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EARTHING & LIGHTNING PROTECTION
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CODES OF PROTECTION OF STRUCTURES AGAINST LIGHTNING.BS 6651 : Protection of structures against lightning.
BSEN 62305 : Embrace the whole concept of lightning protection from design to installation.
IEC 61024-1 : Protection of structures against lightning.IEC 60364-5-54 : Earthing arrangements and protective conductors.
KS C 9609 : Lightning rod.
UL96 : Lightning Protection Components.
EARTH RODS.When earth rods are used, they should be driven into the ground beneath, or as close as practicable to,
the structure and down conductor. The practice of siting terminations away from the building is normally
unnecessary and uneconomical.
Where ground conditions are favourable for the use of rods in parallel, the reduction in earth resistance
is small when the separation between the rods becomes less than their driven length.
Lightning protection system for tall buildings(over 20m high) showing air terminations, down
conductors, bonds to projections above roof.
Earth terminations : arrangement of earth electrodes.
Air termination mesh should be not greater than 10m X 20m. Down conductor should be not more than 10m apart.
Air termination bondedto steel reinforcing orsteel frame of buliding.
Earth electrode
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EARTHING & LIGHTNING PROTECTION
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AIR TERMINATIONS.Air termination networks may consist of vertical or horizontal conductors or combinations of both.
For large flat roofs, this is achived typically by use of an air termination network mesh of approximately 10m x 20m.
On multiple ridge roofs, additional conductors are necessary if the separation, S(in metres), of the ridgesis greater than 10 +2H, where H is the height of the ridge (in metres). See Fig.5
On a reinforced concrete structure, the air termination should be connected to the reinforcing bars in the number
of positions needed for down conductors.
Air terminations for a flat roof
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EARTHING & LIGHTNING PROTECTION
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Air terminations for flat roofs at different levels
Air terminations for large areas of roof of various profiles.
Perimeter = 24 + 24+ 12+ 12 = 72mNumber of down conductoors required= 72/20 = 4.
NOTE 1 If S > 10 +2H, additional longitudinal conductors are needed so that the distance between conductorsNOTE 1does not exceed 10m.NOTE 2 If the length of the roof exceeds 20m. additional transverse conductors are necessary.NOTE 3 Down conductors are omitted for clarity.
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EARTHING & LIGHTNING PROTECTION
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Air terminations for tall conducting structures.
Example of lightning protection system for brick chimneys.
The air termination network for a tall reinforced concreteor steel structure should be as follows:a) horizontal conductors on roofs from a 10m X 20m network;b) bonds to steelwork at comers, at 20m intervals around theb) periphery and on the tower 0.5m above the lower roof level;c) key bonding to the building steelwork.
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EARTHING & LIGHTNING PROTECTION
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DOWN CONDUCTORS.The function of a down conductor is to provide a low impedance path from the air termination to the earth
electrode so that the lightning current can be safely conducted to earth.
Depending upon the form of the building, it is often necessary to have multiple down conductors in parallel,some or all of which may be part of the building structure itself. For example, a steel framed or reinforced concrete
structure might need no added down conductors as the framework itself provides an efficiant natual network
of many paths to earth ; conversely a structure made entirely from non-conducting materials would need
down conductors deployed according to the size and form of the structure.
Patterns of down conductors(natural or not) for various forms of tall building.
The down conductors may be natural (parts of the building framework) or added strips or rods on external faces.On structures exceeding 20m in height, down conductors should be spaced not more than 10m apart.
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EARTHING & LIGHTNING PROTECTION
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Air termination and zone of protection for simple structure with explosive or
highly flammable contents.
CORROSION.Electrolytic corrosion between dissimilar metals :
The contact of dissimilar metals, unless the contact surfaces are kept completely dry and protected
against the ingress of moisture, is likely to initiate and accelerate corrosion.
Chemical corrosion of copper :
Although copper is highly resistant to many types of chemical attack, lead coating is recommended where
it is subject to serve corrosion due to the presence of sulphur compounds.
INSPECTION.All lightning protection systems should be visually inspected by a competent person during installation,
after completetion and after alteration or extension, in order to verify that they conform to the recommendations in
BS6651, Visual inspections should be repeated at fixed intervals, preferably not exceeding 12 months.
To prevent flashover between mast/conductor and protected building, the minimum clearance distance has to be 2m,whichever is the greater.
This clearance has to under maximum sag conditions, i.e. snow ice on the aerial conductor.
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COPPER CONDUCTOR & COPPER TAPE
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ANNEALED STRANDED COPPER CONDUCTOR
COPPER CONDUCTOR PVC INSULATED GROUNDING WIRE
Stranded constructionNumber/diameter
No./mm
ConductorSize(mm
2
)
ElectricResistance max.
/mm2
10
16
25
35
50
70
95
120
150
185
240
300
-
1.15
0.727
0.524
0.387
0.268
0.193
0.153
0.124
0.0991
0.0754
0.0601
-
4.7
5.9
7
8.1
9.6
11.4
13
14.4
16
18.3
20.5
-
142
225
312
427
617
854
1034
1280
1600
2064
2641
7/1.35
Compact
Stranded
C.C
Reference
Overall Diametermm(approx.)
Approximately Weightkg/km
PART NO
CT - 2003
CT - 2503CT - 3003
CT - 3806
CT - 5003
CT - 5006
20
2530
38
50
50
3
3
3
6
3
6
50M
50M
50M
25M
40M
20M
0.27kg
0.67kg
0.80kg
1.45kg
1.33kg
2.68kg
W TQ’ty per coil
Dimensions(mm)Weight per m
ConductNominal sectional area
mm2
ConstructionNo./mm
610162535507095
120150185240300
7/1.047/1.35C.C.C.C.C.C.C.C.C.C.C.C.
C.C.C.C.C.C.C.C.C.C.
2.42.42.42.62.62.82.83.1
3.13.43.64.04.5
--
0.190.290.410.530.731.00
1.161.542.012.493.05
Nominal thicknessof insulation
mm
IEC Standard Designation : IEC60228
Soft drawn stranded copper : BS6360
HIGH CONDUCTIVITY COPPER TAPE (BS EN13601)
*C.C. : Circular Compact stranded shape
Remarks : The numerical values in this table are taken at 20
**Tinned Copper Tape : 30M*Steel Tape(H.D.G) is available.
•High conductivity copper
•Insulation : Green Color (UV stability)
PART NO
IBCB - 253
IBCB - 256
IBCB - 506
25
25
50
3
6
6
5M
5M
5M
0.77kg
1.53kg
2.95kg
W TQ’ty per coil
Dimensions(mm)Weight per m
PVC COVERED COPPER TAPE
T
T
W
W
Approx. weight of cable
kg/m
Green/Yellow PVC Covered Soft drawn stranded copper : BS 6004 / PVC Green or Green/Yellow insulation : IEC60502