Published: 30 September 2009
Category: Q&A
Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning earth loop impedance tests on an installation after mains upgrading, is answered by SELECT:
Question: I've just completed an earth loop impedance test to an installation we have completed and have just learned that the mains are to be upgraded. So obviously, this will mean that the Ze value will change. Can I take the original Ze value and compare it with the new Ze value, and calculate the difference? Or do I have to completely re-test the whole job again?
Answer: You have not specified any dates, but you should complete the certification with the original value of Ze, as this was the supply arrangements at the time of the inspection and test.
Answer: You have not specified any dates, but you should complete the certification with the original value of Ze, as this was the supply arrangements at the time of the inspection and test.
If the mains are upgraded prior to your certification being handed over to the customer, the distributor will have carried out his testing and you may wish to measure the new Ze, and amend your certification to reflect this new value.
There would be no requirement to re-test the whole installation, as it will only be Zs values that may be different. Again, if you wish to amend these values you can do so by calculation.
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