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Capillary Action in Cables.

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Capillary Action in Cables.

Posted by Zoomup on Jan 18, 2020 8:17 pm

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.

Re: Capillary Action in Cables.

Posted by mapj1 on Jan 18, 2020 11:19 pm

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
regards Mike

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 18, 2020 11:53 pm

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.

Re: Capillary Action in Cables.

Posted by Zoomup on Jan 19, 2020 10:00 am

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.

Re: Capillary Action in Cables.

Posted by perspicacious on Jan 19, 2020 10:37 am

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

Regards

BOD

Re: Capillary Action in Cables.

Posted by Zoomup on Jan 19, 2020 5:43 pm

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.

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 19, 2020 10:28 pm

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 

Re: Capillary Action in Cables.

Posted by AJJewsbury on Jan 19, 2020 10:33 pm

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.

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 19, 2020 11:20 pm

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.

Re: Capillary Action in Cables.

Posted by mapj1 on Jan 19, 2020 11:37 pm

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.
regards Mike

Re: Capillary Action in Cables.

Posted by Zoomup on Jan 20, 2020 10:20 am

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.

Re: Capillary Action in Cables.

Posted by AJJewsbury on Jan 20, 2020 10:35 am

1mm dia. seems a bit small to me - you'd likely get a pool of water inside the fitting as surface tension will almost certainly hold the water back against the small force of gravity - there being no water pressure behind it. I think the recommendation used to be for a drainage hole in conduits systems of at least 3mm - and I'm pretty sure MK recommend 5mm for their masterseal range.

  - Andy.

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 20, 2020 11:06 am

Make it too small and you will get capillary action or pumping.

Andy B.

Re: Capillary Action in Cables.

Posted by Alasdair Anderson on Jan 20, 2020 12:39 pm

Reminds me of the Suez Canal Authority requirements. All ships passing through the Suez Canal require an approved 'Suez Canal Searchlight'. Any ship not having one, or whose searchlight was deemed on inspection not to comply, had to hire a searchlight from the Authority. Among the requirements were two interesting ones:  "The enclosure must be gas-tight" and "The enclosure must be provided with a drain hole at the bottom".
Alasdair

Re: Capillary Action in Cables.

Posted by mapj1 on Jan 20, 2020 2:11 pm

Which makes sense when you consider that much Suez traffic is carrying either oil or more dangerously distillates  or natural gas. Although if the rules are well drafted then I;d expect to see that drain hole /vent in the form of a hose nipple, so that expanding and contracting air can be exchanged to a place outside the hazardous zones for any accumulations of explosive vapours.
regards Mike

Re: Capillary Action in Cables.

Posted by Alasdair Anderson on Jan 20, 2020 2:39 pm

Mike,
No need to worry about hazardous vapours as the mounting of the searchlight is right at the prow, forward of any hazardous areas, though to further solve the problem very few tankers (possibly none) are allowed passage through Suez. These two conflicting requirements were seen by us on the ships as a way of guaranteeing that they would be able to hire out the searchlights they had in store as there would always be at least one regulation that was not met.

Re: Capillary Action in Cables.

Posted by OMS on Jan 20, 2020 3:00 pm

I thought QuatarGas was shipping via Suez to West Wales ?

Regards

OMS
The trap we've fallen into is to believe that a thousand incompetents properly organized can do the job of a few dozen outstanding people

Re: Capillary Action in Cables.

Posted by Alasdair Anderson on Jan 20, 2020 3:08 pm

You are probably right. I have been thinking back, and in my day, which was ... well let's just say it wasn't yesterday, I have sort of dredged up a memory and I think it was that tankers were not allowed through the canal as part of the main convoy. Though in reality gas ships have a very good safety record, much better than oil tankers. The only near miss with a gas ship was one that lost power off the American east coast and drifted for several days, because the crew couldn't get the generators going again. Apparently they tried everything, including by-passing the HV Safety Interlocks......
[Further edit]
I should also have added that the majority of large oil tankers could not go through the canal while full of oil due to their draft. They could only go through when in ballast. Unless they have dredged the canal by a significant amount then this will likely still be the case.

Re: Capillary Action in Cables.

Posted by Zoomup on Jan 20, 2020 4:48 pm

AJJewsbury:
1mm dia. seems a bit small to me - you'd likely get a pool of water inside the fitting as surface tension will almost certainly hold the water back against the small force of gravity - there being no water pressure behind it. I think the recommendation used to be for a drainage hole in conduits systems of at least 3mm - and I'm pretty sure MK recommend 5mm for their masterseal range.

  - Andy.

 
I drill at least two per enclosure, one to let the water out, and the other to let air in. A 1.0mm dia. hole will allow water to drain through, but vapour is mostly catered for.  I use that small drill on things like P.I.R. sensors. It is better to use a 2 or 3mm dia. drill for sockets and switches outdoors I agree.

Z.

 

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 20, 2020 7:32 pm

5424ec6029f9736ed6c664bacb8cc04d-huge-20
bba66f224c1b4bd37401e9c3d095f639-huge-20
One from this afternoon.
Andy B. 
 

Re: Capillary Action in Cables.

Posted by perspicacious on Jan 20, 2020 7:43 pm

No fixing screws through the back of the box?

Regards

BOD

Re: Capillary Action in Cables.

Posted by Sparkingchip on Jan 20, 2020 7:50 pm

perspicacious:
No fixing screws through the back of the box?

Regards

BOD

 
That is the minor issue.

Andy B.



 

Re: Capillary Action in Cables.

Posted by Zoomup on Jan 21, 2020 7:42 am

Sparkingchip:
5424ec6029f9736ed6c664bacb8cc04d-huge-20
bba66f224c1b4bd37401e9c3d095f639-huge-20
One from this afternoon.
Andy B. 
 

It is always best to keep the connectors above the high tide mark. A small "V" cut into the box at the bottom allows water to drain out.

Z.

Re: Capillary Action in Cables.

Posted by gkenyon on Jan 21, 2020 10:00 am

The water here doesn't have to come through cables - initially sealed in when the enclosure lid is fitted, then you can get migration of moisture in air through the water seals. As the temperature drops, the water condenses, and repeat.

As Zoom says, a drain hole is required.

Often a problem even on metal IP55/IP65 outdoor enclosures - special "drain plugs" and ventilation "periscopes", "snail vents" and similar are made to help prevent this.

In this particular case, looks very close to the ground, so to prevent condensation completely is rather difficult.
Graham Kenyon, Managing Director, G Kenyon Technology Ltd www.gkenyontech.com G Kenyon Technology Ltd Logo © G Kenyon Technology Ltd 2015-2019

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