Fire-protective coating on cable trays and ladders — intumescent cable protection systems

The guides on [fire-resistant cable penetration seals](/guides/cable/brandwerende-kabeldoorvoeringen) and function-retention cable and circuit integrity in fire cover two well-known measures for safeguarding the fire safety of a cable route: restoring the fire resistance of a building compartment boundary where a cable passes through it, and using a cable that intrinsically retains its function during fire. This article covers a third, less well-known measure: an intumescent cable protection system, in which an expanding coating or wrap is applied directly to the cable tray, ladder, or cable bundle itself.

What an intumescent coating does

At ambient temperature, an intumescent coating is a thin, relatively inert layer. When exposed to the high temperature of a fire, the coating reacts chemically and expands significantly into a porous, carbon-rich foam layer with a much greater volume than the original coating thickness. This expanded layer acts as thermal insulation: it slows heat transfer to the underlying cables, thereby extending the time until the cable insulation itself fails and short-circuiting or loss of function occurs.

Two application forms

An intumescent cable protection system is typically applied in one of two ways:

Coating, applied as a paint or render layer directly to the outside of a cable bundle or to the cable tray itself (including the lid, if this forms part of the tested system).
Wrap or tape, applied as a spirally wound band around a cable or cable bundle, particularly suited to individual cables or smaller bundles where a coating is less practical.

Why the system must be tested as a whole

As with a penetration seal system (see the guide on fire-resistant cable penetration seals), the fire-resistance classification of an intumescent cable protection system under EN 13501-2 is only valid for the exact combination tested as a whole: the specific coating or wrap product, the layer thickness, the cable types and diameters, the bundle density, and the method of fixing to the cable tray or ladder. A coating tested on a loosely laid cable bundle does not offer a guaranteed performance on a densely packed bundle of a different cable type, and vice versa. The manufacturer's certificate and accompanying installation instructions therefore define the exact limits within which the system may be applied.

Relationship to penetration seals and function-retention cable

An intumescent cable protection system is not a substitute for a penetration seal where a cable tray passes through a fire compartmentation boundary — that seal remains necessary to restore the fire resistance of the building boundary itself. The intumescent system is typically applied along a longer run of the cable tray or ladder itself, for example through an escape-route space or along a route where multiple circuits converge, to prevent the cables from failing along the way (not only at the location of a penetration seal). Compared with function-retention cable (which intrinsically, without external protection, retains its function), an intumescent coating offers an alternative when replacing existing, already installed standard cable with function-retention cable is not practical or cost-effective — for example in a retrofit project in an existing building.

Practical relevance

When assessing a cable route that runs through an escape-route space, or that must retain a vital function during fire (for example a supply to emergency lighting, a fire detection system, or a smoke extraction system), it should be checked whether the chosen intumescent cable protection system is certified for exactly the cable type, cable diameter, bundle density, and tray dimensions applied. For a retrofit application, it must also be verified that the existing cable occupancy has not been increased after the coating was applied, since this could exceed the tested bundle density — and therefore the validated fire-resistance duration.

Common mistakes

Treating an intumescent coating as a substitute for a penetration seal at a fire compartmentation boundary, rather than as additional protection of the route itself.
Applying the coating to a cable bundle with a different composition, density, or cable type than the one the system was tested with, without verifying that this falls within the certification limits.
Adding extra cables to an already coated cable tray without assessing whether the new bundle density still corresponds to the tested system.
Assessing only the coating on the cables themselves without checking whether the lid and fixing method of the cable tray also formed part of the tested system, where these components were included in the classification.