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11kV Overheads and Water Spray.

You a are farmer. You have potato fields that need watering due to the lack of rain and the hot weather. You tow your water sprayer trailer out to the potato field and connect up the pipes. The water can be mains or deep bore hole sourced. The spray is very high pressure and reaches a great height. In fact it reached the 11kV overhead cables that run across your field.

Is there any danger?

Here is a static system, but yours is mobile on a tyred trailer. It does though show the height of the sprays.

Large Lawn Field Irrigation System - Bing video

Parents
  • I agree with much of the above. here is the reply I had written to the post that then disappeared on Thursday It duplicates some of what others have said but hangs some nos on it.

     

    Some risk, but probably not as sure fire electrocution as the films would like to depict . As we know from how long a length of plastic water pipe needs to be to limit a mains shock to less than 30mA , the resistance of tap water is of order 1 to 10k ohms per cm cube, depending on purity. Rain water is higher resistance, up to 100k and water from springs and wells is similar to tap, by the time you get much below 1k per cm cube, the water will taste distinctly odd.

    In the jet, even if unbroken, and that is not likely, the current path will be a few tens of sq cm in cross-section at most  and several metres if not tens of metres long. 

    The resistance of a really badly placed jet, giving solid tube of tap water say 100cm2 and 10m (1000 cm) long would be  10k to 100k  ohms,  and the 11kV line is 6kV to  ground, and in the UK protected by an earth fault relay, so some hundreds of mA potentially (10k ohms, 6kV,  600mA !!  but with purer water more like 60mA).  That 6KV is shared between the series resistances of the water column and all the parallel paths that conspire to connect the trailer to earth.   If the trailer is well insulated from ground, then you could get a potentially lethal shock from it, but it probably isn't. Far more risky is when the human is the sole path to earth - this gets  folk carrying fishing rods and  other long poles, and the odd  driver who loses concentration with a tipper truck or digger. Dry rubber  tyres can be  a very good insulator so if the person bridges between the vehicle and ground it ends badly.

    Mike

Reply
  • I agree with much of the above. here is the reply I had written to the post that then disappeared on Thursday It duplicates some of what others have said but hangs some nos on it.

     

    Some risk, but probably not as sure fire electrocution as the films would like to depict . As we know from how long a length of plastic water pipe needs to be to limit a mains shock to less than 30mA , the resistance of tap water is of order 1 to 10k ohms per cm cube, depending on purity. Rain water is higher resistance, up to 100k and water from springs and wells is similar to tap, by the time you get much below 1k per cm cube, the water will taste distinctly odd.

    In the jet, even if unbroken, and that is not likely, the current path will be a few tens of sq cm in cross-section at most  and several metres if not tens of metres long. 

    The resistance of a really badly placed jet, giving solid tube of tap water say 100cm2 and 10m (1000 cm) long would be  10k to 100k  ohms,  and the 11kV line is 6kV to  ground, and in the UK protected by an earth fault relay, so some hundreds of mA potentially (10k ohms, 6kV,  600mA !!  but with purer water more like 60mA).  That 6KV is shared between the series resistances of the water column and all the parallel paths that conspire to connect the trailer to earth.   If the trailer is well insulated from ground, then you could get a potentially lethal shock from it, but it probably isn't. Far more risky is when the human is the sole path to earth - this gets  folk carrying fishing rods and  other long poles, and the odd  driver who loses concentration with a tipper truck or digger. Dry rubber  tyres can be  a very good insulator so if the person bridges between the vehicle and ground it ends badly.

    Mike

Children
  • Thanks Mike. The steel framed sprayer trailer will have dirty muddy tyres and they will be located on wet mud in the field.

  • And the tractor tyres may be filled with water as ballast!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  • So?

  • so the area of contact of the bottom of the tyre with the ground may well be much larger than anticipated. Or much less if it has been overfilled and has no air in it at all, water being almost in-compressible, but 1000 times denser than air, as in round numbers the molecules in water are ten times closer together.

     I have a colleague at work who narrowly avoided injury when removing  a wheel that turned out to be mostly water filled.

    Mike