Published: 19 July 2010
Category: Q&A
Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning a distribution board feed via a sub-main cable in a block of flats, and loop readings, is answered by the NICEIC:
Question: I have a distribution board feed via a sub-main cable from the origin intake in a block of flats. When I take my loop reading at this distribution board, should I remove the values from those taken at the origin, or leave them in?
The reason I ask is that in some flats, the Zs is greater than the Ze.
Answer: The true Ze should be assessed at the origin intake position (usually just after the energy meter position). Zdb would be taken and recorded at the distribution board, where this distribution board is remote from the origin.
Zs will be greater than Ze for longer cables runs, but may be less if parallel return paths exist - ie metal services etc.
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