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Lightning Protection and Foundation Earthing webinar

Your questions answered

Are there any formal training courses that offer further guidance on the subject/provide the participant with the necessary competency to complete design work in this field?

There are formal NVQ qualifications available for the installation, test & commission of lightning protection systems but these courses do not include the risk assessment & design of lightning protection systems nor do they cover surge protection.

The UK trade association ATLAS has an accredited designer qualification however this is strictly limited to ATLAS members only. There are other CPD courses available.

How can an ESE LP system to the French Standard be tested to British Standards to ensure compliance?

ESE systems do not comply with BS EN 62305 and it is not possible to inspect & test one with reference to the British Standard. The French manufacturing standard NFC 17-102 is not applicable in the UK and there is no English language version of this standard available for this reason.

Does the FE still need to be main bonded to the incoming DNO service?

the FE is terminated at the MET along with all other bonds as part of "normal " practice. They can be disconnected for testing if required.

When utilising the rolling sphere method of assessment, as defined in 62305-3 2011, on a hazardous area; does the subsequent design of air-termination system need to ensure the rolling sphere cannot touch/enter the hazardous zone boundary that extends beyond the physical equipment or is it sufficient just to ensure the sphere cannot make contact with the physical entity from which there is a potential for hazardous areas to be created?

This is dependent on the type of EX zone you are dealing with.

If we accept that zone 0 is almost always internal and zone 2 is generally safe so lightning energy can exist here, the only zone we need to consider is zone 1.

The air termination rods should be positioned so that the tip (which would be the anticipated point of strike) would be outside of the zone.

Where did the minimum 20ohms come from? Which is the standard that requested this value?

The 20ohms value comes from the new proposed Annex on foundation earthing within the draft of BS 7671:2018+A2:2022.

How common is this FE installation in the UK?

At present, for dwellings, it is very limited, very usual for larger installations but until mandated by BS 7671 as part of the proposed new prosumer regulations it would not have gained much attention. It is of course a very good basis for any earthing system.

Is there a maximum acceptable resistance value for individual earth electrodes in an LPS? As the 10x rule is no longer applicable under BS EN 62305.

No there is no longer a requirement for individual earth resistance readings. Instead, BS EN 62305 focuses on the overall resistance.

The recommended target for overall resistance is 10 ohms but even this is only mandatory for explosive structures. Of course, 10 ohms should remain the target and represents best practice but equally a compliant system can be achieved by installing the minimum lengths of electrode which the standard also describes.

Do you advise putting material into the foundation concrete to reduce its resistance e.g. Macronite?

Given the larger surface area in contact with the soil I doubt that this is required, you also need to consider the impact on the properties of the slab for any swelling.

What is the maximum value allowed for earth reference in LP systems and what are the allowed variations in readings during the regular service visits?

There is no specific ohmic value required for a reference electrode, they are simply there to assist with monitoring possible changes in the soil conditions so that this can be cross-referenced with any changes in the reading achieved from a foundation/type B earthing arrangement.

Why would a building be in island mode where they are fed from the local network?

Island or disconnected mode is when the installation relies on the power generation on-site only, it is the case that for exporting there is a connection to the DNO but true island mode is off-grid.

Is Foundation Earthing needed for PV systems in island mode where battery storage is providing power to the house during a power cut?

If the system is fully disconnected then yes, but a power cut does not normally remove the earthing provided by the public network.

For new installations having PV and battery systems the FE will be very useful, part of the proposed prosumer regulations also introduces the EEMS or electrical energy management system and this may require the FE to ensure safe operation in all modes of connection or island mode.

Would installing a foundation earth on domestic premises not put their cable at risk during a fault if they are next to a large electrical supply, such as a house adjacent to a medium factory unit?

This relates to a fault like loss of PEN where the fault saw the FE installation as the sink for that current.

To be clear this may be possible under those conditions but it is felt that the benefits outweigh that risk. Other measures on the larger site can be installed to protect from loss of PEN conductors; to begin with, this may be a risk but as more dwellings in a development get FE as well then the global earthworks very much in the dispersal of fault currents.

In Germany, new housing developments have each house connected to a larger mesh of FE sites to get better global earthing values. In any event, each site is assessed on its own merits.

Could you please explain the process of testing a lightning protection system, and what the expected values should be?

As part of the requirements of BS EN 62305 all systems should be visually inspected and electrically tested every 12 months as a minimum (more frequent PPM may be required on higher risk sites).

All clamps, bonds & joints should be visually inspected. If there are concealed conductors/clamps etc. these should be tested for continuity to ensure that they are still performing correctly (a maximum resistance of 0.2 ohms is set).

Individual earth electrodes should be tested, preferably using the Fall of Potential method, and an overall earth resistance test should be made, again using the FoP method wherever possible.

It is advisable to test for continuity from the air termination to the earth termination (again a reading of 0.2 ohms is required), as part of the PPM consideration should be given to replacing the oxide inhibiting compound in the joints and bonds on a regular basis (at least every 5 years would be appropriate).

The system should achieve an overall reading of 10 ohms where possible.

Regarding clamped joints below the surface. BS Earth Standards state all joints below the surface should be exothermically welded, are clamped joints now allowed?

For clamps in a concrete foundation earth, there is no problem, welded connections are not required, there are clamps that are a push-fit or have torque rated sheer heads so the connection is assured, BS 7671 does not propose to require welded joints for FE. Not sure that welding is mandated apart from some sub-station installations.

Potentially FE is a lot of work and cost, and as it will generally still require RCDs for fault protection, where do you see FE as an advantage against standard TT? Will it be for larger buildings rather than domestic ones?

For a dwelling the cost is low and the performance will always be far better than a simple TT rod.

Compared to a rod the FE will record very low values (less than 20ohms). It would take a rod farm to get that, and the effort and cost and labour would be higher using rods.

The risk of damage due to using those rods would also be significant.

Will FE completely negate the need for earthing rod(s)?

There will be a place and application for rods, but to get far lower values the FE route will be more cost-effective and copper theft-proof long term.

It is a far better earthing solution even if the installation is not prosumer.

Should an LP finial be higher than a communal aerial mast?

Yes, if you are using air rods to create an area of protection then they must be higher than any item of plant/aerial etc.

Is it necessary to install air terminals on the roof of a building that is flat roofed?

It is never 'necessary' to install air rods on any installation. They simply provide one possible option in designing the appropriate protection. They can easily be positioned on a flat roof area if you are trying to reduce conductor tape and quickly protect a large volume of space without needing bonds.

When changing from DSO supply to island mode, the DSO earth has to be disconnected. How is the DSO earth monitored for reconnection when going back from island to DSO supply?

The proposed Regulation says that the earthing system need not be disconnected, but part of the prosumer installation will be the EEMS or electrical energy management system. This together with the invertors for PV or batteries etc. would have some monitoring facility.

Does the draft for Amendment 2 to the 18th Edition IET Wiring Regulations specify that FE is a must for islanding or can it still be achieved by the current TT system?

It is likely that either TT or FE can be used if the 20 ohms to meet the PEI requirements can be met. For the least amount of effort, the FE on new builds is the way to go and rods are not proposed to be accepted as an FE solution in Amendment 2.

We have a building with LPS, where the earth reference electrodes (2no.) have been 'lost'. Is it possible to provide new reference electrodes to allow the system to be tested?

Yes, you can replace reference electrodes if they have been 'lost'.

Do you need to do a risk assessment even though you are doing an L1 anyway? example electronic labs, NHS, MoD work, etc.?

I think this question is asking about whether a risk assessment is required if you are installing a level I LPS.

I would ask why you are installing a level I system without first carrying out a risk assessment to fully ascertain the risks and determine the level of protection required? Just because a structure is for the NHS or the MoD does not automatically mean it will require a level I system.

Only structures which fall under the remit of DOSG and are covered by DSA03 OME (formally JSP 482) require a mandatory level I LPS, everything else should be risk assessed.

If I'm looking for an 'Ng' value (lightning flash density/km²/yr) for cities in Africa, i.e. Congo, where can I find specific Ng values without guessing?

This information would normally be published locally in the appropriate standards documentation.

There is a global map in IEC 62305 that can be used. This shows 'Thunderstorm days per year' rather than flash density (Ng). There is a ratio between the two figures however of 10:1 so 10 thunderstorm days per year equals a flash density figure of 1.0Ng (5 would be 0.5Ng & so on). Figures for sub-Saharan Africa are very high compared with the UK & Northern Europe.

For designing an LV Switchboard in a building feeding external loads such as external lighting and carrying out a Lightning Risk Assessment: where it mentions including for SPDs, what would you recommend? Should we as the designer design the SPDs, or should we leave that to the electrical subcontractor to go to a specialist to carry out the SPD designs?

This depends on the location of the external loads relative to the LPZ zone.

For those external loads within the zone of LPZ0B or that protected area, the SPDs can be type 2. If, however, the external loads are some distance beyond the protected area and now in LPZ0A then a type 1 may be considered if the lighting was rather tall and the consequences of failure are high in terms of risk to persons.

If it is normal street lights then type 2 SPDs are normally used to give LED drivers some additional protection above that afforded by the inbuilt protection within the circuit of the driver.

As to who designs this, well the quality of the knowledge of the contractor can vary, so it can be worth asking a specialist.

What's the view on lightning protection for solar farms in the UK? Is it typical to carry out a lightning risk assessment as part of the system design? If protection is required, what would be a typical solution?

Large ground-mounted PV installations should be risk assessed. The whole area of the site should be taken into consideration with the occupiable internal areas of structures being included as separate zones.

The main risk is not from a direct strike but from secondary effects of lightning energy. The large area and volume of cables in these projects creates considerable risk from surges and transients.

Structural protection and earthing can be designed to minimise the impact and reduce the effects of 'shadow' and help to protect the asset and maintain the considerable value in capital expenditure involved.

Can you explain isolated and non-isolated?

In a non-isolated installation, separation distance is not considered and all exposed metallic items are bonded into the system, by which we mean a physical connection is made from the lightning protection system to the metallic item. This could be air handling plant, aerial and dishes, handrails, trunking or cable tray, CCTV cameras etc. By bonding these services we expose them to lightning energy and any of the services which have conductive cores must have the corresponding type 1 'lightning arrest' SPDs installed. That means lots of bonds and lots of SPDs. In an isolated system, we deliberately do not bond. We calculate separation and maintain this physical distance.

An air termination system is installed to protect a 'volume of space' rather than specific points on the structure and by doing so we ensure all of the lightning energy travels around the outside of the structure (a true Faraday Cage) and no lightning energy enters the structure. This is a far safer method and is essential in structures where the possibility of ignition from lightning energy would cause a considerable risk.

BS 7671 asks for safety circuits to be protected by SPDs. Would you class emergency lighting a safety circuit, and if so, does that mean each DB within a large building that feeds lighting be protected via an SPD?

Under BS 7671 it is not the case that an SPD at the MDB will solve all the issues.

There is in section 534 the 10m rule, so those DBs throughout the installation may be required to have SPDs anyway with or without the emergency light aspect. If a risk assessment determined that the loss of the E-lights was a safety issue (I guess it will be) then those DBs will have to have SPDs.This applies to those systems that have a central battery system as well to protect the system.

The proposed new Regulations do ask us to rethink the overall topology of LV systems with regard to external circuits and sensitive loads and what DB they are fed from, this may mean that a selected DB is dedicated to external loads only.

What happens if you use more down conductors, instead of 10m say every 8m to align with columns?

There is nothing wrong with having additional down conductors. The spacings are determined by the level of protection, which in turn is established by the risk assessment.

There is a +/- 20% factor in positioning down conductors. Technically speaking more down conductors mean more current division which means a safer overall result.

How do you size the down conductors for the LPS system?

All products used within a lightning protection system should comply with BS EN 62651.

The installation standard, BS EN 62305 requires conductors to have a minimum cross-sectional area of 50mm square. There is also a minimum thickness table to determine the thickness of different materials if hot spots, penetration, melting and ignition are wanting to be avoided.

After how many years could be a lightning protection system installation be completely removed and a new one be put in place.

Lightning protection systems are almost always external and exposed to the elements.

A reasonable amount of wear and tear should be expected. Most systems should be adequate to last 25+ years without needing wholesale changes or major replacements, provided that they are adequately inspected, tested and maintained during their lifetime.

Should the height of the installation in the UK be 6 or 18 metres?

There is no specific height at which lightning protection becomes required. It should always be determined via a risk assessment in accordance with BS EN 62305-2.

Is there any guidance on when to work on these systems through maintenance? I'm thinking along the lines of weather checking prior to working on the system.

This is very sensible and of course, anyone planning maintenance on an external system should make consideration of the likely weather conditions in their site specific risk assessment and method statement.

Lightning protection frequently requires work at height to be carried out and the weather is always a major consideration in any project requiring working at height.

Is the 45-degree zone of protection still used for an upper building conductor?

The 45-degree angle of protection is not a fixed absolute and has not been since 2006.

The angle of protection is determined by applying the level of protection and the height above the reference plane to the graph in figure 1 section 5.2.2 graph table in BS EN 62305-3. So, we can say that for a certain level of protection at a certain height above the reference plane yes an angle of 45 degrees would be applicable but this is virtually never actually realised in real life.

45 degrees is one of the great myths of lightning protection, often quoted, rarely correct.

It should also be pointed out that the angle of protection is one of the three methods of protection described in BS EN 62305-3 along with the rolling sphere and the mesh method.

The overwhelming majority of structures in the UK use the mesh method so no angle of protection would be appropriate in this scenario as the designer of the system has selected the mesh method.

How do you size the earthing cable?

For an FE system, you do not size in the same way as you would for an LV fault. It is possible there will be more information on the size requirements in any future amendments to BS 7671.

When installing an LEV extract fan and stack on a building roof, if the stack is the highest point is any SPD required? Although the fan and stack are plastic the support is metal.

Height alone is not a determining fact in the requirement for protection.

If the stack is plastic then it would not require a 'bond' to the lightning protection system even if it were the 'highest point'.

Plastic would not conduct any lightning energy so as long as none of the service cables was exposed to lightning energy then no lightning arrest SPD would be required.

A type 2 SPD may be considered if the extract fan were considered essential or critical equipment.

Is there any way of determining the LPL of a building without using a software package?

Technically speaking you could attempt to carry out the risk assessment calculation longhand but I would not recommend it.

Software packages are very affordable, quick and easy I would see no reason for attempting to use any other method.

Training on software is available. Alternatively, it is possible to employ a specialist to carry out the assessment on your behalf.

What training and qualifications are available for Lightning and surge protection design?

There are virtually no formal qualifications for risk assessing and designing lightning protection and surge protection systems.

The UK trade association ATLAS does have an 'Accredited Designer' course but this is strictly limited to ATLAS members.

There are other training courses available.

For down conductors, is there a distance limit between them?

The spacings between down conductors are detailed in BS EN 62305-3. These are different for each level of protection and the level of protection is based on the risk assessment.

The range is from 20m intervals to 10m intervals depending on level. There is also a +/- 20% factor within the standard to enable the conductors to be positioned correctly but sympathetically.

What is meant by the term "Prosumer" with respect to foundation earthing?

Prosumer is a term that links the production and consumer of electricity on an installation so we have bidirectional flow.

The connection to FE is that in island mode you are off-grid so you will need to provide your own local earthing arrangement separate from the DNO. FE is the most effective method in cost and effort to do this.

What was meant by specialist training in regards to FE?

We have become aware that many electrical contractors are wary of FE as it requires them to be on-site when they would not normally be.

Any new concept may require training to ensure compliance and a level of competence as once the concrete is poured over the electrode there is no going back.

The LPS installers are on the other hand happy to add this to the basket of services that they already offer and we expect civil contractors to step up once they have the knowledge to do what is basically a simple task.

Some experience in earthing calculations may also be required.

If FE is installed then what happens to PME supplies?

This will not mean that PME is negated or is not required. In connected mode, the PME will be the earthing method to use but in island or disconnected mode FE will be the local earthing arrangement.

There seems to be a lot of interest in Early Stream Emitters (ESE) simply because they seem to offer great value and ease of installation. What is your opinion on these systems?

These systems do not comply with BS EN 62305. They do not meet any currently accepted pan-European installation or manufacturing standard (such as BS NE 62561 for example).

What are the requirements for temporary structures - e.g. pop festival stages, temporary seating at the Edinburgh Tattoo?

This is always a difficult subject to approach.

The current risk assessment procedure in BS EN 62305 does not really take into account any temporary structure, nor does it adequately address the requirement for protection in a mass populated open spaces. It focuses very heavily on fixed structures. There is of course a tangible risk of lightning damage in these open areas (as witnessed recently at two different German festivals).

I believe that a practicable approach should be adopted including earthing of large temporary metallic structures, installation of SPDs in temporary power supplies to critical equipment (PA equipment, radio transmitting equipment for on site first aid/ emergency services etc) beyond this the solutions for protection become very complex and would border on being a semi-permanent solution (such as building in ring conductors to help prevent step potential).

Can you describe how an LPS is tested? Differences between testing the whole system vs testing each connection to ground and values needed.

As part of the requirements of BS EN 62305 all systems should be visually inspected and electrically tested every 12 months as a minimum (more frequent PPM may be required on higher risk sites).

All clamps, bonds and joints should be visually inspected. If there are concealed conductors/clamps etc. these should be tested for continuity to ensure that they are still performing correctly (a maximum resistance of 0.2 ohms is set).

Individual earth electrodes should be tested, preferably using the Fall of Potential method and an overall earth resistance test should be made again using the FoP method where ever possible.

It is advisable to test for continuity from the air termination to the earth termination (again a reading of 0.2 ohms is required), as part of the PPM consideration should be given to replacing the oxide inhibiting compound in the joints and bonds on a regular basis (at least every 5 years would be appropriate).

SPD Type 2 requires less energy than Type 1 to trip. So could Type 2 be used as well as type 1?

We do have combined type 1 and 2 SPDs so this has the energy handling of the type 1 together with the low output voltage or Uplevel of the type 2.

Normally it is not OK to just have type 1 SPDs due to the higher voltage let thru and this would mean additional type 2 SPDs would be required at SDBs or closer to end equipment.

What are the differences regarding Transient Overvoltage Protection Devices and SPD?

Nothing! The term TVSS or transient voltage surge suppressor comes from the USA, whereas the SPD is an IEC term.

Have you seen the use of SPDs in a hazardous area (ATEX certified) distribution board?

Sadly no which is rather surprising really as it is not difficult to do. SPD solutions in ATEX applications are common, but so long as the enclosure is capable of handling the SPD I do not see any reason why not to use them.

Can the building earthing system (cast into concrete) still be used even if enclosed in a waterproof membrane - which would be an electrical insulating material by default?

Even with a membrane, the slab is still part of the FE installation, there will also be in addition a link to a larger concentric loop electrode beyond the insulated area.

How does an earthing grid differ from the prosumer Foundation Earthing 8mm continuous metal? How many points of contact to the building FE are required on the prosumer installation?

The FE closed loop of round conductor will provide the best earthing solution compared to other methods for a new build with less risk (compared with rods or mats that is).

In a dwelling installation, there may be one upstand that is taken to the MET, but there can be other access points as cast in concrete earth points for the purposes of local bonding of DBs or equipment to the FE.

These are also good positions to test the FE if required.

What specific tests are conducted as part of the annual statutory inspection on a lightning protection system?

As part of the requirements of BS EN 62305, all systems should be visually inspected and electrically tested every 12 months as a minimum (more frequent PPM may be required on higher risk sites).

All clamps, bonds and joints should be visually inspected. If there are concealed conductors/clamps etc these should be tested for continuity to ensure that they are still performing correctly (a maximum resistance of 0.2 ohms is set).

Individual earth electrodes should be tested, preferable using the Fall of Potential method and an overall earth resistance test should be made again using the FoP method where ever possible.

It is advisable to test for continuity from the air termination to the earth termination (again a reading of 0.2 ohms is required), as part of the PPM consideration should be given to replacing the oxide inhibiting compound in the joints and bonds on a regular basis (at least every 5 years would be appropriate).

If the internal rebars of a building foundation are used as part of the lightning protection, wouldn't it affect the structural integrity of the building if an actual lightning strike occurs on the building? Possibly making it not safe for habitation?

Unlikely to impact adversely as the rebar mesh provides excellent current division at each joint or cross on the mesh, energy dissipation is not going to damage the integrity of the structure, in fact the more current division the better as this will have a positive influence on the separation distances within the structure as well.

If a power cable leaves a building to supply a feeder pillar some 40m away, which end or both does the SPD go? In the building to protect the switchgear of the feeder pillar to protect the switchgear?

The standard in 534.4.1.2 requires an SPD when the cable crosses a zonal interface so in this case the cables leaves LPZ 1 the internal zone out to LPZ 0 the external and back inside again at the other end so a SPD would be required at each end. They may both be type 2 SPDs if no LPS is fitted or type 1 and type 2 at the other if one end has a fitted LPS.

When using a vertical busbar system in a commercial building, can you provide an SPD type 2 at the start of the busbar/the main LV switch panel rather than at each possible busbar tap-off or tenant distribution board?

We need to bear in mind the regulation that describes the 10m rule in section 534, so that first SPD at the start of the riser only goes so far!

Also fitting the SPDs in the riser tap-off boxes may still place them too far away, so additional SPDs would be better located closer to the tenants CU or closer to the sensitive end equipment.

How about Wind Turbine FE? What standard is applicable?

Wind turbines already have a standard for the FE of the base IEC 61400-24 covers this.

Would you connect the FE direct to the MET bar?

Yes as it forms part of the equipotential bonding network, there are some earth bars that can take the round conductors as standard.

What advantages does an FE installation have over a simple buried earth mat or rod system?

A far higher performance for less effort and it is also safer. The slab gives a far greater contact area with the soil so gives the lower sub 20 ohms value that we are looking for.

None of the risks with driving deep rods either.

Can an SPD for multiple external cables be provided at the DB, or should each cable have a separate device?

It depends, if one DB is the focus of several external loads then often one SPD is enough. But if we consider the surge path from the external into the internal zone, we need to look at two things.

First are we saying we are happy that the surge enters the building and we are happy that the surge goes down cables in containment with other normally unaffected cables or circuits?

If we have concerns then we intercept the surge where the cables cross the zonal interface of external to internal zone.

Then if we are happy with the surge path we need to understand what the surge sees next.

Is it the MCB or a control device and are we happy if that fails? If not we fit the SPD at the zonal crossing point.

Please clarify the requirement of ring conductors in high rise buildings and also the spacing between ring conductors.

There are two different considerations here, the first is the requirement for protection from side flash, the second is the requirement for additional rings for equipotential bonding purposes.

  1. BSEN 62305 only requires you to consider side flash on structures over 60m in height. Under this height can be disregarded regardless of level of LPS required. Once you exceed this height only the top 20% of the structure need be considered (so for a 100m height building only the top 20m is considered E.5.2.3). This area of the structure should be protected with a mesh equal to the mesh size required for the level of protection determined by the risk assessment.
  2. For the equalisation of potential, consideration should be given to figures E4 & E25 in BS EN 62305-3 annexe E and the section on equipotentialization in annexe E E.4.3.8. Generally speaking if a large structure is using the reinforced concrete or the structural steel frame and the associated metallic rain screen cladding, this is a relatively easy process to carry out with regular bond to the conductor structures and earth points arranged both internally and externally to facilitate the bonding.

Can a lightning protection down conductor system be linked to a common bonding network (CBN) run around the outer perimeter of a building rather than that system having independent earth electrodes per down conductor?

Yes, it can and this is described in BS EN 62305 as a 'type B' earthing arrangement.

It is particularly recommended for high-risk structures with explosive storage facilities, EX zones, highly flammable contents etc. but it can be deployed on any lightning protection system and is actually the preferred method in most continental European nations.

Is it possible/recommended to combine ESE LP with a traditional LP system in a building complex?

Not if you wanted to be compliant with BS EN 62305. ESE systems are not compliant with this standard which does not accept any system claiming to offer an enhanced area of protection or 'attraction' capability.

How often should you perform maintenance checks on LPS and FES?

A lightning protection system should be visually inspected every 12 months (more frequently for higher risk sites).

It should be electrically tested every 12 months to include individual earth resistance readings, overall earth resistance readings and continuity readings between air termination and earth termination.

More details regarding foundation earthing inspection and testing will made available if it is included in BS 7671:2018+A2:2022 in the future.

I live in a mountainous tropical location with very intense electrical storms. I have 2 questions - I didn't see or hear anything about lightning dissipators as a means of preventing a lightning strike - as the last thing I want to do is to attract a lightning strike by installing a lightning rod etc. I also didn't hear anything about RF damage from lightning, although I assume a surge protector will limit this damage?

As yet there is no proven method of being able to either attract a lightning event or prevent one from occurring in a given area.

Both IEC 62305 and BS EN 62305 are quite clear on this, no system which claims to be able to attract or prevent a lightning event would be compliant, it is a protection system not an 'attraction' or 'prevention' system.

With regards to any RF damage, a correctly installed protection system would have to include the appropriate protection for aerials, which would include any surge protection requirements.

Concrete is a good conductor used for earthing. Why is an additional earth conductor used for building earthing?

Sometimes the concrete electrode does not give us the earthing performance that we need to cover certain conditions or functions, so an additional soil electrode is required to get better values in poor value areas.

When in island mode, does the DNO earth need to disconnect?

According to the proposed text the earthing of the DNO need not be disconnected but if it is then the process of the prosumer installation will need the earthing arrangement to be made again as required.

Please elaborate the requirements in the standard for LPS bonding of building facade cladding in high rise buildings and the possibility of having sacrificial cladding instead of a strike pad connected to a ring conductor?

For the rain screen cladding system to require bonding, you would first need to carry out a separation distance calculation (BS EN 62305-3 section 6.2/6.3).

Once the need to bond has been established you would bond to the cladding at the top and bottom of each down conductor (as a very minimum but depending on height additional bonds may be required).

You would also need to be able to prove electrical continuity (of no more than 0.2 ohms). If the cladding/cladding rails are not continuous then continuity links would be required across each joint.

Obviously, only conductive materials need to be bonded. If the cladding is used to cover the down conductors then the cladding itself would become the most external part of the system and you would need to ensure that it is of sufficient thickness (see BS EN 62305-3 table 3 column 2) for it to be used for this purpose.

If the material is of sufficient thickness than no additional strike pad would be required. (BS EN 62305-3 figure E8 is of use in this scenario).

For a car charging point, earth pit is required with RCD. If EV is fed from the building would the local DB need to be provided with surge protection at the DB, as earthing isolated from the building? The building has surge protection at the incoming in the building. Do we require additional surge protection local to DB serving EV?

Under the Regulation 534.4.1.2 a cable crossing a zonal interface, for example from inside to outside, will need a SPD, also if the EV CP is some distance from the EV DB in the structure then a SPD at each end may be required.

If the EV CP is publicly accessible then the risk assessment in 443 would require SPDs to be fitted.

If FE is bonded to incoming DNO then what figure we can assume for Ze?

If the DNO is providing PME then we may get the usual 0.35 ohms from them, the standard requires that FE is less than 20ohms.

Recently, at a 5-year-old school, we had this C2 on the EICR - is this new? "No main protective bonding conductor present at the MET bonding the lightning protection to the installation's earthing conductor".

In terms of this appearing on an EICR, I am not aware of it being a codable item however this requirement is certainly not new and an equipotential bond has been required between the lightning protection system and the MET since 1985 with the introduction of BS 6651.

What size cable is required for FE connection to the MET bar?

The round conductor of the FE loop can come up to the MET, there are bars that accept the 8mm round conductor and this equals 25mm2.

When would you use a type 1 and type 2 SPD?

There are two reasons to use type 1 or type 1 and 2 combined SPDs. First if there is a fitted LPS as this SPD provides the bonding of the services to the MET in lightning strikes and prevents flashover, the second reason is if there is an overhead line at risk of a direct strike.

What is the difference between Passive lightning protection and Active lightning protection?

BS EN 62305 does not recognise any form of "active" lightning protection. These types of systems would not be compliant.

Where reinforcement is bonded to the FE, is there any concern with connecting them together? i.e. galvanic corrosion?

The materials selected for the bonding clamps are such that no issues with corrosion are to be expected, for example, stainless steel or steel, the same as the rebar.

Re. individual earth resistance 2:1 ratio for minimising separation requirements see 6.3.2 Table 12 Note.

The requirement for the 2:1 ratio in BS EN 62305 is only applicable when considering separation in an isolated lightning protection system that does not use a type B earthing arrangement, i.e. an isolated system terminated onto individual earth electrodes. It is not applicable in any other scenario.

Given that over 90% of installations in the UK are non-isolated installations and the overwhelming majority of isolated installation in the UK use a type B earthing arrangement, it means that this very specific scenario is so rare it was not appropriate to mention this during the limited time we had to discuss the subject during the Q&A session, though I do acknowledge that this requirement does indeed exist.

The fact remains that for the majority of those wanting to know the basics of lightning protection, it's more important for them to understand that the individual rod reading requirement from BS 6651 has been removed and they should no longer be slavishly looking to achieve this or be misguided into believing that this is still a requirement.

Is FE required to be installed in the foundation of an extension, when adding an extension to an existing building?

The regulations propose that new builds or extensions are suitable for foundation earthing systems. So should the original building now be used as a prosumer installation, then the foundation earth could provide the value to meet the requirements. It depends on the size of the extension.

With LPS on explosive structures, do we still need to test for unseen joints as the reading is now overall below 10 ohms?

The standard has not changed in its requirement that all joints, bonds and connections should be visually inspected at least every 12 months.

If you cannot visually inspect then you must be able to carry out continuity testing to establish that the unseen parts of the system are still in good working condition.

I believe that not enough continuity testing is currently being undertaken to ensure that all joints and bonds meet the 0.2 ohm requirement for electrical continuity set out in BS EN 62305.

FE only has 1 Test point so can you rely on the original test readings at installation?

We see most new build dwellings having one upstand to the MET, so it is possible to use a cast in or fixed earth point into the floor or wall to enable testing at any point in time.

Assuming that the roof of a building is accessible only for technical maintenance, would installing mesh tapes at floor level be a suitable methodology to protect operators working on the roof? I believe this methodology is not suitable to protect people working on roofs, however, this seems the most common system installed.

This should be a consideration when designing the lightning protection system.

If the roof is intended to be an area that is not readily accessible then is it wise to introduce a system that requires an annual inspection at a minimum?

Protection can be achieved using other methodologies which would be more appropriate. CDM regulations require designers to consider not only the risk during installation but also the risk of ongoing maintenance so in this scenario I would agree adding a tape mesh network to this type of roof would not seem appropriate.

If the industrial area is very large, are specific rules and calculations specifically considered for the connection of the earthing material sizing?

For a dwelling using a foundation earth we need to be aware of the maximum fault currents, typically 16kA, so a 8mm round conductor would be OK.

If, however, there was a lightning protection system this would go up to 10mm round so the conductor sizing of BS EN 62305 is met.

As part of the proposed changes to the IET Wiring Regulations, will foundation earth be required on all commercial & residential buildings even if they do not have PV/export planned as part of the initial install?

It could be the case that the FE is provided as it is the basis of a good earthing system in itself, and future proofs the installation as once the slab is down the options are limited and retrofitting is not an option.

Can we run down conductors inside the building with protective covers on top?

You can run down conductors internally but you would need to give consideration to a number of potential risks.

  1. Why would you want to introduce lightning energy into your internal areas when the whole purpose of lightning protection is to try and prevent this?
  2. Touch potential, the down conductor must be installed in such a fashion that it is not possible for any resident/occupant to be able to come into contact with the conductor.
  3. Visual inspection, the standard requires that there is an annual visual inspection of components. This would need to be considered and some means of visual inspection incorporated that did not prevent readily available inspection.
  4. Separation distance, if the internal down conductors were in close proximity to metallic items these may require bonding which in turn increases the risk of touch potential. it also makes it more likely for lighting energy to be induced into internal services such as cables or pipes and would therefore increase the requirement for surge protection devices.

On a building with 4 basement levels with the substation being on basement 1, where would you have the electrical system earth for your substation/DNO etc and the lightning loop?For example, if there is lightning protection down-conductors through columns connecting to lightning loop.

In this instance, we would recommend that the building foundation be utilised as the FE and the lightning protection earth. It should be supplemented with an additional 8mm galvanised steel conductor connected to the reinforcing.

This would be at the lowest basement level with additional connections made into the pile caps.

Would you normally require to connect the roof lightning protection for two buildings (3 storey residential building) if they have a common roof (level 1)? How would you connect the equipotential bonding if both buildings have their own DNO incoming connection?

This depends on the type of lightning protection that is being installed.

If it is a non-isolated system (which is the most likely) then yes the different roof levels do need to be connected.

The connection between the LPS and the MET is carried out at low level from the most convenient down conductor position.

When testing for global earth impedance on a power station for calculating the Rise Over Earth Potential, as you say weather and conditions impact on the impedance value. Would %2B/- 25% value be an acceptable variance?

This is a question about HV power earthing that is not covered by either Foundation Earthing or Lightning Protection. We would recommend that you consult BS EN 50522 and BS 7430 for more advice on the subject of power station earthing and maximum impedance values.

What is the difference between a lightning protection system and an earthing system?

Earthing & lightning protection are fundamentally different systems.

There are different standards for both and different requirements for both, though, of course, a lightning protection system contains a requirement for earthing and requires an equipotential bond to the main earthing system of the structure to which it has been installed.

We would suggest that you study BS EN 62305 to gain a greater understanding of the specific requirements for lightning protection earthing and BS EN 50522 & BS 7430 for a greater understanding of both LV earthing and power earthing systems.

For foundation earthing - in buildings with waterproof membrane/insulation below the slab, is rebar earthing still possible or should perimeter ring conductors then be used?

Yes, it is possible to have a FE system with such waterproofing. On a practical level, the outer conductor ring can be connected to the concrete embedded electrode via the round conductor passing through a waterproof bushing to maintain the membrane or insulation properties.

Is a foundation earth applicable to an earth nest for a transformer?

It could be. I would model this using earthing software first, an additional benefit being the prevention of copper theft if the values using other materials can be met.

With regards to FE, is earthing to rebar an inferior option to earthing via a dedicated 8mm conductor?

I would not say inferior as this depends on the extent of the installation, images I see do use a ring electrode clamped to the rebar.

Using the closed-loop and clamps tested to the required current handling levels gives assurance that the performance of the FE system is not compromised.

This is as opposed to any accidental contact by overlapping sheets of rebar connected by twisted wire.

Could a reinforcing mesh under a new driveway be used instead of a single earthing rod in a TT domestic supply?

Yes, that would be a good proposal. The earth in touch with the buried surface area of the drive would be far greater than a rod or group of rods.

Is there free software that allows you to design the earth mat, spacing between rods, etc.? And how does this differ between MV & LV - is there a minimum distance between them?

As far as we are aware there is not currently any free software for this purpose.

For a multi-storey car park with lighting columns on the top deck - can the lighting columns be used as part of the lightning protection system, using rolling sphere or angle of protection with the lighting columns connected to the lightning protection system?

Yes, lighting columns could be used as part of a lightning protecting system if the following were adopted:

  1. The column material would need to meet the minimum thickness requirements (BS EN62305-3 table 3 column 1) if it did not then an additional short air rod would need to be added to the top of the column.
  2. The cut out within the lighting column would need to be provided with an appropriate surge protection device and the feed pillar/distribution board feeding the column would also require an appropriate lightning arrest SPD.

Is there any software we can download that will determine our air networks in the rolling sphere format? Or is this only available to lightning protection specialists?

There are a variety of software packages available that can be used to determine the area of protection afforded by an air rod or a series of air rods in an overall protection system.

Most 3D software packages can be used from simple systems such as SketchUp through to more complex packages like Revit or SolidWorks.

None of these are dedicated 'lightning protection' software packages though so a high level of knowledge of BS EN 62305 would be required to apply these, taking into account the varying size of rolling sphere, the separation distance and the height above reference plane of the air rod tip.

Can you use foundation earthing for lightning protection earth termination network?

Yes, this is possible subject to some calculations to meet the requirements of BS EN 62305.