Putting fire rated cables in focus

THE USE of fire rated cables has certainly come to prominence in the UK in recent years, which can only be a good thing for everyone – from installers to end users and on to emergency service responders. They can be seen in use virtually anywhere, but are most commonly installed in commercial, residential, and public spaces like universities, hospitals, and schools, where the risk of fire poses a big threat to life. Their purpose is simple - to maintain critical electrical functionality during fires to enable safe evacuation.

What are fire rated cables?

Fire rated cables, also referred to as fire performance or fire resistant cables, are specifically engineered for deployment in environments where the cable's functionality should remain unaffected in the event of a fire. Typically crafted from materials capable of withstanding high temperatures and flames, these cables boast extreme resilience, sometimes up to 1,100°C.

Key considerations when installing fire rated cables

When installing such cables, there are two key considerations:

• Maximum normal operating temperature of the cable – most cables, including fire rated ones, have normal operating temperatures ranging from +70 to +90°C.
• Fire resistance temperature of the cable – fire rated cables undergo testing and are rated for a duration of typically 1-2 hours, withstanding temperatures of up to 1,100°C. Despite potential destruction of the cable insulation during a fire, the essential conductors inside the cable (protected by a metallic layer and/or mica tape) remain intact, enabling the provision of emergency/essential power supply.

Damaged cables can pose hazards, including tripping or, more critically, electrocution. Therefore, comprehensive fire safety planning should integrate measures to protect firefighters from cable-related dangers.

The role of cable cleats in fire rated installations

In scenarios where fire rated cables are in use, cable cleats play a pivotal role in providing support and securing cables during fires or short circuits. Installers and specifiers must ensure that the cable cleats they select have a service temperature equal to or higher than the cable's maximum operating temperature and have been tested to safely restrain cables in extreme high temperature conditions.

The fire performance of these cable management systems needs to take into account fire survival, fire resistance, flame retardancy, flame propagation, smoke toxicity, and emissions in exactly the same way the cables they are supporting do. This can only be proven by thorough testing prior to bringing them to market. In our case, every fire resistant cleat has undergone testing to temperatures of 1,200°C, while also enduring periodic water spray and shock testing.

British Standard BS 5839: Key provisions

The British Standard BS 5839, which today governs fire detection and alarm systems in buildings, now stipulates that cable supports - including cable cleats - must endure fire, maintain circuit integrity, endure the same temperature as the cable, and provide adequate support.

This small reference to the fire resistance of cable supports in the standard has made a world of difference when it comes to addressing the safety of emergency responders, especially firefighters operating in challenging conditions. Prior to its introduction, fire rated cables didn’t need to be secured and supported by fire rated products such as cable cleats, which in one tragic case led to the death of fire fighter Jeff Wornham in 2005 - who passed away having become entangled in cables in the lobby of a fourteenth floor flat in Stevenage.

Products that comply with the requirements of BS 5839 go beyond their previous role in simply helping to maintain electrical functionality during fires; they now play an essential role in effectively securing fire rated cables during fires.

Even for non-fire critical cable installations, where the systems will not be required to function in a fire, wiring and cables must still be adequately supported. It is critical to ensure wiring does not prematurely collapse before the public and firefighting personnel evacuate the building.

Selecting cable cleats for fire rated installations

When selecting cable cleats for fire rated cable installations, the key performance considerations should be as follows:

• Cleats must safely support and restrain cables for means of escape, while maintaining circuit integrity.
• Cleats must safely support and restrain cables for firefighting purposes, while maintaining circuit integrity.
• Any composite materials used in manufacture are produced in Low Smoke and Fume (LSF) as standard.
• Any composite materials used in manufacture are flame retardant and ideally rated V0 in accordance with UL94 as standard.
• Where possible, London Underground (LUL) approved and certified polymers are used, for some of the most stringent smoke toxicity and smoke emission requirements.

It’s also vital to understand that all typical polymeric materials will melt and burn away in a fire, which means standard liners will no longer be in position to help grip the cables during a fire. Therefore, fully metallic fire-rated cable cleats will likely be the best solution.

Ensuring common sense in specification and installation

What it boils down to is common sense during the specification and installation process. In the same way that regular electrical cables won’t continue operating during a short circuit scenario if secured by underspecified cable cleats, then fire rated cables will only perform during a fire if they are secured using properly fire rated cable cleats. By following that simple rule, electrical supplies will continue during fire and lives of building users and emergency responders will not be put in unnecessary risk.

In response to market demands, CMP recently introduced a comprehensive range of fire-rated cable cleats – Themis, Solace, and Helios. All three have been subjected to rigorous fire testing to comply with EN 50200, BS 5839, BS 8491, and BS 8434.

The fire-rated range, which is available in cast and fabricated 316L stainless steel, demonstrates resilience by withstanding temperatures of more than 1,000°C, while providing excellent corrosion resistance. Suitable for indoor, outdoor, and corrosive environments, these cable cleats exemplify a commitment to ensuring both the integrity of fire safety systems and the safety of emergency responders.

And the products' capabilities don’t just stop with fire resistance. Both Themis and Solace are designed with a unique twin arc internal design profile, offering extreme axial and lateral load retention.

Lee Frizzell is technical director at CMP Products

For more information:

www.cmp-products.com/fire-rated-cable-cleats

Tel: 0191 607 1901