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

  • I doubt that the danger is significant for two reasons. Firstly the water is in a spray with air gaps between each drop, no worse than heavy rain in say a thunderstorm. Most people do not worry about walking under 11kv lines in a thunderstorm.

    Secondly, the equipment is widely used and serious accidents due to overhead lines are rare.

    Greater hazards are from the often improvised electrical supply to any electric water pump. Permanent pumps should be properly installed and portable water pumps are better engine driven rather than electric. The other risk is carrying around the rigid water pipes used in some systems, and these contacting overhead lines.

    If I was operating such equipment I would be careful, and in particular if the water spray was touching overhead lines, I would not touch or very closely approach any metal trailer upon which the equipment was mounted. Turn the water off remotely, THEN move or adjust the equipment, move clear and turn the water back on.

  • Some of those high pressure water jets can be very powerful and travel almost continuously up to the overhead H.V. lines.

    High pressure Water Spray on Field || Super Agriculture Technology in India - Bing video

    Z.

  • Reasonably clean fresh water isn't a particularly good conductor. We already know that a few cm of water in a plastic pipe usually has sufficient resistance to prevent an electric shock. An 11kV line is 11kV L-L so around 6.35kV L-earth -  so less than 30x 230V - so even if we had a continuous column of water between the nozzle and HV line, and taking into account the larger c.s.a. compared to a 15mm pipe, it seems plausible we'd still have a reasonable resistance in our favour.

        - Andy,

  • We get our brollies out.  What happens if the rain is conductive "acid" rain?

    Z.

  • We get our brollies out.  What happens if the rain is conductive "acid" rain?

    Z.

    It kills the moss and lichen on roofs and other surfaces, just like water does dripping off overhead electric cables.

  • There is not actually a continuous jet of water, the water spurts out in blobs so even if were an ideal electrical conductor, it would not be an issue.

  • And bore hole water?

    In terms of dissolved salts, I doubt it's much different to tap water - after all quite a few domestic supplies come from bore holes with little more than a bit of filtering and sterilization.

       - Andy.

  • 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