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2014-09-25

Defining Weatherproof - what do you need to consider?

How exactly do you define ‘weatherproof’ protection or ‘suitable for outdoor use’?  When it comes to cable protection it is time to be more specific argues Ian Gibson, Technical Director for Flexicon Ltd.

The claim that a product is suitable for outdoor use or provides protection from the weather is a term that is laden with potential pitfalls for the unwary specifier of equipment.

Quite simply there are so many different factors at work that you need to tread with care, not least because the weather varies dramatically from country to country and there are so many different factors to consider.

As a flexible conduit manufacturer it is an important question that we face daily, since cable protection is often required outdoors for any application requiring power and data.  It may include applications as diverse as CCTV cameras, solar panels and boats.  As a manufacturer, we sell into 55 countries and our flexible conduit systems are used in far more, in climates as diverse as the desert, the artic, the Himalayas and under the ocean.

And it is important to get the specification right because a material’s properties will change as it conditions to the weather around it.

The only sensible approach is for the specifier to make a full risk analysis to identify what hazards the cabling may need protecting from.

When thinking about the term weatherproof most people would probably start by considering the IP rating.

Starting with dust ingress, as far as conduit systems are concerned you should set a minimum level of IP5x where dust will not enter the system in harmful quantities and better still 6x which means that dust will not enter at all.

Protection against water ingress is more complicated.  Potentially ingress could come from rain, spray, possible immersion plus capillary action and suction caused by the rise and fall of temperature.  Using a vented conduit system, which allows the air inside the enclosure to expand and contract with temperature changes, can prevent the latter action.

You should also treat the IP rating system with caution, because the tests are over the short term on samples that the manufacturer has assembled under ideal conditions.   In practice the flexible conduit may be exposed to a constantly changing environment over several years.

With the latter point in mind BS EN IEC 60529 states that above IPx6 you cannot assume that the product will meet a lower level.  This is because when you look at each of the tests you will see that each is a different type of test and subjected to different conditions and environments.

I would recommend that the specifier takes a belt and braces approach to prevent water ingress over the lifetime of the installation.  You should specify a minimum level of IPx6 plus IPx7 if you do not know the orientation of the conduit fittings.  If, however, the installer assembles the fittings on the underside of an enclosure then you may find that IPx5 or IPx6 is suitable.

You should also check what material the conduit is manufactured from, since nylon conduit and fittings will attract and absorb water.  When it is wet a nylon conduit system will become more flexible with better impact strength and fatigue life but lower compression strength.  In dry conditions the opposite will happen.

Corrosion resistance

Corrosion is another issue that needs considering in relation to water.  Coated steel conduits will be suitable as long as the IP rating is sufficient to prevent water ingress.  Grade 316 stainless steel fittings are probably best used since nickel-plated brass fittings will discolour through oxidation overtime, particularly in coastal areas due to salt spray.

UV degradation

Another variable factor depending on location, climate and altitude is the affect of UV radiation.

UV rays from the sun will degrade plastic materials by breaking down the long polymer chains.  This will result in lower impact strength, less flexibility and a lower fatigue life. 

To resist the effects of the sun, check that product has carbon black added, which protects the polymer chains.   As an indication, where Flexicon describes a product as “UV resistant” there is enough carbon black added to ensure UV resistance around the world. 

I believe that you should check what a manufacturer means by UV resistant and ask whether there is any independent test results that can be used to verify the claim.  Flexicon has tested numerous products to UL1660 test criteria for weather resistance.

There are ways of making other colours UV resistant, such as by adding a chemical UV resistant additive, but this tends to be more expensive than using carbon black.

Temperature

Generally it is low temperature that may cause an issue and you should check that the conduit has a low enough minimum operating temperature to prevent damage by impact or bending during installation or use.

Other factors

There are of course a number of other factors that you should consider in relation to the outdoor environment.  These may well vary according to the application.

For wind turbine applications, for example, one of Flexicon’s conduit systems has been tested to withstand the effect of a direct lightning strike.

You may also need to protect the system against vandalism and/or attack by animals.  We have even had to produce Cockatoo proof conduit for an application in Australia.

The problem with the term weatherproof is how you define it.  Climates change in different locations and even from season to season.  It is a lazy term that should probably not be used; rather the specifier should define what hazards the conduit will face.

 


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