• • • CABLING & CABLE MANAGEMENT • • •
Cable management corrosion – a material choice
Paul Nolan, projects director for the Hudson Group, says nothing will eat into the total life cycle cost of a cable management system quite like corrosion. Get the material specification wrong – and you will be paying for your mistake before you know it
You’ll probably only notice cable containment systems when they are rusty and look like they are about to fall apart – not something that as an engineer you want to be associated with. Equally though you don’t want to fall into the trap of over specifying a system that will deplete your capex budget. And there are lots of materials and finishes to choose from, so when would you specify pre-galvanised, powder coated, stainless steel or GRP, to name just a few of the options available to you?
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Clearly the first thing that you need to do is understand what sort of environment the system will face. There is a world of difference between an office block and a coastal marina. Fortunately, there is some guidance that we can refer to EN ISO 12944-2 which classifies corrosion and gives examples of where you may find it – see attached diagram.
f you want to specify a cable management system that you can fit and forget, then you need to guard against the ravages of corrosion.
Getting the material right Let’s go through the table above and look at what materials would suit each environment. If you are facing a very low corrosive environment, such as an office, school or shop, then specifying electro zinc plated or pre- galvanised steel systems is fine.
In a C2 environment, where there is a low to moderate corrosivity, such as industrial premises, sports halls or perhaps partially covered outdoor areas, you should think about a pre-galvanised steel cable management system as a minimum specification. For outdoor or light industrial areas with moderate corrosivity, or C3 in the table above, then you need to go beyond a pre-galvanised solution. Here you need to consider hot dip galvanised, CPC or powder coated steel or PVC systems.
When you are faced with seriously corrosive applications with a high humidity or significant pollution, such as in chemical plants, dockyards or
ATMOSPHERIC CORROSIVITY CATEGORIES ACCORDING TO EN ISO 12944-2 WITH INDOOR AND OUTDOOR EXAMPLES OF TYPICAL ENVIRONMENTS
C1 VERY LOW EXAMPLE INDOOR:
Heated areas with dry air and minor amounts of impurities e.g. OFFICES / SCHOOLS / SHOPS / HOTELS
EXAMPLE OUTDOOR: N/A C4 HIGH EXAMPLE INDOOR:
Areas with high air humidity and high atmospheric pollution from production processes e.g. CHEMICAL PLANTS / SWIMMING POOLS / SHIPYARDS
EXAMPLE OUTDOOR:
Environments with moderate salinity e.g. INDUSTRIAL & INLAND COASTAL AREAS
swimming pools, you will need hot dip galvanised, powder coated steel, stainless steel, PVC or GRP systems. This is a C4 environment.
Beyond this are two C5 classifications for when the going gets really tough. For C5I you will need deep galvanised steel, stainless steel either a 304L or 316L or GRP cable management systems. And finally for marine environments, where there is a high moisture salinity or salt which adds to the corrosion, then you will need to specify 316L stainless steel or a GRP system.
Different materials and treatments
C2 LOW
EXAMPLE INDOOR: Unheated areas with varying temperature & humidity levels. Low frequency of condensation and low level of atmospheric pollution e.g. SPORTS HALLS / WAREHOUSES
EXAMPLE OUTDOOR: Environments with low levels of atmospheric pollution e.g RURAL AREAS
C5-I
VERY HIGH (INDUSTRIAL)
EXAMPLE INDOOR: Areas with almost constant condensation and high levels of atmospheric pollution.
EXAMPLE OUTDOOR: Industrial areas with high air humidity and aggressive atmospheres e.g. TUNNELS / DOCKYARDS
But that brief outline does not tell the whole story. Starting with galvanised products, not all are the same. Pre-galvanised steel will typically have a coating of between 8-20 microns while hot dip galvanised will give a standard coating of between 45 – 65 microns, but this is an average and the product will not be coated equally. For greater protection manufacturers can provide deep galvanised solutions where different carbon steels attract more zinc when dipped to provide an even thicker coating of greater than 160 microns. But if you hear the term “double dipping” then take no notice because someone is trying to fool you. Dipping steel a second time will make no difference to the thickness of the coating. Often corrosion is not the only factor that you need to consider when specifying a material for your cable containment system. If you are dealing with a project where there are lots of electronics, perhaps a data centre, then you need to be aware of zinc whiskers. These are very thin strands that form on the underside of galvanised products. Over time they will grow and break off. And because they are small, air filters and fans won’t always catch them before they enter the inner workings of devices. When they pass through electronics or IT loads, they can cause anything from intermittent short circuits to longer outages and equipment failure.
So galvanised products are not always the best C3 MODERATE EXAMPLE INDOOR:
Areas with moderate air humidity and some atmospheric pollution from production processes e.g. BREWERIES / DAIRIES / LAUNDRIES
EXAMPLE OUTDOOR:
Environments with low salinity or moderate atmospheric pollution e.g. URBAN AREAS / LIGHT INDUSTRIAL / SOME COASTAL INFLUENCE
C5-M
VERY HIGH (MARITIME)
EXAMPLE INDOOR: Areas with almost constant condensation and high levels of atmospheric pollution e.g. PURIFYING PLANTS
EXAMPLE OUTDOOR: salinity e.g. OIL RIGS
answer, even if corrosivity is low, and you may need to specify a different material or a non- zinc-based coating.
Stainless Options
And just like galvanised products are not all the same, stainless-steel alloys are different and have different properties and this can affect what you specify. Two common alloys that manufacturers use are 304L and 316L. The L shows that both are low carbon versions of their alloys which makes them more weldable.
12 ELECTRICAL ENGINEERING • SEPTEMBER 2023
electricalengineeringmagazine.co.uk
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