Effects of weathering on PVC cables: What you should know
Understanding how environmental factors affect PVC cables is vital when it comes to choosing or installing the right product.
Although PVC cables are widely used in the electrical industry thanks to their durability and ease of use, prolonged exposure to the outdoor elements can lead to degradation of any cable. Weathering resulting from UV radiation from the sun, extreme temperatures and moisture ingress, can eventually lead to brittleness or in serious cases, cracking of outer and inner sheaths – and even insulation. This can potentially lead to circuit failure from an electrical fault.
What causes weathering in PVC cables?
Although PVC cables are robust and have a long service life, if they are used outside, they are at risk from long-term deterioration caused by several factors.
Sunlight/UV radiation
Some PVC cables are not designed for outdoor use, so installing these cables for an outdoor lighting project, for example, may lead to a reduced life expectancy of the cable. Prolonged exposure to UV radiation from normal daylight can lead to the breakdown of chemical bonds in the polymer chains in the sheath and insulation material. This process is known as photodegradation and can lead to colour fading, brittleness, and reduced flexibility of the cable. Even if a cable has a UV-stable sheath, it is recommended to limit a cable’s exposure to direct sunlight.
Extreme temperatures
If a cable is too cold, then it can harden and become brittle, making the installation process difficult. In extreme cases, it can crack and potentially lead to damage inside the cable. It is advised that cable is no lower than its recommended minimum temperature. The recommended minimum temperature is dependent on the type of cable, the temperature surrounding the cable and the total mass of the cable.
Moisture
UV-radiation and extreme temperatures can also lead to cracks in the PVC material, allowing moisture to slip through and corrode the conductors inside the cable. This will potentially lead to electrical faults or short circuits.
Effects of weathering on PVC cables
Weathering can typically affect PVC cables in three ways:
Physical
Electrical
Mechanical
Physical – Some of the physical or visible changes include fading or discolouration, cracking or peeling on the sheath, and increased brittleness.
Electrical – Weathering can lead to the potential breakdown of insulation or simply reduce the dielectric strength. If a cable has a high dielectric strength, that means the insulation can resist the voltage and retain the current within the conductor. Any reduction in dielectric strength means a higher risk of short circuits and faults, which could pose significant safety risks.
Mechanical – PVC cables that have been affected by weathering tend to become stiff, making them harder to bend without cracking. That means they become more susceptible to damage during installation and termination.
How to mitigate the risks
Although all PVC cables can be affected by weathering, it is important to only use cables intended for outdoor use. Outdoor PVC cables have UV protection built into their sheath, because they are specifically designed for outside use. For example, according to BS 7671 (IET Wiring Regulations), cables exposed to direct sunlight must be suitable for the application. That means using UV-resistant PVC cables for applications such as solar panel installations.
Indoor cables do not have UV protection so should not be used outdoors. Twin and earth cables, for example, are indoor cables designed to meet British Standard BS 6004, they are not suitable for outdoor use. Installing these cables outdoors will likely lead to a breakdown of the cable sheath and insulation and expose the live conductors. This poses serious safety risks, such as electrical shock and fire, and cause the circuit to fail.
Prysmian design and manufacture a range of cables in the UK, specifically designed for outdoor use. This includes BS 5467, which is a steel wire armoured (SWA) cable. BS 5467 cable can be directly buried into the ground and is designed to withstand harsh outdoor environments such as UV exposure from sunlight, water, mechanical damage, extreme temperatures, and rodent attacks.
Other cables include Prysmian LSX, a Low Smoke Zero Halogen (LSOH) and flame-retardant cable for low voltage wiring circuits. The cable has a white sheath, which means it reflects sunlight, giving it some UV stability. That means LSX cables can withstand normal UK sunlight, however, it’s recommended that it is installed in voids or surface and shaded from strong sunlight.
In some cases, if you are installing Prysmian 6491X single core cable for an outdoor lighting project for example, it should be installed in a surface mounted or embedded conduit or trunking system to protect it from mechanical and environmental damage.
As well as manufacturing cables, Prysmian develops its own specialist PVC compounds. This level of expertise ensures consistent quality, reliability, and ensures compliance with all British Standards.
PVC cables are a reliable choice for many electrical applications, but their performance outdoors can be compromised by UV-rays, temperature extremes and moisture. Following guidance set out by the British Standards and installing Prysmian cable ensures long-lasting, safe, and reliable installations.
Looking for more guidance on the use of PVC cables? Contact us today to speak to an expert.