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. To avoid the ordeal of calculating the current-carrying capacity of cables, where possible, utilise the installation methods and rating factors already published: someone has already done the hard work for you! Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. Should that not be treated as two circuits? There are nine parts to the ERA 69-30 report series, covering different types of cables and installation methods. %PDF-1.4 Cable Current Rating 6. ambient temperatures > 30C. 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. Table 4C6 of BS 7671:2018+A1:2020 provides rating factors for cables enclosed in concrete floor troughs. 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. Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. 0000009580 00000 n Selecting Copper, XLPE, 3*50+25 mm 2 , its current is 185 A, Derating this current 185 * 0.93 = 172 A. . Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. %PDF-1.3 F/T 183 issued by the ERA. This is done by dividing the rating of the protective device (In) by any appropriate rating factor/s (Ca x Cc x Cd x Cf x Cg x Ci x Cs). xref Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. I!m6~8Rq" At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. 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. Cable grouping factors. Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. However, I see some publications that apply these factors to ccts, in trunking, for example, with no reference to cables being equally loaded (as though it's a belt-and-braces approach and apply the factors . Cable Derating (Factors) Cable Sizing Input Data Checklist. Bs7671 cable derating factors: CEF TechTalks are back - with a focus on renewables and regulations. Do you need to include all cables fixed to a cable tray when calculating grouping factors. 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. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. Cables Derating Factor Explained for beginnersVisit my electrical site https://www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt. Promoting, selling, recruiting, coursework and thesis posting is forbidden. For example, Table 310.15 (C) (1) requires a THWN No.4 copper conductor, normally valued at 85 amps according to Table 310.16, to be derated to 80% of its value when there are 4-6 current-carrying conductors bundled together. Sb t8 Bare Batten Led Wiring. Table 4: Cable surrounded by thermal insulation length in insulation mm derating factor 50 0.89 100 0.81 200 0.68 Found inside - Page 258The correct way to derate for socket - outlet ring circuits when more than two . 0000004805 00000 n 0000001839 00000 n British Cables Company introduces new cables to its range. 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 . xdq%_OL`-6G%ZHz`C 1~>c??h'TJc1txz}6z-zL:7XrXsz It is important to remember that it is unlikely the cable will be buried throughout its entire length, at some point the cable will exit the ground to be terminated, where it will no longer be buried in the ground and a different reference method will also need to be considered. *NOTE: The third harmonic content expressed as total harmonic distortion. 0000001244 00000 n 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. 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. More than six cables grouped together require a de-rating factor of 0.85. lol!!! <<95D84A24FD5A1F4C8152C1D91F51EC80>]>> I'm still pondering how to alter the factors for cables that are not equally loaded but which shouldn't be ignored. But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . Drop us a text: Want to participate in the discussions? The first parts of the ERA 69-30 series of reports were published in 1969. Appendix 4 (BS 7671:2018)gives guidance determining the current capacity and voltage drop for cables. A. Non-sheathedcablesinconduitina 0000078301 00000 n The ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today. Cable current capacity calculations in BS 761 are based on the derating factor method, seeCable Derating (Factors). 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. 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. The parameters considered in the standard are, ambient temperature, soil thermal resistivity, the installation methods and grouping of cables. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. The derating factor accounts for the added thermal resistance present when a. Total derating factors = K1*K2*K3 = 0.95*0.9*0.91 =0.77, Then multiply this value by the cable current. Whilst I have no intention of exploring the minefield of complex heat loss equations in this article, I would like to provide a very high-level overview of the concept and complexities of calculating the current-carrying capacity of cables. 0000071888 00000 n If every possible cable and installation method was identified in BS 7671:2018+A1:2020, the size of the Standard would increase significantly. k = factor which is 143 for Copper cable (from IEC 60364-4-43). 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. 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). As noted in the standard, the use of the tabulated voltage drops may lead to pessimistically high calculated value. Empirical equations are based on observations and experience, rather than theories. Determination of the current-carrying capacity by calculating the actual heat transfer is likely to result in a less conservatively sized cable. The IET jointly publish BS 7671 so who better to confirm the changes. 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. 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. 3H])Uw.?lJ `Vqh2SM The current-carrying capacity of a cable is determined by the maximum permitted conductor temperature and the rate at which it dissipates heat into the environment, taking into account the surrounding material, which will have thermal properties and resist the dissipation of heat, this is called I2R losses. 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). All cable sizing methods more or le ss follow the same basic six step process: 1) Gathering data about the cable, its installation conditions, the load that it will carry, etc 2) Determine the minimum cable size based on continuous current carrying capacity 3) Determine the minimum cable size based on voltage drop considerations 4) Determine the factor to obtain the current - carrying capacity I required for the cable . Other losses include dielectric losses from insulating materials, skin effect introduced by alternating current, and eddy current losses. Iz is the minimum cable current carrying capacity - see BS7671 Appendices 4.5 as per sheet. Cable sizing compiles with: - BS 7671, IEE Wiring Regulations Cable size is selected as follows: 1. Some studies have found the empirical method to be conservative, owing to the fact that it does not take account of the specific thermal environment outside of the cable. CJX7b.zd@c41DV3+l[r~SKT? 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. 0000002616 00000 n % If the main load is half way round, that's the whole lot in two adjacent cables. How much current a cable can carry is down to physics and is a highly technical subject in its own right. 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 . In this electricians Q&A, Joe Robinson takes a deep dive into ther. 0000011561 00000 n The purpose of performing a cable calculation is to ensure that a cable is not overloaded. By definition only one circuit, but imagine a circuit high up in conduit: down and up, over a door, down and up again, etc; or domestic under the floorboards, down and up (or up and down) under the capping, down and up again, etc. 0000088221 00000 n This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. (No. Up to six cables can be bunched together without derating. 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. Calculation of voltage drop uses tables of resistive and reactive voltage drop. Both the load factor and the RHO value of the backfill also play large roles in determining the potential derating of the conductors in the duct bank. The ERA series of reports are still available and can be purchased from the RINA website. The same conductor must be derated to 70% of its normal value when there are 7-9 current-carrying conductors bundled . Soil resistance is the ability to pass electrical current, which is relevant to earthing systems. 0000078513 00000 n Even then couldn't group more than 4 power circuits. Annex B is popular because it is simple to use. These values were based on the conditions identified in the supplement to Report No. *Eng-Tips's functionality depends on members receiving e-mail. 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. 5K)xIOa[QfER]Q $x+X -"^Fqa! Want to participate in the discussions? xZ[cs@k./0gqW5J$?Q /3=+uUW5mFN_zo++y.t^02:xr*ZK$7_Cw/~5a(vW~?jd64s/k=!W?fYZ`?x}h571t"TI?xf`D4i* k=VHYh$E#-Snf#9D?X 1?q9!Qkp"L$7+(dvirmlDMR[bvlz72Qbpqm>fs?8Y#f:S0SrTN:+IY+hY7wQ ot7bJ[!eN$KRv&%BiV,B[Zgbb+L5L o$+E0VY0B 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. Z+7`Mq!p#pg Py_!!G/[3A`.TOuL. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. 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. Figure - 2 (reference fuse . over lhe range of conductor sizes and types illclllrkd in the n:kvailitabics in this appendix. 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