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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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 of laying rating factor selected from Tables 28 1 and 28 2 ; and iii the soil thermal resistivity rating factor selected from Table Three criteria are given for cable selection, as follows: From the derating factors of Table 26 2 for groups of underground enclosures, it can be shown that four conduits or ducts, each containing a circuit of mm2 conductors and touching, as illustrated, are required.
The rating factors are based on the assumption that the effective thermal resistivity of the az is constant from a depth of 0.
Enter the email address you signed up with and we’ll email you a reset link. In determining the short-circuit stresses which will be imposed on a cable, the characteristics of the protective devices used az be considered. Appropriate calculations are as follows: Furthermore, a still smaller supply voltage is required to maintain the given load voltage when the current leads the load voltage.
Where different materials or installation conditions are used 300 that the rate of heat dissipation is adversely or favourably affected, lower or higher current-carrying capacities may be obtained respectively.
Cable short circuit fault current calculator AS/NZS |
The single-phase value is then determined in accordance with Clause 4. From the derating factors of Table 26 1 for groups of underground enclosures, it can be shown that four trefoil groups of single-way underground ducts, each group representing a circuit of mm2 conductors, as illustrated, are required.
Where the soil is known to be of poor quality and has a thermal resistivity greater than 1. Final Australian edition AS It can be seen that in the particular instance where the cable power factor and the load power factor are equal, the voltage drop V d is a maximum of IZc as discussed in Clause 4.
However, care must be taken that the cable environment and means of support can withstand the higher temperatures. Where it can be shown that intermittent load variations will occur or that all conductors cannot be loaded simultaneously, appropriate uprating factors may be applied. 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.
Each Part is a complete Standard and requires no reference to the other. These temperatures are for materials where there is no electrical or other requirements necessary, i. 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.
Where this occurs the current-carrying capacity given in this Standard is considered to be more accurate, but either value is acceptable for the application of any appropriate requirements of ASe. For conductors and metallic sheaths it is sufficient to take the nominal cross-sectional area but in the case of 3008, this quantity requires careful consideration.
For derating factors applicable to other arrangements of cables in underground wiring enclosures, refer to ERA Report or alternative specifications. The value of 1. A more accurate assessment can be made of the actual voltage drop V d using 308 appropriate equation of Clause 4. To convert three-phase values to single-phase values, multiply nss three-phase values by 1.
The minimum cable size will be the smallest cable that satisfies the three requirements. Where other ambient temperatures apply, the appropriate rating factors shall be as given in Table See Note 3 to Table 1. However, the current-carrying capacity of neutral-screened aerial cables shall be determined as follows: 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.
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.
Up to 10 percent of the technical content pages of a Standard may 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. Columns 14 and 15 4 One three- Table 12 core cable Columns 16 and 17 Table 13 Columns 14 and 16 5 Single-core Tables 3 and 4 Two enclosures laid— cables Columns 18 and a directly under 19 continuous concrete paved areas; or b minimum 0. The generalized form of the adiabatic temperature rise equation which is applicable to any starting temperature is as follows: Where values for soil resistivities other than 1.
For grouped cable circuits see— a Clause 3. Tables 2 12 22 3 nzz 2 4 provide guidance to the installation methods and derating factors applicable to the common elastomer 0308 thermoplastic-insulated cables. Part 2 will deal with cables for use with alternating voltages over 1 kV.
In the preparation of this Standard, reference was made to IEC and acknowledgment is made of the assistance received from that source. Reflective foil laminates are not mzs to be bulk thermal insulation. However, if work on an installation commenced before publication of this edition, the inspecting authority may grant permission for the installation to be carried out in accordance with the superseded edition. For the purpose of determining the maximum voltage drop value in Clause 4.
Higher continuous operating temperatures 30088 permissible for bare metal-sheathed cables, particularly stainless steel sheathed cables, dependent upon factors such as the following: Longitudinal expansion of a cable during a short circuit can be significant and when this expansion is restrained the resultant forces are considerable.
Cable short circuit fault current calculator AS/NZS 3008
Assuming worst case conditions of cable operating temperature and load power factor, the simplified method of Clause 4. If thermal separation is not provided, the temperature limits of the insulation should be used if it is lower than that of the sheath. For cables in air it is also desirable to avoid fixings at a bend which may cause local pressure on the cable.
The results of these calculations, the current-carrying capacity given in Table 12 and its ratio to the load current, are as follows: Where a number of installation conditions exist along a cable run or variations to the specific conditions occur, reference shall be made to Clauses 3.
This may be achieved by one of the following means: Note that these methods result in approximately the same answer.
There will be many cable installations where, because of cable selection practices or demand patterns, the current is not sustained at the maximum specified in this Standard.
Determine the minimum conductor size if a voltage drop of 2. This Standard was issued in draft form for comment as DR