Firestopping electrical conduits

An electrical conduit is a metal or plastic pipe through which electrical wires run.

Conduits are usually laid and hidden within walls or floors to secure easier connections to outlet boxes. Electricians also use conduits for surface mounted cableways. This makes sense for projects where later re-cabling is required, and it helps avoid the need for heavy chiseling work. Conduits can go through fire-rated walls and floors, meaning they should be treated as penetrants and therefore fire resistant with a tested and approved firestop systems. Helping to avoid the passage of fire and smoke from one compartment to another.

Reasons for using conduits

There are many advantages of conduits. Typically, they are installed either embedded in concrete, laid into a space after chiseling, or are surface-mounted on the wall or floor, in concrete (flush-mounted) or after chiseling space in a wall. Wires or cables can then be routed through the conduit so that they connect one electrical box to the next. The installation and arrangement of conduits is regulated in national building codes (or just general “building codes”). Conduits are used for the orderly installation of communication, networking, telecom or other smaller cables. When installed on the outer surface of walls and floors, conduits help to protect cables against mechanical forces or damage.
 
Conduits are available not only in plastic, but also in steel, stainless steel (for better fire protection purposes) or aluminum. Typical diameters range between 13-35 mm but they can go up to 63 mm. Normally conduit is circular in cross-section.

Insights into conduits acc. to test standard EN1366-3

When used for wall or floor assembly, conduits create a space between the penetrant and the surrounding structure which can potentially support the spread of fire between rooms or floors. Plastic conduits burn and melt, whereas metal conduits transfer heat, deflect, and melt. Conduits can also allow smoke transfer within the conduit itself. Building codes Therefore a firestop system for the penetration is required. In addition, authorities require conduit openings to be sealed in almost any penetration.

The test standard EN1366-3 provides rules for the fire testing of through penetrations also containing conduits, along with guidelines of configurations and related field-of-direct-application rules.

Different categories of conduits exist and are clearly described in the EN1366-3 test standard. Below is a general summary with some explanations:

 
1.    Continued conduit: a conduit that passes through the compartments adjacent to the separating element without any interruption or opening.
2.    Flush conduit: a conduit that is positioned within the building element, ends flush with the wall/floor surface and includes a seal inside the conduit itself.
3.    Projecting conduit: a conduit that projects on both sides of the building element for a particular length and includes an interior seal at both ends.
4.    Conduit bundle: bundle consisting of a number of parallel conduits.
5.    Metal conduit: a conduit of class A1 in accordance with EN 13501-1, which has a melting or decomposition point higher than the nominal furnace temperature at the intended classification time. Examples: conduits made of galvanized steel, stove enamel coated steel, stainless steel or aluminum.
6.    Plastic conduits: those not classified to A1 or A2 in accordance with EN 13501-1 and which are made of thermoplastic or thermosetting material.
7.    Solid, pliable and flexible conduits. In the case of flexible/pliable conduits, these have different so-called “wave heights” (the distance between the outer and inner surface of the conduit’s wall, including inner or outer layers.
 
For pliable and flexible conduits, the dimension wall thickness is not applicable as the wall is corrugated. The dimension relevant for selection of pliable and flexible conduits to be tested is the ‘wave height’ instead of the wall thickness (see fig 1).
 
 

Fig 1: pliable conduit and the definition of the so-called “wave height” (source: EN1366-3)
 
 

The EN1366-3 test standard also describes the situation of infill cables. Conduits are tested with infill cables to simulate the additional heat transfer caused by the cables. Different scenarios are given for manufacturers, to simulate worst-case situations in a fire test.  The field of application rules in the test standard allows the use of defined cable types, with the exception of non-sheathed cables (wires). This is because according to some national electro-technical rules, non-sheathed cables are not permitted in conduits except within a wall/floor installation.

For pliable and flexible conduits the same rules of testing apply. The only major difference is that pliable conduits suffer plastic deformation on bending, whereas flexible conduits return to their original straight form after the release of the bending force. Additionally, EN1366-3 describes different cases of end configurations. Different end configurations determine how conduit openings should be sealed and tested.

As an example, continued conduits cannot be treated as analogous to pipes regarding their end configuration. This is because they always have two open ends somewhere within the building, e.g. in a switchbox (see fig 2), whereas open pipe systems always have one or both ends outside the building (e.g. sewage pipes with a ventilation outlet above the roof).

For the case with a seal inside the conduit a Firestop Acrylic or Silicone Sealant (for example Hilti CFS-S ACR or CFS-S SIL Firestop Acrylic or Silicone Sealant) can be taken.

Fig 2: example of conduit configuration within a building (source: EN1366-3)
  

The majority of conduits run through mixed openings in which minimum distances also have to be considered (see fig. 3), as described in the different European Technical Assessments of firestop products tested for electrical applications.

 
Fig 3: different minimum distances in a mixed cable opening, including a conduit on a cable tray (5) (source: EN1366-3)
 

Solutions and approvals of firestop systems for conduit applications

As a manufacturer, Hilti strives for a broad approval range for its products. The testing of firestop products and systems for conduit applications is always part of Hilti fire tests. Many European Technical Assessments (ETAs) with Hilti solutions therefore offer a dedicated field of application for conduits.

Products with an ETA include those for use with conduits in flexible and rigid concrete walls, as well as rigid floors. These include the following solutions, listed with excerpts of the respective ETAs.


Hilti Firestop Flexible Foam CFS-F FX:
Small plastic and steel conduits diameter ø <=16mm with or without cables; plastic, flexible plastic and rigid plastic (Polyolefin and PVC) with diameter up to 32mm with fire resistance ratings in accordance with EN 13501-1 of up to EI120 U/U.

Hilti Firestop Sleeve CFS-SL GA:
Rigid, flexible and pliable plastic conduits and metal conduits with a diameter Ø ≤ 25mm with or without cables. Rigid, flexible and pliable plastic conduits and metal conduits with a
diameter Ø ≤ 63mm with or without cables. Conduits with a max. single conduit diameter Ø ≤ 25mm with or without cables can be bundled to a diameter Ø ≤ 48mm. Conduits with a max. single conduit diameter Ø ≤ 63mm with or without cables can be bundled to a diameter Ø ≤ 92mm, with fire resistance ratings in accordance with EN 13501-1 of up to EI120 U/U.

Hilti Firestop Cable Collar CFS-CC:
Small plastic and steel conduits up to diameter ø 16mm, and many specific other plastic flexible and rigid conduits (Polyolefin and PVC) with diameter up to 32mm, fire resistance ratings in accordance with EN 13501-1 of up to EI120 U/U.

Hilti Firestop Block CFS-BL:
Small plastic and steel conduits diameter ø <=16mm with or without cables with no distance to each other, and many more specific plastic conduits (Polyolefin and PVC) with diameter up to 40mm, fire resistance ratings up to in accordance with EN 13501-1 of up to EI120 U/U.



Pic.: Different Hilti Firestop products offer a broad range of tested applications for conduits in the respective ETAs
 
Conduits: important information for engineers needing to correctly plan fire-rated penetrations

Typically, electrical cable runs and distributions are planned in an early stage of a project. Conduits play an important role for installing cables in an appropriate way. However, these conduits need to be firestopped correctly in accordance with the specific European Technical Assessment (as do cables and pipes) when routed through fire-rated walls and floors.

Conduits pose a fire risk in respect to integrity, heat transfer and smoke propagation. The test standard EN1366-3 clearly defines rules for the fire tests, which then can be transferred into an ETA with defined fire resistance ratings. A specific ETA with clear fire resistance ratings helps to select the correct firestop products to be specified and installed.  As a result, specifiers require good approval knowledge in order to select the most appropriate solutions in the early planning and design phases. This helps to avoid installation and inspection problems at a later phase of the project.

Hilti offers many suitable products within respective field of application for plastic, rigid and flexible/pliable conduits. Hilti also offers dedicated global engineering services, helping to support planners and designers in the early specification phases.