This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. 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. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. . 0000001839 00000 n These values were based on the conditions identified in the supplement to Report No. Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. F/T 183 issued by the ERA. Do you need to include all cables fixed to a cable tray when calculating grouping factors. 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. 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. Fictitious Dimensions. 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. . Derating factors, given in BS7671, for cables in touching trefoil formation are appropriate for cables in quad bundles Voltage drops for circuits in quad formation should be calculated using the values tabulated in BS7671 for cables in flat touching formation stream SOMAS_Si-101EN. Please read our. Resistive component of voltage drop factor mV r - (mV / A / m) r Reactive component of voltage drop factor mVx - (mV / A / m) x over lhe range of conductor sizes and types illclllrkd in the n:kvailitabics in this appendix. 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. xref 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). He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator. Hzd}-/ *@. Cable grouping factors. %PDF-1.4 % Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE 0000085335 00000 n Part 1 . (heat). 0000071888 00000 n The derating tables have been derived from IEC 60287 and aligned with IEC 60364 (although there is some fundamentaldifference). Not every installation method is provided in BS 7671, as there are too many permutations. Soil resistivity is affected by many factors including geographic location, soil composition and water flow and it will also change seasonally. %PDF-1.4 For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. Step 1 Determine if the highest ambient temperature a conductor is subjected to exceeds 30 degrees Celsius. 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. 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. Voltage drop value should be in the accepted limits. However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. 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. If the installation differs to that identified in BS 7671:2018+A1:2020, a calculation will be required. Myth Busters #7 - Out with the old, in with the new. Cable Derating (Factors) Cable Sizing Input Data Checklist. But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . ERA 69-30. 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. CEC Designer Veli has nearly two decades of experience in the renewable industry. Therefore consider the worst possible case, within the limit imposed by this fuse. 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. 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. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. Knowing this we can select the size of the protective device (In) and in this instance we are going to use a 32A circuit breaker. 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 . 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. The resulted current should be the new current carrying capacity for the cable. Created for free using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation. When multiple cables are in proximity, each contributes heat to the others and diminishes the amount of external cooling affecting the individual cable conductors. Register; Login. Annex B is popular because it is simple to use. Soil resistance is the ability to pass electrical current, which is relevant to earthing systems. Iz is the minimum cable current carrying capacity - see BS7671 Appendices 4.5 as per sheet. Consider a 20/3.3 kV, 12.5 MVA transformer to be fed by direct buried, 3 core XLPE, SWA, PVC, copper conductor cable. 1.5mm cable but circuit only loaded with a couple of amps. 193 0 obj <>stream 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). 0000088434 00000 n The ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today. The generally accepted depth for cables direct buried and cables buried in duct is 600mm to 650mm. . This applies to a cable in a partition where the construction includes metallic parts other than fixings irrespective of the depth of the cable. Ive even run my own electrical contracting company. Already a member? 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. Cable Sizing - derating factors - Wiring and the Regulations BS 7671 - IET EngX - IET EngX This site uses cookies. 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. 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. Re: Cable Size for 7.5 KW motor 03/29/2010 1:30 AM By applying derating factor as 0.7 to 0.75 to 3Cx4Sq.mm, u may . Promoting, selling, recruiting, coursework and thesis posting is forbidden. - Andy. Whilst technology has advanced significantly since then, the laws of physics remain unchanged. 0000078301 00000 n Manufacturers provide data . At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. 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. Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. WTOT is the total power dissipated in the trough per metre length (W/m), p is that part of the trough perimeter that is effective for heat dissipation (m), tr is the temperature rise of the air in a cable trough (K). 0000002031 00000 n It is always best to consult cable manufacturers for advice when carrying out any non-standard cable calculations. vi}z7{?8x=l"t\F1'lnxN+h'qVs6GX1Cyx8N"/V*#JP%/~7d_}l?A#NLXh\h|gq$vtmO89dp|d{;>1-bSJb_" RT'C? 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. Even then couldn't group more than 4 power 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). Note 1 of table 4C1 in Apdx 4, says that the factors are applicable to uniform groups of cables, equally loaded. BICC or BS7671 comply for design Anthony Sullivan over 4 years ago Hello IET guys I have a problem where a cable installed on site doesn't comply to Bs7671 current carrying capacity for underground cable reference method D the engineer who design the cable used amtech and data from bicc with reference method 110. Cable Heating Effects due to Harmonic Distortion in Electrical Installations. BS7671 18 th Edition Cable Sizing Calculation Show 1 CABLE SIZING OR Doing it in Groups . 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. %%EOF SOMAS_Si-101EN. For higher temperatures, a derating will have to be applied according to NEC. The purpose of performing a cable calculation is to ensure that a cable is not overloaded. 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! We're about to take you to the IET registration website. 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 Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. 0000004990 00000 n 0000000016 00000 n The same conductor must be derated to 70% of its normal value when there are 7-9 current-carrying conductors bundled . Derating: No derating is currently applied to the current ratings tables 310.15 (B) (16) and 310.15 (B) (17).. 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. This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. Determine the application. soil resistivity (K3) Derating factor formula = Cable current * K1*K2*K3*K4*Kn, While K's are the derating factors of the cable. ERA is a UK based organisation, and these standards reflect this. Cable Sizing Standards. of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? 0000004517 00000 n UTg-3[f;"v,u|==:vao~|?m{?=?;9#<=}?^7||o}=oOOKo~4o04qzt:o>oO{? If the appropriate correction factors are applied, the results will be the same. Manage and size all your cables, from low voltage to 33 kV. 0000002616 00000 n Total derating factors = K1*K2*K3 = 0.95*0.9*0.91 =0.77, Then multiply this value by the cable current. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. 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. 148 46 apply some engineering judgement). 0000009088 00000 n whether in a raceway or cable. Thanks. 0000084854 00000 n The references in the document indicate that it was produced in the late 1940s or early 1950s. We'll go into more detail and get you ready to pass your 18th Edition exam when we go through the book together fully in your 18th Edition online course at . We have received your request and will respond promptly. ;;u(1*z/}3oG'0 ^Am;Oy4?~ Et'sQh)sF&)O It is tabulated current carrying capacity of cable with derating factors. 0000003576 00000 n 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. 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). It is important to remember that anyone carrying out these calculations should work directly from a copy of the relevant standard. 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. 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