Why Thermal Conductivity and Resistance Matter for Duct Sealing Systems
When cables pass through ducts, the material used to seal them plays a crucial role in managing heat dissipation. Materials with high thermal resistance can trap heat, causing cables to overheat and reducing their performance—a process known as cable de-rating. On the other hand, sealing materials with excellent thermal conductivity help disperse heat effectively, ensuring cables operate safely and efficiently. This is particularly relevant when discussing the concept of non-adiabatic conditions, where heat transfer between a cable and its surroundings directly impacts performance.
Our duct sealing systems, incorporating GreyStuff and RedStuff sealants, are engineered to address these challenges. Used in our DuctSeal LG, DuctSeal HG, and DuctSeal FR kits, these sealants offer the best thermal resistance and conductivity on the market, ensuring compliance with BS 7671:2018+A3:2024 for electrical installations.
What Does Non-Adiabatic Mean in Duct Sealing?
In the context of electrical installations, non-adiabatic conditions occur when heat is exchanged between a cable and its surroundings rather than being entirely retained (adiabatic). This means that the effectiveness of duct sealing materials in allowing or preventing heat dissipation becomes critical.
- Non-adiabatic systems, like those using GreyStuff or RedStuff, promote heat dissipation, reducing the risk of overheating and maintaining the cable’s current-carrying capacity.
- In contrast, materials with high thermal resistance trap heat, creating more adiabatic-like conditions and increasing the likelihood of cable de-rating.
By using sealants with low thermal resistance, such as those in our duct sealing systems, you ensure that cables remain in non-adiabatic conditions, where heat dissipation is optimised.
Examples of Heat Dissipation Using Duct Seal LG
This image demonstrates how heat dissipates when using Duct Seal LG. Heat escapes:
- Around the circular foam backing, which allows air to circulate.
- Through the foam backing itself, thanks to its open-cell structure.
- Finally, out through the 20mm layer of sealant, ensuring effective thermal management.
Examples of Heat Dissipation Using Duct Seal HG & Duct Seal FR
This image illustrates the process of heat dissipation with Duct Seal HG & FR. Heat escapes:
- Around the circular rubber sleeves, which provide pathways for airflow.
- Through the hollow design of the sleeves, enabling heat to transfer outward.
- Finally, through the 20mm layer of sealant, maintaining optimal heat dissipation.
The Best Thermal Resistance in the Market
Our sealants are engineered with advanced materials, including expandable graphite, to enhance thermal conductivity and reduce thermal resistance. This unique formulation gives GreyStuff and RedStuff a significant edge over traditional sealing technologies like, standard silicones, hybrids, EPDM or expanding polyurethane.
How BS 7671 Standards Relate to Thermal Performance
Compliance with BS 7671:2018+A3:2024 requires consideration of various factors affecting cable performance, including:
- Thermal Conductivity: The ability of duct sealing materials to conduct heat away from cables.
- Thermal Resistance: The resistance a material offers to heat flow, which can affect a cable’s current-carrying capacity.
- Installation Conditions: Including whether ducts are below ground and the thermal properties of the surrounding soil.
By selecting materials like GreyStuff or RedStuff, which support non-adiabatic heat transfer, you can maintain compliance with BS 7671 standards, ensuring safe and efficient installations.
Comparison of Duct Sealing Materials
Here’s how our products compare with other materials commonly used in duct sealing:
| Material | Used In | Thickness | Thermal Conductivity | Thermal Resistance | De-Rating Impact | Current Rating (From 100A) |
|---|---|---|---|---|---|---|
| GreyStuff or RedStuff | DuctSeal LG, HG, FR Kits | 20mm | 0.5 W/m·K | 5.1 K/W | No significant de-rating | ~100 A |
| Silicone Sealant | General Applications | 20mm | 0.2 W/m·K | 12.74 K/W | Slight de-rating | ~95 A |
| EPDM | Some Sealing Applications | 40mm | 0.25 W/m·K | 20.38 K/W | Moderate de-rating | ~90 A |
| Expanding Polyurethane | Low-Cost Duct Sealing Solutions | 100mm | 0.025 W/m·K | 509.6 K/W | Significant de-rating | ~50 A |
| Expanding Polyurethane | Low-Cost Duct Sealing Solutions | 200mm | 0.025 W/m·K | 1019.2 K/W | Severe de-rating | ~25 A |
Calculation for GreyStuff or RedStuff
Step 1: Thermal Resistance (Rt)
The formula for thermal resistance is:
Rt = d ÷ (k × A)
Where:
-
d = 0.02 m(20mm thickness) -
k = 0.5 W/m·K(thermal conductivity of GreyStuff or RedStuff) A = π × dcable2 ÷ 4
For a 50mm diameter cable:
dcable = 0.05 m
A = π × (0.05)2 ÷ 4 = 0.001963 m2
Thermal resistance calculation:
Rt = 0.02 ÷ (0.5 × 0.001963) ≈ 5.1 K/W
Step 2: De-Rating Factor
Based on BS 7671:2018+A3:2024, the thermal resistance (Rt) of 5.1 K/W results in a de-rating factor of approximately 1.00.
Step 3: Current Rating
The derated current (Iderated) is calculated as:
Iderated = Ir × De-Rating Factor
Where:
-
Ir = 100 A(nominal current-carrying capacity) - De-Rating Factor = 1.00
Iderated = 100 × 1.00 = 100 A
Key Benefits of GreyStuff and RedStuff
- Exceptional Thermal Performance: With a thermal conductivity of 0.5 W/m·K, our sealants allow heat to dissipate efficiently, significantly outperforming traditional materials like polyurethane and EPDM.
- Minimal Impact on Cable Performance: At a standard thickness of 20mm, the thermal resistance of 5.1 K/W ensures no significant cable de-rating (~100% current capacity maintained).
- Tailored for Duct Sealing Kits: These sealants are integral to our DuctSeal LG, DuctSeal HG, and DuctSeal FR kits, providing industry-leading performance across a range of installations.
- Market-Leading Technology: Designed to outperform all other duct sealing materials currently available, offering the best combination of sealing effectiveness and thermal management.
- Compliance with BS 7671: Designed to meet the strict requirements of BS 7671:2018+A3:2024, including considerations for buried ducts and thermal environments.
- Optimised Non-Adiabatic Performance: Promotes heat dissipation to prevent cable overheating.
Why Choose Our Duct Sealing Systems?
Our duct sealing kits are designed not only to provide water-tight and gas-tight seals but also to ensure cables perform at their best under non-adiabatic conditions. With GreyStuff and RedStuff, you can minimise thermal resistance, maintain compliance with BS 7671, and ensure your installation is both safe and efficient.
Choose DuctSeal LG, DuctSeal HG, or DuctSeal FR for the most advanced thermal management solutions on the market today.
Conclusion
By understanding the principles of thermal conductivity, thermal resistance, and non-adiabatic conditions, you can make informed decisions about your duct sealing materials. Our systems, incorporating GreyStuff and RedStuff, set the standard for thermal performance, compliance, and safety in accordance with BS 7671:2018+A3:2024.
Choose our duct sealing systems to ensure your cables remain safe, efficient, and fully operational—no compromises, just the best technology on the market today.