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Why Using Expanding Polyurethane Foam in Cable Ducts is a Bad Idea

Why Using Expanding Polyurethane Foam in Cable Ducts is a Bad Idea


To jump straight to our duct sealing solutions to replace poor performing expanding polyurthane foam, please use the links below: 

  • Compound based sealing systems (Duct Seal LG & Duct Seal HG) Click HERE
  • Mechanical duct sealing systems (Kraso Gmbh) Click HERE

In the world of electrical installations, the importance of safety and efficiency cannot be overstated. Cabling and wiring systems are the lifeblood of modern infrastructure, and it's crucial to ensure that these systems are protected and maintained to the highest standards. However, one common mistake in this regard is the use of expanding polyurethane foam, (or sometimes reffered as spray foam) in cable ducts. While it may seem like a convenient option for sealing cable ducts, there are several compelling reasons why this practice should be avoided. In this blog post, we'll explore the pitfalls of using expanding foam in cable ducts and provide several strong arguments against this approach.

Redundant Insulation
One of the primary reasons to avoid using expanding polyurethane foam in cable ducts is that it introduces an unnecessary layer of insulation. Electrical cables are already insulated within their protective sheaths, which are specifically designed to prevent current leakage and provide thermal insulation. Adding expanding foam on top of this can lead to the cables overheating, as it obstructs the dissipation of heat. This additional insulation can lead to a dangerous buildup of heat, increasing the risk of electrical fires and cable damage.

Inaccessibility for Future Use
Using expanding foam to seal cable ducts may initially seem like a good idea to create a watertight seal, but it has a significant drawback – it renders the duct nearly unusable for future modifications or maintenance. As the foam expands and hardens, it effectively encapsulates the cables, making it extremely difficult to access or replace them. When the time comes to add new cables or perform repairs, you may find yourself faced with the arduous and costly task of removing the foam, which can be a daunting and time-consuming process.

Hazardous Chemicals
Another critical concern is the use of isocyanates, specifically MDI (Methylene Diphenyl Diisocyanate), which is a hazardous component in many polyurethane foams. MDI is known to be a respiratory and skin irritant, and prolonged exposure can lead to serious health issues. Inhaling MDI fumes or having direct contact with the skin can cause sensitization, allergic reactions, or even long-term health problems. Therefore, the presence of MDI in expanding foam adds an unnecessary health risk to workers who are applying it in cable ducts.

Chemical & UV
The chemical composition of the foam may react with the cable sheath material, causing it to break down slowly over time. It's crucial to choose foam and cable sheath materials that are chemically compatible.

UV Exposure
Some types of polyurethane foam are sensitive to UV light. If used in outdoor or exposed environments, prolonged exposure to sunlight may indirectly affect cable sheaths.

Fire Hazard
Polyurethane foam, especially when used in excess, can create a potential fire hazard. While polyurethane itself is not highly flammable, it produces toxic gases and smoke when it burns. In a confined space like a cable duct, this can exacerbate the spread of fire and create a more dangerous situation in the event of a fire emergency. Using materials that do not contribute to fire propagation is essential in ensuring safety within cable ducts.

Regulatory Non-Compliance
Expanding polyurethane foam also fails to comply with important safety regulations. The Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) are in place to protect workers from the risks associated with explosive atmospheres, which can be created when certain substances, like polyurethane foam, are used in confined spaces. Using expanding foam in cable ducts may lead to non-compliance with DSEAR regulations and pose a legal risk to those responsible for the installation.

Water Industry and WIMES
In the water industry, the use of expanding foam within ducted networks has been banned. The Water Industry Mechanical and Electrical Specifications (WIMES) sets out industry standards and best practices, and it prohibits the use of expanding foam in cable ducts. This decision has been made to ensure the safety, reliability, and longevity of infrastructure within the water industry. While these standards may not be directly applicable to all industries, they serve as a clear indicator of the risks associated with expanding foam in cable ducts.

Some Installation examples clearly showing why expanding foam shouldn’t be used.

Classic example of what happens to expanding foam over time in damp areas. The foam has a very weak adhesion to the cables and duct, which means the slightest bit of pressure will push the cured foam out.

The heavy-handed use of expanding foam – its very easy to keep holding that trigger and think the more the better.

This will fail over time, and the engineer will be called back to replace it with a better system.

The best four solutions for sealing pipes & cables within ducted networks are the following: All available from AC Cable Solutions

Duct Seal LG
When it comes to sealing cables and pipes within ducts, Duct Seal LG stands out as a superior choice compared to traditional expanding foam. Specifically designed for applications involving cables or pipes with an overall diameter of less than 25mm, this system offers a remarkable combination of features that make it a top-performing solution.
Duct Seal LG provides an impressive level of protection, capable of withstanding up to 1 bar of water and gas pressure, ensuring the integrity of your ducts even under challenging conditions. Notably, it goes beyond mere sealing and extends its defensive capabilities to resisting toxic gases and hydrocarbons, offering a comprehensive safeguard against potential environmental hazards.

One of the standout advantages of Duct Seal LG is its practicality for future maintenance and cable management. In the event that you need to re-enter the sealed duct to replace or add cables, the process is both efficient and user-friendly. With a sharp tool, you can effortlessly remove the layer of GreyStuff sealant, which has a thickness of just 20mm and a similar hardness to a rubber eraser. This straightforward procedure allows you to add or replace cables as needed, and once completed, re-sealing the duct is a breeze.

In summary, Duct Seal LG not only excels in sealing cables and pipes but also provides an exceptional level of protection against pressure, toxic gases, and hydrocarbons. Its user-friendly design makes it an ideal choice for those seeking a reliable and practical solution for their cable duct sealing needs, ensuring a secure and accessible system for the long term.

Duct Seal HG

Duct Seal HG represents an advanced solution in cable and pipe duct sealing, offering exceptional benefits that parallel those of Duct Seal LG. What sets Duct Seal HG apart is its enhanced pressure resistance and the unique circular rubber sleeve system that accommodates cables of all sizes, including large and heavy power cables.

Duct Seal HG is engineered to withstand an additional 1 bar of pressure, totalling an impressive 2 bars of water and gas pressure resistance. This remarkable capability ensures that your ducts remain impervious to even more challenging conditions, providing an added layer of security for your installations.

The hallmark of Duct Seal HG is its innovative circular rubber sleeve system, which sets it apart from our competitors. This system is versatile and adaptable, allowing you to connect the sleeves in long strips or as rings. Moreover, they can be joined to create a cross shape, offering an extra level of convenience when working with trefoil cables. This adaptability makes Duct Seal HG an ideal choice for a wide range of cable sizes and configurations.

Both Duct Seal LG and Duct Seal HG are anchored by our rigorously tested, high-quality intumescent sealant, proudly MADE IN BRITIAN. This sealant boasts innovative Hybrid technology, ensuring it performs at the highest standards while also being eco-friendly by containing zero MEKO, making it a non-hazardous product.

An additional benefit of our sealant is its boosted microbial resistance, which safeguards against the growth of mould, fungi, and bacteria on the surface of the duct seal. This feature not only ensures the long-term durability of your installation but also contributes to a healthier and safer environment.

In summary, Duct Seal HG takes cable and pipe duct sealing to the next level with its exceptional pressure resistance and adaptable circular rubber sleeve system. Supported by our high-quality, British-made intumescent sealant, it offers a comprehensive and innovative solution for duct sealing, suitable for various cable sizes and configurations, all while maintaining a focus on safety and sustainability.

Kraso Universal & SD Mechanical Sealing Systems
In a rapidly evolving world of mechanical transit solutions, our innovative sealing option has emerged as the preferred choice for sealing ducts with precision and efficiency.

How it Works:
Our sealing system features robust stainless-steel plates, sandwiching a resilient EPDM rubber core. The magic happens with our patented self-torque-rated nut, which gently compresses the rubber. This compression causes the rubber to expand, forming a watertight seal around your cables and the inner surface of the duct. It's a revolutionary method that offers unparalleled advantages.

Key Benefits:
Exceptional Performance: The Kraso system can effortlessly seal pressures of up to 10 bar, making it a reliable choice for various applications. Whether you're dealing with gases, hydrocarbons, toxic gases, or natural ground gases, our system provides a secure barrier.

Installation Ease: Our seals can be installed with running water, saving you time and effort trying to find creative ways to stop running water while installing a sealant-based seal.

Reusable and Re-enterable: Not only is our sealing system highly effective, but it's also eco-friendly. It can be easily reused and re-entered when needed, reducing waste and saving resources.

Versatility: The Kraso Universal Seal is a versatile off-the-shelf solution that accommodates various duct sizes and cable configurations. It's designed to handle the most common duct sealing requirements encountered on-site.

Customisation: For those unique site conditions, our SD Sealing System offers the same exceptional specifications and can be tailored to match your specific cable and site requirements. It's a versatile solution that ensures your needs are met precisely.

Choose the Kraso GMBH Universal & SD Sealing System and experience the future of duct sealing. Whether you opt for our Universal Seal or require a customised solution with the SD Sealing System, you can trust this duct sealing system to deliver uncompromised quality and performance.

Sealing Large Cable Penetrations Made Easy with Hawke HTS Multi Cable Transit Sealing System

Expanding foam has often been the go-to solution for sealing large cable penetrations, but it comes with its fair share of challenges, especially when dealing with extensive openings. The Hawke HTS system emerges as a game-changer, making the sealing of larger penetrations a hassle-free and cost-effective endeavour.

Hawke HTS offers a comprehensive range of products designed to cater to various penetration sizes and cable types. Moreover, they provide rapid technical support, offering guidance on both design and installation. With Hawke HTS, you're not just purchasing a product; you're gaining a reliable partner in ensuring the integrity of your cable penetrations.

Ingenious Tolerant Blocks for Versatile Sealing
The heart of the Hawke HTS transit system lies in its metal frames, housing Hawke's Tolerant Blocks. These blocks are ingeniously designed to adapt to a wide range of cable or pipe diameters without the need for on-site modifications. Featuring five sealing faces that adjust during the sealing process, these blocks offer a remarkable tolerance of up to 4 mm for cable diameters. This wide acceptance range accommodates cable tolerance deviations, simplifying the installation process and saving valuable time.

Effortless Compression with Hawke's Compression System
Once the Tolerant Blocks are in place, the entire transit system is tightened and compressed using Hawke's Compression System. This system comprises two essential elements: the End Packer and the Compression Plate. Unique steel insert pins on both sides of the Compression System ensure the correct level of compression during installation, eliminating the need for specialised knowledge or decisions by the installer. The Compression Plate efficiently distributes pressure from the compression tool, ensuring a secure and reliable seal.

Comprehensive Protection for Your Assets
When you choose the Hawke system for sealing penetrations, you are not only securing the passage of cables but also safeguarding the assets within your building. This system effectively shields against gas, water, rodents, fire, and explosions, and even provides EMC protection if required.

Say No to Expanding Foam
Say goodbye to the hassles and limitations of expanding foam. Instead, call AC Cable Solutions, and our experts will recommend the best Hawke HTS system tailored to your specific application needs. Your cable penetration sealing just got easier, more efficient, and more reliable. 

Call the experts
In order to guarantee the appropriate utilisation of duct sealing systems, AC Cable Solutions specialises in sealing cables and pipes by employing a distinctive methodology encompassing a diverse range of cutting-edge technologies. Our commitment lies in assisting you in identifying the ideal components for your project and offering comprehensive support throughout the entire process, which includes everything from initial design and specification to procurement and installation guidance. We comprehensively comprehend the requirements of your project and accompany you at every phase.

For additional support, Contact Us on 0161 806 1666 or email for help & advice.


Written by Carl Pike - The Duct Sealing Man 

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