Gromit Posted September 14, 2010 Share Posted September 14, 2010 (edited) So my brother-in-law wants to temporarily hack a 12v indicator system into his 6v (non Land Rover) vehicle. I've drawn up a circuit diagram with indicators and hazards. I'm trying to calculate the max cable size required. I can't find (or is blocked from work ) a chart listing amps and cable sizes for 12v. By my reckoning 4 bulbs @ 21W = 84W. These will draw 7A in total. How do I calculate the required cable size for a nominal length of say 2m? Cheers, Edited to add: so VWP show amps for their cables, but I'd still like to know how to calculate it Edited September 14, 2010 by Gromit Quote Link to comment Share on other sites More sharing options...
rtbarton Posted September 14, 2010 Share Posted September 14, 2010 This page should give you an idea. My link 14/030 should do your job OK. Cable size depends on amps, not voltage. For long runs (e.g. one end of a bus to the other) use the next size up. It's worth mentioning that modern cables can handle a higher current per cross-sectional area than older ones because the newer types of insulation can operate at a higher temperature. Quote Link to comment Share on other sites More sharing options...
Gromit Posted September 14, 2010 Author Share Posted September 14, 2010 Thanks for that. Didn't realise it was dependent on the insulation, which seems counter-intuitive. After a fair bit of hunting I came across this table, which is useful: Strands mm2 Resistance /diam Amps V drop over 5m 9/030 0.65 0.0294 5.75 0.845v 14/030 1 0.0189 8.75 0.827v 21/030 1.5 0.0125 12.75 0.797v 28/030 2 0.0094 17.50 0.823v 35/030 2.5 0.0075 21.75 0.816v 44/030 3 0.0060 25.5 0.765v 206/030 16 110 194/040 25 170 Quote Link to comment Share on other sites More sharing options...
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