance of the tower ground ring
L – length of the ring tape in m
ρE – soil resistivity in Ωm
Resistance of the grounding rod
L – length of the grounding rod in m
ρE – soil resistivity in Ωm
Resistance of the grounding system
Applied products:
G100 11
G103 97
G110 75(30M)
G100 14
G104 03
G110 83
G100 12
G100 22
G103 10
G103 80
G103 82
G104 02
G104 12
G104 13
G110 73(40M)
G110 74(30M)
G110 81(20M)
G111 50
G114 01
G114 02
As the tapes and vertical rods of the external rods’ system are connected with the steel immersed
in the stop footing concrete of the antenna tower, they have to made of precious metals, such as
copper-bonded steel, stainless steel or solid copper. Copper-bonded steel materials were applied
in the presented installation. This allowed to decrease the grounding (earthing) costs by 45%
comparing to the stainless steel or solid copper.
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4
4C
POWER STATION (HV and MV)
IEEE Std 80-2000
14.3 Schwarz’s equations
(...) Schwarz developed the following set of equations to determine the total resistance of a grounding
system in a homogeneous soil consisting of horizontal (grid) and vertical (rods) electrodes. Schwarz’s
equations extended accepted equations for a straight horizontal wire to represent the ground resistance,
R1, of a grid consisting of crisscrossing conductors, and a sphere embedded in the earth to represent
ground rods, R2. He also introduced an equation for the mutual ground resistance Rm between the grid
and rod bed.
Schwarz used the following equation introduced by Sunde and Rüdenberg to combine the resistance of the
grid, rods, and mutual ground resistance to calculate the total system resistance, Rg.
R1 – ground resistance of grid conductors in Ω
R2 – ground resistance of all ground rods in Ω
Rm – mutual ground resistance between the group of grid conductors,
R1, and group of ground rods, R2 in Ω
Ground resistance of the grid
ρE – is the soil resistivity in Ωm
Lc – is the total length of all connected grid conductors in m
’ – is
for conductors buried at depth h in m
2 – is the diameter of conductor in m
S – is the area covered by conductors in m2
k1, k2 – are the coefficients [see Figure 1 and 2]
Lr – is the length of each rod in m
2b – is the diameter of rod in m
nR – number of rods placed in area S
A ‒ is the length of the grid, B ‒ is the width of the grid,
A/B ‒ is the length-to-width ratio,
h ‒ is the depth of the grounding grid
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5
Figure 1
curve 1 for depth h = 0
y1 = – 0.04x + 1.41
curve 2 for depth
y2 = – 0.05x + 1.20
curve 3 for depth
y3 = – 0.05x + 1.13
Figure 2
curve 1 for depth h = 0
y1 = 0.15x + 5.50
curve 2 for depth
y2 = 0.10x + 4.68
curve 3 for depth
y3 = – 0.05x + 4.40
Applied products:
G100 11
G100 12
G100 14
G100 22
G103 10
G104 02
G110 73(40M)
G110 83
G103 82
G104 12
G110 75(30M)
G114 01
G103 80
G103 97
G104 03
G104 13
G110 74(30M)
G110 81(20M)
G111 50
G114 02
As the tapes and vertical rods of the external rods’ system are connected with the steel immersed
in the stop footing concrete of the antenna tower, they have to made of precious metals, such as
copper-bonded steel, stainless steel or solid copper. Copper-bonded steel materials were applied
in the presented installation. This allowed to decrease the grounding (earthing) costs by 45%
comparing to the stainless steel or solid copper.
www.goodgrounding.eu
6
4D
GROUNDING SYSTEM OF HIGH-VOLTAGE LINES
WIND TURBINE
FACILITIES CONSTRUCTION
(IEC) BS EN 62305-3
E.5.4 Earth termination system
E.5.4.1 General
(...) the LPS designer and the LPS installer should make special provisions for protection against dangerous
step voltages in the vicinity of the earth-termination networks if they are installed in areas accessible to
the public (see Clause 8).
The recommended value of the overall earth resistance of 10 Ω is fairly conservative in the case of structures
in which direct equipotential bonding is applied. The resistance value should be as low as possible in
every case but especially in the case of structures endangered by explosive material. Still the most
important measure is equipotential bonding.
www.goodgrounding.eu
7
E.5.4.2 Types of earth electrode arrangements
E.5.4.2.1 Type A arrangement
(...) This type of arrangement comprises horizontal or vertical electrodes connected to each down-conductor.
Where there is a ring conductor, which interconnects the down-conductors, in contact with the soil the
earth electrode arrangement is still classified as the type A if the ring conductor is in contact with the soil
for less than 80% of its length.
E.5.2.2 Type B arrangement
(...) This type of arrangement comprises either a ring earth electrode external to the structure, in contact
with the soil for at least 80% of its total length, or a foundation earth electrode.
For bare soild rock, only the type B earthing arrangement is recommended.
As the tapes and vertical rods of the
external rods’ system are connected
with the steel immersed in the stop
footing concrete of the antenna tower,
they have to made of precious metals,
such as copper-bonded steel, stainless
steel or solid copper. Copper-bonded
steel materials were applied in the
presented installation. This allowed to
decrease the grounding (earthing) costs
by 45% comparing to the stainless steel
or solid copper.
Applied products:
G100 11
G104 12
G100 14
G110 73(40M)
G100 12
G100 22
G103 10
G103 80
G103 82
G103 97
G104 02
G104 03
G104 13
G110 74(30M)
G110 75(30M)
G110 81(20M)
G110 83
G111 50
G114 01
G114 02
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8
5.
Resistivity of soil
Resistivity measurements for good earthing (grounding) system according to IEEE Std 80-2000
(...) A number of measuring techniques are described in detail in IEEE Std 81-1983. The Wenner four-pin method,
as shown in Figure below, is the most commonly used technique. In brief, four probes are driven into the earth
along a straight line, at equal distances a apart, driven to a depth b. The voltage between the two inner (potential)
electrodes is then measured and divided by the current between the two outer (current) electrodes to give
a value of resistance R.
Wenner four-pin method
then for b « a:
where
a ‒ is the apparent resistivity of the soil in Ωm
R ‒ is the measured resistance (R = U/l) in 
a ‒ is the distance between adjacent electrodes in m
b ‒ is the depth of the electrodes in m
Resistivity for types of soil according to IEC 60364-5-54:2011
Nature of ground
Resistivity Ωm
Malleable clay
Marl and compact clay
Jurassic marl
50
100 to 200
30 to 40
Marshy ground
Alluvium
Humus
Damp peat
Clayey sand
Siliceous sand
Bare stony soil
Stony soil covered with lawn
Soft limestone
Compact limestone
Cracked limestone
Schist
Mica-schist
Granite and sandstone according to weathering
Granite and very altered sandstone
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From some units to 30
20 to 100
10 to 150
5 to 100
50 to 500
200 to 3 000
1 500 to 3 000
300 to 500
100 to 300
1 000 to 5 000
500 to 1 000
50 to 300
800
1 500 to 10 000
100 to 600
9