LICENCE for AS/NZS Electrical installations – Selection of cables – Cables for alternating voltages up to and including /1 kV – Typical. Electrical installations – Selection of cables – Cables for alternating voltages up to and including /1 kV – Typical Australian installation. The calculator calculates the short circuit fault current at a specified distance in a cable run, based on the source short circuit fault current level. See also the full.
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In many situations, however, the cable operating temperature is considerably less than the maximum figure.
In general, the current-carrying capacity requirement will be the most demanding in the relatively shorter route lengths of domestic premises and the like where factors such as semi-enclosed rewirable fuse protection, cable grouping, and thermal insulation occur. The time limit for the use of the adiabatic method has a different definition, being a function of both the short-circuit duration and the cross-sectional area nas the current-carrying component.
nas The need to increase cable size to meet the short-circuit temperature rise requirements will only occur in special situations for the voltage ratings of the cables covered by this Standard.
The contents of the Standard are a development of the limited provision of Appendix B to AS and it is expected that over subsequent revisions of ASAppendix B will be modified and reduced in size and reference made to this Standard. The following two types of material have a worst-case or dried-out thermal resistivity in the order of 1. If thermal separation is not provided, the temperature limits of the insulation should be used if it is lower than that of the sheath.
Actual values would need to be calculated according to loading. The use of nzzs in print form or in computer software programs to be used commercially, with or without payment, or in commercial contracts is subject to the payment of a royalty.
A, the current-carrying capacity of neutral-screened aerial cables shall be determined as follows: This Standard differs from the edition as follows: The current-carrying capacity assigned to the underground portion of the cable run may be assigned to the above-ground portion where the prevailing installation conditions maintain the final operating temperature of the cable within the limits given in Table 1.
Where applicable, divide the value of current determined in Step b by — i the ambient air or soil temperature rating factor selected from Tables 27 1 and 27 2 ; ii the depth ss laying rating factor selected from Tables 28 1 and 28 2 ; and iii the soil thermal resistivity rating factor selected from Table For the purpose of determining the maximum voltage drop value in Nzzs 4.
Specific guidance on the use of Tables 0308 to 26 is given in Clauses 3.
Cable short circuit fault current calculator AS/NZS |
Higher current-carrying capacities are obtained in clay or peat soils which may have resistivities as low as 0. However, the cables are generally installed in areas of high ambient temperature, such as equipment wiring, and it will be necessary to apply an appropriate temperature correction factor from Table Care should be taken to ensure that material used is from the ss edition of the Standard and that it sa updated whenever the Standard is amended or revised.
Part 2 will deal with cables for use with alternating voltages over 1 kV. The time taken to reach this steady state temperature will vary depending on the type of cable and installation conditions.
It is important therefore that Standards users ensure that they are in possession aas the latest edition, and any amendments thereto.
Cable short circuit fault current calculator AS/NZS 3008
The relative importance of these different factors for a particular installation will, in general, determine the cable arrangement selected. A specific installation condition is defined and illustrated and alternative installation conditions deemed to have the same current-carrying capacity are also given. On the other hand the voltage drop limitation is usually the deciding factor for longer route lengths which are not subject to the factors mentioned above.
Such cables, which would include earthing conductors, lightly loaded neutrals and unloaded control wiring, may be placed adjacent to, or between, groups of associated loaded conductors.
Specific conditions of installation are laid down in Clauses 3. Also, provided in 300 5 is information on cable selection based on short-circuit temperature limits. The subject qs assigning a current-carrying capacity to a cyclically or intermittently loaded cable is not covered in this Standard as it normally relates to HV cable installation.
Method D would be operating at near maximum load. Suggestions for improvements to Joint Standards, addressed to the head office of either Standards Australia or Standards New Zealand, are welcomed.
The limits quoted are based on average hardness grades of PVC and some adjustment may be necessary for other grades, especially those compounded for improved low-temperature properties.
In other situations of load power factor the difference between the magnitudes of the supply voltage E and the load voltage V L is smaller. Table 2 4 contains a reference to the appropriate current-carrying capacity table for cables installed in underground wiring enclosures. Where other depths of laying apply, the appropriate rating factors shall be as given in Table From the derating factors of Table 22, which vary according to the number of enclosed circuits, it can be shown that five parallel circuits of mm2 conductors, as illustrated, are required.
Where applicable, divide the value of current determined in Step a by the derating factor so determined. The work carried out by Dr V. For thermoplastic insulating materials the limits must be applied with caution when the cables are either directly buried or securely clamped when in air.
Such factors will invariably determine the minimum current requirements for the application of this Standard.
In such cases appropriate rating factors may be obtained from ERA Report These conditions have been used to derive the current-carrying capacities tabulated in Section 3. Attention is drawn to the minimum bending radius recommended for the type of cable.
For further information on the effects of ultraviolet radiation it is recommended that the cable manufacturer be consulted. However, in doing so the following factors which may determine the system to be selected are highlighted: The rating factors are based on the assumption that the effective thermal resistivity of the ground is constant from a depth of 0.
Tables 2 1 to 2 4 also draw attention to the different methods of installation which may be assigned the same current-carrying capacity and refers to tables of derating factors applicable where one circuit is run in close proximity to another circuit or circuits. Up to 10 percent of the technical content aa of a Standard nzzs be copied for use exclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia or Standards New Zealand.
See Appendix B for recommended circuit configurations for ass installation of single-core cables in parallel. In addition the values for bare conductors are based on black weathered conductors and the values for insulated conductors are based on the use of black PVC or XLPE.
For nzx types of cable installed in locations exposed to direct solar radiation it will be necessary to make some provision for the effects of the increased heating.