How to choose electrical conduit?

What are the different types of electrical conduit?

The choice of electrical conduit (or protective duct) depends mainly on the environment in which it will be installed. For example, the NF C 15-100 standard prohibits the use of certain indoor conduit types outdoors or underground. To make things clearer, let’s look at the different types of conduit and their specific applications.

There are two main types of protective conduit: flexible and rigid:

Flexible conduit

ICTA electrical conduit (flexible corrugated insulating conduit) and ICTL

This is the most popular and most commonly used flexible corrugated conduit. It is particularly suitable for indoor environments thanks to its flame-retardant properties. It offers very good resistance to impact and crushing and provides IP44 protection. It can be installed concealed, surface-mounted or embedded in concrete. It is most commonly grey, but is also available in blue and black. Typical diameters are 16, 20, 25, 32, 40, 50 and 63 mm.

It is also available in a smooth ICTL version.

ICA conduit and ICL conduit

The main difference compared with ICTA conduit is its lower resistance and the fact that it is not transversely elastic.

It is also available in a smooth ICL version.

TPC CONDUIT (Cable Protection Tube)

Ideal for buried cable runs, this electrical conduit is intended for outdoor use. Although it is non-flammable, under the NF C 15-100 standard it cannot be used for the internal electrical installation of a home. It is available commercially in diameters from 40 to 160 mm and in coil lengths of 25, 50 or 100 m.

CSA CONDUIT (Flexible Corrugated Composite) AND CTL (Flexible Smooth Composite)

This is a steel protective conduit used in industrial installations with moving walls or numerous connection bends. It is flame-resistant and watertight.

In its smooth CTL configuration, it also includes an external insulating layer.

Semi-rigid conduit

IRL CONDUIT (Rigid Smooth Insulating Tube)

Formerly known as IRO, this semi-rigid PVC tube is used for surface-mounted installations. It is particularly suitable for non-living areas where services remain visible, such as garages. It can be installed with or without fittings and can save a significant amount of installation time. IRL tubes are typically available in lengths of 2 to 3 m.

MRL CONDUIT (Rigid Smooth Metal Tube)

MRL steel tube is made from electro-galvanised steel or stainless steel and provides a high level of protection for electrical wires and cables. Its welded construction provides strong resistance to ageing and corrosion. This type of conduit is mandatory for safety reasons in electrical installations located in premises presenting fire or explosion risks.

What are the different categories of electrical conduit?

Bare conduit or conduit with a pull wire

You can buy bare conduit or conduit fitted with a pull wire. Often made of steel, the pull wire is used, as its name suggests, to pull electrical wires or cables through the conduit. Pulling wires through conduit is often a tedious and dreaded part of wiring work and is not always easy. When cables must be pulled through several dozen metres of conduit, it is therefore preferable to use tools such as a nylon electrician’s fish tape and conduit lubricant gel.

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Split conduit

Split conduit is a corrugated protective duct that is split longitudinally. This configuration naturally removes the insulating effect around the cables. Its main advantage, however, is that it can be installed quickly and easily using a fibre pull-through tool. This type of conduit is mainly used for routing telecommunications cables.

Pre-wired conduit

This is conduit in which the cables have already been inserted before purchase. More expensive than bare conduit, its main advantage is the time saved during installation. Pre-equipped conduit generally contains between 2 and 5 predefined conductors. However, this type of conduit has its limits, and if you need more customised configurations, you will need to use bare conduit.

What electrical conduit diameter should you choose for your electrical work?

When it comes to conduit diameter and the number of cables or electrical wires to be routed through it, the choice should not be made at random. Even though the NF C 15-100 standard does not impose a restriction on the number of wires or on the space they must occupy inside the conduit, it is preferable to follow the “one-third rule”.

Good practice states that electrical cables should occupy no more than ⅓ of the conduit cross-section. The reason is simple: the more cables you have, the harder it will be to pull them through the conduit. Following this rule also leaves room for an additional cable that may need to be added in the future. One important precaution: never mix high-current and low-current circuits in the same conduit.

Now that we know the one-third rule, how do we determine how many cables can be routed through a conduit? Simply determine the total cross-sectional area of the cables in mm² and compare it with the internal cross-sectional area of the conduit. The total occupied area must not exceed ⅓ of the conduit’s internal area.

But how do you determine the cross-sectional area of the wires and conduit? There are two options: calculate it yourself using the formula n × s = ⅓ S, or refer to the tables below.

n = number of cables

s = cable cross-sectional area

S = conduit cross-sectional area

• 1.5 mm² electrical wire: total area including insulation = 8.55 mm²
• 2.5 mm² electrical wire: total area including insulation = 11.9 mm²
• 6 mm² electrical wire: total area including insulation = 22.9 mm²
• 10 mm² electrical wire: total area including insulation = 36.3 mm²
• 16 mm² electrical wire: total area including insulation = 50.3 mm²
• 20 mm² electrical wire: total area including insulation = 75.4 mm²