briofoz Posted April 29, 2013 Share Posted April 29, 2013 I need some help on theory. Heres the background. Bro in law has bought aLamyai orchard at Lumphun. Well established with dam. It is 2 rows wideand about 25 m wide, is 4 rai of land, which means its very long andskinny.He has put in irrigation pipes to a sprinkler on each tree. He runs a3Hp electric motor to run the pump from the dam. The electrical problemis that its 200m from the supply pole.He is using 2.5mm single core copper to run the distance. It needs to be wound up after each use because it will go missing.I have suggesting doubling the cable (parallel) to cut down losses.Anyway, its 40 years since I did the theory. 200m to supply a 3HP Motor....3HP is about 2200Watts, so motor will be drawing 10 amps. Loss of copper is 18mV/m from a chart I found. So...18mV x 200 x 10 is a 36V loss in perfect conditions. But where I amlost, copper is a resistive load, motor inductive load, so are my calcscorrect? Link to comment Share on other sites More sharing options...
David48 Posted April 29, 2013 Share Posted April 29, 2013 Some issues there surely. And, as you said, in perfect conditions ... presuming that there was 220V available at the take off point for the pump line. Motors certainly can burn out. Have a read of this The Mod crossy is your man for an answer. Link to comment Share on other sites More sharing options...
Crossy Posted April 29, 2013 Share Posted April 29, 2013 That 3hp motor will be pulling 30A+ on start. Doing the design properly, as a minimum he would be needing 6mm2 cable in copper (that would be under-volting the motor by 20% on start), a magnet for metal thieves That run of 2.5mm2 is probably dropping nearly 50% of the supply voltage when the pump starts, pretty amazing that it starts at all Once it's running you're looking at a 16% volt drop which is just about acceptable if the supply is 220V or a bit above, so if he's only doing one or two starts a day the pump will probably be fine.A solution would be to use 10mm2 aluminium cable, it's MUCH cheaper than copper and the thieves will only nick it once (or put a nice big sign on it). String it up on bamboo poles and the jobs good to go 1 Link to comment Share on other sites More sharing options...
timaloy Posted April 30, 2013 Share Posted April 30, 2013 6mm twin and earth will do job.......or double up on your 2.5mm. This will do......if any doubt triple your 2.5mm. Just make sure all cable lengths are the same Link to comment Share on other sites More sharing options...
briofoz Posted April 30, 2013 Author Share Posted April 30, 2013 Thanks all for the input. I like the idea of 6mm Al on poles. Harder to steal and not as attractive to steal. Link to comment Share on other sites More sharing options...
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