Q & A of the Day – Can you explain Table 12A in Appendix 12, the 17th Edition?

Question: I am intending to apply Table 12A (of Appendix 12 in the 17th Edition) to a design. I’m trying to understand the logic behind the two sets of figures in rows (i) and (ii). Can anybody help, and please advise with the methodology behind the two sets?

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.

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