IEC 60502 is an International Electrotechnical Commission standard, which gives current ratings for medium voltage cables. Guidance on the use of finite element methods for calculating cable current ratings is given in IEC TR 62095:2003 Electric cables Calculation of current rating Cable current rating calculations using finite element method. If the main load is half way round, that's the whole lot in two adjacent cables. It is assumed that the maximum ambient temperature is 30C and the maximum ground temperature id 20C. xref
In our example we have an ambient temperature of 35 deg C (Ca = 0.94 From Table 4B1) and some thermal insulation in a stud wall but with the cable touching the inner surface of the wall (aka reference method 102 in table 4D5). The IET jointly publish BS 7671 so who better to confirm the changes. Three criteria are given for cable selection: (a) Current-carrying capacity (b) Voltage drop (c) Short-circuit temperature rise This standard provides sustained current-carrying capacities and voltage drop values for those types of electrical cable and installation practices in common use in Australia. Following on from my previous post about the use of 'YY' type cables, our esteemed client has stated that BS7671 does not have grouping factors for multicore cables. of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. Table & Column 5. 0000011561 00000 n
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The international standards that cover the current-carrying capacity of cables are the IEC 60287 series for steady-state conditions and IEC 60853 for cyclic conditions for most practical applications. BS7671:2018+A2:2022 Let's take a quick run through the new 18th Edition Wiring Regulations book, which includes Amendment 2 that was introduced in March 2022, BS7671:2018+A2:2022. 0000002616 00000 n
Many of the equations in these standards are based on fundamental heat transfer theory, and others are empirical equations derived from test work. Cables Derating Factor Explained for beginnersVisit my electrical site https://www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt. The values used for calculation will depend on the actual ground conditions and material used for backfilling. These values were based on the conditions identified in the supplement to Report No. This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. The current-carrying capacity of cables has often been discussed on the IET Engineering Communities Forum and we also receive several enquiries on the IET technical helpline on the topic. 0000015597 00000 n
The software is able to simulate and analyze both steady-state and transient conditions, seasonal changes and effects such as soil drying out, much more quickly than would be achieved by carrying out separate calculations. 0000001839 00000 n
stream BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. For a cable with a base current rating of 42A, the installed current rating would be I c = 0.799 x 42 = 33.6 A {\displaystyle I_{c}=0.799x42=33.6A} . Already a Member? The physics involved with heat loss have similarities with those of mechanical engineering and are based on heat transfer principles. The ERA 69-30 report assumes a soil thermal resistivity of 1.2 K.m/W, which corresponds with typical soil thermal resistivity for the UK in Annex A (A.22.2) of BS IEC 60287-3-1 Electric cables - Calculation of the current rating: Operating conditions - Site reference conditions, although this is considered to be a broad-brush statement. Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). Weve not finished yet though as we need also to make allowances for anything that may restrict a conductors ability to disperse any heat that it may produce. Irnd`u3=](tdd=
L8z[Wlm`= MV Cable Derating Factors NF C 13-200 [France] MV Cable Derating Factors NF C 13-200 [France] Mothafukin Morrissey. Fictitious Dimensions. For more details on BS 7671 voltage drop calculations, see. Use the linkon the left to access our cable sizing application. Where I think that this concept fails is in ring circuits. k2-3,Kw#`nu>+LKYgT CJX7b.zd@c41DV3+l[r~SKT? The current-carrying capacities identified in BS 7671:2018+A1:2020 were derived from a combination of IEC standards and a piece of work carried out by an organization called RINA, formerly ERA (the Electrical Research Association). Cable sizing compiles with: - BS 7671, IEE Wiring Regulations Cable size is selected as follows: 1. You have to look at using the <30% of the grouped rating for the cable i.e. 5K)xIOa[QfER]Q
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<. Part III of the ERA 69-30 provides values of current-carrying capacity and calculation methods for, sustained current ratings for 600/1000 V and 1900/3300 V cables with 70C thermoplastic insulation (ac 50 Hz and dc). The values of current-carrying capacity tabulated in the report are in accordance with IEC 60287 Electric cables - Calculation of the current rating. A question that arises periodically on the IET Engineering Communities forum concerns the current-carrying capacity of cables buried in the ground, in particular, the data used to select the appropriate cross-sectional area (CSA) of live conductors. Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. For example, the temperature in an attic reaches 125 degrees F (52 C) in the summertime. . Cable Current Rating 6. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. 0000002160 00000 n
Applying the BS7671:2008 de-rating rule would have resulted in that cable installation being limited to 107.5 amps, just over half of the measured current flow in the cable. 0000078301 00000 n
201 A is now the allowable ampacity of the 300 kcmil copper conductor for this circuit. soil resistivity (K3) Derating factor formula = Cable current * K1*K2*K3*K4*Kn, While K's are the derating factors of the cable. If every possible cable and installation method was identified in BS 7671:2018+A1:2020, the size of the Standard would increase significantly. Empirical equations are based on observations and experience, rather than theories. To utilize temperature and power correction factors accurately, BS 7671 offers voltage drop factors separately in resistive and inductive components for cables above 16 mm 2. 0000007414 00000 n
Just a point of interest if you are using twin and earth cable and your cable comes into contact with insulation as per any of the reference methods 100, 101, 102 or 103 then just use the table 4D5 and Ci = 1 in any calculations. Want to participate in the discussions? of Cables) 16 x 18.0 (Factor for 4mm cable) = 289.6 Total Cable Factor = 1239.6 Standard Trunking Cable Factors Standard Trunking Capacity Factors Show entries Search: . By joining you are opting in to receive e-mail.
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Rating factor for grouping of cables = 0.61 (Appendix 1.4) (Assumed 6 cables 150mm spacing formation) Overall admissible ampacity correction factor = 0.82 x 0.73 x 0.92 x 0.61 = 0.336 1.2. If cables are buried in the ground, either direct or inside ducting, reference method D (Figure 1) is applicable and the appropriate value should be selected according to its type from the relevant table identified in Appendix 4. Metal 3D printing has rapidly emerged as a key technology in modern design and manufacturing, so its critical educational institutions include it in their curricula to avoid leaving students at a disadvantage as they enter the workforce. According to the IEEE document Ampacity Calculations for Cables in Shallow Troughs (G. Anders, M. Coates and M. Chaaban), a draft document has been found that derives a simple equation for the calculation of thermal resistance of a trough. Calculating cables in troughs poses a particular problem, as there tend to be few defined sizing methods. }fq>w)6o
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&hT ;;u(1*z/}3oG'0 ^Am;Oy4?~ Et'sQh)sF&)O Impedance and voltage drop to IEC 60909 and CENELEC CLC/TR 50480. However, this is unlikely to be a cost-effective option for smaller CSA cables when compared with using a more conservative cable size. 148 0 obj
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SOMAS_Si-101EN. A software algorithm has been developed which can determine the derating factors for multiple cable circuit crossings or heat sources. Others, of course, may disagree. Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a parts function at the center of their design considerations. Z Note: myCableEngineering does not use the BS 7671 tables, but instead calculations the circuitimpedances in accordance with IEC 60909 and directly calculations voltage drop from this. ]M&r;:QKGBdBeW2JFX)@wN#$RA)0S3)i`nmh Even then couldn't group more than 4 power circuits. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. Iz is the minimum cable current carrying capacity - see BS7671 Appendices 4.5 as per sheet. 0000009088 00000 n
Typically, electrical design software is used for cable selection on larger installations. (heat). APPENDIX 1: Correction Factors for Sizing of Cable Conductors (1) Correction factors for ambient temperature Table 1: Correction factors for ambient temperature Note: Ths table applies where the associated overcurrent protective device is intended to provide shor circuit protection only. Cable current carrying capacity. So the design current (Ib) would be 5000/230 = 21.73 Amps. 3H])Uw.?lJ `Vqh2SM Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. The first parts of the ERA 69-30 series of reports were published in 1969. For smaller projects, this may not have much of an impact, but for larger projects and high design currents, this could be extremely beneficial, in terms of both physical size and cost. 0000002031 00000 n
If the installation differs to that identified in BS 7671:2018+A1:2020, a calculation will be required. Looking for a partner to deliver your sustainable vision? The installation method takes into account assumed parameters, such as ambient ground temperature (Ca), soil thermal resistivity (Cs), depth of laying (Cd) and spacing factor (Cg), the correction factors for which can be found in Tables 4B2, 4B3, 4B4 and 4C2 respectively. Cable is calculated on current . . I'm still pondering how to alter the factors for cables that are not equally loaded but which shouldn't be ignored. To ascertain that the current-carrying capacity of the circuit is sufficient factoring the presence of harmonics in the system, Table 4Aa (BS7671 - 2011) provides some factors in determining the cable sizes. In the first example, a 4,000-amp duct bank with a design load of 3,600 amps is simulated based on an earth RHO factor of 90, dirt RHO factor of 90 and a load factor of 100 . 0000003576 00000 n
If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. Register; Login. 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. Simultaneous Overload - can the other cables on the cable tray that are alongside your cable be subject to simultaneous overload?? HD 60364-5-52 Selection and erection of electrical equipment. Under such conditions the current ratings given from the standard AS/NZS 3008.1 shall be corrected by the application of an appropriate factor or factors. Failing that, speaking to the manufacturers of the cable is always a good place to start. Correction Factor 4. The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). 0000005266 00000 n
Whilst technology has advanced significantly since then, the laws of physics remain unchanged. This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. In this scenario, the designer will have to make an engineering judgement to determine the current-carrying capacity of the cable or seek advice from cable manufacturers. Figure 3: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966. Some electrical design software packages specifically refer to BICC cable data but other manufacturers data also exists, other software packages refer to ERA 69-30. Traditionally, tabulated values were not provided in the IEE Wiring Regulations, the current-carrying capacity ratings for cables buried directly in the soil first appeared in the 13th Edition of the IEE Wiring Regulations in 1955 as seen in Figure 2. Unless specific details are known, the electrical designer should use the tabulated values provided in BS 7671:2018+A1:2020. The current-carrying capacity of cables identified in Appendix 4 of BS 7671:2018+A1:2020 will cover most installations, but the values will be on the conservative side and will not necessarily provide the most efficiently sized cable (depending on how you define efficient). The same conductor must be derated to 70% of its normal value when there are 7-9 current-carrying conductors bundled . 0000088434 00000 n
Extra holes not really required unless the parallel length of touching cables in the joist was so long that no significant heat conducted along the cable, and the fit so tight that no air could move between them - so perhaps a very thick joist like a ship's timber, but not the average bit of 2*8 or 3*10 - (even less of a concern in the 'engineered joists' that are an I beam of 2 bits of what looks like roof batten attached to a strip of plywood)If in doubt a slight slotting in the direction of the grain is enough to open up an air path, though to be honest T &E being flat, in a round hole, I'd not worry.Because the heat generated (and in the simple systems the temperature rise ) is proportional to the square of current you may find do not need to de-rate so much - 70% of the current in 2 cables is the same total heating as 100% of the heat in one cable (as 1.4 is sqrt of 2), but of course the surface area to sweat it out over is increased over the single cable case (but not quite doubled as the sides in contact are unable to lose heat in the way they would be if there was a gap between the cables) Also flat cables touching on the thin edge cool better than touching on the broadside - but this sort of thing rapidly becomes subject to too many subtle effects to be safely captured in a simple set of rules.However a round bundle of cables is the worst case, for the one in the middle, and keeps getting worse the more cables are added, while if you can lay your cables side by side, then only the nearest few neighbours to any given cable have much effect, and the effect on the grouping factor is that for more than a few cables the change in cg of adding another cable is small - the greatest steps are between 1 and 2 and then 2 and 3 cables, and a flat lay of 4 cables is almost the same as a flat lay of 40.Mikeregards,Mike. 4 0 obj Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. 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