David asks about the high voltage drop in a 200m cable run, and whether increasing the cable size is the answer. His question is answered by SELECT (Theme – Cables and Wiring):
Question: I have grow lights that I need to install in a glasshouse, and they will need a 63A three-phase supply. My problem is that the glasshouse is 200m away from the three-phase supply.
I have used the voltage drop calculations found in the On-Site Guide, applying a cable size of 25mm2, but the voltage drop was 18.9V, which is very high considering that the recommended voltage drop for the lights is 6.9V.
The only solution that I can think of is increasing the cable size, which will be very expensive. What do you think?
Answer: It would appear that in order to comply fully, a larger cable will be required.
However, there is some permissible dispensation because of the length of the run. Reference to BS 7671:2008 including Amendment No1, Appendix 4, Section 6.4 may help in this instance.
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