Conventional Lightning Protection System Components – Part Five


In Article Introduction to Lightning System Design- Part One ", I listed all terms, abbreviations and Symbols used in lightning field.

Also, in Article Introduction to Lightning System Design- Part Two ", I answered the following questions:

  • What is Lightning? 
  • What are the types of Lightning flashes?
  • What is the shape of The Lightning Waveform?
  • How Lightning strikes can affect the electrical and/or electronic systems of a building?
  • What are the main effects of Lightning?

And in Article Types Of Lightning Protection Systems LPS ", I list the main types of Lightning Protection Systems as follows:






Types of Lightning Protection Systems LPS




Types of Lightning Protection Systems LPS

Lightning protection systems for buildings and installations may be divided into three principal types as follows:

1- LPS for Protection for buildings and installations against direct strike by lightning, which includes:

A- Conventional lightning protection system, which includes:

  1. Franklin Rod LPS,
  2. Franklin/Faraday Cage LPS.


B- Non-Conventional lightning protection system, which includes:

a- Active Attraction LPS, which includes:

  1. Improved single mast system (Blunt Ended Rods),
  2. Early streamer Emission System.


b- Active Prevention/Elimination LPS, which includes:

  1. Charge Transfer System (CTS),
  2. Dissipation Array System (DAS).


2- LPS for Protection against overvoltage on incoming conductors and conductor systems,

3- LPS for Protection against the electromagnetic pulse of the lightning.





And in Article 
Conventional Lightning Protection System Components – Part One ", I indicated the Conventional Lightning Protection System parts and components as follows:





Conventional Lightning Protection System LPS Components

The Conventional Lightning Protection System consists of two main parts:

1- The External Lightning Protection System, which includes:

  • Strike Termination Subsystem,
  • Conductor Subsystem,
  • Grounding Electrode Subsystem.


2- The Internal Lightning Protection System, which includes:

  • Equipotential Bonding Subsystem,
  • Surge Protection Subsystem.


Another important components of the Lightning Protection System is the Connection Components which include but not limited to:

  • Clamps,
  • Connectors,
  • Terminal components,
  • Bridging components,
  • Expansion pieces,
  • Measuring points.





And I explained the Strike Termination Subsystem in this Article.

Also, in Article 
Conventional Lightning Protection System Components – Part Two ", I began explaining the Conductor Subsystem through the following points:
  • Function of Conductor Subsystems,
  • Effects of Lightning Strikes on Conductor Subsystems,
  • Conductor Subsystem Material Requirements.

And in Article 
 " Conventional Lightning Protection System Components – Part Three ", I explained Types of Lightning Conductors and Installation Requirements for Down Conductors.

And in Article " Conventional Lightning Protection System Components – Part Four ", I explained How to use Natural Structure Components as down Conductors.

Today, I will explain The Third Subsystem of the External Lightning Protection System; Grounding Electrode Subsystem.




1- The Correct Choice Of Lightning Protection Components (LPC)


  • The correct choice of material, configuration and dimensions of the lightning protection components is essential when linking the various elements of an LPS together. 
  • The designer/user needs to know that the components, conductors, earth electrodes etc will meet the highest levels when it comes to durability, long term exposure to the environmental elements and perhaps most importantly of all, the ability to dissipate the lightning current safely and harmlessly to earth.
  • Various standards series have been compiled with this very much in mind. At present these standards are as follows:



Standards for Lightning Protection Systems


1- Within Europe:

Various standards series have been issued by (2) National Committees which are:

  1. The European Committee for Electrotechnical Standardisation (CENELEC).
  2. The International Electrotechnical Commission (IEC)


The CENELEC has released the EN 50164 series of standards. The EN 50164 series are component standards to which the manufacturers and suppliers of lightning protection components should test their products to verify design and quality. The EN 50164 series currently comprises of:

  • EN 50164-1 Lightning protection components (LPC) – Part 1: Requirements for connection components,
  • EN 50164-2 Lightning protection components (LPC) – Part 2: Requirements for conductors and earth electrodes,
  • EN 50164-3 Lightning protection components (LPC) – Part 3: Requirements for isolating spark gaps,
  • EN 50164-4: Lightning Protection Components (LPC) – Part 4: Requirements for conductor fasteners,
  • EN 50164-5: Lightning Protection Components (LPC) – Part 5: Requirements for earth electrode inspection housings and earth electrode seals,
  • EN 50164-6: Lightning Protection Components (LPC) – Part 6: Requirements for lightning strike counters,
  • EN 50164-7: Lightning Protection Components (LPC) – Part 7: Requirements for earthing enhancing compounds.


Notes:

  • The standards generally have an IEC prefix to their number (CEI for French versions). IEC standards are produced in English and French languages.
  • IEC and CENELEC generally work in parallel, and CENELEC members vote to adopt new IEC standards as CENELEC standards. The committees of CENELEC may choose to make some alterations to the IEC version.
  • Additionally, CENELEC produce their own standards to which IEC have no counterpart. CENELEC documents are produced in English, French and German and an approved CENELEC standard will have an EN prefix (or NE in the French language versions).


For example:

IEC 62305-1 (IEC version) is parallel to EN 62305-1 (CENELEC adopted copy of the above)
And both are parallel to BS EN 62305-1 (British National Standard adoption ofthe above)



2- Within USA:

Various standards series have been issued such as:

  1. Underwriters Laboratory (UL96 & 96A),
  2. The National Fire Protection Association (NFPA 780)
  3. The Lightning Protection Institute (LPI-175)


Note:

For heavy fault conditions, Conductor Size should be calculated in accordance with IEEE Std 80.







1- Grounding Electrode Subsystem (Earth Termination System)

The reliable performance of the entire lightning protection system is dependent upon an effective earthing system. The grounding electrode subsystem to be effective, it must has:

  • Low electrical resistance between the electrode and the earth: The lower the earth electrode resistance the more likely the lightning current will choose to flow down that path in preference to any other, allowing the current to be conducted safely to and dissipated in the earth.
  • Materials with Long term performance (Good corrosion resistance for example): The choice of material for the earth electrode and its connections is of vital importance. It will be buried in soil for many years so has to be totally dependable.




Earthing Materials with Long Term Performance


Notes:

  • In line with BS 6651, the standard recommends a single integrated earth termination system for a structure, combining lightning protection, power and telecommunication systems. So, earth-termination system must be connected to the equipotential bonding (MEBB – main equipotential bonding bar) in the structure.
  • The agreement of the operating authority or owner of the relevant systems should be obtained prior to any bonding taking place and according to local code/standard requirements.


Functions of Grounding Electrode Subsystem:

  1. Dispersion of the lightning current safely and effectively from the conductor subsystem into the ground in such a way that other installations in the earth are not damaged by the lightning strike.
  2. Clamp the electrical potential of the system (touch and step potential) as close to zero volts, or ground potential, as possible, to minimize the risk of injury to personnel or damage to equipment.







2- Grounding System – General Overview

The grounding system must have a low impedance to disperse the energy of the lightning strike. Grounding systems are highly variable from site to site due to geographical considerations. However, The Variables that affect the design, performance and Impedance of the grounding system are:

  • Electrode Configuration,
  • Number of Interconnected Electrodes,
  • Depth of Burial,
  • Spacing Of the Electrodes,
  • Soil Resistivity.


Notes:

  • The earthing system (and down-conductors) should be located away from entrances and exits of the structure and places where people may congregate.
  • If the earthing system is in locations accessible to the public, then measures should be taken to minimize step potential risks.
  • The earthing system should be located away from other metallic buried items (e.g. pipelines and services).
  • Test points should be installed between the local electrode sections and down-conductor to enable isolation and measurements of sections of the system during future inspection and testing.
  • The risk of corrosion shall be borne in mind in choosing metal in earth.


In the following Articles, you can review The Introduction And Components Of Earthing Systems:




And In the following Articles, you can review The Design Steps Of Earthing Systems:




Also I explained the Methods of Grounding Design Calculations of Domestic, commercial and industrial premises in the following Articles:




And I explained The Grounding Design Calculations for second type of buildings: AC Substations in the following Articles:









3- Resistance value for Grounding Electrode Subsystem

  • As per BS 6651, the resistance to earth of the complete lightning protection system (L.P.S) measured at any point, should not exceed 10Ω (i.e. 10 ohms or less).
  • IEC 62305-3 (EN 62305-3) assumes a common earth termination system with systematic lightning equipotential bonding; no particular value is required for the earth electrode resistance.


Note:

The resistance to earth of the complete lightning protection system (L.P.S) must be measured at a frequency of, or multiple of the power system frequency.





4- Grounding Electrode Subsystem Types

Three basic earth electrode arrangements are used:

  • Type A arrangement,
  • Type B arrangement,
  • Type C arrangement: Foundation earth electrodes.






Type A arrangement





4.1 Type A arrangement

This consists of horizontally star-type earth electrodes or vertical earth electrodes installed outside the structure footprint (see Fig.1), There must be earth electrodes installed at the base of each down-conductor fixed on the outside of the structure. A minimum of two electrodes must be used.


Fig.1: Type A arrangement


Type A Arrangement Criteria:

  • In the case of vertical electrodes (rods) when used in soils of resistivity 500 ohms meters or less, then the minimum length of each rod shall be 2.5m.
  • However, the standard states that this minimum length can be disregarded provided that the earth resistance of the overall earth termination system is less than 10 ohms.
  • Conversely, if the 10 ohm overall value cannot be achieved with 2.5m long earth rods, it will be necessary to increase the length of the earth rods or combine them with a Type B ring earth electrode until a 10 ohm overall value is achieved.
  • For combinations of the various earth electrodes (vertical and horizontal) the equivalent total length should be taken into account.
  •  If less than 10 ohms resistance is measured (not at a frequency of, or multiple of the power system frequency), then these minimum requirements do not need to be followed.
  • The top of vertical electrodes must be buried at least 0.5 m below ground surface. This requirement is to reduce the risk of dangerous step potentials. The use of insulated inspection pits is also considered sufficient.
  • Preference should be given to the use of vertical electrodes.
  • Care should be exercised with horizontal electrodes, as long runs are not as effective as a smaller number of shorter lengths (crows foot arrangements) (see fig.2). The length of a horizontal electrode should not exceed about 30 m. Other than equipotential rings, the main use of horizontal runs should be for the spacing apart of multiple vertical electrodes.

Fig.2: Crows Foot Arrangements

  • Earth electrodes are permitted to be installed inside the structure, such as through a basement. This can be useful in locations where limited external area is available.
  • The electrodes (rods) should be distributed around the structure as uniformly as possible to minimize any electrical coupling effects in the earth.
  • The following table gives an indication of how many earth rods would be required to achieve 10 ohms or less for varying soil resistivities. As the most popular size of earth rod used in many countries is 1.2m (4ft) or multiples thereof, the values are based on a 2.4m (2 x 4ft) length of earth rod electrode.


Resistivity (ohm m)
Number of earth rods
Length of earth rod (m)
500
50
2.4
400
38
2.4
300
28
2.4

200
18
2.4
100
8
2.4
50
3
2.4

Table: Earth rods required to achieve 10 ohms






4.1.1 Calculating the minimum total length of electrode at each down-conductor for Type A arrangement

The minimum total length of electrode at each down-conductor is:

  • L1 for horizontal electrodes
  • 0.5 L1 for vertical (or inclined) electrodes


Where L1 is obtained from Fig.3 (Figure 2 of BS EN 62305-3).


 Fig.3: Minmum Length of Earth Electrode


Notes:

  • The design and configuration of the earth termination system should attempt to find the most effective balance between installation effort (cost) and material cost.
  • Lightning protection systems Class III and IV require a minimum length of 5 m for earth electrodes.






Example#1:

A Class I lightning protection system is installed with 6 down conductors in 2000 ohm.m soil. What will be the effective design and configuration of the earth termination system?


Solution:


From Fig.3  it is seen that L1 = 50 m. So, Requirements could be met with:

6 x 50 m horizontal conductors, or
6 x 25 m vertical electrodes.

Alternative scenarios for each down-conductor by using 1.2 m driven ground rods are as follows:



Example#1 Alternative Scenarios


1- Use of single vertical electrode:

25 m of electrode would need to be installed (25.5 m for sites affected by freezing soil), with the top of electrode buried at a depth of at least 0.5 m. (Total requirements 21 x 1.2 m ground rods, 20 couplers and 1 rod clamp)
The installation of a single deep electrode could be difficult to install in many soil types without specialist driving equipment. More practical would be a greater number of parallel connected shorter rods.


2- Use of multiple vertical electrodes:

For sites not affected by freezing soil, a solution could be achieved by 11 parallel electrodes connected with vertical conductors (the effect of the vertical conductor interconnecting these rods was not considered).
Each electrode could be comprised of 2 x 1.2 m coupled ground rods. For optimum effectiveness these electrodes should be spaced apart a distance equal to 1 to 2 times their length, i.e. 2.4 to 4.8 m apart.
(Total requirements 22 x 1.2 m ground rods, 11 couplers, 11 rod clamps & 24 to 48 m conductor).


3- Use of multiple vertical electrodes connected with horizontal bare conductors:

Assuming vertical electrodes were placed at 2.4 m apart, and bare conductor interconnects the rods, then the presence of horizontal conductor has the same effect as adding 1.2 m to each vertical electrode.

11 x2x 1.2 m required ground rods in case#2 above will be minimized to 8 x2x 1.2 m electrodes would be required.
(Total requirements 16 x 1.2 m ground rods, 8 couplers, 8 rod clamps & 17 m of conductor).





4.1.2 Type A Arrangement For Sites With Extreme Weather Conditions

  • In countries where extreme weather conditions (such as Potential corrosion, soil drying out, or freezing) are found, they will limit the effectiveness of any electrode. it is recommended to consider the first 100 cm of a vertical earth electrode as ineffective. Given that the top of vertical electrodes must be buried at least 0.5 m below ground surface. So, for every vertical electrode (rod) the standard recommends that 0.5 meter should be added to each length, to compensate for the detrimental effect from seasonal soil conditions that are likely to be encountered.
  • For sites affected by freezing soil, as the first 0.5 m of each electrode is considered as not adding to the effectiveness, it is more economic to use less parallel rods.
  • Also as the horizontal interconnection between rods is unlikely to be below the 0.5 m additional depth, its effect should not be included in the calculation.







Example#2:

Considering case in example#1, and for sites affected by freezing soil. What will be the effective design and configuration of the earth termination system?


Solution:


If using parallel 2.4 m electrodes, only the lower 1.9 m would be “effective”, requiring 14 electrodes. A more appropriate configuration may be 6 x 4.8 m electrodes (total requirements: 24 x 1.2 m ground rods, 18 couplers, 6 rod clamps and 24 to 48 m conductor).







Type B arrangement





4.2 Type B arrangement

This arrangement is essentially a ring earth electrode or natural elements within the foundation that is sited around the periphery of the structure and is in contact with the surrounding soil for a minimum 80% of its total length (i.e. 20% of its overall length may be housed in say the basement of the structure and not in direct contact with the earth).(see fig.4)



Fig.4: Type B arrangement


Type B Arrangement Criteria:

  • The ring electrode should preferably be buried at a minimum depth of 0.5 m (1.0 m or deeper for areas subject to permafrost) and about 1m away from the external walls of the structure.
  • Where bare solid rock conditions are encountered, the type B earthing arrangement should be used.
  • If it is not possible to have a closed ring outside around the structure, it is permitted to use conductors in the structure such as foundation earthing or permanently connected conductive metal items such as pipes and conduit as part of the ring. Such items must meet the requirements of natural components (Table: Earthing material requirements in paragraph of Type C arrangement) and allow the ring to be in contact with the soil of at least 80% of its total length. The 80% requirement also allows for situations where the ring conductor may be imbedded in concrete foundations of part of nearby structure, such as retaining walls, etc.
  • Type B is recommended for bare solid rock and for structures with extensive electronic systems or great risk of fire.
  • Type B is preferential from the point of view of providing equipotential bonding between the down conductors (assuming no ground level equipotential ring is used) and providing better potential control in the vicinity of conductive building walls.
  • For structures with non-conducting walls (brickwork, wood, etc), and no interconnection to foundation reinforcing, a type B system or earth equipotential bonding ring is highly recommended.






4.2.1 Calculating the minimum length of the ring earth electrode
 for Type B arrangement

For earth electrodes Type B arrangement, the average radius re of the area enclosed by the earth electrode must be not less than the given minimum length L1 provided from Fig.3 (Figure 2 of BS EN 62305-3).So:

re L1

To determine the average radius re, the area under consideration is transferred into an equivalent circular area and the radius is determined as shown in Fig.5.



Fig.5: Calculation of re



Notes:

  • If the required value of L1 is greater than the value re corresponding to the structure, supplementary star-type earth electrodes or vertical earth electrodes (or slanted earth electrodes) (see fig.6) must be added per the following requirements:


Fig.6: Type B arrangement with additional Vertical Rods


  1. The number of supplementary earth electrodes must not be less than the number of down conductors, but a minimum of 2 equidistant supplemental electrodes should be installed and ideally connected at the each point where the down-conductors connect to the ring electrode.
  2. Their respective lengths Lr (radial/horizontal) and Lv (vertical) being given by the following equations:

  • Additional horizontal electrode length at each down-conductor Lr = L1 re.
  • Additional vertical electrode length at each down-conductor Lv = ( L1 re ) / 2.
  • Based on the above requirements, if the building perimeter is greater than 9 x 9 m and resistivity is less than 500 ohm.m, then the length of a ring installed at 1 m distance from the building will exceed the requirements and there is no need for additional electrodes.
  • Based on the above requirements, If the building is less than 9 x 9 m or resistivity greater than 500 ohm.m, then additional electrodes may be required in addition to a ring installed at 1 m distance and the minimum length of electrode shall be 5m







Example#3:

A class I lightning protection system is installed with 6 down-conductors in 2000 ohm.m soil. The building perimeter is 60 m (20 x 10 m).
Determine if additional electrodes are required or not?
If additional electrodes are required, determine numbers and quantity for horizontal radials, or vertical electrodes?


Solution:

From Fig.3, it is seen that L1 = 50 m (where re is the mean radius of the area enclosed by the ring).

Installing a ring electrode at 1 m from building perimeter would require 68 m of conductor, and the ring would contain an area of 264 m2 (22 x 12 m). The equivalent radius of this ring would be

re = √Area/∏ = 9.16 m

Since, re < L1 Therefore, in addition to the ring, we require additional electrodes at the base of each down-conductor. Either:

Lr = L1 re = 50 – 9.16 = 40.84 m or
Lv = ( L1 re ) / 2 = (50 – 9.16)/2 = 40.84/2 = 20.42 m

So, additional electrodes will be:

6 x 40.84 m horizontal radials, or
6 x 20.42 m vertical electrodes.



Example#4:

Residential building, LPS Class III, L1 = 5 m with dimensions as shown in below:
Determine if additional electrodes are required or not?
If additional electrodes are required, determine numbers and quantity for horizontal radials, or vertical electrodes?

Solution:










4.3 Comparison of Type A and Type B arrangements

  • For Class III and IV systems, a type A system will require less material.
  • For Class I & II systems, a type A system will require less material for lower soil resistivity, and type B system will require less materials for higher soil resistivity.
  • For type A, the earthing should be symmetrical and completed for all down-conductors, for type B the complete counterpoise should be installed.
  • The Type B ring earth electrode is highly suitable than Type A for:

  1. Conducting the lightning current safely to earth,
  2. Providing a means of equipotential bonding between the down conductors at ground level,
  3. Controlling the potential in the vicinity of conductive building wall,
  4. Structures housing extensive electronic systems or with a high risk of fire.







Type C arrangement




4.4 Type C arrangement: Foundation earth electrodes

This is essentially a type B arrangement. It comprises conductors that are installed in the concrete foundation of the structure (see fig.7).


Fig.7: Type C arrangement


Type C Arrangement Criteria:

  • If any additional lengths of electrodes are required they need to meet the same criteria as those for Type B arrangement.
  • Foundation earth electrodes can be used to augment the steel reinforcing foundation mesh. Earth electrodes in soil should be copper or stainless steel when they are connected to reinforcing steel embedded in concrete, to minimise any potential electrochemical corrosion.
  • There should be at least 50 mm of concrete covering the steel to protect against corrosion. Materials used should meet the minimum requirements of below Table (or see IEC 62305-3 Table 14 for further material choices).


Material
Application
Requirements
Copper or tin plated copper
Conductor
50 mm2 solid
Conductor
50 mm2 stranded conductor (minimum strand size 1.7 mm diameter)
Conductor
50 mm2 solid tape (minimum thickness 2 mm)
Rod
15 mm solid copper rod
Rod
20 mm pipe with 2 mm wall thickness
Plate
500 x 500 mm, 2 mm minimum thickness
Plate
4.8 m lattice grid – 600 x 600 mm lattice made from 25 x 2 mm minimum material
Copper-bonded-steel
Rod
14 mm with 250 μm minimum copper coating – intrinsically bonded (i.e. not clad, should be electroplated)
Galvanized Steel

Not recommended by ERICO. Refer to standard for material requirements
Table: Earthing material requirements







5- Earth Termination System Testing

  • Although lightning current discharges are a high frequency event, at present most measurements taken of the earthing system are carried out using low frequency proprietary instruments.
  • A test joint (or Measuring point) should be fitted on every down conductor that connects with the earth termination. This is usually on the vertical surface of the structure, sufficiently high to minimize any unwanted third party damage/interference (see fig.8).


Fig.8: Test Joint (or Measuring Point)

  • Alternatively, the test or disconnection point can be within the inspection chamber that houses the down conductor and earth rod. The test joint should be capable of being opened, removed for testing and reconnected. It shall meet the requirements of BS EN 50164-1.
  • Measuring points are required to allow the inspection of the following characteristics of the lightning protection system:
  1. Connections of the down conductors via the air-termination systems to the next down conductor,
  2. Interconnections of the terminal lugs via the earth-termination system, e.g. in the case of ring or foundation earth electrodes (earth electrode Type B),
  3. Earth electrode resistance of single earth electrodes (earth electrode Type A).





In the next Article, I will explain the second part of Lightning Protection System; The Internal Lightning Protection System. Please, keep following.


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