FAQs

 
1 ....I've got a LP system installed....how often should it be tested?

For buildings built/designed to BS6651:1999, the recertification interval is every 11 months to achieve a seasonal change over 12 years. For buildings built/designed to BSEN 62305:2006 the interval stipulated for Europe is every 2 years subject to local statutory requirements. For the UK, this falls under the Electricity at Work regs 1989, which requires testing no greater than every 12 months.

2 ....What can happen if I let the retest 'slip'...?

…”for a building/structure with explosive or volatile contents or critical nature, the risks are pretty obvious but for the ‘normal’ everyday kind of commercial building, surely one can let things slip a bit, no?” Err, no! A poorly maintained system can fail with devastating results…joints are weakened through the heating and cooling of temperature changes over time, this can lead to a build-up in system impedance, so when struck the intended path to earth is no longer the ‘preferred’ route for the current. Instead it can ‘punch’ through brickwork, mortar, etc. and at best blow a part of your structure apart, or worst still initiate a fire locally to the strike or at some distance by travelling along cables before punching out to other parts. All this ‘punching’ out is another term for ‘sparking’! On tall buildings a bunch of debris falling several storeys onto innocent bystanders below is not a good scenario to contemplate. Let alone the potential weakening of the structure itself. Even on the modern steel framed or reinforced structures; the sparking issue can be a significant hazard in itself and careful equalisation of hazardous voltages relies on a well maintained LPS. The joint integrity example above is just ONE very real issue.

3 ....How can I find out if a building needs protection?

BS6651 and the later BS62305 codes for lightning protection both have a set of calculations to assess the potential ‘Risk’ of a structure. By completing this assessment one can quantify if any protection is required, what form this protection might take and evaluate the impact these measures will have in reducing the risk. Due to its complexity, EES has invested in the software tools to provide a Risk Assessment service. Please fill in the 'Risk assessment' for more details…

4 ....What is the latest code for lightning protection?

BS EN 62305:2006 Protection against lightning. This comes in 4 parts covering structural and electronic protection.

5 ....How many earth electrodes will I need...?

This will depend on many variables not least what kind of soil are you dealing with? i.e. what is its soil ‘resistivity’ and how is it layered? EES offer a soil assessment and modelling service so you can, with confidence, know the extent of any potential earthing design….no if’s, no but’s….no woolly “let’s wait and see what we get and go from there!”

6 ....What size conductor should I use for a substation?

It is normal practice to have a rating for the earthing system inline with the maximum system design fault level. You can then apply the formula from EA TS 41-24 [6] which is in our downloads.

7 ....Is there a degree of flexibility to the down conductor spacings?

Yes, BSEN62305 clause 5.3.3 for non-isolated systems the down conductors should be distributed around the building perimeter 'subject to architectural and practical constraints'.

8 ....What 'mesh' size do I need?

BS62305 has four classes of protection, and depending on the class required, will determine the size of mesh. For example, Level 1=5x5m, II=10x10m, III=15x15m and IV=20x20m.

9 ....Have you got a spec for Surge Protection?

Yes, as a registered user or member you will be able to download a spec from the download area.

10 ....What's my legal responsibility to install LP?

Electricity at Work Regulations 1989, Earthing and other suitable precautions (Reg 8). Also, employers have a 'duty of care' to employees and visitors to their premises under the Workplace regs.

11 ....I need to earth a transformer, what calculations do I need to do?

There are at least a dozen technical codes of practice, standards and guidelines covering earthing. From 400kV substations, generators, transformers…to LV domestic installations. These include: • Characteristics of Different Power Systems Neutral Grounding Techniques: fact or Fiction. F J Angelini and D D Ship, IEEE. • J&P Transformer Book. • IEEE Std. 141-1986, "IEEE Practice for Grounding of Industrial Power Systems" (IEEE Green Book, • IEEE, NY). • M.G. Say, Electrical Earthing and Accident Prevention, NEWNES. • Neutral Earthing in the Hungarian System, F. Kovacs, Z. Reguly, UNIPEDE, Lisbon, October 25-27, • 1989. • The National Electric Code Handbook; NFPA 1987. • Electricity Safety, Quality and Continuity Regulations, 2002 - N° 2665 • BS6651 Lightning protection for structures 2000 • BS7430 Code of practice for Earthing, 1999 • EA TS 41-24 Guidelines for the design, installation, testing and maintenance of main earth systems in • substations. • NGTS 3.1.2 Substation Earthing • ER S/34. It is also true that once one starts to analyse earthing systems in detail, using Carson's equations and extensive algorithms, the techniques are amongst the most difficult in electrical engineering. With this in mind, EES can offer consultative advice on system design using the latest software tools as well as resources to install.

12 ....I've got a Test Certificate which is showing 'high readings'....what does this mean?

If your building pre-dates September 2008, then it’s more than likely the inspection was carried out under BS6651. The compliance target for BS6651 is 10 times the number of down conductors, i.e. if your building has 10 down conductors (DC’s) then each DC reading must be under 100 ohms. The reason for this is to avoid any part of the system having a higher resistance than another (within reason), as this would place an increased current loading on the remaining parts. Ultimately, a system with a high resistance present may cause a chain reaction to occur when one part of the system is stressed beyond its capacity, which may cause other parts of the system to fail (like a house of cards).

13 ....Does lightning strike twice?

YES! For lightning to have struck something....that 'something' has demonstrated it has all the necessary components to accept a strike. So, unless something changes in one or all of these components, then lightning may indeed strike twice.....and it has done! This myth has been busted many times, so BEWARE!