You might be aware that eventually BS 6651 is to be withdrawn and replaced by new IEC and Cenelec Standards that are at the "work in progress" stage. Section 6 (Codes and Standards) of the American paper "CONTEMPORARY LIGHTNING SAFETY FOR ENVIRONMENTS CONTAINING SENSITIVE ELECTRONICS, EXPLOSIVES AND VOLATILE SUBSTANCES by Richard Kithil, President & CEO, National Lightning Safety Institute, states as follows: "The European International Electrotechnical Commission IEC 61024 series for lightning protection is the single best reference document for the lightning protection engineer. Adopted by many countries, IEC 1024 is a science-based document applicable to many design situations."
Section 4.4 (Grounding) of Richard Kithil's paper states as follows: "The grounding system must address low earth impedance as well as low resistance. A spectral study of lightning's typical impulse reveals both a high and a low frequency content. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies. A considerable part of lightning’s current responds horizontally when striking the ground: it is estimated that less than 15% of it penetrates the earth. As a result, low resistance values (25 ohms per NEC) are less important that volumetric efficiencies. Equipotential grounding is achieved when all equipment within the structure(s) are referenced to a master bus bar which in turn is bonded to the external grounding system. Earth loops and consequential differential rise times must be avoided. The grounding system should be designed to reduce AC impedance and DC resistance. The use of counterpoise or "crow's foot" radial techniques can lower impedance as they allow lightning energy to diverge as each buried conductor shares voltage gradients. Ground rings connected around structures are useful. Proper use of concrete footing and foundations (Ufer grounds) increase volume. Where high resistance soils or poor moisture content or absence of salts or freezing temperatures are present, treatment of soils with carbon, Coke Breeze, concrete, natural salts or other low resistance additives may be useful. These should be deployed on a case-by-case basis where lowering grounding impedances are difficult an/or expensive by traditional means."
Note: NEC means the National Electric Code. It is a document sponsored by the National Fire Protection Agency. It is a book US electricians have to learn before obtaining their licence.
Please use the following link to read Richard Kithil's paper in full:
The article "Measuring Ground Resistance - The Fall of Potential Method" by Jeff Jowett of AVO International has information that might be useful to you. Please use the following link:
I hope that the above references will give you some food for thought on what is a rather interesting and complex area, particularly in the field situation. Regards, John
You might be aware that eventually BS 6651 is to be withdrawn and replaced by new IEC and Cenelec Standards that are at the "work in progress" stage. Section 6 (Codes and Standards) of the American paper "CONTEMPORARY LIGHTNING SAFETY FOR ENVIRONMENTS CONTAINING SENSITIVE ELECTRONICS, EXPLOSIVES AND VOLATILE SUBSTANCES by Richard Kithil, President & CEO, National Lightning Safety Institute, states as follows: "The European International Electrotechnical Commission IEC 61024 series for lightning protection is the single best reference document for the lightning protection engineer. Adopted by many countries, IEC 1024 is a science-based document applicable to many design situations."
Section 4.4 (Grounding) of Richard Kithil's paper states as follows: "The grounding system must address low earth impedance as well as low resistance. A spectral study of lightning's typical impulse reveals both a high and a low frequency content. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies. A considerable part of lightning’s current responds horizontally when striking the ground: it is estimated that less than 15% of it penetrates the earth. As a result, low resistance values (25 ohms per NEC) are less important that volumetric efficiencies. Equipotential grounding is achieved when all equipment within the structure(s) are referenced to a master bus bar which in turn is bonded to the external grounding system. Earth loops and consequential differential rise times must be avoided. The grounding system should be designed to reduce AC impedance and DC resistance. The use of counterpoise or "crow's foot" radial techniques can lower impedance as they allow lightning energy to diverge as each buried conductor shares voltage gradients. Ground rings connected around structures are useful. Proper use of concrete footing and foundations (Ufer grounds) increase volume. Where high resistance soils or poor moisture content or absence of salts or freezing temperatures are present, treatment of soils with carbon, Coke Breeze, concrete, natural salts or other low resistance additives may be useful. These should be deployed on a case-by-case basis where lowering grounding impedances are difficult an/or expensive by traditional means."
Note: NEC means the National Electric Code. It is a document sponsored by the National Fire Protection Agency. It is a book US electricians have to learn before obtaining their licence.
Please use the following link to read Richard Kithil's paper in full:
The article "Measuring Ground Resistance - The Fall of Potential Method" by Jeff Jowett of AVO International has information that might be useful to you. Please use the following link:
I hope that the above references will give you some food for thought on what is a rather interesting and complex area, particularly in the field situation. Regards, John
