To protect the wires and cables in your electrical installation, it is essential to place them in a protective electrical sheath that will keep them safe from the elements and prevent any physical contact, thereby limiting the risk of electrocution. But how do you choose between all the different types of electrical conduit on the market?
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What are the different types of duct?
The type of sheath you choose will depend mainly on your installation. And yes, you can’t put a duct designed for outside inside a house, for example. Because according to the NF C 15-100 standard, your inner sheath must be fireproof, i.e. designed to improve fire resistance, which is not the case for all sheaths. For a clearer picture, let’s take a look at all the different types of duct and their applications.
There are 2 main types of protective sheath: flexible and rigid:
Flexible sheath
ICTA (Insolant Cintrable Transversalement élastique Annelé) and ICTL electrical conduit
This is the most popular and frequently used flexible corrugated sheath. Particularly suitable for indoor use thanks to its fire-retardant properties. It is highly resistant to knocks and crushing and is perfectly waterproof to IP44. You can use it flush-mounted, surface-mounted or embedded in concrete. Mostly grey, it also comes in blue and black. You’ll find it in sizes 16, 20, 25, 32, 40, 50 or 63 mm.
It is also available in a smooth ICTL version (Insolant Cintrable Transversalement élastique Lisse).
ICA (Insolant Cintrable Annelé) and ICL (Insolant Cintrable Lisse) ducts
The main difference with ICTA sheathing is that it is less resistant and is not transversely elastic.
It is also available in a smooth ICL (Insolant Cintrable Lisse) version.
GAINE TPC (Cable Protection Tube)
Ideal for underground cable ducts, this electrical sheath is designed for outdoor use. It’s not flammable, so you can’t use it in your home’s electrical installation under standard NF C 15-100. You’ll find it on the market in diameters ranging from 40 to 160 mm and in coil sizes of 25, 50 or 100 m.
GASINE CSA (Corrugated Flexible Composite) AND CTL (Smooth Flexible Composite)
This is a steel protective sheath used in industrial installations with movable walls or where there are many connection bends. It is flame-resistant and waterproof.
In its smooth CTL configuration, it also has an insulating outer layer.
Semi-rigid sheath
GAINE IRL (Isolant Rigide Lisse)
Formerly known as IRO (Insolant Rigide Ordinaire), this semi-rigid PVC pipe can be used for exposed installations. Particularly used in uninhabited rooms where the networks are exposed, such as garages. It can be installed with or without fittings. It saves considerable installation time. IRL tubes are available in lengths of 2 to 3 m.
GAINE MRL (Smooth Rigid Metallic)
The MRL steel tube is made of electro-galvanised or stainless steel and offers a high level of protection for electrical wires and cables. Welded It provides high resistance to ageing and corrosion. This type of flue is compulsory for safety reasons on electrical installations in premises where there is a risk of fire or explosion.
What are the different categories of electrical conduit?
Bare sheath or with thread puller
You can find bare sheaths or sheaths fitted with a wire puller. Often made of steel, it is used, as its name suggests, to pull wires or cables through the sheath. Often a tedious and dreaded operation during cabling, sheathing is not the easiest task to carry out. When you have to pass cables through a sheath over several dozen metres, it’s best to use tools such as a nylon electrician’s needle and lubricating sheath gel.
If you are a professional and want to optimise your sheathing time, we recommend that you take a look at our range of automatic pre-wiring machines, which will save you a considerable amount of time on your sites. If you want to see for yourself how effective it is, why not come and see it in our showroom?
The split sheath
The split sheath is a ringed sheath split in the longitudinal direction. Of course, this configuration will remove any insulation effect from the cables. But its main advantage is that it is quick and easy to install with the fibre grommet. This type of sheath is mainly used to run telecommunications cables.
The pre-wired sheath
This is a sheath with the cables already inserted inside at the time of purchase. More expensive than bare sheathing, it essentially saves time when installing the sheathing. In general, you will find pre-equipped ducts with between 2 and 5 predefined conductors. However, this type of duct has its limits and if you are looking for more customised configurations, you need to switch to a bare duct.
What diameter electrical conduit should you choose for your electrical work?
When it comes to the diameter of the sheath and the number of cables or wires to be passed through it, you can’t do just anything. Although standard NF C 15-100 imposes no restrictions on the number of wires or the space they must occupy in the sheath, it is preferable to respect the “one-third rule”.
In accordance with good practice, electrical cables should occupy no more than ⅓ of the cross-sectional area of the sheath. The reason is simple: the more cables you have, the more difficult it will be to pass them through the sheath. Choosing to respect this rule also allows you to reserve space for any additional cables that may arrive in the future. Be careful not to mix strong and weak currents in the same sheath.
Now that we know the rule of thirds, how do we know how many cables we can pass through the sheath? We simply determine the total surface area in mm² of the cables and subtract it from the surface area in mm² of the sheath. The sum obtained must therefore not exceed ⅓ of the surface area of the liner.
Yes, but how do you know the surface area of the wires and sheaths? There are 2 ways of doing this: either you can calculate it yourself using the formula n x s = ⅓ S, or you can refer to the tables below.
n = number of cables
s = cable cross-section
S = duct cross-section
1.5mm² electrical wire: total surface area with insulation = 8.55mm².
2.5mm² electrical wire: total surface area with insulation = 11.9mm².
6mm² electrical wire: total surface area with insulation = 22.9mm².
10mm² electrical wire: total surface area with insulation = 36.3mm².
16mm² electrical wire: total surface area with insulation = 50.3mm².
20mm² electrical wire: total surface area with insulation = 75.4mm².
