SOLUTION

(i) The clamp-on ground method of measurement is not suitable for a single or isolated grounding system as there is no return path for the current.

(ii) Clamp ground testers effectively make loop resistance measurements. Clamp measurements are loop measurements. For the clamp method to work, there must be a series-parallel resistance path (and the lower the better).

(iii) The clamp-on method is only effective in situations with multiple earthing electrodes are in parallel and a closed circuit is available for the current circulation.

(iv) This method does not give the actual value of the ground resistance if the clamps are placed at the bonded lightning protection system.

(v) It may also give a very low reading due to the interaction of two buried water pipes and conduits.

(vi) It cannot be used on isolated grounds, thus making it in-applicable for installation checks or commissioning new sites.

(vii) Measurement of low earth resistance of the order of 0.5 ohms is difficult with this method.

(viii) The internal diameter of the clamp is usually small of the order of 25 mm which prevents the measurement of earth rods greater in size.