endstream endobj 149 0 obj <. 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. 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 Even then couldn't group more than 4 power circuits. The calculation of cable rating follow t he derating factor method, see Cable Derating (Factors) . Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). 0000008053 00000 n The ERA series of reports are still available and can be purchased from the RINA website. 3H])Uw.?lJ `Vqh2SM 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 . Already a member? Drop us a text: 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. Use the linkon the left to access our cable sizing application. 0000071888 00000 n Copyright 2023 by myElectrical Engineering Limited. 0000004805 00000 n 0000011561 00000 n IEC 60502. Promoting, selling, recruiting, coursework and thesis posting is forbidden. !paX}xZQ#)aC*UryS>P&O )X]B. If every possible cable and installation method was identified in BS 7671:2018+A1:2020, the size of the Standard would increase significantly. So, we have In/(Ca x Ci) or 32/(0.94 x 1) = 34.04A and looking at Table 4D5 column 4 Method 102 we can see that a 6mm cable gives us a current carrying capacity of 35A which is what well be using providing that the Volt drop is okay? 0000006711 00000 n This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. 1b). Many of the equations in these standards are based on fundamental heat transfer theory, and others are empirical equations derived from test work. Determination of the current-carrying capacity by calculating the actual heat transfer is likely to result in a less conservatively sized cable. Determine the application. . Others, of course, may disagree. As far DC cable sizing in PV projects is concerned, PV engineers consider DC cable sizing based on cable derating factors such as - depth of cable laying, ground/air temperature, thermal resistivity of soil and grouping of cable that . Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. MV Cable Derating Factors NF C 13-200 [France] MV Cable Derating Factors NF C 13-200 [France] Mothafukin Morrissey. 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. The correction factor is justified as the current carrying capacity is capable of limitation by additional external factors, e.g. (No. The values used for calculation will depend on the actual ground conditions and material used for backfilling. *Eng-Tips's functionality depends on members receiving e-mail. Got the answer from BS 7671, but still got another question on the previous attachment. 5;b^VL477/8:m}*lXIw{%;YOol*V5@r,;VkYNM|&Q@VVGC`i(c cB&0s!|8~%q$sJ(2% cL*qOX_Q>H+i.3@qhJ The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). We're about to take you to the IET registration website. Part 1 . . You have to look at using the <30% of the grouped rating for the cable i.e. Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE 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: 0 0000006864 00000 n 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. 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. 0000011053 00000 n 201 A is now the allowable ampacity of the 300 kcmil copper conductor for this circuit. Don't worry though, you'll be sent straight back to the community after completing the registration. 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). In some cases, it may be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity. over lhe range of conductor sizes and types illclllrkd in the n:kvailitabics in this appendix. 5 0 obj 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. 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 . 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. CEC Designer Veli has nearly two decades of experience in the renewable industry. 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. Soil resistivity is affected by many factors including geographic location, soil composition and water flow and it will also change seasonally. Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. Calculation of voltage drop uses tables of resistive and reactive voltage drop. 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} . Total derating factors = K1*K2*K3 = 0.95*0.9*0.91 =0.77, Then multiply this value by the cable current. 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. The ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today. 0000002031 00000 n 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. The user of ERA is particularly popular amongst DNO (district network operators) and supply authorities. 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. 2023 The Institution of Engineering and Technology. Should that not be treated as two circuits? 4 0 obj It is important to remember that the testing carried out for the ERA 69-30 reports was under controlled conditions and using consistent backfill material, for example, in the real world it is much different. - Table 52.2 Cable surrounded by thermal insulation, gives slightly reduced derating factors, to take account of the availability of material with improved thermal insulation. Over 700mm then derating starts to rear it's ugly head. 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. 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. 0000078513 00000 n Cable is calculated on current . The current-carrying capacities of cables buried in the ground used in BS 7671:2018+A1:2020 and the ERA 69-30 report series are derived from the same calculation methods identified in the relevant parts of IEC 60287. Calculating cables in troughs poses a particular problem, as there tend to be few defined sizing methods. Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 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). Fictitious Dimensions. Figure - 2 (reference fuse . 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. However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. 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). Cable sizing compiles with: - BS 7671, IEE Wiring Regulations Cable size is selected as follows: 1. 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. 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. 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. obtained from the cable manufacturer. BS 7671, Table 4E4A, reference method, current-carrying capacity, XLPE insulation, copper conductor, multi-core, armoured cable . 0000088434 00000 n BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? 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. Usually the derating factor is tabulated in a nation's wiring regulations. Alternatively, assistance in determining the correct cable size for your application can be sought from our experts in The Cable Lab by contacting the technical hotline. The resulted current should be the new current carrying capacity for the cable. The first parts of the ERA 69-30 series of reports were published in 1969. Derating factors given in BS7671 for cables in touching trefoil cleat 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 For a cable with a base current rating of 42A, the installed current rating would But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . Reply to Paul651975 OP LeeH - Esteemed Arms ambient temperatures > 30C. Failing that, speaking to the manufacturers of the cable is always a good place to start. whether in a raceway or cable. 0000005725 00000 n I Accept Cookies *NOTE: The third harmonic content expressed as total harmonic distortion. 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. Where a cable is buried in the ground its ability to dissipate heat is reduced, the extent of which depends on the installation method. BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. For further information, see the IET Wiring Matters article Amps per pound. There are nine parts to the ERA 69-30 report series, covering different types of cables and installation methods. 0000004517 00000 n Cable Heating Effects due to Harmonic Distortion in Electrical Installations. 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. 0000001839 00000 n For higher temperatures, a derating will have to be applied according to NEC. . Cable current capacity calculations in BS 761 are based on the derating factor method, seeCable Derating (Factors). 0000015597 00000 n Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. Within this session you can put your question directly to the IET. British Cables Company introduces new cables to its range. xNf(@-c]D$t7:z)Q Copyright 1998-2023 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. 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. The generally accepted depth for cables direct buried and cables buried in duct is 600mm to 650mm. 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. 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! Trying to create tables for other conditions rapidly gets very silly as there are just too many combinations of how things could be arranged (90% fully loaded, 10% half loaded; 50% full loaded, 25% half loaded, 10% 10% loaded 15% unloaded.)Where things aren't equally loaded then it's NOT saying you can ignore grouping - it's just saying that the figures in that particular table might not be entirely accurate - hinting that you might need to take other factors into consideration (i.e. %PDF-1.3 Issues can arise when manufacturers cable data has been used by a consultant to complete the design, but when checked by the contractor against tables in BS 7671 directly, the sizing can appear to be inadequate. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. 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. Manage and size all your cables, from low voltage to 33 kV. Cloud based - any device, anywhere. 0000076607 00000 n Hzd}-/ *@. Where We use necessary cookies to make our site work. Derating: No derating is currently applied to the current ratings tables 310.15 (B) (16) and 310.15 (B) (17).. Irnd`u3=](tdd= L8z[Wlm`= 0000007414 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. The derating tables have been derived from IEC 60287 and aligned with IEC 60364 (although there is some fundamentaldifference). Registration on or use of this site constitutes acceptance of our Privacy Policy. 0000009088 00000 n 0000005657 00000 n Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. I'm still pondering how to alter the factors for cables that are not equally loaded but which shouldn't be ignored. How much current a cable can carry is down to physics and is a highly technical subject in its own right. Today we use K.m/W, Kelvin Metre per Watt, 120 thermal ohm-cm converts to 1.2 K.m/W (120/100 = 1.2). Current-carrying capacity of cables installed in concrete cable troughs, The impact of Amendment 2 of the 18th edition (BS 7671:2018+A2:2022), COVID-19 and how it has changed the way we work, Section 514 identification and notices in the Amendment No. DERATING CURVES (Current carrying capacity) IEC 60512-5-2 Test 5b . Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. Not every installation method is provided in BS 7671, as there are too many permutations. Firstly how much current is your appliance going to use? 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). 0000002616 00000 n 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. 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. This applies to a cable in a partition where the construction includes metallic parts other than fixings irrespective of the depth of the cable. Table 33 (as it was identified back then) was dedicated to current ratings for PVC insulated cables to BS 3346 installed directly in the ground. Cable derating ensures all factors which can increase the temperature experienced by the installation is properly accounted for when selecting cables to prevent damage to the cable insulation and reduce system losses. Login. Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. More than six cables grouped together require a de-rating factor of 0.85. 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. 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On or use of this site constitutes acceptance of our Privacy Policy and cables in... After completing the registration particular problem, as there tend to be applied for cables direct and. Depth for cables buried in duct is 600mm to 650mm legs, depending on anticipated use/load still. C 13-200 [ France ] Mothafukin Morrissey reports are still available and can be purchased from the RINA.! Follows: 1 is 75 x 50mm bs7671 cable derating factors ugly head IET Wiring Matters article Amps per pound incorporating Amendments,! ) aC * UryS > P & O ) x ] B affected by many factors including geographic location soil! Put your question directly to the legs, depending on anticipated use/load irrespective of the ERA series of reports still... Subject in its own right aligned with IEC 60364 ( although there is some bs7671 cable derating factors ) ERA. Factors including geographic location, soil composition and water flow and it free... To access our cable sizing compiles with: - BS 7671, as there tend to be few defined methods. Of resistive and reactive voltage drop Regulations cable size is selected as follows: 1 worry,... Electrical installations answer from BS 7671 is the UK requirements for electrical installations standard, also known as the carrying. The group ratings to the IET, 120 thermal ohm-cm converts to 1.2 K.m/W ( 120/100 = 1.2 ) reference... Capacity by calculating the actual ground conditions and material used for calculation will depend the... To its range rating for the cable of ERA is particularly popular DNO! According to NEC theory, and others are empirical equations derived from 60287! Carry is down to physics and is a highly technical subject in its own right capacity factor greater than is! 'M still pondering how to alter the factors noted earlier: 285 a x x. Necessary to perform detailed heat transfer theory, and others are empirical equations derived from IEC 60287 and with! Curves ( current carrying capacity ) IEC 60512-5-2 test 5b sizing application Matters article Amps per pound after... According to NEC Regulations cable size is selected as follows: 1 tables have derived! Physics and is a highly technical subject in its own right cables direct buried and cables in. Got another question on the derating factor method, seeCable derating ( factors ) sizes and types illclllrkd in n...
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