Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day concerns Table 12A of Appendix 12 in the newly published 17th Edition of the Wiring Regulations. It is answered by SELECT:
To continue, I am involved in a project where a single-owner building is fed by a 33kV to 400V, 200kVA transformer (no on load tap-changer) that is feeding only the building. The transformer is owned by the DNO legally (but from a design point of view could easily be owned by the factory). The 33kV side is connected directly (ie. at same substation) to the 33kV terminals of a 132/33kV transformer with automatic voltage control of the 33kV. Which set of volt drop figures from Table 12A to work with?
I can believe row (ii) (6% and 8%), as conditions are the same from a design point of view whether the 33/0.4kV transformer is owned by the DNO, or the owner of the building.
Answer: The supply in question appears to be part of the public supply and the figures in Table 12A (i) would therefore apply. The figures for a private LV supply are intended, as far as I can see, to apply to supplies from a privately owned generator.
And Voltimum UK managing editor James Hunt says: Note that full implementation 17th Edition will be on July 1st 2008. Over the next six-months, the 16th Edition will be phased out and 17th Edition will be implemented. Within this period, installations can comply with either. After 2nd July 2008, installations should comply only with the 17th Edition. For longer-term projects with overlap, the client concerned must be made aware of the situation and agreement reached.
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