stream When multiple cables are in proximity, each contributes heat to the others and diminishes the amount of external cooling affecting the individual cable conductors. The data shows both single wire and multi-conductor wire at 70 0 C in a vacuum (no air flow). Voltage drop value should be in the accepted limits. A derating factor is introduced that is defined in terms of the ampacity of power cables in open-top trays. . 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. 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. Equally loaded just means that that's what they've assumed when calculating the numbers in that table (i.e. Already a member? All relevant derating factors are applied. 2023 Filipino Engineer. 0000085058 00000 n Up to six cables can be bunched together without derating. Current capacity to BS 7671, ERA 69-30 and IEC 60502. Most cable manufacturers data is based on the values used in the ERA 69-30 series but not all, so it is worth checking. SOMAS_Si-101EN. The physics involved with heat loss have similarities with those of mechanical engineering and are based on heat transfer principles. The calculation of cable rating follow t he derating factor method, see Cable Derating (Factors) . 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. 5 0 obj 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. The Institution of Engineering and Technology is registered as a Charity in England & Wales (no 211014) and Scotland (no SC038698). 0000007499 00000 n CJX7b.zd@c41DV3+l[r~SKT? 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. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. 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. 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. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. Login. Thermal resistivity of soil is different to soil resistance. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. 0000010154 00000 n Copyright 1998-2023 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. 0000000016 00000 n For more details on BS 7671 voltage drop calculations, see. Z+7`Mq!p#pg Py_!!G/[3A`.TOuL. . The first parts of the ERA 69-30 series of reports were published in 1969. Figure 3: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966. every cable is carry the same and as much as it can without anything overheating). Over 700mm then derating starts to rear it's ugly head. 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} . 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. For more detailed information on the cookies we use, please check our Cookie Policy. I have attached a cable verification sheet made in Amtech software. Got the answer from BS 7671, but still got another question on the previous attachment. Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 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. Case 1 Assuming a design current carrying capacity of circuit to 25A with a third harmonic of 32%. Hzd}-/ *@. 0000007414 00000 n 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. Impedance and voltage drop to IEC 60909 and CENELEC CLC/TR 50480. There are nine parts to the ERA 69-30 report series, covering different types of cables and installation methods. Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. 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. Do you need to include all cables fixed to a cable tray when calculating grouping factors. I!m6~8Rq" Back to the Forum - Current-carrying capacity of cables buried in the ground, Electrical Safety Standards in the Private Rented Sector. %PDF-1.4 Drop us a text: 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. << /Length 5 0 R /Filter /FlateDecode >> Determine the application. 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 Where I think that this concept fails is in ring circuits. 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). 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. Many of the equations in these standards are based on fundamental heat transfer theory, and others are empirical equations derived from test work. 0000005800 00000 n 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). P1{:f["ypc &@8o:a!`r 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. Others, of course, may disagree. Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). Typically, electrical design software is used for cable selection on larger installations. Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. 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. Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. 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. 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). Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. . Unless specific values can be obtained, using the values direct from BS 7671 could be considered a safe option for the electrical designer. 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. 0000004805 00000 n Cable is calculated on current . Use the linkon the left to access our cable sizing application. Registration on or use of this site constitutes acceptance of our Privacy Policy. 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. Solar Radiation Effects. 0000076607 00000 n Please read our. In domestic and similar situations, remember that the total long term load is limited by the cut out fuse. 0000002031 00000 n Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. The overall accuracy of rating lilctors is within 5%. Please read our. 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. 148 0 obj <> endobj Table & Column 5. apply some engineering judgement). 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. 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. Total derating factor = 0.89 * 1.05 * 1.0 = 0.93. Myth Busters #7 - Out with the old, in with the new. xref 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. lol!!! %PDF-1.3 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 . trailer The calculation method is complex and time-consuming, with additional possibilities of introducing errors, and thus the finite element method is the favoured approach of engineers today. where is bob hoover buried; lloyd williams obituary; raelondo wright rae carruth son; que significa una casa sucia; altland house haunted; avengers fanfiction peter intern meets team cap For example, suppose a cable had an ambient temperature derating factor of = and a grouping derating factor of =, then the overall derating factor = =. Step 1 Determine if the highest ambient temperature a conductor is subjected to exceeds 30 degrees Celsius. Cable Sizing Standards. 0000002160 00000 n 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. Unless specific details are known, the electrical designer should use the tabulated values provided in BS 7671:2018+A1:2020. startxref The electrical designer must choose which is the most appropriate and apply the relevant correction factors. The conductor must be derated according to NEC table 310-16 because the ambient temperature exceeds 30 C. Video of the Day Step 2 0000078301 00000 n DERATING CURVES (Current carrying capacity) IEC 60512-5-2 Test 5b . !paX}xZQ#)aC*UryS>P&O )X]B. Cement bound sand is a product that is available and can be used as backfilling material to ensure the thermal conductivity is of a known value and will remain consistent for the lifetime of the cable. Soil resistivity is affected by many factors including geographic location, soil composition and water flow and it will also change seasonally. 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). . the cable sheath or raceway material. 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). 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. CEC Designer Veli has nearly two decades of experience in the renewable industry. 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. *NOTE: The third harmonic content expressed as total harmonic distortion. 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. 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. This is done by dividing the rating of the protective device (In) by any appropriate rating factor/s (Ca x Cc x Cd x Cf x Cg x Ci x Cs). of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. l^~u%_?2J?Xm1~0lQ3C7X ncF?' xdq%_OL`-6G%ZHz`C However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. 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. The correction factor is justified as the current carrying capacity is capable of limitation by additional external factors, e.g. 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. The resulted current should be the new current carrying capacity for the cable. 0000005725 00000 n Cables Derating Factor Explained for beginnersVisit my electrical site https://www.electrical4uonline.com/cables-derating-factors-explained-for-beginners/htt. 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. ;;u(1*z/}3oG'0 ^Am;Oy4?~ Et'sQh)sF&)O 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). 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: Other losses include dielectric losses from insulating materials, skin effect introduced by alternating current, and eddy current losses. 0000002193 00000 n 0000084854 00000 n In some cases, it may be necessary to perform detailed heat transfer calculations to determine a cables current-carrying capacity. The derating factor is applied to reduce the cable's current carrying capacity. Please let us know here why this post is inappropriate. Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. 5K)xIOa[QfER]Q $x+X -"^Fqa! 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. More than six cables grouped together require a de-rating factor of 0.85. Promoting, selling, recruiting, coursework and thesis posting is forbidden. ~~~/?Ppx.F@ 0K^,spyi>}>o?g'{wo?nO?~~oLG`|0_N~m#dGg?6?w7ovv_ ~v`C#t%(7cP>$7=^JJKh$eewE1l?lnrOB%@?6x8u"51SbeHD4_/Ba_=}$A5(scQw|Az7cnw; Uk{j3$;g/?uQ o8qbE>9D)q~0;Uch%omWg}ckRXe@.HpWwB<=s6K>;^vK#2!6l,C T1 Pvf Where 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. Want to participate in the discussions? So the design current (Ib) would be 5000/230 = 21.73 Amps. 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. 0000076394 00000 n This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. Determination of the current-carrying capacity by calculating the actual heat transfer is likely to result in a less conservatively sized cable. 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. The purpose of performing a cable calculation is to ensure that a cable is not overloaded. The ERA series of reports are still available and can be purchased from the RINA website. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10mm 2 . The presence of harmonic current in a power system increases the current in the neutral conductor due to phase current imbalance (refer to Fig. The calculation of cable rating follow t he derating factor method, see Cable Derating (Factors) . 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. The question is, what is the difference between manufacturers data and BS 7671? In this article we look at the information available and why the information is perceived as different. The thermal resistivity of soil refers to its ability to dissipate heat, which is relevant to the current-carrying capacity of cables. Part 1 . But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . 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. Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a parts function at the center of their design considerations. 0000078513 00000 n Resistive component of voltage drop factor mV r - (mV / A / m) r Reactive component of voltage drop factor mVx - (mV / A / m) x 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. The assumed values for ambient ground temperature, soil thermal resistivity and installation depth used in each publication are different which will result in a different cable size being selected. 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). The IET jointly publish BS 7671 so who better to confirm the changes. Created for free using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation. 0000015597 00000 n %%EOF Manage and size all your cables, from low voltage to 33 kV. 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 . BS7671 18 th Edition Cable Sizing Calculation Show 1 CABLE SIZING OR Doing it in Groups . Reference method Exampleofinstallationmethod Relevanttablefrom BS7671:2008 Image. This can produce an excessive amount of heat which in turn can damage the cable and the installation and may even cause a fire. 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. 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. Cable Derating (Factors) Cable Sizing Input Data Checklist. 0000011053 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). 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. 0000003576 00000 n Return to FAQs People also ask Appendix 4 of BS 7671 by Mark Coles Appendix4,Current-carrying capacity and voltage drop for cables and flexible cords,hasseensignificant . If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. 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. I Accept Cookies This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. - Andy. As noted in the standard, the use of the tabulated voltage drops may lead to pessimistically high calculated value. 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 . 0000001244 00000 n The reports are still available and can be purchased here. It is important to remember that anyone carrying out these calculations should work directly from a copy of the relevant standard. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. 0000011561 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: extract from the Thirteenth Edition of the IEE Wiring Regulations. Want to participate in the discussions? %PDF-1.4 % Examples 1 and 2. For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. 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 . 0000071888 00000 n BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. Whilst technology has advanced significantly since then, the laws of physics remain unchanged. Consider a 20/3.3 kV, 12.5 MVA transformer to be fed by direct buried, 3 core XLPE, SWA, PVC, copper conductor cable. 193 0 obj <>stream 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).

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