AS/NZS Specifies the construction, dimension and test requirements for single-core and multi-core polymeric insulated and non-metallic sheathed. AS/NZS (R). Electric cables – Polymeric insulated – For working voltages up to and including / V. standard by. AS/NZS Category: Cord and Cables. Description: Electric cables – Polymeric insulated – For working voltages up to and including / V.
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There has been much publicity recently about the recall of non-compliant building cables, but what does compliance actually mean as far as a cable is concerned and how does it actually relate to performance? Introduction In this article I will try to unravel some jzs the less known aspects of cable compliance with the overall aim to give the user the correct information to make better informed decision when selecting cable products.
AS/NZS – Standards Australia
Due to the level of detail required to address this topic it will be presented in two parts. This first part looks at the electrical and physical dimensional testing requirements for cables, whilst the second part looks at the range of material tests that cable materials must meet to enable compliance to be obtained.
This is a legally mandated document, and therefore the risk of non-compliance is not only unsafe it is also illegal.
This document defines the principles upon which electrical installations must be designed and installed in order to protect people, livestock and property from the risk of electrical shock, fire and physical injury hazards.
In terms of cables the wiring rules makes direct reference to Australian and New Zealand Standards as the principle means to ensure that its scope is fulfilled. The following sections refer to a range of tests that are conducted on cables to ensure compliance. Type tests need not be repeated unless changes are made in the cable materials or design or manufacturing process. Ability to Carry Rated Current The ability of an electrical cable to carry its design electric current is largely dependent on the electrical resistance of the conductor.
The actual area is not critical nor is it a parameter that must be measured. This is a very important and often misunderstood issue. A 35mm2 copper conductor, for example, does not need to have 35mm2 of copper in it. It only needs to meet the specified resistance value. And neither is the diameter of a conductor important as far as compliance is concerned.
Smaller diameter conductors, such as compacted, or the larger diameter non-compacted conductors, do not matter. Only the electrical resistance is mandatory. When looking at the impact of non-compliant resistance on the current rating of a cable, its impact is relatively small, as its current rating is proportional to the inverse of the square root of resistance.
Then there is the material that is in contact with the conductor. The manner in which compliance of these materials is confirmed is complex and will be covered in some detail under the discussion later on insulating materials.
A variety of cable insulating materials exists in the cable manufacturing industry, all having differing properties, but all having the primary attribute of being suitable as an electrical insulating material. Their differences lie in their cost, processability, dielectric performance, mechanical strength and flexibility to name a few.
Some of the common cable insulating materials are listed below:. To confirm that a cable can hold its rated voltage the cable is subjected to the following checks and test:.
In the case of insulation thickness, this varies with material type and conductor size. The insulation thickness for LV cables is not primarily based on electrical requirements, but more on mechanical considerations. The insulation thickness on large conductor sizes is greatest due to the greater risk of mechanical damage during handling of large and heavy cables.
The improved electrical properties of XLPE is a result of the chemical makeup of the material, being almost exclusively polyethylene. PE has significantly greater dielectric strength compared to PVC, which is a blend of a number of ingredients of which Poly Vinyl Chloride is one.
AS/NZS 5000.2 Standard Switchboard Flat TPS Electric Wiring and Cable
Cross-Linked materials are more thermally stable compared to Thermoplastic materials and will not flow when subjected to high operating temperatures. They may ss, but will not flow. Voltage tests performed on cables are done at higher than normal operating levels. This is a common testing principle where the test object is subjected to a higher stress than it would normally be expected to operate at, with the intention to flush out extrusion defects or weaknesses in the insulation materials.
These performance requirements are largely based on the mechanical properties of the materials used in cables.
The following briefly describes each of the above tests, their purpose and how they relate to the mechanical performance of the cable in terms of installation and long term operation of the cable. The standards referred to in details the test method used to conduct each test.
In the first part of this article I will address the first dot point only. The remaining dot points will be addressed in part 2. It will be fairly obvious that the thickness of the insulation and sheath material must be aligned with the typical use of the product.
As previously explained it is common for low voltage cable standards to define an insulation thickness which varies for different conductor sizes, with the largest conductor having the thickest insulation and sheath. What may be not so obvious is how the thickness is actually measured. The thickness of insulation and sheath of cables is done by taking six measurements at the location where the material is thinnest using optical magnification equipment of at least 10X to allow a reading of 0.
See examples in Figure 1 for various types of extrusions. These are the two measurements that compliance is confirmed and is required by nearly all cable standards today. The measurement method described above has traditionally been carried out by manual methods and is therefore subject to human error.
Modern manufacturing techniques have seen the introduction of automated electronic measurement systems to replace manual methods that provide a significant improvement in repeat accuracy.
To be continued in Part 2.
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