BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. The physics involved with heat loss have similarities with those of mechanical engineering and are based on heat transfer principles. ERA is a UK based organisation, and these standards reflect this. vi}z7{?8x=l"t\F1'lnxN+h'qVs6GX1Cyx8N"/V*#JP%/~7d_}l?A#NLXh\h|gq$vtmO89dp|d{;>1-bSJb_" RT'C? The data shows both single wire and multi-conductor wire at 70 0 C in a vacuum (no air flow). Want to participate in the discussions? 1. Firstly how much current is your appliance going to use? 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. Solar Radiation Effects. Judgement could be based on published correction and derating factors in BS 7671:2018+A1:2020, further corrected by the electrical engineer, or by guidance from the manufacturer, which is preferable. Figure 3: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966. Already a member? startxref It is tabulated current carrying capacity of cable with derating factors. Thanks. 0000015597 00000 n The IEC 60502 standard is in two parts; part 1 for voltages up to 1 kV and part 2 for voltages from 1 kV to 30 kV. The derating factors of Section 310.15 (B) (2) (a) apply only to multiconductor cables of three or more current carrying conductors in cable, not in cable tray. There are certain types of cables and installation methods that are not identified and the electrical designer must make an engineering judgement or carry out bespoke calculations. A. Non-sheathedcablesinconduitina 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). BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. For example, suppose a cable had an ambient temperature derating factor of = and a grouping derating factor of =, then the overall derating factor = =. 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. Already a Member? Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. obtained from the cable manufacturer. }fq>w)6o @yawz8?%"VsKON]*~zX/*`qb};q7N NLt?k;~?|qo?zD6r!u5c9.F)Zz bZ\OZO>CRW !ol4]NO'n] &hT 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. 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 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. Use the linkon the left to access our cable sizing application. 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. Thermal resistivity of soil is different to soil resistance. The derating factor is applied to reduce the cable's current carrying capacity. 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. So the design current (Ib) would be 5000/230 = 21.73 Amps. 5K)xIOa[QfER]Q $x+X -"^Fqa! ambient temperatures > 30C. 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. BS 7671. UTg-3[f;"v,u|==:vao~|?m{?=?;9#<=}?^7||o}=oOOKo~4o04qzt:o>oO{? Empirical equations are based on observations and experience, rather than theories. The most important part of carrying out cable current rating calculations is the determination of the conductor temperature for a given load, or conversely, the determination of the tolerable load current for a given conductor temperature. Ive also been qualified tutor since 2008 and have taught electrical installation C&G, EAL and Logic courses and weve been successfully teaching the Wiring Regulations online here at the-regs.co.uk since 2014 and have had hundreds of students pass 18th Edition exam why not join them today? 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. Back to the Forum - Current-carrying capacity of cables buried in the ground, Electrical Safety Standards in the Private Rented Sector. apply some engineering judgement). Figure 2: extract from the Thirteenth Edition of the IEE Wiring Regulations. 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. Simultaneous Overload - can the other cables on the cable tray that are alongside your cable be subject to simultaneous overload?? The calculation of cable rating follow t he derating factor method, see Cable Derating (Factors) . It is important that these calculations are carried out by someone who is experienced in this field of work (which may not necessarily be an electrical engineer). AbstractThis paper analyses the derating to the current rating of buried cables which are crossing with heat sources or other cables.Calculating the derating factors will avoid overheating and prevent premature cable failures. 0000005800 00000 n The reports are still available and can be purchased here. The table below provides derating guidelines for 200 0 C rated Teflon (type PTFE) wire. 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 AFAIK, this refers to several cable trays stacked one above the other, as might be used when space does not permit of wider tray or multiple trays side by side. In some cases, it may be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity. Although the document is a British Standard, it is also known as (and jointly labelled as) the IEE Wiring The ERA series of reports are still available and can be purchased from the RINA website. For further information, see the IET Wiring Matters article Amps per pound. Usually the derating factor is tabulated in a nation's wiring regulations. These are related to the line voltage for three phase circuits and phase voltage for single phase circuits. 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). Z 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. IEC 60502. 1a If it is a fan, centrifugal pump or centrifugal compressor use steps 2 to 4 to determine which graph applies from illustration 1.1 - 1.9. Appendix 4 (BS 7671:2018)gives guidance determining the current capacity and voltage drop for cables. The parameters considered in the standard are, ambient temperature, soil thermal resistivity, the installation methods and grouping of cables. Where I think that this concept fails is in ring circuits. 0000006864 00000 n BS 7671, Table 4E4A, reference method, current-carrying capacity, XLPE insulation, copper conductor, multi-core, armoured cable . 0000009088 00000 n In domestic and similar situations, remember that the total long term load is limited by the cut out fuse. The question is, what is the difference between manufacturers data and BS 7671? In this article we look at the information available and why the information is perceived as different. , #gc6aa5 Iasked the nic about that, some time ago, and they said that for domestics they read it as for ccts, so wouldn't be concerned about individual legs if the ring was generally lightly loaded most of the time. 0000002193 00000 n 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). 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. stream 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. 1.5mm cable but circuit only loaded with a couple of amps. Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. 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. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. We have received your request and will respond promptly. If the tray is covered for more than 6 ft. with a solid unventilated cover, the ampacities allowed are 95% of those shown in the tables. Not every installation method is provided in BS 7671, as there are too many permutations. 0000085058 00000 n Part 1 . Got the answer from BS 7671, but still got another question on the previous attachment. (heat). Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. Items to consider include the thermal resistance of separate parts, such as the cable, the cable surface to the inner trough, the troughs internal surfaces and the outer surface of the trough with its environment. % Appendix 4 of item 7.1 reference method D states if the specific installation parameters are known (thermal resistance of the ground, ground ambient temperature, cable depth), reference can be made to the cable manufacturer or the ERA 69-30 series of publications, which may result in a smaller cable size being selected. as seen in Figure 5. 0000004805 00000 n 2023 The Institution of Engineering and Technology. IEC 60502 is an International Electrotechnical Commission standard, which gives current ratings for medium voltage cables. 2023 Filipino Engineer. Rosa Ponce. Note 1 of table 4C1 in Apdx 4, says that the factors are applicable to uniform groups of cables, equally loaded. Cable Calculations Part 1 - the-Regs : BS7671 18th Edition Online Training Cable Calculations Part 1 13 June 2016 by the Regs Guy The purpose of performing a cable calculation is to ensure that a cable is not overloaded. . What does the number of trays mean in the IEC derating factors table? 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} . Promoting, selling, recruiting, coursework and thesis posting is forbidden. ~~~/?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 . Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). It was not until the Seventeenth Edition of the IEE Wiring Regulations in 2008 that tabulated values were reintroduced as Table 4D4A (thermoplastic) and Table 4E4A (thermosetting). 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. Soil resistance is the ability to pass electrical current, which is relevant to earthing systems. Cloud based - any device, anywhere. 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. Unless specific values can be obtained, using the values direct from BS 7671 could be considered a safe option for the electrical designer. 0000003576 00000 n Step 1 Determine if the highest ambient temperature a conductor is subjected to exceeds 30 degrees Celsius. The thermal resistivity of soil refers to its ability to dissipate heat, which is relevant to the current-carrying capacity of cables. Where a cable is buried in the ground its ability to dissipate heat is reduced, the extent of which depends on the installation method. By the time tabulated values for buried cables were reintroduced in the Seventeenth Edition of the IEE Wiring Regulations in 2008, the IEE Wiring Regulations had become a British Standard, BS 7671:2008, based on the European CENELEC HD 60364 series of standards. 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. Soil resistivity is affected by many factors including geographic location, soil composition and water flow and it will also change seasonally. 0000001244 00000 n Annex B is popular because it is simple to use. Over 700mm then derating starts to rear it's ugly head. The presence of harmonic current in a power system increases the current in the neutral conductor due to phase current imbalance (refer to Fig. 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: BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. Don't worry though, you'll be sent straight back to the community after completing the registration. However, when the appropriate correction factors are applied, the results will be the similar as they are based on calculation methods derived from IEC 60287 Electric cables - Calculation of the current rating. Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. The purpose of performing a cable calculation is to ensure that a cable is not overloaded. Fictitious Dimensions. Copyright 1998-2023 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. xNf(@-c]D$t7:z)Q Correction Factor 4. Bs7671 cable derating factors: CEF TechTalks are back - with a focus on renewables and regulations. What is the maximum number of cables that can be installed in a pre-formed concrete cable trough? Are still available and can be purchased here is in ring circuits 0000004805 00000 n 2023 the Institution of and... Manufacturers data and BS 7671, as there are too many permutations cable-free rating! 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