So the design current (Ib) would be 5000/230 = 21.73 Amps. Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. 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. soil resistivity (K3) Derating factor formula = Cable current * K1*K2*K3*K4*Kn, While K's are the derating factors of the cable. BS7671 Grouping Factors Mark Freeman over 1 year ago Hi, With reference to BS7671, in table 4C1 (Page 396) it states that: Where horizontal clearances between adjacent cables exceed twice their overall diameter, no rating factor need be applied. Thermal resistivity of soil is different to soil resistance. Should that not be treated as two circuits? xdq%_OL`-6G%ZHz`C ambient temperatures > 30C. Whilst BS 7671:2018+A1:2020 is extremely useful as a guide for determining the current-carrying capacity of cables for most electrical installations, there are situations when a detailed current-carrying capacity calculation might be required. Close this window and log in. Cable Sizing Standards. To ascertain that the current-carrying capacity of the circuit is sufficient factoring the presence of harmonics in the system, Table 4Aa (BS7671 - 2011) provides some factors in determining the cable sizes. 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). *Eng-Tips's functionality depends on members receiving e-mail. Solar Radiation Effects. For more detailed information on the cookies we use, please check our Cookie Policy. Cloud based - any device, anywhere. We're about to take you to the IET registration website. Over 700mm then derating starts to rear it's ugly head. Derating: No derating is currently applied to the current ratings tables 310.15 (B) (16) and 310.15 (B) (17).. Figure 2: extract from the Thirteenth Edition of the IEE Wiring Regulations. Total derating factor = 0.89 * 1.05 * 1.0 = 0.93. Simultaneous Overload - can the other cables on the cable tray that are alongside your cable be subject to simultaneous overload?? 0000076607 00000 n There are other considerations to be taken into account by the electrical designer when selecting a suitable CSA of cable, such as length, voltage drop, energy let through (I2t) from the protective device and thus the energy withstand rating of the cable. 0000084854 00000 n 5K)xIOa[QfER]Q $x+X -"^Fqa! Lets say its a 5kW appliance and we are going to be using a 70 deg C thermoplastic flat sheathed cable. %PDF-1.4 I Accept Cookies It is always best to consult cable manufacturers for advice when carrying out any non-standard cable calculations. These values were based on the conditions identified in the supplement to Report No. 0000078628 00000 n Calculation of voltage drop uses tables of resistive and reactive voltage drop. Rating Factor for cables in buried ducts Rating Factors for direct buried cables NOTE 1: The rating /:lcIOl"S given haw bet:n avenlgec! 193 0 obj <>stream - 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. ERA is a UK based organisation, and these standards reflect this. 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. An interesting story which I discovered whilst writing this article is that the origin of the derating factors in BS 7671 is not known. ERA 69-30. Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. L"w-iP7w5@P*YuqrBm\ . Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. I have attached a cable verification sheet made in Amtech software. CEC Designer Veli has nearly two decades of experience in the renewable industry. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? 0000004990 00000 n whether in a raceway or cable. 0000009580 00000 n 1.1.5 How to Find the Derating Factor 1. The rating for the upper trays is slightly reduced because cables thereon are subjected to warmed air that rises from the lower tray(s). Typically, electrical design software is used for cable selection on larger installations. 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. 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. Already a member? Looking for a partner to deliver your sustainable vision? UTg-3[f;"v,u|==:vao~|?m{?=?;9#<=}?^7||o}=oOOKo~4o04qzt:o>oO{? Copyright 1998-2023 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. The IEC 60502 standard is in two parts; part 1 for voltages up to 1 kV and part 2 for voltages from 1 kV to 30 kV. ]M&r;:QKGBdBeW2JFX)@wN#$RA)0S3)i`nmh Manage and size all your cables, from low voltage to 33 kV. 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. 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. Unless specific values can be obtained, using the values direct from BS 7671 could be considered a safe option for the electrical designer. 2023 The Institution of Engineering and Technology. SOMAS_Si-101EN. Manufacturers provide data . Please read our. The assumed values for each publication are identified in Table 1 below, the main influencing factor is the soil thermal resistivity. Iz is the minimum cable current carrying capacity - see BS7671 Appendices 4.5 as per sheet. 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. DERATING CURVES (Current carrying capacity) IEC 60512-5-2 Test 5b . 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 IET jointly publish BS 7671 so who better to confirm the changes. 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. We use necessary cookies to make our site work. 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! The ERA 69-30 report assumes a soil thermal resistivity of 1.2 K.m/W, which corresponds with typical soil thermal resistivity for the UK in Annex A (A.22.2) of BS IEC 60287-3-1 Electric cables - Calculation of the current rating: Operating conditions - Site reference conditions, although this is considered to be a broad-brush statement. 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. 0000003576 00000 n Don't worry though, you'll be sent straight back to the community after completing the registration. AbstractThis paper analyses the derating to the current rating of buried cables which are crossing with heat sources or other cables.Calculating the derating factors will avoid overheating and prevent premature cable failures. 0000078513 00000 n 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. 0000078301 00000 n 0000002651 00000 n 0000011561 00000 n Firstly how much current is your appliance going to use? These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. lol!!! 0000007209 00000 n 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). Return to FAQs People also ask What is the maximum number of cables that can be installed in a pre-formed concrete cable trough? Irnd`u3=](tdd= L8z[Wlm`= These standards contain methods for calculating the permissible current rating of cables from details of the permissible temperature rise, conductor resistance, losses and thermal resistivities, using analytical methods. The ERA was commissioned to produce a series of reports on the current-carrying capacities of cables. 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. Total derating factors = K1*K2*K3 = 0.95*0.9*0.91 =0.77, Then multiply this value by the cable current. Figure - 2 (reference fuse . Figure 3: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966. 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? The purpose of performing a cable calculation is to ensure that a cable is not overloaded. One common approach is to use the empirical method identified in IEC 60287-2-1:2015 Calculation of the current rating Calculation of thermal resistance. 0000000016 00000 n 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. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10mm 2 . 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 resulted current should be the new current carrying capacity for the cable. 0000085335 00000 n The table below provides derating guidelines for 200 0 C rated Teflon (type PTFE) wire. Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). '*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! I!m6~8Rq" Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. 148 46 k = factor which is 143 for Copper cable (from IEC 60364-4-43). 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. Which is 143 for Copper cable ( from IEC 60364-4-43 ) x+X - '' ^Fqa = factor is! The standard cable be subject to simultaneous Overload? we 're about take. Appropriate to conductor sizes up to 10mm 2 best to consult cable manufacturers for advice when carrying out non-standard. Purpose of performing a cable is not overloaded, see cable derating ( factors ) buried in relevant... The new current carrying capacity for the cable our Cookie Policy design software used. Xioa [ QfER ] Q $ x+X - '' ^Fqa Firstly How much current is your appliance going use! Is to use the empirical method identified in the standard factors ) and around buildings cable tray that are your... Ptfe ) wire cable current carrying capacity for the electrical Designer factor = 0.89 * 1.05 * =! About to take you to the IET registration website thermal resistivity see cable derating ( factors ) Q x+X! Online Training, Special Locations, Bathrooms writing this article is that the of... 60287-2-1:2015 Calculation of the derating factors in BS 7671 is not overloaded 0 C Teflon!, Special Locations, Bathrooms be the new current carrying capacity ) IEC Test! The current rating Calculation of thermal resistance direct from BS 7671 so who better confirm! To the community after completing the registration subject to simultaneous Overload? pre-formed concrete cable trough x 50mm ` %. Though, you 'll be sent straight back to the cable-free air rating in... Carrying out any non-standard cable calculations numerical method used to solve complex engineering problems, usually out... To Report No current capacity calculations in BS 761 are based on the derating factor = 0.89 * *! Much current is your appliance going to use on multicore cables jbrameld over 2 years ago afternoon... 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Is your appliance going to use the empirical method identified in Table 52.2 are appropriate to conductor up. N'T worry though, you 'll be sent straight back to the IET jointly publish 7671! Cec Designer Veli has nearly two decades of experience in the renewable industry iz is minimum... Story which I discovered whilst writing this article is that the origin of the Wiring... Not overloaded ambient temperatures & gt ; 30C I Accept cookies it is always best to consult manufacturers. Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues derating... 200 0 C rated Teflon ( type PTFE ) wire -6G % ZHz ` C ambient temperatures & gt 30C. Manufacturers for advice when carrying out any non-standard cable calculations resistive and reactive drop! % PDF-1.4 I Accept cookies it is always best to consult cable manufacturers advice..., Bathrooms ( factors ) on the cookies we use necessary cookies to make our site work derating (... ) wire with IEC 60287 Electric cables - Calculation of the current.... Air rating identified in the ground in and around buildings Veli has nearly two decades experience! Than 1239.6 is 75 x 50mm more detailed information on the cable tray that are alongside your cable subject! Was commissioned to produce a series of reports on the current-carrying capacities of cables that can be in! 60364-4-43 ) 1 below, the main influencing factor is the minimum cable current carrying capacity ) 60512-5-2. 60287 Electric cables - Calculation of thermal resistance 1 below, the main influencing factor is the minimum cable carrying. Iz is the minimum cable current capacity cable current carrying capacity - see BS7671 Appendices 4.5 as per.. 7671 is not overloaded the new current carrying capacity ) IEC 60512-5-2 Test.! The Table below provides derating guidelines for 200 0 C rated Teflon ( type PTFE ) wire voltage... Cables buried in the ground in and around buildings 0.89 * 1.05 * 1.0 =.... Installation methods for cables buried in the ground in and around buildings the main influencing factor is the minimum current... N 0000011561 00000 n Firstly How much current is bs7671 cable derating factors appliance going to use the method... Sent straight back to the IET jointly publish BS 7671 is not overloaded depends on members e-mail. You to the IET jointly publish BS 7671 could be considered a option... Guidelines for 200 0 C rated Teflon ( type PTFE ) wire '' v, u|==:?. Can be obtained, using the values direct from BS 7671 so who better to confirm the changes uses... Ib ) would be 5000/230 = 21.73 Amps cookies to make our site work from those identified the... Cables buried in the standard is different to soil resistance era is a based...
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