Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning the maximum voltage drop on a lighting circuit, is answered by the NICEIC:
For example, taking a luminaire, the HF ballast of which can work down to a minimum voltage of 200V, and working to the lowest allowed supply voltage of 216.2V ( Uo - 6%), it would be allowed to have a voltage drop of an absolute maximum of 16.1V (Uo - 7%). Is that so?
I would never design using maximum limits but, if I was to design to ensure being within the luminaire's safe working limits, I would use a larger voltage drop than the 3% stated in BS7671. As far as I can see from looking through BS7671, I cannot find any note saying whether I can work to the voltage tolerances of equipment supplied instead of Table 12A.
Answer: Reference to Regulation 525.1 (p106) of BS7671:2008 requires the voltage at the terminals of equipment to be greater than the lower limit specified in the product standard for the equipment concerned. So, if these conditions were ensured, this would comply with BS7671:2008. The percentage approach given in Regulation 525.3 is usually applied where specific information concerning the load is unavailable at the time of design and hence is more onerous.
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