Megger offer their technical advice regarding the stakeless method.
You ask: I’ve just finished testing a lightning protection system using the traditional three-wire system for checking the resistance of each of the earth electrodes. It took much longer than I expected. Is there a faster method I can use next time I do a job like this?
We answer: Provided that the earth system has multiple earth electrodes, you can save a lot of time and effort by using the stakeless method. With this, there is no requirement to disconnect the protective earth or use temporary earth spikes. You simply place a special twin coil instrument or two individual clamps around the cable or tape of the electrode you’re testing, initiate the test and read off the result. This method used to only be available on dedicated earth test instruments, like the Megger DET14C, but some models in Megger’s MFT multifunction tester range, including the new MFT1741, support stakeless testing. The only extras you need are the two auxiliary test clamps. The stakeless method has some limitations – it can’t be used in systems that only have one earth electrode, for example – but it’s a great time saver for most lightning protection installations.
If you’d like to know more, you can download a comprehensive guide to earth testing, “Getting Down to Earth”, by going to: https://assets.tequipment.net/assets/3/7/GettingDownToEarth.pdf