Cable protection conduit — classification code per IEC 61386

The [guide on cable type designations (VOB, YMvK, XVB)](/guides/cable/kabeltype-aanduiding-vob-ymvk-xvb) covers how a cable itself is marked. This article covers the tube such a cable is often pulled through: the conduit or cable protection tube, for which IEC 61386 ("Conduit systems for cable management") defines a set of performance properties and a corresponding classification code printed on the conduit material or its packaging.

Why a digit code instead of just a material name

"PVC conduit" or "steel conduit" by itself says little about actual mechanical and thermal suitability for a specific application — a thin-walled, flexible PVC tube and a heavy, impact-resistant rigid PVC system tube can both be called "PVC" while delivering entirely different performance. IEC 61386 addresses this with a standardised classification code: a fixed sequence of digits (and sometimes letters) each representing a specific, tested property, so the code alone provides enough information to judge whether a conduit is suitable for the intended application.

Structure of the classification code

The IEC 61386 classification code assigns, among other things, the following characteristics, each on an ascending scale:

Compression resistance: from very light (1) to very heavy (4/5), indicating how much static pressure the conduit wall withstands without permanent deformation.
Impact resistance: also on an ascending scale, indicating how much mechanical impact the conduit withstands without cracking or unacceptable deformation — relevant when embedded in a floor slab or in a location exposed to construction traffic.
Minimum and maximum service temperature: the temperature limits within which the conduit retains its mechanical properties, including a separate assessment of low-temperature flexibility for flexible conduit systems.
Electrical continuity: whether the conduit (in a metallic or metal-reinforced version) is suitable for use as an earthing or bonding conductor, or only provides mechanical protection without an electrical continuity function.
Resistance to bending: for flexible and bendable conduit systems, how well the conduit maintains a bend radius without kinking or obstructing the passage of the conductors.

Note: a conduit not classified as electrically continuous must not be used as a substitute for a separate protective conductor, even if the conduit is metallic. Metal conduit without an explicit continuity classification is intended purely for mechanical protection of the cable; the earth connection must then run through a separate conductor.

Practical application of the code

When selecting a conduit for a specific application — for example a tube embedded in concrete, a surface-mounted tube in a facility with forklift traffic, or a flexible tube to a moving machine part — every digit of the classification code must be checked individually against the requirements of that application. A conduit that comfortably meets one characteristic (say, compression resistance) but just misses another (say, minimum temperature for a winter outdoor installation) is still unsuitable for that application.

Practical relevance

When assessing or specifying a cable protection system, it is important not to rely on the material designation alone ("PVC", "steel", "flexible"), but to check the conduit's full classification code against the actual mechanical, thermal and, where applicable, electrical requirements of the installation location.

Common mistakes

Using a metal conduit as the sole earth connection without verifying that the conduit is explicitly classified for electrical continuity.
Relying only on the material name ("PVC" or "steel") instead of checking the full classification code against the application.
Using a conduit with too low a compression or impact class in a location with construction traffic or mechanical loading, resulting in damage to the conduit and the cable inside it.
Ignoring the minimum service temperature of a flexible conduit in an outdoor installation, causing the conduit to become brittle in frost and potentially crack during installation or maintenance.