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Capillary Action in Cables.

Has anyone any real life examples of this causing problems please?

https://www.lec-expert.com/topics/waterproof-led-lights--preventing-capillary-action-in-power-supply-cables


Z.
  • its not new - its how the green rot spreads along wiring in cars.  However, only short lengths breathe significantly, and solid core cables not at all. If you really cannot manage it, then gel filled cable is the answer
  • and the plasticiser in the old PVC cables that ends up in the accessory boxes.


    Balls of filler valves in hot water cylinder header tanks filling up with water due to a pin hole below the water line, there's another thing.


    Andy B.

  • mapj1:

    its not new - its how the green rot spreads along wiring in cars.  However, only short lengths breathe significantly, and solid core cables not at all. If you really cannot manage it, then gel filled cable is the answer




    Yes Mike I understand that the problem is not a new one. But I was wondering about real life examples. I had an old Series 3 Land Rover years ago and its underfloor wires got wet and the copper strands turned black inside the insulation. The copper strands became externally non conductive and could not be mechanically cleaned or soldered. I had to renew them. Perhaps road salt didn't help.


    Z.

  • Former Community Member
    0 Former Community Member
    I don't consider the "symptoms" described here are capillary in a strict definition. It is more of a pumping action.


    Regards


    BOD

  • perspicacious:

    I don't consider the "symptoms" described here are capillary in a strict definition. It is more of a pumping action.


    Regards


    BOD




    I suppose that the pumping action with a higher air pressure at one point moving water along a fine tube or route inside a cable involves both pumping and capillary action to some extent. And a lower air pressure at some point compared to another sucks water along. The capillary refers to a "tube" with a hair like thinness of diameter, like fine copper wires contained in a P.V.C. insulation. Capillary, the origin is from the Latin capillus meaning  hair.


    Z.


  • perspicacious:

    I don't consider the "symptoms" described here are capillary in a strict definition. It is more of a pumping action.


    Regards


    BOD




     

    To “pump” one end of the cable has to be in a sealed enclosure with a volume of air that goes through cycles of heating and cooling.


    Take a ball float valve in a hot water cylinder header tank which has a pin hole in the ball float below the water line, as the cylinder heats the hot water expands into to header tank which heats up the ball and the air in it, the air expands and comes out through the pinhole below the waterline, then as it all cools down water is drawn back into the ball and eventually it sinks.


    Now consider an IP rated enclosure, is it better sealed or with a drain hole in the bottom of it?


    Andy Betteridge

  • Now consider an IP rated enclosure, is it better sealed or with a drain hole in the bottom of it?



    Depends on the IP rating you're trying to achieve. If you need to protect from jets of water from any direction (including vertically upwards) then perhaps a hole in the base isn't the best approach...

       - Andy.
  • A drain hole will equalise the pressure inside and outside of the enclosure, so moisture won’t be “pumped” through the cables.


    But it might let the spiders into the enclosure.


     Andy B.
  • Truly hermetically sealed is almost impossible to do in the field. Unless immersion is expected,  when filling with resin or gel are the better options, for things like joint boxes a vented approach is often best, maybe with a swizzle of rock wool insulation in the hole to act as a deterrent to small creatures. Care is needed about the direction of the vent hole.Down into a sheltered place is best. That said,  even quite simple things like a peaked hat overhang on the support for the enclosure for both a rainshield and sun shade can make a very large improvement in how wet things get, or rather do not.

  • Sparkingchip:

    A drain hole will equalise the pressure inside and outside of the enclosure, so moisture won’t be “pumped” through the cables.

     




    I am a great believer in small drain holes at the bottom of outside equipment like lights, sockets, switches, P.I.R. sensors or adaptable boxes. Also I try to ensure that all cables only enter at the bottom of enclosures. The holes that I drill are very small, usually less than 1.0mm in diameter. But we must be aware that if the hole is too small it may become blocked by dirt, dust or dead insect bodies. Some outdoor weatherproof accessories have the provision for drainage of water by a drain hole in their boxes and the position is marked inside boxes and have to be drilled out. I also like to provide drainage holes at the lowest points in external conduit at boxes and accessories. This prevent the build up of condensation and aids drainage. 


    Z.