Differences between Thermoplastic and Thermosetting cables PVC and XLPE

by Editor on June 1, 2016

What are the differences between Thermoplastic and Thermosetting cable insulations?

There’s not a great deal of difference in cost between XLPE and PVC SWA cables, so I always tend to use XLPE and often the Low Smoke version. But for the purpose of specifying the cheapest cable for a job I’ve taken a look at the actual spec differences between Thermoplastic and Thermosetting cables. Here’s some background info about thermoplastic PVC and thermosetting XLPE cable insulations. Also a video shows some testing of Low Smoke vs PVC insulation.

The IEE Regs Table 52.1 states– Maximum operating temperature limits for types of cable insulation-
Thermoplastic as 70 °C at the conductor and Thermosetting as 90 °C.

PVC Thermoplastics
Thermoplastics are commonly used and are known for their ability to melt and remold repeatedly. They are able to do this because thermoplastic materials are composed of chains of molecules which will separate once heat is applied. Common thermoplastics include PVC, polyurethane, polypropylene, TFE, and FEP.

XLPE Thermosetting
Because thermoset materials do not melt, they are usually a more appropriate choice for insulation on wire and cable to be used in higher temperature applications.
Thermoset materials are made of polymer structures which are cured to become natural or synthetic rubber materials.
During production process of thermosetting cables the polymer chains are cross-linked with other molecules. This is why thermoset materials are sometimes called cross-linked. This is abbreviated with an XL, as in XLPE for cross-linked polyethylene. Other common thermoset materials are natural rubber, SBR, EPDM, silicone rubber, Neoprene, and Hypalon.

Unlike thermoplastics, once thermoset materials are molded, it is irreversible. If heat is continually applied to thermoset insulation it will burn rather than melt.

Spot the Difference
There is no easy way of identifying thermosetting without any info printed on the cable sheath. PVC to BS6346, XLPE to BS5467 or BS6724 (Copper Conductors). Non-armoured thermoset cables are often white or grey but SWA armoured cables are black.
Thermoset XLPE is generally thinner material than thermoplastic PVC (which is no bad thing for installation!) and XLPE armoured cable has a smaller amount of steel. The difference between the resistance of the armouring is negligible. SWA Chart.

How are cables made? Watch this video:

Low Smoke
As well as being enhance by thermosetting, cable insulation can also be enhanced by low smoke properties. XLPE/LSF, LS0H or LSZH (Low Smoke Zero Halogen or Halogen Free) cables are slightly more expensive but have the advantage of not giving off toxic fumes when exposed to fire.

It is now widely accepted that the poisonous fumes given off by burning cables are often a much greater risk to life than the fire itself. Low smoke halogen free cables are applicable to many electrical installations in public places such as the London Underground.

This video shows how PVC melts and burns vs Low Smoke cable:


ElectriciansBlog.co.uk

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