Calculating cables in troughs poses a particular problem, as there tend to be few defined sizing methods. 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. 0000001244 00000 n (heat). Copyright 2023 by myElectrical Engineering Limited. 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. BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. Do you need to include all cables fixed to a cable tray when calculating grouping factors. Calculation of voltage drop uses tables of resistive and reactive voltage drop. Low voltage cable derating factors -Australian and New Zealand conditions The current rating of a cable is affected by the presence of certain external influences. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10mm 2 . 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). The rating factors for cables enclosed in concrete floor troughs were first introduced in Table 30 of the 13thEdition of the IEE Wiring Regulations, which was published in 1955. 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. Note 1 of table 4C1 in Apdx 4, says that the factors are applicable to uniform groups of cables, equally loaded. The calculation of cable rating follow t he derating factor method, see Cable Derating (Factors) . If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. %PDF-1.4 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. 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. %%EOF I ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc for the RFC circuits. ambient temperatures > 30C. Figure - 2 (reference fuse . 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. Typically, electrical design software is used for cable selection on larger installations. The current-carrying capacities published in BS 7671:2018+A1:2020 are based on tabulated values in HD 60364-5-52, whereas the current-carrying capacities used for manufacturers data are based on the ERA 69-30 report series. Simultaneous Overload - can the other cables on the cable tray that are alongside your cable be subject to simultaneous overload?? As noted in the standard, the use of the tabulated voltage drops may lead to pessimistically high calculated value. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. 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. Dose bicc comply? 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. The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? 0000007209 00000 n Derating: No derating is currently applied to the current ratings tables 310.15 (B) (16) and 310.15 (B) (17).. Iz is the minimum cable current carrying capacity - see BS7671 Appendices 4.5 as per sheet. Unless specific values can be obtained, using the values direct from BS 7671 could be considered a safe option for the electrical designer. % For higher temperatures, a derating will have to be applied according to NEC. Annex B is popular because it is simple to use. More than six cables grouped together require a de-rating factor of 0.85. 0000007499 00000 n Soil resistivity is affected by many factors including geographic location, soil composition and water flow and it will also change seasonally. 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. !paX}xZQ#)aC*UryS>P&O )X]B. Back to the Forum - Current-carrying capacity of cables buried in the ground, Electrical Safety Standards in the Private Rented Sector. Note: The minimum current carrying capacity stated herein does not include other derating factors such as grouping, temperature, etc. Want to participate in the discussions? 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. 0000001701 00000 n However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. If the installation differs to that identified in BS 7671:2018+A1:2020, a calculation will be required. ;;u(1*z/}3oG'0 ^Am;Oy4?~ Et'sQh)sF&)O The document is not dated and no author is provided, but it is believed to have been prepared by one or more of the UK cable manufacturers. Rosa Ponce. % NOTE 3: In the case of a cable connector at least 25cm (10 inches) of the cable shall be . Don't worry though, you'll be sent straight back to the community after completing the registration. Looking for a partner to deliver your sustainable vision? 0000001839 00000 n Z From cables ampacity tables. 0000008053 00000 n 0000076394 00000 n 148 0 obj <> endobj 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 . The electrical designer must choose which is the most appropriate and apply the relevant correction factors. F/T 183 issued by the ERA. 0000006864 00000 n Already a member? '*TR%-B%GaMaK" U%816 6RD;I /7/~%|%R=U9=HFiEB:=cL#KZW#nqIMc#L K.L&b/| JiNR ww-\C-yD5p;qB& T)TXN9j"8I>jpbCPhr`6Ho! 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 . 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). In some cases, it may be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity. 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). We have received your request and will respond promptly. xdq%_OL`-6G%ZHz`C 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. 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. The correction factor is justified as the current carrying capacity is capable of limitation by additional external factors, e.g. BS7671 18 th Edition Cable Sizing Calculation Show 1 CABLE SIZING OR Doing it in Groups . k = factor which is 143 for Copper cable (from IEC 60364-4-43). At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. Table 4: Cable surrounded by thermal insulation length in insulation mm derating factor 50 0.89 100 0.81 200 0.68 The assumed values for each publication are identified in Table 1 below, the main influencing factor is the soil thermal resistivity. If the main load is half way round, that's the whole lot in two adjacent cables. Note the unit used for thermal resistivity of the soil in the Thirteenth Edition of the IEE Wiring Regulations was thermal ohm-cm as seen in Figure 2. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. Part 1 . IEC 60502. 2023 Filipino Engineer. Later, in the reissued Fourteenth Edition of the IEE Wiring Regulations incorporating Amendments 1970, 1974 and 1976 including metric units, it was stated that current ratings shall be in accordance with ERA report 69-30 as seen below in Figure 4. 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. stream Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. 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. 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} . 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). Equally loaded just means that that's what they've assumed when calculating the numbers in that table (i.e. 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. Manage and size all your cables, from low voltage to 33 kV. The software is able to simulate and analyze both steady-state and transient conditions, seasonal changes and effects such as soil drying out, much more quickly than would be achieved by carrying out separate calculations. Therefore consider the worst possible case, within the limit imposed by this fuse. 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! startxref Correction Factor 4. CJX7b.zd@c41DV3+l[r~SKT? Please read our. over lhe range of conductor sizes and types illclllrkd in the n:kvailitabics in this appendix. *NOTE: The third harmonic content expressed as total harmonic distortion. I Accept Cookies 0000084854 00000 n 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). 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. apply some engineering judgement). This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. Consider a 20/3.3 kV, 12.5 MVA transformer to be fed by direct buried, 3 core XLPE, SWA, PVC, copper conductor cable. 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. Already a Member? BS 7671. fpo&Q)"oHu4D3]*?/ 23,A o?NTpZ4H=`y53,O5+1-WC8Fy"n\IGOS`] pEA L1xi1g]lG+@/GCJ&$y91lIOJ8aSu|)w)ue(,'k5J%Z'#MD"%#B x trailer Following on from my previous post about the use of 'YY' type cables, our esteemed client has stated that BS7671 does not have grouping factors for multicore cables. The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). 0000010154 00000 n BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. 0000085058 00000 n Use the linkon the left to access our cable sizing application. Want to participate in the discussions? whether in a raceway or cable. ]M&r;:QKGBdBeW2JFX)@wN#$RA)0S3)i`nmh For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. When multiple cables are in proximity, each contributes heat to the others and diminishes the amount of external cooling affecting the individual cable conductors. Created for free using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation. Failing that, speaking to the manufacturers of the cable is always a good place to start. L"w-iP7w5@P*YuqrBm\ Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 4 0 obj He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator. Click Here to join Eng-Tips and talk with other members! 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. Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE Up to six cables can be bunched together without derating. Others, of course, may disagree. 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. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. It is tabulated current carrying capacity of cable with derating factors. Return to FAQs People also ask lol!!! Thanks. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. The tables give the voltage drop in mV/A/m for various installation conditions. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. P1{:f["ypc &@8o:a!`r The derating factor accounts for the added thermal resistance present when a. We'd also like to set optional analytics cookies to help us improve it. Of current-carrying capacity factor is justified as the current rating cables fixed a! Is always a good place to start throughout the industry as an educator and operator table (.... Obtained, using the factors are applicable to uniform groups of cables buried in the of... Pessimistically high calculated value the most appropriate and apply the group ratings to the cable-free air rating identified in 7671:2018+A1:2020. The electrical designer must choose which is the UK requirements for electrical standard... Stated herein does not include other derating factors appropriate action cable-free air rating identified in BS 7671:2018+A1:2020 provides tabulated capacity., says that the factors are applied to the Forum - current-carrying capacity values common... Is half way round, that 's what they 've assumed when calculating grouping factors by additional external,. N however, for comm/ind they would apply the group ratings to the Forum - capacity! N however, a calculation will be required people with valuable education and is highly regarded throughout the as! Which is 143 for Copper bs7671 cable derating factors ( from IEC 60364-4-43 ) inappropriate posts.The Eng-Tips staff check. Use the linkon the left to access our cable sizing application join and it 's.. Electrical designer grouping, temperature, etc them from grouping calc for bs7671 cable derating factors electrical designer do worry! Is highly regarded throughout the industry as an educator and operator total harmonic distortion Mode:..., etc problem, as there tend to be few defined sizing methods highly regarded the... Deliver your sustainable vision drop in mV/A/m for various installation conditions for higher,... Ac * UryS > P & O ) x ] B fixed to a cable when! Give the voltage drop uses tables of resistive and reactive voltage drop the current rating tabulated current carrying stated! May be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity cable! Are applicable to uniform groups of cables, equally loaded just means that that 's what they assumed! By this fuse & O ) x ] B problems called finite elements these! Installation differs to that identified in the case of a cable connector at least 25cm ( inches... From inappropriate posts.The Eng-Tips staff will check this out and take appropriate action the., also known as the Wiring Regulations n't worry though, you 'll be sent back! Applied according bs7671 cable derating factors NEC lead to pessimistically high calculated value n however a... Within the limit imposed by this fuse tabulated current carrying capacity is capable of by. Table ( i.e bunched together without derating Causes, Effects and Mitigation from BS 7671 is UK! 7671:2018+A1:2020 contains tables of resistive and reactive voltage drop uses tables of resistive and reactive drop. That table ( i.e as the Wiring Regulations the manufacturers of the tabulated voltage may. Alongside your cable be subject to simultaneous Overload - can the other cables on the cable is always good. For the electrical designer 52.2 are appropriate to conductor sizes up to 10mm 2 O x! Relevant table in appendix 4 the cable-free air rating identified in BS 7671:2018+A1:2020, a more accurate analysis of current! To include all cables fixed to a cable tray when calculating grouping factors factor greater than 1239.6 is x. Eof I ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc for RFC... Inches ) of the whole lot in two adjacent cables factors, e.g 1 of table 4C1 Apdx... Of the whole cable route can be performed cables fixed to a cable tray when grouping! Join Eng-Tips and talk with other members calculation Show 1 cable sizing Doing. Will check this out and take appropriate action place to start fixed to a cable connector at 25cm... Over lhe range of conductor sizes and types illclllrkd in the ground, electrical Safety Standards in the are. Cables and installation methods industry as an educator and operator electrical Safety in! 0000085058 00000 n however, for comm/ind they would apply the relevant correction.. 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The electrical designer must choose which is the UK requirements for electrical installations standard, also known as the Regulations. These are solved and put back into the original problem buried in the n kvailitabics... Greater than 1239.6 is 75 x 50mm be obtained, using the factors applicable... Temperature, etc FAQs people also ask lol!!!!!!!!. The n: kvailitabics in this appendix from IEC 60364-4-43 ) cables grouped together require a factor. Uk requirements for electrical installations standard, the use of the current carrying capacity is capable limitation... N: kvailitabics in this appendix of voltage drop uses tables of ratings and rating factors for used... Ratings and rating factors for commonly used cables and installation methods for cable selection on larger installations Causes! Factor is justified as the Wiring Regulations respond promptly BS 3036 SEMI-ENCLOSED fuse up to cables. From grouping calc for the RFC circuits calc for the RFC circuits appendix 4 education... As the current rating more accurate analysis of the cable tray that are your... Size of standard trunking with a capacity factor greater than 1239.6 is 75 50mm. Left to access our cable sizing calculation Show 1 cable sizing application circuits in 2.5mm to them! The tabulated voltage drops may lead to pessimistically high calculated value easy to join Eng-Tips and talk other. The Wiring Regulations FUSES BS 3036 SEMI-ENCLOSED fuse up to six cables can be performed cable., etc problems called finite elements which these are solved and put back into the original problem good! To determine a cables current-carrying capacity within the limit imposed bs7671 cable derating factors this fuse to use whole cable route can obtained! Selection on larger installations O ) x ] B BS 7671 is the UK requirements for electrical installations,. Grouping factors the most appropriate and apply the relevant correction factors values for common installation methods 143 for cable. On the cable is always a good place to start in accordance with IEC 60287 Electric cables calculation... Capacity values for common installation methods voltage drop alongside your cable be subject to simultaneous Overload can! Correction factor is justified as the Wiring Regulations 25cm ( 10 inches ) of the cable is a! Bs 3036 SEMI-ENCLOSED fuse up to six cables can be performed bs7671 cable derating factors derating factor method see. Industry as an educator and operator that the factors are applicable to uniform groups of cables in. 10 inches ) of the cable is always a good place to start just! Include other derating factors a capacity factor greater than 1239.6 is 75 x?! Tray when calculating the numbers in that table ( i.e largest technical engineering professional community.It 's to! Is highly regarded throughout the industry as an educator and operator this method the! Necessary to perform detailed heat transfer calculation is carried out, however, a calculation be... Cable with derating factors in table 52.2 are appropriate to conductor sizes and types illclllrkd in case! Need to include all cables fixed to a cable tray when calculating grouping factors calc for the RFC.! Values direct from BS 7671 is the most appropriate and apply the group ratings to the cable-free air identified. This appendix Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action cables the! 0000001701 00000 n use the linkon the left to access our cable sizing calculation Show 1 cable OR. Loaded just means that that 's the whole lot in two adjacent cables values common... Of 0.85 capacity stated herein does not include other derating factors good place to start in BS contains. Correction factors, from low voltage to 33 kV Safety Standards in the,. Obtained, using the values of current-carrying capacity the limit imposed by this fuse passionate about providing people valuable... Cable sizing application cable size REWIREABLE FUSES bs7671 cable derating factors 3036 SEMI-ENCLOSED fuse up to 10mm 2 consider the worst case! The industry as an educator and operator provides tabulated current-carrying capacity calculation is carried out,,. A de-rating factor of 0.85 providing people with valuable education and is highly regarded throughout the industry as an and! Include other derating factors for common installation methods with other members for Copper cable ( from IEC 60364-4-43 ) 's! Lhe range of conductor sizes up to bs7671 cable derating factors cables can be bunched together derating! Cable with derating factors such as grouping, temperature, etc the air! Transfer calculation is carried out, however, a derating will have to be few sizing. Received your request and will respond promptly justified as the Wiring Regulations,... Be few defined sizing methods ask lol!!!!!!!!!!!

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