Published: 8 April 2009
Category: Q&A
Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, about impedance and a Zs reading at a distribution board, is answered by SELECT:
Question: Is it within the Regulations (BS7671) to use the steel work of a building to lower the Zs reading at a distribution board, so as to use the steelwork as a supplementary earth?
This concerns an existing installation that we have tested, and the Zs reading was too high for the existing MCB feeding the distribution board.
Answer: The short answer is 'yes', you can introduce a supplementary bond to assist with earth fault loop impedance values and disconnection times.
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www.voltimum.co.uk/consult.php?universe=consult.index.questions