Cables are critical to the functionality of almost all modern infrastructure projects. However, there is still confusion when making cable selection on flame-retardant and fire-resistant products. This blog tackles the growing misinterpretation over the terminology, standards, and what should be used where and when.
The difference between flame-retardant and fire-resistant cables is stark. Flame-retardant cables are designed to slow down the spread of a fire from one area to another, whereas fire-resistant cables are designed to continue functioning during a fire for a specified period of time. Understanding the differences is crucial to maintaining critical systems during a fire, and ensuring the safe evacuation of people.
Flame-Retardant Cables
These cables have been designed to reduce the spread of flames from one area of a building to another, by using self-extinguishing materials that stop the propagation of flames. Flame-retardant products can’t guarantee functionality in a fire and will quickly fail to deliver any data, commands, or instructions to the systems they are connected to.
There are also different levels of flame retardance to look out for. Some have extremely limited ability to reduce flame spread, can be made from PVC materials, and release poisonous gases and fumes when they burn, but may have been tested to a basic flame retardance test as listed below.
Other flame-retardant standards require a cable to limit spread by height and by time to ensure they don’t spread fire quickly, which gives more time for evacuation, nevertheless even these cables can and will stop functioning once they have caught alight.
IEC 60332-1-2 / BS EN 60332-1-2 Test (IEC and BSEN are standards)
This is the most basic of flame-retardant tests. It’s a 60-second test on cables below 25mm in diameter, which is supported vertically by two clamps. The flame is applied near the bottom of the cable and is taken away after 60 seconds. The charring/burning is recorded and pass or fail generated.
IEC 60332-3-24C / BS EN 60332-3-24C / BS EN 50399 Test (IEC and BSEN are standards)
This is a more difficult test. Cables are generally made from good flame-retardant materials, which usually have low smoke and low halogen properties. This makes them ideal for public buildings that are straightforward to evacuate, and are likely to keep functioning for a limited amount of time.
The test consists of multiple lengths of the same cable, each a minimum of 3.5m, and the total number of lengths is calculated based on the total amount of non-metallic material in the cable, being a nominal 1.5l/m. Each length is tied next to each other, and on top of each other - on to a metal ladder with metal cable ties, until the correct volume is reached and a large ribbon propane gas burner is placed near the bottom. The test lasts for 20 minutes, after which the gas is turned off and the cable is left to either self-extinguish or is extinguished manually after a maximum of 1 hour. If the cable has not burnt higher than 2.5m from the bottom each of the burner it’s deemed to be a pass.
There are other flame-retardant tests for cables which vary in the amount of non-metallic material and length of burn time, but the above are the most popular for land-based infrastructure.
Each of the above tests must not be confused with cables that are fire-resistant. These tests haven’t been created to check longevity or continuous functioning of cable in fire conditions, but solely how well they limit the spread of fire.
Fire-Resistant Cables
Fire-resistant cables are designed to keep critical systems running for a minimum amount of time during a fire. This ensures that escape routes and emergency signage are lit, fire alarms and suppressors are working, and security cameras are feeding pictures back to their source. Of course, cables can’t be designed to last forever, but they should keep working during the critical phases and times and are vital in aiding evacuation.
Cables that are fire-resistant use the best materials, which are flame retardant, have superior screenings, and usually have a fire barrier in the form of a mica tape. These all help the circuit integrity of the product and system.
There are many fire-resistant standards to choose from, and some are specific to cable types such as fire alarm cables or fibres cables, but they all have one thing in common - the continuous working of critical systems.
BS 6387 Test (All BS, IEC and BSEN references are standards)
This standard not only includes a fire resistance test, but also includes mechanical shock and water stress tests. This is one of the most popular fire resistance standards in the world and is adopted in many countries in addition to the UK. It tests three separate pieces of the same cable; one subjected to fire alone, another to fire with water spray, and the third with fire and mechanical shock. Each test records whether the cable is sending a signal to its source. If it doesn’t at any point it is deemed to be a failure.
BS 8434-2 Test
This is a 2-hour test on a single sample of cable and it’s subjected to fire, water, and indirect mechanical shock all at the same time throughout the test. This test is one of the requirements for any cable classified as ’enhanced’ fire-resistant. It must also meet BS EN 50200:2015 PH120 too.
BS EN 50200:2015 Test
This standard covers cables for emergency circuits with a voltage rating no greater than 600/100V and includes those rated below 80V and fibre optic cables. It is popular for cables used in alarm, emergency lighting, video, and communication systems. The cable is subjected to a constant direct flame of 842 degrees C. The standard version of this test, known as PH30, suits cables for fire alarm systems where they are required to work up to 30 minutes. The enhanced version, PH120, is for cables to maintain circuit integrity for up to 120 minutes. If a cable has passed both PH120 and BS 8434-2 it’s classed as having ’enhanced’ fire resistance.
IEC 60331 Test
The most popular European standard for fire-resistant cables, this test method subjects a cable to a flame of at least 830 degrees C, and to both fire and mechanical shock.
IEC 60331 Part 25 Test
This is for fibre optic cables and specifies the test procedure, timing, and performance requirements under fire conditions. This is the most popular fire-resistant standard for fibre cables in both the UK and Europe.
Choose Wisely
As you can see, fire resistance cables are subjected to more than just a flame. They’re tested to ensure circuit integrity throughout the test, are tested for longer periods of time, and some include water and mechanical shock treatment too.
If you are specifying or installing cables for critical public infrastructure, hard to evacuate buildings, or alarm systems, emergency lighting, video, or communication systems, check whether you should be referencing a cable to a flame-retardant or fire-resistant standard. As outlined above, there’s a significant difference that’s ultimately critical to preserving life in emergency situations in the context of cable fire safety. .
Need technical help & advice to choose the right cable for your project? Talk to our dedicated Webro Team for expert advice sales@webro.com or call 0115 972 4483. Or you can get in touch.
