AS/NZS 3008.1 (2017) "Electrical installations - Selection of cables - Cables for alternating voltages up to and including 0.6/1 kV" is the standard governing low voltage cable sizing in Australia and New Zealand. AS/NZS 3008.1.1 is for Australian conditions and AS/NZS 3008.1.2 is for New Zealand conditions.
Therefore the current carrying capacity of PVC insulated low voltage cables, as documented in Australian Standards AS/NZS 3000:2007 and AS/NZS 3008.1.1:2009,.are based on a maximum operating temperature of 75C.
NZS 3008.1.1 2009 Electrical Installation Selection Of Cables..pdf
The intent of the higher rated PVC cables, with V-90 and V-90HT insulation, is to allow these cables to operate at their higher rated temperature only under certain special conditions. These conditions are outlined in AS/NZ 3000:2007 and in AS/NZS 3008.1.1:2009, and they generally restrict their usage to only those installations where the risk of mechanical damage is low. This is because PVC softens considerably at higher temperatures and therefore is more vulnerable to mechanical damage. Examples of these special conditions might include cables that are enclosed in a manner that affords mechanical protection, ie installations in conduit, or in situations where the cable is installed within thermal insulation that restricts the dissipation of heat from the cable.
Other cable insulation materials exist that do not exhibit the same thermal properties as PVC, include Cross Linked Polyethylene (XLPE). Being a Cross Linked material XLPE (designation X-90 within AS/NZS 3008.1.1) has the property of maintaining its shape and does not flow at the higher operating temperatures and hence does not have the same installation and operation restrictions of PVC.
The standard designations of PVC insulation used in Australia are V-75, V-90, and V-90HT. Regardless of their designation all grades of PVC are rated at 75C operating temperature for continuous use.Therefore the current carrying capacity of PVC insulated low voltage cables, as documented in Australian Standards AS/NZS 3000:2007 and AS/NZS 3008.1.1:2009,.are based on a maximum operating temperature of 75C.The intent of the higher rated PVC cables, with V-90 and V-90HT insulation, is to allow these cables to operate at their higher rated temperature only under certain special conditions. These conditions are outlined in AS/NZ 3000:2007 and in AS/NZS 3008.1.1:2009, and they generally restrict their usage to only those installations where the risk of mechanical damage is low. This is because PVC softens considerably at higher temperatures and therefore is more vulnerable to mechanical damage. Examples of these special conditions might include cables that are enclosed in a manner that affords mechanical protection, ie installations in conduit, or in situations where the cable is installed within thermal insulation that restricts the dissipation of heat from the cable.Other cable insulation materials exist that do not exhibit the same thermal properties as PVC, include Cross Linked Polyethylene (XLPE). Being a Cross Linked material XLPE (designation X-90 within AS/NZS 3008.1.1) has the property of maintaining its shape and does not flow at the higher operating temperatures and hence does not have the same installation and operation restrictions of PVC.
Targeted at electricians, engineers and other electrical enthusiasts, Wire Wizard is a tool designed to assist the appropriate selection of wires and cables according to the Australian and New Zealand standard AS/NZS 3008.1.1:2009.
Cable Planner launched in August 2010. At the moment it calculates maximum demand for both domestic installations (houses and units) as well as other installation types (residential institutions, factories, offices, etc). One day I plan to improve it so that it guides you through the Cable Selection rules too (AS/NZS 3008.1.1:2009).
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