All relevant derating factors are applied. 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. Voltage drop value should be in the accepted limits. Case 1 Assuming a design current carrying capacity of circuit to 25A with a third harmonic of 32%. 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 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. lol!!! 0000005800 00000 n Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. 1.1.5 How to Find the Derating Factor 1. 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. 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. Part 1 . 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. BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. NOTE 3: In the case of a cable connector at least 25cm (10 inches) of the cable shall be . 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. 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 motor cable length and type has an affect because due to the high switching frequency of . Back to the Forum - Current-carrying capacity of cables buried in the ground, Electrical Safety Standards in the Private Rented Sector. Cable current capacity calculations in BS 761 are based on the derating factor method, seeCable Derating (Factors). It is assumed that the maximum ambient temperature is 30C and the maximum ground temperature id 20C. 0000001701 00000 n Z Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE 0000011561 00000 n . 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. Cable Derating (Factors) Cable Sizing Input Data Checklist. BS7671:2018+A2:2022 Let's take a quick run through the new 18th Edition Wiring Regulations book, which includes Amendment 2 that was introduced in March 2022, BS7671:2018+A2:2022. *NOTE: The third harmonic content expressed as total harmonic distortion. vi}z7{?8x=l"t\F1'lnxN+h'qVs6GX1Cyx8N"/V*#JP%/~7d_}l?A#NLXh\h|gq$vtmO89dp|d{;>1-bSJb_" RT'C? 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. ERA 69-30. 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. Myth Busters #7 - Out with the old, in with the new. Failing that, speaking to the manufacturers of the cable is always a good place to start. 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. Don't worry though, you'll be sent straight back to the community after completing the registration. We're about to take you to the IET registration website. }fq>w)6o @yawz8?%"VsKON]*~zX/*`qb};q7N NLt?k;~?|qo?zD6r!u5c9.F)Zz bZ\OZO>CRW !ol4]NO'n] &hT Created for free using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation. Table & Column 5. I'm still pondering how to alter the factors for cables that are not equally loaded but which shouldn't be ignored. wire cross section and unequal current distribution. of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. The international standards that cover the current-carrying capacity of cables are the IEC 60287 series for steady-state conditions and IEC 60853 for cyclic conditions for most practical applications. DERATING CURVES (Current carrying capacity) IEC 60512-5-2 Test 5b . Selecting Copper, XLPE, 3*50+25 mm 2 , its current is 185 A, Derating this current 185 * 0.93 = 172 A. . If a detailed heat transfer calculation is carried out, however, a more accurate analysis of the whole cable route can be performed. The assumed values for each publication are identified in Table 1 below, the main influencing factor is the soil thermal resistivity. 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. He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator. %%EOF 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. Cloud based - any device, anywhere. Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 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. stream 0000078513 00000 n BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. By joining you are opting in to receive e-mail. I Accept Cookies over lhe range of conductor sizes and types illclllrkd in the n:kvailitabics in this appendix. Fictitious Dimensions. HD 60364-5-52 Selection and erection of electrical equipment. 201 A is now the allowable ampacity of the 300 kcmil copper conductor for this circuit. 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. BS 7671:2008 . 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). 0000076607 00000 n Other than the conductor sizes changing to metric, these ratings have remained unchanged. These are known as rating factors. Hzd}-/ *@. For further information, see the IET Wiring Matters article Amps per pound. 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). 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. Electric power & transmission & distribution Forum, https://files.engineering.com/getfile.aspx?folder=13c66bdb-39dd-4639-a3e2-7, https://files.engineering.com/getfile.aspx?folder=94810acb-102b-494c-ad52-a, Low-Volume Rapid Injection Molding With 3D Printed Molds, Industry Perspective: Education and Metal 3D Printing. Want to participate in the discussions? 193 0 obj <>stream 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. The user of ERA is particularly popular amongst DNO (district network operators) and supply authorities. 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. 0000002160 00000 n 0000002193 00000 n 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. 0000002616 00000 n For more details on BS 7671 voltage drop calculations, see. 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. Knowing this we can select the size of the protective device (In) and in this instance we are going to use a 32A circuit breaker. Current Capacity Cable current capacity calculations in BS 761 are based on the derating factor method, see Cable Derating (Factors). Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. There are consultancies that specialize in this type of work. The thermal resistivity of soil refers to its ability to dissipate heat, which is relevant to the current-carrying capacity of cables. If the appropriate correction factors are applied, the results will be the same. For example, the temperature in an attic reaches 125 degrees F (52 C) in the summertime. A. Non-sheathedcablesinconduitina If any of the rating factors do not apply to your cable then simply remove them from the equation. ]M&r;:QKGBdBeW2JFX)@wN#$RA)0S3)i`nmh But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . These values were based on the conditions identified in the supplement to Report No. % 5 0 obj We'd also like to set optional analytics cookies to help us improve it. 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. k2-3,Kw#`nu>+LKYgT If the wire is rated to 150 0 C derate the values in the table by 80%, 70% for 135C wire, and 115% for 260 0 C. 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. 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