Published: 18 November 2009
Category: Q&A
Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning a TN-C-S electrical installation and Ze values (earth loop impedance external to installation), is answered by SELECT:
Question: I've just been testing a new installation - a TN-C-S system. The Ze measurement is 0.4 ohms. With the maximum stated value for the system being 0.35 ohms, the measurement is above this value. However, all other test results are OK and match up, and all disconnection times are achieved. Should the local supply authority be informed of the Ze value?
Answer: Earth fault loop impedance values are important, particularly when trying to meet disconnection values. The distributor however also has a responsibility and if an earth connection has been provided then certain parameters should be met. In this instance, I would inform the distributor and request an improved value.
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