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Student & Learning Zone - City & Guilds
Voltage Drop
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<blockquote data-quote="Doc Hudson" data-source="post: 501850" data-attributes="member: 1607"><p>Whilst technically correct that 525.202 refers to the origin of the installation, (usually the supply terminals), if you are considering an average domestic dwelling, the real-world effects meter tails have on compliance with volt-drop is generally negligible. Try calculating (mv/A/m) on the "tails part" of a circuit compared to the actual final circuit itself. e.g. a 45m radial supplying a 30A load, with 3m long supply tails. </p><p></p><p>If tails are 16mm (2.8x30x3)/1000 = 0.25v or If tails are 25mm (1.75x30x3)/1000 = 0.16v</p><p></p><p>If circuit is 6.0mm (7.3x30x45)/1000 = 9.86v or If circuit is 10.0mm (4.4x30x45)/1000 = 5.94v</p><p></p><p>So if volt-drop was a problem, any potential improvements you could make by upgrading the tails are so small (less than 0.1v), whereas the final circuit can get significant improvements by cable size selection. (even if tails were running at 80A or 100A you are still only looking around half a volt if you had 3m tails. Do the calculations with 1.5m tails and you will see how small and insignificant the values become.</p><p></p><p>Doc H. </p></blockquote><p></p>
[QUOTE="Doc Hudson, post: 501850, member: 1607"] Whilst technically correct that 525.202 refers to the origin of the installation, (usually the supply terminals), if you are considering an average domestic dwelling, the real-world effects meter tails have on compliance with volt-drop is generally negligible. Try calculating (mv/A/m) on the "tails part" of a circuit compared to the actual final circuit itself. e.g. a 45m radial supplying a 30A load, with 3m long supply tails. If tails are 16mm (2.8x30x3)/1000 = 0.25v or If tails are 25mm (1.75x30x3)/1000 = 0.16v If circuit is 6.0mm (7.3x30x45)/1000 = 9.86v or If circuit is 10.0mm (4.4x30x45)/1000 = 5.94v So if volt-drop was a problem, any potential improvements you could make by upgrading the tails are so small (less than 0.1v), whereas the final circuit can get significant improvements by cable size selection. (even if tails were running at 80A or 100A you are still only looking around half a volt if you had 3m tails. Do the calculations with 1.5m tails and you will see how small and insignificant the values become. Doc H. [/QUOTE]
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