4.4

Question:

 

In the technical data for ÖLFLEX® HEAT cables, what is the meaning of "adequate ventilation provided" under the temperature range specification?

 

 

Answer:

 

Many operators and users are unaware that special factors have to be considered when installing cables in areas with raised ambient temperatures. This not only includes the self-heating resulting from the current load, but also the material-specific behaviour of the core and sheath insulation in high ambient temperatures. Non-electricians in particular are mostly not familiar with the fact that the ampacity of a cable is reduced as the temperature increases.
For example, an ÖLFLEX® CLASSIC 100 3 G 1.5 mm² can carry 18 A (100%) at an ambient temperature of +30°C. If the temperature rises to +60°C, the ampacity is reduced to 9 A (50%) – calculated on the basis of VDE 0298-4 / catalogue appendix table T12-1 or T12-2.


Due to a complex chemical conversion process (formation of orthosilicic acid), insulation materials like silicone, which are regularly used in ambient temperatures up to +180°C, can harden and embrittle prematurely as of +100°C in the absence of adequate ventilation. If the max. permissible ampacity and associated self-heating of the cable is also exceeded, the ageing process accelerates accordingly. To counteract this effect, adequate volumes of air or oxygen must be supplied to such cables and wires when operated in high ambient temperatures. If closed ducts, tubes or pipes are packed full of cables, this can often result in premature damage as a result of disintegrated insulation and cable sheaths or even corrosion of the copper conductor.