The evolution of cable products

Over time requirements for cable product performance have evolved to meet demand for not just mechanical and electrical performance, but also to meet industry recognised standards for safety. The latter was given little thought until cables were identified as a key cause of fatal fires, which necessitated the need for the development of products to meet more complex requirements.

Until the mid-1990s cables were generally quite conveniently grouped by technology and application. Examples of this include:

  • Virtually all house wiring cables, both incoming supplies and internal final circuit cables, were made from PVC
  • High temperature cables (both application and technology) were often silicone rubber or fluoropolymer based
  • Aircraft cables were lightweight thin wall engineering polymers, aramid or fluoropolymers, and
  • Data cables were polyethylene and PVC

While there are exceptions, these basic types had been established and recognised over several years.

In the first half of the 20th century the safety of cable products was given little thought, with testing for electrical and mechanical performance of cables forming the main requirement.

It was not until the 1980s, when cables were identified as key contributors to some of the most high-profile fires, that testing cable products for fire performance became an important requirement.

Tragic fires spark requirements for new cable materials

In the 1970s the developments in cable product materials began to focus on minimising the risk posed to public safety. The materials were selected to limit the release of smoke, corrosive and toxic fumes emitted during a building fire. These early products were initially only available for specialised applications, such as for use in metros, with most cable products around this time being produced with PVC sheathing. It was not until the 1980s that the technology became far more cost effective and more widely available.

The Falklands War

The importance of using materials with low smoke emissions in cable production was highlighted in 1982 when the HMS Sheffield was hit by a missile during the Falklands War. The ship contained PVC cables that gave off thick smoke when they caught fire, resulting in serious fatalities and injuries. This particular incident created an immediate demand for the requirement of improved fire performance in cables, especially those which were designed for military applications. Careful attention was to be taken to avoid compromising their ability to operate in the highly aggressive environments of military operation.

Reinforcement works on London Underground  | Shutterstock 1204732297 London Underground Cable Evo Web
Reinforcement works on London Underground

King’s Cross Underground

In 1987, a fire in the King’s Cross Underground Station served to further emphasise the need for cable materials with improved fire performance characteristics. As a result of large quantities of PVC cable products within the station, the fire was able to spread quickly and as the products burned smoke and toxic gases were released. This made it increasingly difficult for passengers to evacuate the station. The fire at King’s Cross is often mentioned as one of the main catalysts for the development of cable designs with better and safer performance in a fire. The incident gave birth to the BS7211:1989 standard, which was introduced to evidence the quality and safety of cable products used in restricted spaces.

Materials for performance

Before polymer technology was developed, rubber was used as one of the main materials for cable insulation and sheathing. Polymeric materials typically fall into two categories: thermoset polymers which do not melt once formed, and thermoplastic polymers which can be heated and reformed continuously. The flexible nature of these materials represented, at the time, a significant development for cable products as it would enable the creation of specialised materials, which could demonstrate higher performances across a range of characteristics.

In the case of cable quality and safety, polymer technology has indeed led to the development of higher performance cable products. Polymers act as both thermal and electrical insulators, can be processed in different ways and are resistant to chemicals. This in turn provides more variety in cable material technologies. Polymer technology can additionally be combined with numerous additives during the production of cable materials, which can act to enhance performance in specific applications.

The evolution in polymer technology has enabled system designers across all sectors to specify designs in line with the specific properties they require. One example of this technology is Dupont’s Hytrel® thermoplastic polyester elastomer, which is an option for applications that require a slimmer profile of insulated cables. The use of polymer technology means that insulation can take up a smaller proportion of the cable construction without losing any of the strength, giving more space for larger conductors, but also making it suitable for use in tight spaces or in applications where the product needs to be flexible and may be moving continuously.

Some key milestones within the development of polymer technologies include:

  • 1909 – Bakelite manufactured first synthetic plastic
  • 1927 – Otto Rohm (Ger.) developed poly methyl methacrylate clear plastic
  • 1933 – Fawcett and R. O. Gibson (ICI) discovered low density polythene
  • 1935 – Nylon manufactured, a thermoplastic material
  • 1940 – PET – polyethylene-terephthalate developed
  • 1953 – Karl Ziegler with E. Holzkamp produced high molecular weight, low pressure polyethylene, using organo-metallic catalysts, which was a major step forward
  • 1953 – Drs H. Schnell (Bayer) and D. Fox (General Electric) independently produced polycarbonate, a pioneering engineering polymer
  • 1959 – Polyformaldehyde polymer developed
  • 1965 - PEEK – Polyether.ether ketone resistant chemical and engineering polymer produced by ICI
  • 1980 – PE-LLD first produced linear, low-density polyethylene
  • 1983 - PEEK, PES and PPS emerge as new engineering thermoplastics, available at a high cost but used in specialist applications creating a lasting market
  • 1990 - Warner Lambert develops Novon, a starch which is also an injection mouldable plastic and ICI launches Biopol - both are biodegradable plastics
The development of chemical structures in polymer technology | Shutterstock 163711058 Polyethylene Terephthalate Pet Pete Polyester Plastic Chemical Structure Web
The development of chemical structures in polymer technology

From the 2000s onwards, the focus for polymer technology shifted to the compounding of existing polymers to create composites with improved performance characteristics.

This technology was then adapted by final circuit wiring and eventually flexible cables with low smoke zero halogen properties. The use of newer materials can also boost other performance criteria. Thermoplastic polyurethanes, for example, offer excellent suppleness for flexible cables, combined with very high resistance to abrasion.

Today, many public buildings such as shopping centres, hospitals, theatres and others are now safer places to congregate or visit thanks to these upgraded properties. However, there is also a danger of wholesale specification changing without sufficient thought. An example to consider here, is a hospital, which may issue a directive that the cable products installed “must be low smoke halogen free” without understanding the consequences of singling out this one characteristic. While this may seem like an appropriate directive, it only addresses one aspect of performance. A suite of electrical, mechanical, material, chemical, fire and smoke tests should be conducted as part of an approved product certification, to ensure the cable will meet all the requirements of the application.

Your solution to ensuring cable performance is suitable for application

One solution is to consult a reputable manufacturer for advice on whether your chosen cable product, especially if it uses new materials, is suitable for long-term use within the application in which you plan to use it. While manufacturers can advise the suitability of the cable materials specific to the cable’s end application, specifiers should ask or look for the BASEC mark of approval. The BASEC mark evidences that the cable products are compliant with applicable standards but also, importantly, denote that they have been independently tested and will be safe to use and fit for purpose.

BASEC is a leading provider of cable product certification, which is amongst the most rigorous in the industry. The product approval process includes comprehensive testing for electrical, mechanical, material, chemical, fire and smoke performance characteristics.

As industry experts in CPR (Construction Products Regulation) testing BASEC has issued over 3,000 CPR classification reports, delivered through in-house laboratory equipment and by working closely with manufacturers and end user demand to raise the level of cable product’s fire classifications for higher performance. Partnering with the industry, BASEC is supporting the education, as well as the need to understand and apply consistent levels of quality. A product certification delivers a full assessment of how the cable’s component materials will behave over time and with respect to all key risk factors.

Conclusion

While cable performance may be given little thought, the materials used in the construction of a cable have a significant impact on suitability for the specified application. Materials evolved significantly throughout the 20th century, however, it was not until the 1980s that requirements for fire-resistant cable products were set. Where measuring only the electrical and mechanical performance characteristics of a cable product was acceptable, the identification of cables as a key cause of fatal fires led to more complex requirements.

Today, industry standards specify a full suite of tests to verify the quality and safety of cable products. With fire-resistance being high on the agenda for building refurbishment and new construction projects, the performance of cable products should be a priority for specifiers and project managers alike. As the materials used to produce cable products will continue to evolve, fire-safety performance will remain an important factor in verifying quality and safety. In addition, specifying cable products that have been independently tested by a third-party certification body like BASEC provides end users with assurance that the cable products installed in their building will operate as they were designed to, and be compliant with all relevant regulatory requirements.

Avoid electrical fires through independent cable testing and compliance to industry standards | Shutterstock 1349684537 Plug On Fire Web
Avoid electrical fires through independent cable testing and compliance to industry standards

Today, industry standards specify a full suite of tests to verify the quality and safety of cable products. With fire-resistance being high on the agenda for building refurbishment and new construction projects, the performance of cable products should be a priority for specifiers and project managers alike. As the materials used to produce cable products will continue to evolve, fire-safety performance will remain an important factor in verifying quality and safety. In addition, specifying cable products that have been independently tested by a third-party certification body like BASEC provides end users with assurance that the cable products installed in their building will operate as they were designed to, and be compliant with all relevant regulatory requirements.