In modern electrical installations the use of thermoplastic materials for installation equipment and distribution boards is very common. Their excellent insulation properties, low weight, high impact strength and corrosion resistance are the reasons for their popularity.

Power losses of components, terminals and cabling leads to higher temperatures inside enclosures, cable junction boxes and distribution boards. Manufacturers of electrical devices provide technical data that indicates the maximum power loss allowed inside enclosures and boards. This assists in selecting enclosures of the correct size. For modern thermoplastics, these temperature levels generally do not pose a problem. Higher temperatures can be the result of the maximum limit of the material temperature being exceeded. For instance if a wire is not correctly fixed inside a terminal the high resistance and possible sparking may cause the temperature to reach very high levels. If this is not detected early enough the result could be that the material starts burning causing flammable substances to drip and ignite other material.

To avoid fires in case of such failures, some materials are enriched with special additives which make the materials self extinguishing and flame retardant.

Unfortunately many of these additives have some other negative effects in cases of fires. While taking away the oxygen from the flame they create toxic gases like halogen at the same time which in many instances causes more harm and injury to people than the fire itself. For this reason regulations and technical specifications were modified and required that products be free of these toxic gases. This resulted in some manufacturers changing or removing the additives that caused toxic gases which in many cases reduced the self extinguishing behaviour of the material again.

These products are often marked as “halogen free”. This marking does not say anything about the self extinguishing behaviour of the material. A study conducted by an insurance company in Europe noticed that the number of fires in agricultural buildings caused by electrical installations had increased since the introduction of halogen free requirements in product specifications. In testing they noticed that many of the well known products did not meet self extinguishing requirements. The products that passed the test were made out of more expensive material and additives that prevented toxic gases in case of fire and improved burning behaviour as well. These products are more expensive because of the material used but provide a far better and safer solution.

For the electrician or the end user it is very difficult to tell from the out side the difference in the type of material being used and to predict the behaviour in case of electrical faults. For this reason, special tests that classify the behaviour of the material in case of electrical faults have been implemented into the standards. The Glow-Wire test according to IEC 60 695-2-11 simulates a glowing wire that makes contact with the surface on the inside of the box. This test is done at different temperature levels for different applications - 650°C, 750°C and 960°C. All electro technical equipment must pass this test with a temperature of 650°C as a minimum.

It is safe to say that the higher the temperature rating the better the quality of the material and the self extinguishing behaviour.

Hensel from Germany is a leading manufacturer of Thermoplastic enclosures and uses different types of materials across their range of modular enclosures and cable junction boxes. The DK and KV range are glow wire tested to 750°C while the KF, KD and Mi are tested to 960°C. All materials are “halogen free”. Hensel are represented in Australia by IPD Industrial Products.