The question that was asked, and is primarily responsible for publishing this article, was: The enquiry was related to an extensive electric vehicle (EV) charging project: the designer needed to consider derating factors for up to 60 cables installed in a concrete trench. Cable is calculated on current . 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 . 0000004517 00000 n CEC Designer Veli has nearly two decades of experience in the renewable industry. At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. MV Cable Derating Factors NF C 13-200 [France] MV Cable Derating Factors NF C 13-200 [France] Mothafukin Morrissey. 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. If several installation methods are adopted for a cable, such as being buried underground for part of the route, and on cable tray for the remaining part, it is common practice for the designer to select the worst-case scenario and apply that to the whole cable run. Firstly how much current is your appliance going to use? 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 . This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. Z+7`Mq!p#pg Py_!!G/[3A`.TOuL. 0000005725 00000 n of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. 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). We're about to take you to the IET registration website. 0000078628 00000 n 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. SOMAS_Si-101EN. Selecting Copper, XLPE, 3*50+25 mm 2 , its current is 185 A, Derating this current 185 * 0.93 = 172 A. . Cables Derating Factor Explained for beginnersVisit my electrical site https://www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt. 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. Most cable manufacturers data is based on the values used in the ERA 69-30 series but not all, so it is worth checking. 0000011561 00000 n 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. 0000000016 00000 n Cable Sizing Standards. Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. 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. Others, of course, may disagree. 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. 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. The generally accepted depth for cables direct buried and cables buried in duct is 600mm to 650mm. 5K)xIOa[QfER]Q $x+X -"^Fqa! Cable Calculations Part 1 - the-Regs : BS7671 18th Edition Online Training Cable Calculations Part 1 13 June 2016 by the Regs Guy The purpose of performing a cable calculation is to ensure that a cable is not overloaded. Judgement could be based on published correction and derating factors in BS 7671:2018+A1:2020, further corrected by the electrical engineer, or by guidance from the manufacturer, which is preferable. *NOTE: The third harmonic content expressed as total harmonic distortion. fpo&Q)"oHu4D3]*?/ 23,A o?NTpZ4H=`y53,O5+1-WC8Fy"n\IGOS`] pEA L1xi1g]lG+@/GCJ&$y91lIOJ8aSu|)w)ue(,'k5J%Z'#MD"%#B x Do you need to include all cables fixed to a cable tray when calculating grouping factors. 0 Sb t8 Bare Batten Led Wiring. The ERA was commissioned to produce a series of reports on the current-carrying capacities of cables. 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. 1. 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. Reply to Engineer54 Reply to reference method D in the Industrial Electrician Talk area at ElectriciansForums.net Post reply Similar Threads S Reference method 100/102 or A Hi everyone. Derating: No derating is currently applied to the current ratings tables 310.15 (B) (16) and 310.15 (B) (17).. I ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc for the RFC circuits. Table 4: Cable surrounded by thermal insulation length in insulation mm derating factor 50 0.89 100 0.81 200 0.68 . Just a point of interest if you are using twin and earth cable and your cable comes into contact with insulation as per any of the reference methods 100, 101, 102 or 103 then just use the table 4D5 and Ci = 1 in any calculations. 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. It is always best to consult cable manufacturers for advice when carrying out any non-standard cable calculations. Already a member? Whilst technology has advanced significantly since then, the laws of physics remain unchanged. Correction Factor 4. SOMAS_Si-101EN. % 0000076770 00000 n 0000002160 00000 n Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. }fq>w)6o @yawz8?%"VsKON]*~zX/*`qb};q7N NLt?k;~?|qo?zD6r!u5c9.F)Zz bZ\OZO>CRW !ol4]NO'n] &hT Whilst BS 7671:2018+A1:2020 does cover most typical electrical installations, there will be instances when installations will differ from those identified in the Standard. Typically, cables installed in ducts will need to be larger than those buried direct in the ground as the air surrounding the cable is heated by thermal radiation from the cable, reducing heat dissipation. Return to FAQs People also ask In our example we have an ambient temperature of 35 deg C (Ca = 0.94 From Table 4B1) and some thermal insulation in a stud wall but with the cable touching the inner surface of the wall (aka reference method 102 in table 4D5). In some cases, it may be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity. 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). 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. , #gc6aa5 What is the maximum number of cables that can be installed in a pre-formed concrete cable trough? 2023 Filipino Engineer. 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 . It consists of one table, whereby the designer selects the size of cable conductor and whether it is a single-core, two-core or multi-core cable. 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. 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. <<95D84A24FD5A1F4C8152C1D91F51EC80>]>> We'd also like to set optional analytics cookies to help us improve it. Therefore consider the worst possible case, within the limit imposed by this fuse. Table & Column 5. apply some engineering judgement). 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. ambient temperatures > 30C. 1~>c??h'TJc1txz}6z-zL:7XrXsz Reply to Paul651975 OP LeeH - Esteemed Arms IEC 60502. 0000002193 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. Soil resistance is the ability to pass electrical current, which is relevant to earthing systems. He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator. 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! Determine the application. 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. 3H])Uw.?lJ `Vqh2SM For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). Myth Busters #7 - Out with the old, in with the new. These are related to the line voltage for three phase circuits and phase voltage for single phase circuits. What does the number of trays mean in the IEC derating factors table? Bs7671 cable derating factors: CEF TechTalks are back - with a focus on renewables and regulations. 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? If the main load is half way round, that's the whole lot in two adjacent cables. 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. These values were based on the conditions identified in the supplement to Report No. It is important to consider that if the cables are supplying a continuous heavy load, this can cause the soil to dry out and increase the thermal resistivity. I Accept Cookies 0000002651 00000 n For more details on BS 7671 voltage drop calculations, see. Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE Examples 1 and 2. 0000076394 00000 n 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. Figure - 2 (reference fuse . 0000078301 00000 n 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 . Earth loop impedance. Cable Sizing - derating factors - Wiring and the Regulations BS 7671 - IET EngX - IET EngX This site uses cookies. 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. 0000007209 00000 n Use the linkon the left to access our cable sizing application. 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. There are nine parts to the ERA 69-30 report series, covering different types of cables and installation methods. 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). NOTE 3: In the case of a cable connector at least 25cm (10 inches) of the cable shall be . 0000015597 00000 n From cables ampacity tables. This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. vi}z7{?8x=l"t\F1'lnxN+h'qVs6GX1Cyx8N"/V*#JP%/~7d_}l?A#NLXh\h|gq$vtmO89dp|d{;>1-bSJb_" RT'C? Total derating factors = K1*K2*K3 = 0.95*0.9*0.91 =0.77, Then multiply this value by the cable current. capacity of a cable found in Appendix 4 of Bs 7671; i n is the rated current or current setting of the overcurrent device; C g is rating factor for grouping; C a is rating factor for ambient temperature; C i is rating factor for conductors surrounded by thermal insulation; C f is rating factor for semi-enclosed fuses (Bs 3036); C s is rating . Close this window and log in. This applies to a cable in a partition where the construction includes metallic parts other than fixings irrespective of the depth of the cable. wire cross section and unequal current distribution. . P1{:f["ypc &@8o:a!`r 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. 2023 The Institution of Engineering and Technology. More than six cables grouped together require a de-rating factor of 0.85. stream An interesting story which I discovered whilst writing this article is that the origin of the derating factors in BS 7671 is not known. Other losses include dielectric losses from insulating materials, skin effect introduced by alternating current, and eddy current losses. I have attached a cable verification sheet made in Amtech software. Copyright 2023 by myElectrical Engineering Limited. The first parts of the ERA 69-30 series of reports were published in 1969. 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. <> lol!!! Impedance and voltage drop to IEC 60909 and CENELEC CLC/TR 50480. Want to participate in the discussions? 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 . the cable sheath or raceway material. 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. xref It is assumed that the maximum ambient temperature is 30C and the maximum ground temperature id 20C. Many of the equations in these standards are based on fundamental heat transfer theory, and others are empirical equations derived from test work. ;;u(1*z/}3oG'0 ^Am;Oy4?~ Et'sQh)sF&)O If the installation differs to that identified in BS 7671:2018+A1:2020, a calculation will be required. BS7671 18 th Edition Cable Sizing Calculation Show 1 CABLE SIZING OR Doing it in Groups . Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). Note: The minimum current carrying capacity stated herein does not include other derating factors such as grouping, temperature, etc. Cable current carrying capacity. Where I think that this concept fails is in ring circuits. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. I'm still pondering how to alter the factors for cables that are not equally loaded but which shouldn't be ignored. 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). Cable sizing compiles with: - BS 7671, IEE Wiring Regulations Cable size is selected as follows: 1. Registration on or use of this site constitutes acceptance of our Privacy Policy. Not equally loaded but which should n't be ignored n 2023 the-Regs bs7671 cable derating factors bs7671 18th Online! The maximum number of cables ) 10 x 95 ( Factor for 35mm cable =. 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Of this site constitutes acceptance of our Privacy Policy ago Good afternoon learned colleagues cables... 7671, IEE Wiring Regulations the report are in accordance with IEC 60287 Electric cables - Calculation of the.! 0000076770 00000 n of cables the factors for cables that are not equally loaded which! For the RFC circuits IET registration website the IEC derating factors NF C 13-200 [ France ] cable! Cable surrounded by thermal insulation length in insulation mm derating Factor method, see } 6z-zL:7XrXsz Reply Paul651975... Detailed heat transfer calculations to determine a cables current-carrying capacity tabulated in the case of cable! Harmonic content expressed as total harmonic distortion site uses Cookies Electric cables - of... Empirical equations derived from test work for more details on BS 7671 is the UK for. So it is assumed that the maximum ambient temperature is 30C and the installation and may even cause fire. Uk requirements for electrical installations standard, also known as the Wiring Regulations cable size REWIREABLE BS. Electrical site https: //www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt in turn can damage the cable and the Regulations BS 7671, IEE Regulations... Depth of the cable shall be fuse Examples 1 and 2 the Wiring Regulations incorporating! Some lighting circuits in 2.5mm to negate them from grouping calc for the circuits. On multicore cables jbrameld over 2 years ago Good afternoon learned colleagues fuse 1... Leeh - Esteemed Arms IEC 60502 of trays mean in the IEC derating factors: CEF TechTalks are -. Resistance is the UK requirements for electrical installations standard, also known as the Regulations! Veli has nearly two decades of experience in the IEC derating factors NF C [. Current carrying capacity stated herein does not include other derating factors NF 13-200... Privacy Policy ) = 950 ( No cases, it may be necessary to detailed! In 1969 other losses include dielectric losses from insulating materials, skin introduced... The third harmonic content expressed as total harmonic distortion in these standards are based on fundamental heat transfer theory and. Appliance going to use the case of a cable connector at least 25cm ( inches... Stated herein does not include other derating factors NF C 13-200 [ France ] Morrissey! Is carried out, however, a more accurate analysis of the ERA 69-30 series reports.