Q4.1. What is step potential?
Step potential is the voltage gradient difference measured in volts existing between the feet of a person standing on the ground.
When a lightning strike reaches earth and is being dissipated in the soil, there can exist a difference in potential between a person’s (or animal’s) feet.
Q4.Galvanized tape underground?
‘Yes’, Providing the galvanized tape, where it enters the ground, has a protective coating to isolate it from the soil and copper rod. The earth rod joint should be sealed to prevent any ingress of moisture. Unless it is unavoidable, we would not recommend the use of dissimilar metals in underground applications.
Q4.3. When installing a lightning protection system, how far from a building should the earth rods be placed?
They should be driven into the ground beneath, or as close as practicable to the structure and down conductor. The aim is to offer a lightning strike as direct a route as possible from the top of the structure to the earth.
Q4.4. What is the minimum distance for spacing earth rods?
Views vary considerably on this question, but it is generally accepted that the distance between rods should be at least equal to, and preferably greater than, its depth.
Q4.5. Must I bond my lightning protection earth to the main electrical earth?
BS EN 62305 in line with other Standards now advocates that all earths, whether they be the lightning protection earth, the main electrical earth, computer earths, etc. should all be bonded. This action minimizes the risk of dangerous step and touch potentials.
Agreement of the local electrical supply authority should be obtained before making any connection to the electrical earth.
Q4.6. Which is the best type of connection to use in earthing and lightning protection system – the crimp connector, bolt connector, or a Thermit welded connection?
The final choice will depend on the application. Bolted connections are obviously suitable for fittings such as test clamps, where the conductors, as they possess the following qualities;-
-mechanical strength
-excellent current carrying capacity
-reliability
-low electrical resistance would be pleased to offer expert technical guidance on the choice and type of fitting to suit your application.
Q4.7. When should I use a solid copper earth rod rather than a copper covered steel one?
A solid copper rod has nothing like the mechanical robustness of a copper covered steel rod and so should only be used in soil that is comparatively easy to drive into, one reason for choosing solid copper could be because of the aggressive nature of the soil, where the presence of steel may ultimately create a corrosion problem.
Q4.8. How do I know what type of earth electrode to use?
The choice of earth electrode type is governed, to a large extent, by the prevailing soil conditions. A soil resistivity survey indicating lower resistivity at greater depths will make the deep driven earth rod electrode a logical choice.
The ground that has a one metre depth of soil before encountering bedrock would best be suited to a buried radial strip electrode; provided the system is installed below the frost line and below the area that is subject to the influence of seasonal weather changes.
Q4.9. I have a problem with moving cranes, can they be earthed?
Assuming that the crane is on rails, it is normal just to earth these at 20m intervals. The crane being all steel forms a natural conductor, but as the crane has a number of moving joints, these may need to be bonded across to avoid damage to bearings, etc. How this is done depends entirely on the type of crane.
At FullSpectrum Energy, we are uniquely positioned by experience and expertise to Advice, Design, Install, Commission Effective Lightning Protection and Quality Earthing System to international best practices irrespective of the sector and Standard.
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Victor Oyedu, FNSE, FNIEEE, CPQ.
Power Quality and Energy Management Specialist.
Publisher at Afrienergyonline.com
CEO, FullSpectrum Energy Solutions Limited, Nigeria.
