There are plastics available as alternatives to PVC which have the advantage of being able to operate at higher temperature . The most usual is XLPE , which is a cross linked polyethylene compound . Another alternative is hard ethylene propylene rubber compound , which is designated HEPR . These materials are normally used olny in cables which have cable armouring over the insualtion and an outer sheath over the armouring . The outer sheath is generally of PVC . The construction is then similar to that of the PVC wire armoured cable shown in Figure 2.3 , the olny difference being that the inner insulation is XLPE or HEPR of PVC .
Butyl rubber
This insulation is used for cables which are to be subjected to high temperatures . It is , for example , used for the final connections to immersion heaters , for the control wiring of gas-fired warm-air heaters and within airing cupboards . it can safety be used for ambient temperatures up to 85 celcius . Buty rubber also has greater resistance to moisture than natural rubber .
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