PVC sheathed cable, including TPS and circular cables should not be installed in direct contact with polystyrene insulation. Polystyrene can cause migration of the plasticizer out of the plasticised PVC cable compound, resulting in the cable sheath becoming brittle over time. It is recommended that conduit or some other separating material be used to keep the plasticised PVC out of direct contact with the polystyrene. Alternatively, cable that is PVC free, such as cable from Nexans Olex’s halogen free Envirolex® range can be used in direct contact with the polystyrene insulation.
A minimum thickness of insulation is required to offer a reasonable level of resistance to mechanical damage. If only enough insulation was used to insulate to 240 volts, the covering would be too easily damaged.
This is the method adopted generally by Australia, UK, Asia and Europe in indicating the voltage rating of a cable. The first number indicates the voltage rating of the insulation to ground and the second number indicates the voltage rating from one insulated conductor to another insulated conductor. Generally if a cable is only referred to by one voltage, the second number is used. For example a 19/33kV cable is often referred to as a 33kV cable.
Some contractors interpreted the V105 rating as a continuous operating temperature of 105°C, which is incorrect. The V105 grade should only be operated at this temperature for limited periods under certain conditions. In order to avoid this confusion, the name has been changed to V90-HT, ie indicating that the cable can operate at high temperatures for limited times. The actual composition of the PVC has not changed.
All grades of PVC are nominally rated at a 75°C operating temperature for normal installations however the higher PVC rated cables can operate at higher temperatures under certain conditions. These conditions are outlined in AS/NZ 3000:2000, but generally limit the time at which they can operate at those temperatures and restrict their usage where there is no potential for mechanical damage (PVC softens considerably at these temperatures). XLPE does not soften at 90°C and hence does not have the installation and operation restrictions of PVC.
Flat sheathed cable has one less operation in manufacture, contains less PVC than a circular cable and is therefore cheaper and being relatively flat it can be easier to install where space is confined. The disadvantage of flat sheath is that any twists makes neat installation difficult and it is very difficult to handle as conductor sizes increase.
There are two main differences between a cord and a cable.
A cord includes conductor sizes up to and including 4mm2 and up to five cores, and is generally rated at 240/440 volts (although some heavy duty flexible cords are rated at 0.6/1kV).
A cable includes conductor sizes of 6mm2 and above and is generally rated at 0.6/1kV. Cables with flexible conductors less than 6mm2 and with a core count greater than five core are also classified as flexible cables.
Tinned conductors resist corrosion and are therefore very suitable for marine applications. It is also necessary to tin conductors where a rubber insulation comes in direct contact with the conductor. The use of tinned conductors also assist in making the conductor easier to solder.
The standard Olex range of instrumentation cables have been tested in our factory at 2kV core-core and will withstand operating voltages in excess of 500 V AC without failure.
However, their insulation thickness of 0.4mm radial thickness does not meet Australian Standard requirements for mains voltage operation (250/440 or 0.6/1kV), hence the cables are supplied for use in Australia in instrumentation and similar applications with nominal working voltage of 110 V AC or 150 V DC. For export use, where Australian Standards compliance is not a requirement, the Instrolex cables are rated 300 V AC/DC.
Instrolex cables are not made to any Australian Standard. The Instrolex design is identical to the Olex manufactured Dekoron product and is an internationally recognised and proven design for industrial instrumentation applications.
Individual components of the product however, do conform to various Australian Standards such as AS/NZS 1125 for the conductors, AS/NZS 3808 for the insulation and sheathing materials and AS3863 for the armouring materials. In addition, the Instrolex cables are manufactured in accordance with the Olex certified Quality Management System complying with AS/NZS ISO 9001.
With regards to the Hazardous Area Standards, Instrolex complies with this standard for Intrinsically Safe circuit provided that it is installed in accordance with the requirements of the relevant Australian Standard.
Some instrumentation cables on the market reduce costs by reducing the amount of twist in the pairs and using a PVC compound with a lower temperature rating. The fewer twists increases the manufacturing speed and with the reduced rating of the PVC, reduces the overall cost of the cable.
Olex continue to use a PVC compound that has reduced flame propagation and a temperature rating of 90°C for superior performance. It still utilises varying twist rates between adjacent pairs for superior crosstalk immunity.
Instrolex instrumentation cables are in fact a “heavy” duty” or industrial type of data cable. The wires are larger and the cable tends to be more substantial, making the whole assembly less fragile. In addition, the high level of noise in an industrial environment places extra demands upon the screening that is required. Hence, pairs are often individually screened as well as overall screened (as explained in the previous question).
The overall screen will protect the interior of the cable from external interference, however individual pairs or triples may create interference between themselves, which has the potential to distort signals in adjacent pairs. The use of individually screened pairs or triples reduces this distortion.
The presence of large machines, welders and other processes in industrial environments create a lot of electrical interference (noise). This noise has the potential to distort the clarity of signals that are transmitted between equipment, which may lead to false readings, For example, a system monitoring the temperature of a boiler may not report the correct temperature. A metallic screen will shield the cores of a cable from interference, thus improving the clarity of a signal.
The AS/NZS 3013:2005 fire test requires that all of the items that comprise a cabling system operating in the fire rated zone must be tested and pass as a system. In other words, it is no longer possible to test the cable in isolation. Other components that may comprise a system include fasteners, saddlers, ladders, cable trays, clamping systems, etc. Joints only need to be tested if they are installed in the fire rated zone. Alsecure® is available in lengths to suit the contractor, hence this requirement should not be necessary.
A length of cable is energised and the impacted with a device, loaded with a predetermined weight. The impact point will consist of two different points, a blunt crushing type of point and a sharp cutting type of point. If the cable maintains circuit integrity through this test, it attains a mechanical rating. Different loads can be applied to attain different levels of rating.
The fire test for determining the fire rating of a cable consists of exposing a cable and fittings to extreme temperature in a furnace over a period of two hours. The temperature builds throughout the period to a final temperature of around 1030°C. The cables are subjected to their round operating voltage and a current flows through the conductors. If the insulation fails, ie shorts to ground, or if the current stops flowing, the test has failed. This test permits comparisons between different manufacturer’s products and provides a benchmark on which installation standards can be based.
No, a cable with a fire rating does not necessarily mean that is it suitable for use in a hot environment. It is necessary to design cables using special materials such as silicone or glass fibre to withstand relatively high temperatures (in excess of 110°C on a continuous basis.)
Fire rated cables are designed to continue functioning during the course of a fire for a specific period of time which allows for safe evacuation of a building by maintaining smoke handling systems, emergency lighting etc. The cable will burn however in a manner that ensures circuit integrity during the fire. The tests to determine the fire rating of a cable system are documented in AS/NZS 3013:2005.
Flexible conductors have a larger diameter compared to a nominal stranded conductor of the same nominal cross-sectional area. Since the diameter of the flexible conductor is larger, it is difficult to insert into the barrel of a lug of the same cross-sectional area.
One method of terminating is by using the next largest lug size and crimping with a half hex and flat dye. Alternatively, a special lug suited to flexible conductors can be sought.
Further information on crimping techniques can be obtained from lug manufacturers.
Compacted conductors have a smaller diameter compared to standard stranded conductors, but their nominal cross sectional area is equivalent and a lug designated for the same cross sectional area must be used on the compacted conductor. Even though the lug will appear to fit more loosely, when crimped in accordance with the lug manufacturer’s recommendations, the end result is the equivalent to the crimping of a standard conductor. Compacting the conductor by the cable manufacturer is just the action of pushing all the wires together, getting rid of the air gaps, ahead of time.
Note: The general practice is for lug manufacturers to manufacture a range of lug sizes that suits both the compacted and standard conductors. However, if there are any concerns, please consult your lug manufacturer.
Yes, orange circular PVC are suitable for use outdoors, since they have an outer sheath which protects the core insulation. Whilst some fading of the colour of the sheath is expected over time, this is restricted to just the outer surface layer and does not penetrate into the bulk of the sheath material. Therefore the sheath will continue to provide protection of the core insulation. In addition AS/NZS 3000:2000 states in Note 1 to Clause 3.3.12 - “Sheathed cables exposed to direct sunlight do not require further protection from ultraviolet radiation as the sheath is considered to provide the necessary protection.”
The term “UV stabilised” has an understanding in the cable industry to mean the addition of a minimum amount of carbon black to a material (2%). In reality, this is only essential for Polyethylene exposed to UV, such as XLPE Aerial Bundled cable or in high density PE in High Voltage cables. This will obviously render the material black and is regarded as the best means of UV protection of a material. Even black PVC sheathed cables, using only 0.5% carbon black, will not suffer from fading. The orange circular PVC cable does not contain carbon black, but the material is still “UV resistant”.
A current which flows in a conductor will cause a voltage drop over the length of conductor due too its resistance. The cable size can be determined to find Vc as shown below:
Vc = 5 x V x 1000
100 L x I
When Vc is found, it is then necessary to look up the appropriate table of volt drop factors in AS/NZS 3008.1.1 to find a cable size which has a lower voltage drop factor than that just calculated. After obtaining the cable size, the continuous current rating must again be checked. If the cable size meets or exceeds the required current, I, then this is the answer. If not, the cable size must be increased until the current, I, is obtained.
A current which flows in a conductor will cause a voltage drop over the conductor’s length. This voltage drop is due to the resistance of the conductor. The Wiring Rules AS/NZS 3000:2000 states a maximum limit for voltage drop of 5% for low voltage systems. Therefore there is a simple calculation which can be done that relates the percentage volt drop, the cable length, and the voltage drop factor for a particular cable. This calculation and voltage drop factors (in mV/A.m –milliVolt per Amp metre) are given in AS/NZS 3008.1.1. The formulae for how much current is:
I = 5 x V x 1000
100 L x Vc
I = cable current that produces the maximum voltage drop
V = system voltage (ie normally 400V for 3 phase and 230V for single phase)
Vc = mV/A.m volt drop factor for cable from AS/NZS 3008.1.1
L = circuit length
Note: In addition to performing this voltage drop calculation, the continuous current rating of the cable must be checked.
The continuous current rating of a cable is determined by the ability of the cable to dissipate the heat generated by the current passing through its conductor. It depends on a number of parameters, but the most important are the:
•Conductors’ DC resistance;
•Thermal resistance of the insulating sheathing materials; and
•Ambient conditions of the environment where the cable is installed (for example the surrounding air temperature).
For standard cables such as PVC building wire, XLPE SDI or circular cables (all rated 0.6/1kV), the ratings have all been calculated and are tabulated in Australian Standard AS/NZS 3008.1.1. This standard includes various circuit configurations such as single and three phase and various installation arrangement such as “in air”, “direct buried in ground”, “in ducts”, etc.
Olex has included the same tables from AS/NZS 3008.1.1 in the Standard Product Search our customer’s convenience.
For ratings of HV XLPE cables, please see the attached HV PDF in the products sections.
If ratings are required for non-standard cables or for cables in non-standard installation or environmental conditions, Olex have specialised software available for performing the rating calculation to suit specific customer requirements.
Cross Linked Polyethylene. A high grade insulation material.
Registered Trade Name for a range of cables insulated with a cross linked flexible polyolefin and sheathed with a TPE. These cables include flexible conductors and are suitable for both fixed and flexing applications. The cables are constructed to comply with AS/NZS 5000.1 (power and control), AS/NZS 3191 (cords), AS/NZS 1995 (welding), IEC 60227.4 (PVC cords), and IEC 60245.4 (EPR cords). The range includes TCWB screened cables. A range is also available with pilot cores for submersible pumps.
Registered Trade Name for a range of cables suitable as Variable Speed Drive supply cables. The cables are insulated with XLPE, overall copper screened, and sheathed with PVC. The range available includes fixed conductors with copper tape screen, or flexible conductors with copper braid screen. The key features include low capacitance of the power cores, high electrical strength insulation, and three earth conductors of maximum size disposed in the cable interstices. These cables are constructed to comply with AS/NZS 5000.1 (0.6/1kV power), but include the extra features to provide a low impedance path to ground for high frequency signals and to withstand the higher voltages at the motor terminal ends.
Thermoplastic Elastomer. A plastic material compounded so it displays characteristics like an elastomer. TPE is normally tough, cut resistant, flexible, smooth, with vibrant colouring.
TCWB Tinned Copper Wire Braid.
Steel Wire Armour. This is used to provide mechanical protection for the cable.
Trade Name for a range of PVC flexible cords and cables compliant with all relevant Australian standards.
Polychloroprene (DuPont Trade Name for this product is Neoprene). This is an oil-resistant, tough sheathing material, that is used mainly in mining cables as an outer sheath.
Low Smoke Zero Halogen.
Registered Trade Name for a range of Instrumentation cables insulated and sheathed with a flame retardant PVC. The standard range includes up to 50 pairs and up to 36 triples in either 0.5mm2 or 1.5mm2 conductors. Larger conductors may be specified, as can options of Lead Sheathing, SWA, or HF insulation and sheath materials.
Heat, Oil and Flame Retardant.
Halogen Free Flame Retardant.
High Density Polyethylene, generally used as a sheathing material where it provides high resistance to water penetration, is very hard, has low coefficient of friction, and is abrasion resistant.
The property of cables to retard or slow the progress of fire and flame along the cable. This is achieved through the use of materials that do not readily burn and will tend to self-extinguish.
The property of cables to continue to function while under the influence of fire. Olex cables that are Fire Resistant provide circuit integrity even when burned and maintains integrity after the fire has extinguished. In most cases, the cables will withstand a water spray and still provide circuit integrity.
Registered Trade Name for a range of Nexans Olex flexible, fire-retardant cables developed for industrial applications. Engineered to reduce environmental impact under fire conditions and assist in reducing emissions of harmful gases that may hinder evacuation processes. Built to comply with AS/NZS 5000.1, AS/NZS 1995, AS/NZS 4507 RHE.
Ethylene Propylene Rubber. A water and ozone resistant, flexile, cross linked high grade insulation material.
Oil, ozone and heat resistant sheathing material. DuPont Trade Name for this product is Hypalon.
Chlorinated Polyethylene. An oil, ozone and heat resistant sheathing compound.
Registered Trade Name for a range of Nexans Olex flexible, fire-rated cables designed to preserve circuit integrity of essential services and electrical equipment during fire. Built to comply with AS/NZS 3013, AS/NZS 5001.1, AS/NZS 4507 RHE.
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