~~~/?Ppx.F@ 0K^,spyi>}>o?g'{wo?nO?~~oLG`|0_N~m#dGg?6?w7ovv_ ~v`C#t%(7cP>$7=^JJKh$eewE1l?lnrOB%@?6x8u"51SbeHD4_/Ba_=}$A5(scQw|Az7cnw; Uk{j3$;g/?uQ o8qbE>9D)q~0;Uch%omWg}ckRXe@.HpWwB<=s6K>;^vK#2!6l,C T1 Pvf Correction Factor 4. As you say for other cases the tabulated values are likely to be erring on the safe side, so applying them directly if you don't really know much more about the loads probably isn't a bad approach. From cables ampacity tables. British Cables Company introduces new cables to its range. The thermal resistivity of soil refers to its ability to dissipate heat, which is relevant to the current-carrying capacity of cables. The ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today. Part P vs BS7671, Why Electrical Installation Training Is Important, All About RCDs (residual current devices), Part 5: Selection and Erection of Equipment, Part 7: Special Installations or Locations. Looking for a partner to deliver your sustainable vision? k = factor which is 143 for Copper cable (from IEC 60364-4-43). The derating tables have been derived from IEC 60287 and aligned with IEC 60364 (although there is some fundamentaldifference). vi}z7{?8x=l"t\F1'lnxN+h'qVs6GX1Cyx8N"/V*#JP%/~7d_}l?A#NLXh\h|gq$vtmO89dp|d{;>1-bSJb_" RT'C? xdq%_OL`-6G%ZHz`C 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. But where you do know something about the nature of the load .. or indeed any upstream overload protection you can often justify some significantly more favourable numbers.In practice, for domestic socket and lighting loads, grouping factors are often ignored - but care is still needed especially for large long-duration loads (traditionally immersion heaters and night storage heaters). 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). The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). The series of reports are called the ERA 69-30 series, previously called F/T183 and first published in 1955 have been referred to in the IEE Wiring Regulations for many years. stream The cause of the electrical overheating of the supply cable was found to be the result of its burial under the 16 inches of loose thermal insulation. Figure - 2 (reference fuse . capacity of a cable found in Appendix 4 of Bs 7671; i n is the rated current or current setting of the overcurrent device; C g is rating factor for grouping; C a is rating factor for ambient temperature; C i is rating factor for conductors surrounded by thermal insulation; C f is rating factor for semi-enclosed fuses (Bs 3036); C s is rating . An important note in the ERA 69-30 report Part III, states cables installed in and around buildings subject to the provisions of the IEE Wiring Regulations, BS 7671, should be rated in accordance with those Regulations., which is probably where the in or around buildings comes from in the description under reference method D in Table 4D4A as seen in Figure 6. The assumed values for ambient ground temperature, soil thermal resistivity and installation depth used in each publication are different which will result in a different cable size being selected. Part 1 . 148 46 BS 7671. 0000076607 00000 n 0000011561 00000 n 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: Many of the equations in these standards are based on fundamental heat transfer theory, and others are empirical equations derived from test work. Cable current capacity calculations in BS 761 are based on the derating factor method, seeCable Derating (Factors). This applies to a cable in a partition where the construction includes metallic parts other than fixings irrespective of the depth of the cable. Whilst BS 7671:2018+A1:2020 is extremely useful as a guide for determining the current-carrying capacity of cables for most electrical installations, there are situations when a detailed current-carrying capacity calculation might be required. For example ambient temperature (Ca), buried cables (Cc), Semi-enclosed fuse to BS3036 (Cf) etc (Take a look at Appendices 4 Section 3 of BS7671 for more rating factors that may apply). 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. 3H])Uw.?lJ `Vqh2SM The rating for the bottom tray is the same as for a single tray, since the cables on the bottom tray do not know that other trays containing other cables are above them. 0000085058 00000 n These standards contain methods for calculating the permissible current rating of cables from details of the permissible temperature rise, conductor resistance, losses and thermal resistivities, using analytical methods. 0000088434 00000 n P1{:f["ypc &@8o:a!`r If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. The ERA was commissioned to produce a series of reports on the current-carrying capacities of cables. Selecting Copper, XLPE, 3*50+25 mm 2 , its current is 185 A, Derating this current 185 * 0.93 = 172 A. . Don't worry though, you'll be sent straight back to the community after completing the registration. 0000004517 00000 n 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. The reports are still available and can be purchased here. I started as an apprentice electrician at the age of seventeen in 1982 and worked for many years as an electrician, a site foreman, a manager, a NICEIC Qualifying Supervisor, and a general manager. Typically, electrical design software is used for cable selection on larger installations. Manage and size all your cables, from low voltage to 33 kV. (No. The references in the document indicate that it was produced in the late 1940s or early 1950s. When considering energy efficiency and the cost associated with a cable throughout its lifetime, it is important to remember that a smaller CSA cable will have higher energy losses (I2R), when compared with larger CSA, this is because more heat is dissipated. Cable Heating Effects due to Harmonic Distortion in Electrical Installations. Although the document is a British Standard, it is also known as (and jointly labelled as) the IEE Wiring Table & Column 5. xNf(@-c]D$t7:z)Q 0000006009 00000 n - Andy. 0000002193 00000 n Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. }fq>w)6o @yawz8?%"VsKON]*~zX/*`qb};q7N NLt?k;~?|qo?zD6r!u5c9.F)Zz bZ\OZO>CRW !ol4]NO'n] &hT The table below provides derating guidelines for 200 0 C rated Teflon (type PTFE) wire. 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. Calculation of voltage drop uses tables of resistive and reactive voltage drop. One common approach is to use the empirical method identified in IEC 60287-2-1:2015 Calculation of the current rating Calculation of thermal resistance. There are consultancies that specialize in this type of work. Within this session you can put your question directly to the IET. !paX}xZQ#)aC*UryS>P&O )X]B. If the designer wants to avoid this conservatism, a full calculation taking into account the environment outside the cable would be required, typically using finite element analysis. Reply to Paul651975 OP LeeH - Esteemed Arms BS 7671:2008 . The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? It is tabulated current carrying capacity of cable with derating factors. UTg-3[f;"v,u|==:vao~|?m{?=?;9#<=}?^7||o}=oOOKo~4o04qzt:o>oO{? Copyright 2023 by myElectrical Engineering Limited. Drop us a text: Table 4C6 of BS 7671:2018+A1:2020 provides rating factors for cables enclosed in concrete floor troughs. 0000071888 00000 n presumably then each leg should also be run separately in floor joists - at the risk of making Swiss cheese out of the joists with all the cables run in separate holes, or upping the cable size based on rating factors. 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. 2023 The Institution of Engineering and Technology, The Institution of Engineering and Technology is registered as a Charity in England and Wales (no 211014) and Scotland (no SC038698). The first parts of the ERA 69-30 series of reports were published in 1969. Other than the conductor sizes changing to metric, these ratings have remained unchanged. %%EOF 5K)xIOa[QfER]Q $x+X -"^Fqa! well, it should be treated as two adjacent cables carrying the same current, and grouped, just the same as you would (I hope) for a hairpin of cables going up and down the wall to call in at a switch for a heater or similar on a radial as well. BS 7671: Introduction and Overview A BS 7671: 2008 - Introduction and Overview A 1 Introduction to BS 7671: 2008 BS 7671: 2008 was published during January 2008 as a signi cant new Edition of this fundamental Standard. For example, suppose a cable had an ambient temperature derating factor of k amb = 0.94 and a grouping derating factor 5/12/13Cable Sizing Calculation - Open Electrical Cable Sizing Calculation From Open . This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. 0000004403 00000 n Do you need to include all cables fixed to a cable tray when calculating grouping factors. For more detailed guidance on calculation methods, see the IEEE document Ampacity Calculations for Cables in Shallow Troughs (G. Anders, M. Coates and M. Chaaban). 193 0 obj <>stream However, the tables were not included in the next publication, the Fourteenth Edition of the IEE Wiring Regulations in 1966 but, instead, stated that current ratings shall comply with ERA report F/T 183 as seen below in Figure 3. of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. 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. Examples 1 and 2. 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 How to use the Table 4Aa. This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. Appendix 4 (BS 7671:2018)gives guidance determining the current capacity and voltage drop for cables. Where I think that this concept fails is in ring circuits. Note: The minimum current carrying capacity stated herein does not include other derating factors such as grouping, temperature, etc. The NEC Table attached has no derating factor for sheath materials because a wire in a home or a business will not be exposed to different environmental conditions. , #gc6aa5 0000076394 00000 n Figure 3: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966. endstream endobj 149 0 obj <. Had the derating factors for conduit fill and ambient not been required, a 3/0 copper conductor would have met the needs for this application. %PDF-1.3 Electric power & transmission & distribution Forum, https://files.engineering.com/getfile.aspx?folder=13c66bdb-39dd-4639-a3e2-7, https://files.engineering.com/getfile.aspx?folder=94810acb-102b-494c-ad52-a, Low-Volume Rapid Injection Molding With 3D Printed Molds, Industry Perspective: Education and Metal 3D Printing. In this electricians Q&A, Joe Robinson takes a deep dive into ther. 0000002160 00000 n IEC 60502. So if derating to 0.88 is required for number of cables, and derating to 0.93 is required for an upper tray, then the final figure is 0.88 multiplied by 0.93. %PDF-1.4 Back to the Forum - Current-carrying capacity of cables buried in the ground, Electrical Safety Standards in the Private Rented Sector. Cables Derating Factor Explained for beginnersVisit my electrical site https://www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt. 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. 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. capacity of the cable shall be reduced appropriately depending on the size of cable, length in Table 4 are appropriate to conductor size up to 10 mmsq in thermal insulation having a thermal conductivity greater than 0.0625 W/K.m. Calculating cables in troughs poses a particular problem, as there tend to be few defined sizing methods. 0000009088 00000 n 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. fpo&Q)"oHu4D3]*?/ 23,A o?NTpZ4H=`y53,O5+1-WC8Fy"n\IGOS`] pEA L1xi1g]lG+@/GCJ&$y91lIOJ8aSu|)w)ue(,'k5J%Z'#MD"%#B x 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. Over 700mm then derating starts to rear it's ugly head. whether in a raceway or cable. 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} . Unless specific details are known, the electrical designer should use the tabulated values provided in BS 7671:2018+A1:2020. The Institution of Engineering and Technology is registered as a Charity in England & Wales (no 211014) and Scotland (no SC038698). The electrical designer must choose which is the most appropriate and apply the relevant correction factors. << /Length 5 0 R /Filter /FlateDecode >> BS 7671, Table 4E4A, reference method, current-carrying capacity, XLPE insulation, copper conductor, multi-core, armoured cable . Others, of course, may disagree. The resulted current should be the new current carrying capacity for the cable. Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. Thermal resistivity of soil is different to soil resistance. 0000005725 00000 n DE-RATING FACTORS Our Company Genesis & Evolution Why Us KEI Power Gallery Beyond Business Certifications Downloads Clients Testimonials Reach Us Locate Us CALL (112) 681-8840 Follow Follow Toggle navigation Products & Solutions Extra High Voltage Cables High Voltage Cables Low Voltage Cables Control Cables House Wire HomeCab-FR BanFire-ZHFR 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. *NOTE: The third harmonic content expressed as total harmonic distortion. Lets say its a 5kW appliance and we are going to be using a 70 deg C thermoplastic flat sheathed cable. Cable sizing compiles with: - BS 7671, IEE Wiring Regulations Cable size is selected as follows: 1. 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