Electrical conduits protect wiring throughout a building, which sounds simple enough. However, the effects of different conduit types on fire resistance through compartmentation lines are often overlooked.
The conduit’s material, whether flexible or rigid, and its outside diameter are key details that support the identification of the correct tested firestopping details.
In this Knowledge Hub article, we take a look at the different cable conduit types we’ve tested, the factors that affect fire resistance, and why early consideration is crucial.
What is an electrical conduit?
When installing cables, MEP contractors may utilise electrical conduits, which are essentially tubes or pipes that protect electrical wiring in a building. 
They are sometimes referred to as ‘ducts’ by MEP designers, though we advise against this terminology because it may cause confusion with ventilation applications.
Simple differences in conduit types, for instance, flexible versus rigid, can be detrimental to overall fire-resistance performance, and that’s why electrical conduits must be tested to comply with BS EN 1366-3. The test standard for service penetrations.
What are the different types of electrical conduit?
At Quelfire, our mission has been to work in partnership with our customers to provide tested firestopping solutions for common and even uncommon scenarios found on site.
The electrical conduit types we have fire tested are:
Flexible plastic conduit
- Flexible conduits (plastic) made up of PE, PP, PE/PP or PO
A flexible plastic conduit can bend to accommodate changes in direction, particularly useful when a more adaptable cable route is needed.
Rigid plastic conduit
- Rigid plastic conduits made up of U-PVC, PE, PP, PE/PP or PO
This type of conduit provides a fixed route for cables and cannot be easily bent or manipulated.
Flexible metal conduit
- Flexible metal conduits made up of steel
- Flexible metal conduits made up of steel with a plastic coating
A flexible metal conduit is an ideal solution for cable protection while allowing flexibility in routing.
Rigid metal conduit
- Rigid metal conduits made up of steel (steel conduit)
- Rigid metal conduits made of steel connecting to metal BESA boxes
This also provides a fixed route for electrical wiring but offers robust mechanical protection against damage. 
What conduit penetration applications has Quelfire tested?
We have tested cable conduits in various orientations and applications, such as:
Plastic conduit applications
- Plastic conduits going directly through a wall
- Plastic conduits partially penetrating a wall
- Plastic conduits going through BWIC (Builders’ Work in Connection) openings through flexible walls, rigid walls, sandwich panel walls, Porotherm walls, and Specwall
- Plastic conduits going through solid concrete slabs, hollow core floor slabs, and profile deck floor slabs
- Plastic conduit single-side access applications
Metal conduit applications
- Metal conduits going directly through a wall
- Metal conduits partially penetrating a wall
- Metal conduits going through BWIC openings through flexible walls, rigid walls, sandwich panel walls, Porotherm walls, and Specwall
- Metal conduits going through solid concrete slabs, hollow core floor slabs, and profile deck floor slabs
- Metal conduit single-side access applications
View these details in our Tested Detail Library.
How is an electrical conduit tested for fire resistance?
What does BS EN 1366-3 Annex C say about conduit testing?
When BS EN 1366-3 was updated toward the end of 2021, Annex C was introduced, focusing specifically on conduits and trunking.
Annex C provides guidance on methods for testing conduits, and these methods differ from those used to test plastic and metal pipework. Therefore, it’s important to note that although a conduit can be made from plastic or metal, it cannot simply use data from plastic or metal pipework.
What factors affect the fire resistance of conduit penetration seals?
When fire testing conduits, manufacturers must ensure they’re tested in accordance with specific requirements to avoid any impact on the achievable fire-resistance rating. For example:
- Both empty and filled conduits*
- *Filled conduits will have designated cable configurations to allow all cables of a certain outside diameter
- Conduit protrusion length
- Both flexible and rigid conduits for certain applications
- Full and partial penetration orientation
- Conduit end configuration
How can installation details affect conduit fire-resistance performance?
A clear example of how these factors can affect performance is shown on Detail QB-FW100-D-14, Pages 1-3.
How does cable configuration affect fire resistance?
Page 1 was first tested before the inclusion of the conduit Annex in BS EN 1366-3, using telecom cables (F-type cables), which achieved 120 minutes of integrity and 60 minutes of insulation.
However, with the new update, specific cable configurations were introduced for conduits that did not use the F-type cable we had previously used. With this in mind, we went out and retested the same application with the new cable configuration, which reduced the fire resistance from EI 60 to EI 45. 
While the 2009 data remains valid, the field of application is limited to the specific cable type tested. We cover the topic of older and new test evidence, and whether older standards are superseded in another Knowledge Hub article.
How do conduit protrusion length and spacing affect fire resistance?
To improve the fire-resistance rating of conduits under the new cable configuration, the R&D team conducted further testing. As shown on Pages 2 and 3 of QB-FW100-D-14, small differences can have a significant impact on the overall performance.
QB-FW100-D-14, Page 2, increases the conduit protrusion from 40mm to 400mm and adds additional QuelStop HPE Sealant, thereby raising the fire resistance from EI 45 to EI 60. 
Pages 1 and 2 grouped three conduits together in what is known as the ‘cluster’ formation, allowing a minimum spacing of 0mm between firestop seals when classified. QB-FW100-D-14, Page 3, shows that simply separating these conduits to provide 50mm between firestop seals increased the fire resistance from EI 60 to EI 120. 
What information is needed when specifying conduit for firestopping?
For fire stopping, the Technical Team requires as much specific information as possible about your application at the design stage. This helps ensure the correct tested firestopping details are identified and used on the project.
The Technical Team will require information on:
- The conduit material
- Whether the conduit is flexible or rigid
- The outside diameter of the conduit
- Are the cables 21mm or less in outside diameter?
Why is early conduit specification important for firestopping?
It is common for MEP designers to have preferences regarding the type of service or method used; however, when it comes to penetrating compartment lines, some flexibility is required.
Certain applications may require specific conduit-type materials, protrusion lengths, or even service spacing, and failing to incorporate these in the early design stages can have a detrimental impact on the project down the line.
It is often found that during the design stage, small penetrations not within BWIC openings – such as cable conduits – are neither listed nor designed. This leads to incorrect selection and installation of these small penetrations, requiring remedial work to correct the issue. Thus, MEP designers must be informed early of any critical information that could affect their decisions.
If you’re just getting started on your project and need help identifying the right tested solutions, we’d be happy to help. Reach out to the Technical Team.
