Earthing

BS EN 62305 – Earthing & Lightning Protection System Design

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Design of Lightning Protection System

The following information has been provided courtesy of AN Wallis, leading UK manufacturers of Earthing & Lightning Protection Systems.

The LPS (Lightning Protection System) is required to:

• Intercept the lightning strike (the air termination network)
• Conduct the lightning strike safely to ground (using down conductors, such as copper earth tapes)
• Disperse the strike safely into the earth (earthing)
• Whilst the structural protection is there to conduct a strike safely to earth this is normally combined with internal protection to prevent sparking within the structure ensuring all metallic services are at equipotential (bonding)

The designer of the LPS should ensure that:

• The safest path to earth is the LPS
• The risk of sparking whilst the strike is conducted safely to earth is minimised (separation distance/s)
• The risk of voltage differential whilst the strike is being dissipated in the ground safely is minimised (step & touch potentials)

The designer of the LPS has to gather all the relevant information to ensure the earthing system design is as safe as possible within any economic restraints:

• A designer may find it impractical to fully install the desired LPS
• A designer may not be able to justify the cost of providing the desired LPS
• A designer may consider using the metal roof or reinforcing bars within a building as the safest and most economic design
• A designer may consider extra bonding and surge protection devices are required to protect the internal space, especially if the space houses sensitive electronic equipment
• A designer may consider a building of such a high risk that additional measures are taken to ensure safety, possibly a flour factory or a building with a combustible roof, in these cases the LPS system may have to stand off the building

Contact Thorne & Derrick for largest UK stocks of copper earth tapes.

Criteria For The Protection Of Structures

The level of protection/Lightning Protection Level (LPL) applied to the structure is identified by the risk assessment.

Lightning Protection System (LPS) Level

• LPL I requires a Class I
• LPS LPL II requires a Class II
• LPS LPL III requires a Class III
• LPS LPL IV requires a Class IV LPS

Design of The LPS General Considerations

To help the earthing system designer, the threat of lightning to a structure or building can be defined in lightning protection zones requiring protection and the type of lightning strike likely to enter the building shown in Figure 2.

S1 – Strike directly to the structure

S2 – Strike on the ground near the structure

S3 – Strike to a service connected to the structure

S4 – Strike on the ground near a service connected to the structure

LPZ1 – The protected zone inside the building, the zone where current is limited by current sharing and SPD’s at the boundary (less the separation distance)

LPZ Oa – At risk from the full lightning strike and the full lightning electromagnetic field

LPZ Ob – Not at risk from a direct lightning strike considering the protected area through the rolling sphere but at risk from the full lightning electromagnetic impulse. (LEMP)

LPZ 2 – Protected zone with further dampened magnetic field

The LPS designer should ensure everything to be protected falls inside the LPZ Ob range in figure 2.

• The bonding measures employed need consideration at the design stage
• The earthing design should consider fully the step and touch potential risks
• The requirements for Surge Protection Devices (SPDs) on incoming mains and conductive services should be considered in accordance with the risk assessment carried out for the structure LPS requirements
• Where combustible wooden type materials are present a distance of 0.15 m should be maintained between the LPS conductors and the roof, for any other combustible surfaces a distance not less than 0.10 m is required
• Some structures will have reinforced sections with expansion joints, if the designer of the LPS considers electronic equipment within the building is at risk then bonding conductors should be provided across the joints to provide low-impedance potential equalization. The separation distance between the bonds should not be more than half the distance between the down conductors
• Natural components within/part of the structure such as the rebars can be made use of provided they will always remain an integral part of the structure conforming to the requirements below

Manufacturer by high conductivity and purity copper the range of earth tapes provide effective protection to buildings and substations

Using natural conductors as part of the LPS

The building’s natural components, metal roof, rebar, steelwork etc can be considered as part of the LPS provided they meet the minimum criteria shown in Table 1.

The reinforcing bars within the concrete structure can be used as a natural component of the LPS provided they are electrically continuous by either welding or clamping the joints.

The re-bars are considered as electrically continuous provided that the major part of interconnections of vertical and horizontal bars are welded or otherwise securely connected by clamps conforming to BS EN 50164 standards.

The connecting rebar must overlap and be clamped using rebar clamps or welded to a minimum of 20 times the diameter of the rebar as shown in figure 3. (Welding to be done on either side of the rebars.)

Example of a rebar joined by clamps

To test the continuity of the reinforcing bars the resistance between the re-bar connection to the air termination network and the rebar connection to the earthing network should be measured, the resistance should not exceed 0.252, otherwise proprietary down conductors will be required.

In order to provide a connection to the rebar from outside the concrete a cast-in earth plate can be used as shown in figure 4, the earth point sits in the wall (or within an enclosure) providing a connection to the re-bar with a welded copper tail attached to the earth point and to the re-bar with propriety clamps.

Earth point sits in the wall providing a connection to the rebar

The designer of the structural LPS has 4 main criteria to consider:

• The roof termination system
• The down conductor configuration
• The Earth Termination network including equipotentialization and the risk of step and touch potential (equipotentialization on its own is not effective in reducing the risk against touch voltages)
• Bonding (creating a euipotential zone across all zones, Oa, Ob, Z1, Z2)

The diameter of the sphere depends on the class of LPS selected/determined.

Complete range of earth bars with connection options and number of cable termination ways to provide effective common isolation point.

Methods Of Designing The Air Termination Network

1 – The rolling sphere

2 – The protective angle design

3 – The mesh design

The Rolling Sphere Method

This method simply rolls a sphere around the building to be protected, wherever the sphere touches the building dictates where the protection measure is to be applied, where the sphere does not touch the building, this is accepted as a protected area, this method can be used to design the LPS on complex structures or where the LPS has to be isolated.

The rolling sphere method is especially relevant on complex structures with many different levels, this method easily identifies the protected space and where protection measures should be applied to the structure.

Examples of the air termination system using the rolling sphere technique

Designing The Lightning Protection System (LPS)

The Protective angle design

The Protective Angle method in figure 10 is only used on simple structures or for small sections of larger structures.

The Protective Angle design method cannot be used where the part of the structure/service to be protected is higher than the radius of the rolling sphere corresponding to the class of LPS.

The level of LPS dictates the angle of protection depending on the reference height, see figure 9.

This method of earthing system design is an alternative method based on the rolling sphere and is not offered to give a wider range of protection than the rolling sphere.

In figure 9 the height limits for designers are clear and correspond to the radius of the rolling sphere.

Protective Angle Design

The Mesh design

The most commonly used method, is usually employed where the structure is simple, a square or rectangular building or typical house or block of apartments with a sloping roof, the mesh method is for protection in zone OA.

The mesh design protects the whole area if conductors are positioned on the edge of the roof where the slope of the roof exceeds 1:10.

Protective angle design to protect free standing equipment on the roof of a building

On structures up to 60 metres in height, only consider applying an air termination system to the roof and provide protection to points, corners and edges of the structure. No lateral air termination is required regardless of the class of LPS.

On structures higher than 60 metres lateral air termination systems should be applied to the top 20% of the structure relevant to its class of LPS (or at least conforming to class IV LPS).

The mesh of earth conductors are installed on the roof, the earth conductor must be at the edge of the area to be protected and for metal items such as air conditioning units that protrude above the conductor, the protective angle design should be applied for protection.

The size of earth mesh required is defined by the level of LPS determined/selected

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THORNE & DERRICK

T&D are Specialist Distributors to UK Distribution Network Operators (DNO’s), NERS Registered Service Providers, ICP’s and HV Jointing Contractors of an extensive range of LV, MV & HV Jointing, Earthing, Substation & Electrical Eqpt – this includes 11kV/33kV/66kV cable joints, terminations and connectors for both DNO and private network applications.

Contact our UK Power Team for competitive quotations, fast delivery from stock and technical support or training on all LV-HV products.

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BS EN 62305 – Protection Against Lightning Strikes & Risk Management Notes

BS EN 62305

AN Wallis manufacture earth tapes from high conductivity copper to ensure LPS designs and installations conform to latest Britsh and International standards

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BS EN 62305

The Part 2 of BS EN 62305 provides a comprehensive mathematical model to evaluate and manage the risk posed by lightning strikes and measures to alleviate the risk associated with earthing system designs.

The risk assessment is extremely time consuming to calculate by hand so Wallis, working in conjunction with their distributor Thorne & Derrick International, can offer to do the assessment using bespoke computer software.

The basics of the calculation can be briefly explained as follows taking into account:

The Sources of Lightning

• S1: flashes to a structure
• S2: flashes near a structure
• S3: flashes to a line
• S4 flashes near a line

The Likely Damage

• D1: injury to living beings by electric shock
• D2: physical damage
• D3: failure of electrical and electronic systems

The Likely Losses

• L1: loss of human life (including permanent injury)
• L2: loss of service to the public
• L3: loss of cultural heritage
• L4: loss of economic value (structure, content, and loss of activity).

The following Table 2 from BS EN 62305 explains the link between Sources, Damages & Losses.

Table 2 – BS EN 62305

Sources of damage, types of damage and types of loss according to the point of strike:

Note:

a) Only for properties where animals may be lost.

b) Only for structures with risk of explosion and for hospitals or other structures where failures of internal systems immediately endangers human

Risk: The risks to be evaluated in a structure may be as follows

• R1: risk of loss of a human life (including permanent injury)
• R2: risk of loss of service to the public
• R3: risk of loss of cultural heritage
• R4: risk of loss of economic value.

Risk Management

1. Basic Procedure

The following procedure shall be applied:

1. Identification of the structure to be protected and its characteristics
2. Identification of all the types of loss in the structure and the relevant corresponding risk R (R1 to R4); ­evaluation of risk R for each type of loss R1 to R4
3. Evaluation of need of protection, by comparison of risk R1, R2 and R3 with the tolerable risk RT
4. Evaluation of cost effectiveness of protection by comparison of the costs of total loss with and without protection measures. In this case, the assessment of components of risk R4 shall be performed in order to evaluate such costs.

1. Structure to be considered for risk assessment includes

1. The structure itself
2. Installations in the structure
3. Contents of the structure
4. Persons in the structure or in the zones up to 3 m from the outside of the structure
5. Environment affected by damage to the structure.

Protection does not include connected lines outside of the structure.

1. Tolerable Risk RT

The calculated risks R1, R2 & R3 shall be compared with tolerable risk. The permissible values for the tolerable risk are mentioned in the Table 4 BS EN 62305.

Table 4 – Typical values of tolerable risk R_T

If R < R_T, lightning protection is not necessary. If R > R_T, protection measures shall be adopted in order to reduce R R_T for all risks to which the structure is subjected.

The manual calculations are time consuming. It is recommended to use available Lightning Protection Risk Management Software to perform these calculations – contact T&D.

Thorne & Derrick International

Contact us to discuss all your Substation Earthing, Cable Jointing & Terminating requirements for the installation of LV MV HV cables, copper earthing tapes and infrastructure including switchgear, transformers and electrical equipment up to 33kV.

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Earthing Systems Using Air Rods & Copper Tape Conductors For Roof Termination Network (BS EN 62305)

Earth Tapes – Bare & Covered Copper Tapes

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Copper Earthing Tapes

Thorne & Derrick International, a leading stockist and distributor of copper earthing tapes manufactured by AN Wallis and ABB Furse provide an overview of the role and relationship of earth tapes  and air rods with respect to the design of Lightning Protection Systems for Roof Termination Networks in accordance with British Standard BS EN 62305.

Roof Termination Network

The roof termination network can be concealed below the tiles or cladding provided the air rods/strike pads protrude above the tiles or cladding (see below Figure 15).

Air rods to be selected based on the protection angle method. Strike pads should be provided in accordance with mesh spacing.

The air termination system will usually consist of air rods, flat tape conductors such as copper earthing tapes in a mesh or in some designs a catenary wire (in case of isolated LPS), there are three methods for the earthing system designer to determine the air termination system in the LPS, each is acceptable to BS EN 62305.

The earthing design comes from one of three options already detailed: the rolling sphere, protective angle or mesh alternatives, each method has different criteria for the roof network.

Wherever possible the air termination network should be located:

• At the corners of the building
• At the most exposed points of the building
• As close to the edge of the building as possible (on the parapet wall is usually as close as you can get)

The roof network should follow the most direct route with minimal bends. Where roof tiles are non-conducting the air-termination conductor may be placed either under, or over the roof tiles (over is always preferable), Where the conductor is sited below the tiles vertical finials or flat strike plates should be used These should be spaced at not more than 10 metres for air rods and 5 metres for strike plates (corresponding to class of LPS).

Roof Termination Network concealed below the tiles or cladding provided the air rods or strikes pads protrude above the tiles or cladding

In circumstances where two horizontal LPS air-termination conductors are placed parallel above the horizontal reference plane, the distance that the rolling sphere penetrates below the level of the conductors within the space between the horizontal conductors is:

Where

p = penetration distance r = rolling sphere radius

d = distance between the two parallel air terminal

rods or conductors

The penetration distance (p) should be less than the height of the air terminal/conductor above the roof surface/ reference plane, (ht), minus the height of objects to be protected.

[BS EN 62305-3, E4] p = r — (gr2 – (d/2)²

Protection For Open Roof Car Parks

Open Roof Car Park Protection

For car park structures where the roof is an open parking area (as shown in Figure 17) for cars, normally surrounded by a parapet wall, it is not advisable to have any kind of roof conductors as they are constantly being driven over and walked upon.

In these circumstances the standard allows the use of air rods on the parapet wall with a mesh on the roof hidden between the edges of adjoining slabs or bedded in the concrete with strike pads installed visible above the tarmac or concrete.

Persons and vehicles on this parking area are above the Lightning protection system and not protected from lightning.

If the top level of the car park has to be protected then air rods, catenary wire and natural masts such as lamp posts can be designed in to provide an enhanced protected area.

The step and touch potential risk on the top level of the car park can be overcome provided the roof is constructed of reinforced concrete with interconnected reinforcement steel with continuity provided by welding or clamping.

Conductive fixtures on the roof

Conductive roof fixtures such as AC units outside the zone of protection can be ignored if their height is under 300mm or if it’s under 1 mtr/2 or it’s less than 2mtr long.

Non conductive roof fixtures outside the zone can be ignored if less than 500mm in height.

A conducting fixture such as pipes or an air conditioning unit needing protection should be protected by an air termination system Figure 18. If this is not possible insulated parts, with lengths corresponding to at least twice the specified separation distance, can be installed on the conductive installations. [BS EN 62305-3, E5.2.4.2.4]

Conducting fixtures such as pipes or air conditioning units should be protected by an air termination system

When a non-conductive chimney falls outside the protective zone of the air-termination system, it should be protected by means of air-termination rods or air-termination conductors. The air termination rod on a chimney should be of such height that the complete chimney lies within the protective space of the rod.

[BS EN 62305-3, E 5.2.4.2.4]

Metal roof fixtures should be bonded to the air termination system when the necessary clearance for conformity to the separation distance cannot be maintained.

[BS EN 62305,3, E5.2.4.2.4]

Conductive electrical appliances and fittings on the roof are some of the most difficult problems facing the designer of the LPS if the requirements of BS EN 62305-3 are to fully met and the system be fully compliant. See Figure 19.

To fully comply with BS EN 62305

• Metallic roof fixtures such as air conditioning units must fall within a zone of protection offered in accordance with the angle of protection (or with the rolling sphere method)
• The units must also maintain a separation distance between the fixture and the protective air-termination equipment to prevent dangerous sparking (not required if. metallic fixtures are mechanically and electrically continuous with the structure)

In practice this is very difficult to achieve with the sometimes crowded nature of the average apartment block.

Protecting Fixtures Which Cannot Withstand Direct Strike To Its Casing

This is where the casing is not of sufficient cross-section area to comply with the thickness requirements of the standard, in these cases an air termination system should be installed to cover these units.

A separation distance should be maintained between the fixture and the air-termination to prevent sparking between the air-termination and fixture in the event of a lightning strike.

If it’s not possible to meet the requirements of BS EN 62305 the air-terminal should still be fitted and the fixture should be bonded to the conductor connecting to the air-termination.

Services from the fixture going into the building should be bonded to an equipotential bar and protected by installing a Type 1 Surge Protection Device.

Protecting Fixtures Which Can Withstand A Direct Strike To Its Casing

There is an option here to consider using the casing of the fixture itself as part of the air-termination network, the argument against is that electromagnetic effects of a direct lightning strike are likely to be greater than if the fixture was protected within the air termination network.

If the casing is used as part of the air termination network:

• Fixture should be bonded to the air-termination network when entering the building and connected to a equipotential bonding bar
• Any armouring or screening should be connected to a equipotential bonding bar and their live cores connected to the same bar using SPDs

It could be argued this is introducing the lightning strike into the building but the alternative to this approach would be to ensure that all mechanical services are insulated where they enter the building and split cables fitted with SPD’s which in the majority of cases is not practical.

Electrical Installation outside the zone of protection

If it’s just not possible to have antenna masts, satellite dishes and other electrical equipment within the zone of protection they should as a minimum be bonded into the LPS in at least two positions.

It’s unlikely all cables and other provisions will enter the building in the same place so as a all conductive sheaths and conductive mechanical protection should be bonded to the lightning protection air-termination by means of a common earth bar.

Lightning Protection for Structures Covered by Soil

Structures with a layer of soil on the roof where people are not regularly present should be fitted with a meshed air-termination system sited on top of the soil. Practically, a permanent fixed mesh could be installed. Alternatively, air termination rods sited in accordance with the rolling sphere or protective angle method and connected by a buried mesh may be used see BS EN 62305-3, E.5.2.4.2.8.

If people are likely to be present a mesh 5mtr x 5mtr should be installed beneath the soil to protect against step potentials but practically there would need to be visual warnings to the public advising against being in the area in the event of a lightning storm.

In the case of underground bunkers containing explosives an interconnected isolated LPS should be fitted as well as the mesh.

Natural Components As Part Of The Air Termination Network

Below are all permissible as part of the air termination network in the LPS according to BS EN 62305.

Metal Sheets

• Provided there is reliable and durable electrical continuity between the various parts and it’s not clad with insulation
• The thickness of the metal sheet meets the minimum dimensions shown in Table 1
• R’s permissible to use this metalwork but unlikely any designer would accept puncturing of the membrane in the event of a direct strike so as a minimum air rods should be fitted to the perimeter
• Metalwork on the roof, railings, lights, water tanks, coverings provided the metalwork meets the minimum dimensions shown in Table 1
• Even pipes and tanks carrying combustible materials can be considered provided the provided they are constructed of material with thickness not less than the standard allows (for detailed information [BS EN 62305­3, Annex E]

If the metallic parapet is to be used as part of the air-termination network it has to be both electrically and mechanically continuous, the minimum thickness should comply with the dimensions in Table 1 and Figure 23.

Table 1 

If a metallic roof parapet is not being used in the air-termination network then it should be bonded every 20 metres along the complete length and to each down-conductor (or at down conductor spacing).

Conductive metal objects above the roof surface and passing through the roof structure should be bonded onto the air termination network^., examples of this could be a water tank with pipe work passing through the roof into the structure.

Example of Wallis Earth Bonds

Thorne & Derrick International

Contact us to discuss all your Substation Earthing, Cable Jointing & Terminating requirements for the installation of LV MV HV cables, copper earthing tapes and infrastructure including switchgear, transformers and electrical equipment up to 33kV.

Product Categories: Duct Seals | Cable Cleats | Cable Glands | Electrical Safety | Arc Flash Protection | Cable Jointing Tools | Cable Pulling | Earthing | Feeder Pillars | Cable Joints LV | Joints & Terminations MV HV 

Largest UK Stocks Of Copper Earthing Tapes

Earth Rods | Earth Bars | Earth Mats | Earth Clamps – manufactured from high conductivity copper by AN Wallis and supplied by Thorne & Derrick

Copper Earthing Tapes For Down Conductors – Some General Considerations

Copper Earthing Tapes – Bare & Covered Copper Tapes

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Copper Earthing Tapes

Thorne & Derrick International, a leading stockist and distributor of copper earthing tapes manufactured by AN Wallis and ABB Furse provide an overview of the role and relationship of earth tapes with respect to the design of Lightning Protection Systems in accordance with British Standard BS EN 62305.

Down conductors

Some general considerations for the use of copper earthing tapes as down conductors are as follows unless the Earthing & Lightning Protection System (LPS) is isolated:

• There should be at least two down conductors around the building
• The down conductors should be as equally spaced as possible
• Copper earth tape as down conductors should be installed at exposed corners of building
• Down conductors can be fixed to any wall or surface which is non-combustible, if the surface is combustible refer to BS EN 62305 for guidance
• Down conductors must not be sited in gutters or down pipes
• The down conductor ideally will follow the shortest and most direct path to earth
• The down conductor should as far as possible be straight and vertical
• Wherever possible avoid any re-entrant loops where this is not possible the separation distance shown in Figure 22 Is required as a minimum, if this cannot be achieved another design for the down conductor system should be considered
• A test joint should be fitted on each down conductor to enable disconnection from the earth network and provide access for earth resistance measurement and maintenance

The bottom 3 metres of the down conductor should be protected within a metal guard or PVC covering at least 3mm thick to deter vandalism and copper earthing tapes theft Figure 21. The test clamp should be fixed above the capping wherever possible Figure 21.

Down Conductor should be protected by metal guard of PVC covering at least 3mm thick to deter vandalism

If the air termination is a metal rod on a non conductive mast, at least one down conductor is needed for each mast.

No additional down conductors are required for masts made of metal or interconnected reinforcing steel.

If the air termination consists of one or more catenary wires at least one down conductor is needed at each supporting structure.

Positioning the down conductors

There should be multiple down conductors following the shortest possible path to earth via the conductive copper EARTH tapes.

Typical values of the distance between down conductors, subject to architectural and practical constraints are given in the table below.

Table 5.4 – Typical down conductor spacing’s and distance between ring conductors

It may not be practically possible to space the down conductors exactly as required, so the spacing’s can be adjusted by ±20% but the average spacing of all down conductors must conform to the typical distances for the class of LPS.

If it is not possible to place down conductors at a side or part side of the building the down conductors that should be on that side should be placed as additional down conductors compensating for the other sides. The distance between the installed down conductors should not be less than one-third of the required down-conductor distances dependent upon the class of LPS.

Equipotential bonding to conducting parts of the structure should be performed according to BS EN 62305-3, 6.2.

The distance between the down-conductor and the internal services must satisfy the distance requirements covered in the table above.

If the separation distance required to avoid dangerous sparking between the down conductor and the internal services cannot be satisfied, the number of down conductors should be increased until the required separation distance is met.

Protection on a Cantilevered Structure

There is a risk when the down conductor goes into a cantilever that a strike could flash over to this risk the separation distance, h in metres, should satisfy the the person standing underneath 2.5 as shown in figure 22. To reduce mtrs following conditions.

H > 2.5 + S

S – Is the separation distance in metres calculated.

2.5 – represents the height of a typical person with their hand in the air.

Using natural components as down conductors

The natural components can be used as down conductors provided the components comply with the requirements of BS EN 62305.

The natural components can be used provided there is electrical continuity, where the joints are tightly bolted they can be considered as electrically continuous Figure 23.

Natural components as down conductors

The facade elements, profile rails and metallic sub-constructions of facades can be used provided their dimensions conform to the requirements for down conductors and metal sheets or metal pipes, not less than 0.5mm thick.

If the metal façade of the building is to be used as the down conductor then BS 62305 offers specific guidance.

Each overlapping vertical joint at each down-conductor position should be bridged by flexible metal strapping. See Figure 24.

Overlapping vertical joint bridged by flexible metal strapping

Connections between the sheet metal panels should have a minimum contact surface area of 50 sqmm and be capable of be capable of withstanding the mechanical forces of a lightning discharge.

If access to the rear of the façade is not possible and the only type of fixing available for connections between facade sheets and the air termination or down-conductor tapes is pop rivets then these should be at least four 5mm diameter rivets and used on a length of conductor, such as copper earth tape, a minimum of 20mm long. (C.S.A or conductor (connection component) min 50 sqmm). 

Down conductors not using the

natural components of the building

Where down conductors are installed on the building not using the natural components then consideration needs to be given to the separation distance between the internal columns and internal partition walls with conductive parts.

If these conductive columns and partitions do not satisfy the separation distance conditions they must be connected to the air termination system at roof level and to the earthing network at ground level.

What Is BS EN 62305-3:2011?

Part 3 of EN 62305 sets out all the requirements needed to protect buildings and structures against physical damage by implementing a lighting protection system (LPS). It also looks at how to protect humans and animals (living beings) against injury if they are close to an LPS. By defining these safety measures, this standard helps you to minimise damage, invest in the right electrical protection equipment and maximise hazard prevention in buildings.

Thorne & Derrick International

Contact us to discuss all your Substation Earthing, Cable Jointing & Terminating requirements for the installation of LV MV HV cables, copper earthing tapes and infrastructure including switchgear, transformers and electrical equipment up to 33kV.

Product Categories: Duct Seals | Cable Cleats | Cable Glands | Electrical Safety | Arc Flash Protection | Cable Jointing Tools | Cable Pulling | Earthing | Feeder Pillars | Cable Joints LV | Joints & Terminations MV HV 

Largest UK Stocks Of Copper Earthing Tapes

Earth Rods | Earth Bars | Earth Mats | Earth Clamps – manufactured from high conductivity copper by AN Wallis and supplied by Thorne & Derrick

Tinned Copper Earth Bars – How To Specify The Correct Earth Bar

Earth Bars – manufactured from 50x6mm Tinned Hard Drawn Copper Bar

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Earth Bars

Advantages & Applications Of Tinned Copper

The following article has been written to provide some basic advice and reasoning for the specification of Tinned v Standard Copper Earth Bars when designing earthing systems for LV MV HV building services and substation protection exposed to wet conditions during normal operation.

Copper is used in the manufacture of Earthing & Lightning Protection Systems due to the high thermal and electrical conductivity, ease of manufacture, high recyclability and good corrosion resistance of the material. Copper, a noble metal that occurs naturally in its elemental form, is almost totally impervious to corrosion from soils found worldwide.

But it would be misleading to infer that copper will not corrode.

Tinned copper is a type of copper coated with a thin layer of tin used to provide protection to earth bars against the tarnishing and corrosive effects of oxidisation, commonly referred to as rusting.

The thin layer of tin effectively shields the copper surface of the earth bar inhibiting oxidisation – preventing air from reacting with the copper in the presence of atmospheric moistures. Put simply – no air, no oxide, no corrosion.

The copper tinning process provides enhanced protection against climatic variations and atmospheric conditions without significant reduction in the functionality and electrical conductivity of the copper metal.

Oxidised copper surfaces display poor conductivity compared to clean and smooth tinned copper which prolongs the service life of the earth bar at comparatively low added-on cost.

Tinned copper is higher cost than non-tinned copper but provides extended service life and field performance compared to standard bare type copper especially in wet condition installations.

These types of earth bars are commonly specified and installed in outdoor locations in the water utility, marine and offshore industries where high levels of atmospheric corrosion caused by environmental factors and moisture levels such as rain, fog and condensation necessitate improved levels of corrosion protection. Outdoor air can act as an electrolyte because it contains a variety of components which can cause corrosion of any metal.

Tinned copper handles wet conditions, high temperatures and humidity to maintain the conductive integrity of the earth bar for electrical engineering applications.

AN Wallis manufacture both standard copper and tinned copper earth bars from 6 way up to 30 way on short lead times in standard, single link or twin-disconnection link design. Image: Wallis 6 Way Earth Bar.

Applications & Necessity Of Tinned Earth Bars

Earth bars are used to provide a convenient common earthing point for electrical installations requiring an Earthing & Lightning Protection System – copper earth bars are available with single or twin disconnecting links which means the earthing bars can be isolated for electrical testing.

Tinned copper earth bars could be used in external applications or where atmospheric conditions are more severe than normal i.e. high humidity or moisture content areas and marine and offshore saline atmospheres.

Tinning protects the copper and protects the earth bars from the formation of copper oxide, tin effectively prevents oxidation.

Earth bars are a standard, efficient and convenient way of providing a common earth point with integral disconnection links permitting safe electrical isolation for testing purposes in the switchroom.

Why Should Earth Bars Be Tinned?

Tin is a soft white metal which can easily be polished, scratch brushed or flow melted to provide a bright finish.

Tin is non-toxic and is not greatly affected by the organic acids. Sulphur compounds do not readily tarnish tin and it is not impaired by either air or water but reacts with hydrochloric acid to form stannous chloride.

Tin is one of the less susceptible metals to corrosion attack consequently tin-plated surfaces of copper earth bars are adequately protected against atmospheric corrosion and hence provides longer life when exposed to corrosive atmosphere installations.

In normal state unaffected by corrosion copper is a rich brown colour – pictured below is an instance of copper oxide (“greening”) showing advanced corrosion to underground earth tapes. Tinning of the earth tapes and copper conductors prevents “greening” of the copper surface – furthermore this copper run-off can be very corrosive to galvanised steel support structures on medium/high voltage substations.

Benefits of a Tinned Earth Bar

• Tinning a copper bar protects against atmospheric corrosion providing longer life when exposed to corrosive atmospheres
• Tinning protects the earth bar against the formation of copper oxide (oxidisation)
• Tinned earth bars are an excellent solution to extend longevity and have reasonably low resistance
• Used in external/outdoors applications or where atmospheric conditions are more severe and aggressive than normal i.e. high moisture content areas, high humidity in both onshore (eg water treatment works) or offshore (oil/gas platforms)

Pictured: Here a tinned AWG 4/0 stranded copper conductor is bolted to a galvanised steel flange of a support column on a high voltage substation. Note the high pressure compression fitting installed using hydraulic crimping tools and protective paint for added protection of the copper cable lugs and conductor against corrosion in above-ground outdoor applications.

➡ T&D together with Wallis can offer a bespoke design service for custom earth bars in both tinned and standard copper construction – sizing, number of cable terminations, fixing materials and bases can be tailored to comply with specific site requirements and drawings are available on request to ensure the earthing bars are suitable.

Earth Bars

The following range of Earth Bars without disconnection links are available in both standard copper and tinned copper versions:

Earth Bars With Single Disconnection Link

The following range of Earth Bars with single disconnection links are available in both standard copper and tinned copper versions:

Earth Bars With Twin Disconnection Links

The following range of Earth Bars with twin disconnection links are available in both standard copper and tinned copper versions:

Tin Plating Services For The Electrical & Electronics Industry

The following comments have been kindly provided by Ian Molyneaux of Karas Plating Ltd – the UK’s most respected metal finishing company.

Bright Tin Plating

Tin is a silvery malleable metal that doesn’t get easily oxidized in air and is used to coat other metals to prevent corrosion. The electrical and electronics industry are heavily dependent on tin and tin alloy coatings for solderability most of which is done by electroplating. Tin plated metal is also used for food packaging giving the name to tin cans which are made mostly of steel.

Tin plating is used extensively in the electrical engineering industry to provide protection and to confer solderability. Tin electroplating is also widely used in manufacturing printed circuit boards (PCBs) and electronic components. Most electronic circuit components are made by soldering therefore the surfaces of the conductors being connected are coated in tin or a tin alloy aiding solderability. Additionally tin coating protects the components and connection from corrosion in aggressive atmospheres.

Tin is one of the easiest metals to electro deposit and one of the advantages of electroplating is that no limitation is imposed on the thickness of tin that can be applied. The required thickness can be attained by adjusting the bath parameters and time.

Tin is usually plated with a bright or matt finish. Bright tin is obtained from electroplating solutions containing brighteners, ie. organic additives causing formation of very fine grains of deposit. It has excellent cosmetic appearance.

Matt tin coatings are made in electrolytes with few grain refiners, but without brighteners. It has a dull appearance but the level of internal stresses in matt tin deposits are much less than in that of bright tin.

Bright Tin Plating

Dull Tin Plating

What is the difference between pure tin, bright tin, and matt tin?

Matt tin coatings are made in electrolytes without the addition of brighteners. Matt tin has a dull appearance, but the level of internal stresses in matt tin depositions is much lower than it is in bright tin depositions. Matt tin (in contrast to bright tin) is characterised by low whiskers growing, therefore, it is used in electronics.

Characteristics:

• a dull, semi-bright or satin-bright appearance
• disperse reflectivity
• existence of grains with an average size in the range of a few microns
• the deposit is free of the co-deposited brighteners found in bright tin plating

Dull tin is ideal for electronic or precision components. Deposits give good solder ability even after heat or steam ageing.

Karas Plating can plate onto substrates of aluminium, copper and copper clad aluminium busbars in both bright and dull tin.

Aluminium and copper clad aluminium busbar are generally used for reduction in weight and cost but both are easily tin plated

Contact Karas Plating Ltd : Call FREE today on: 0333 121 0151

AN Wallis Earthing Systems

Earthing and lightning protection manufactured by AN Wallis from high conductivity copper to BS EN 13601 is installed to protect buildings, overhead lines and medium/high voltage substations (MV-HV) against potentially catastrophic damage that can be caused by a lightning strike resulting in short circuiting of power networks.

The Wallis product range includes copper earth rods (solid copper, copper bond and stainless steel types), earth bars, earth tapes, earth clamps and aluminium tapes.

As the leading UK manufacturer of specialist Earthing and Lightning Protection Products, Wallis aims to provide the highest quality products without compromising on price or product performance in a safety critical application.

Quality assurance is integral to Wallis and to ensure this practice continues all earthing and lightning products are manufactured to stringent British and international standards.

Did You Know?

The Escondida copper mine in the Atacama Desert in Northern Chile is currently the world’s largest copper mine by reserve. The copper mine contained more than 32 million tonnes (Mt) of recoverable copper reserves at the end of 2012.

Further Reading

• Earth Tape – The Manufacture of Copper Earthing Tapes
• High Voltage Earthing & Grounding System Design Protecting Lives
• Copper Earthing Tape & Rods Protecting 33kV Substation & Transformer Bund
• Substation Earthing

Specialist Distributors: LV, MV & HV Cable Jointing, Substation & Electrical Eqpt

THORNE & DERRICK are national distributors of LV, MV & HV Cable Installation, Jointing, Duct Sealing, Earthing & Electrical Equipment – we service UK and global businesses involved in cable installations, substation, overhead line and the installation of medium/high voltage cable joints and terminations at LV, 11kV, 33kV and HV.

Contact us for 3M Electrical, ABB, Alroc, AN Wallis, CATU Electrical, Cembre, Centriforce, CMP, CSD, Elastimold, Ellis Patents, Emtelle, Euromold, Filoform , Furse, Lucy Electric & Zodion, Nexans, Pfisterer, Polypipe, Prysmian, Roxtec, Sicame, WT Henley.