BS 7671: Introduction and Overview A BS 7671: 2008 - Introduction and Overview A 1 Introduction to BS 7671: 2008 BS 7671: 2008 was published during January 2008 as a signi cant new Edition of this fundamental Standard. The parameters considered in the standard are, ambient temperature, soil thermal resistivity, the installation methods and grouping of cables. 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 motor cable length and type has an affect because due to the high switching frequency of . I started as an apprentice electrician at the age of seventeen in 1982 and worked for many years as an electrician, a site foreman, a manager, a NICEIC Qualifying Supervisor, and a general manager. 5 0 obj Cable Heating Effects due to Harmonic Distortion in Electrical Installations. You have to look at using the <30% of the grouped rating for the cable i.e. 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. All cable sizing methods more or le ss follow the same basic six step process: 1) Gathering data about the cable, its installation conditions, the load that it will carry, etc 2) Determine the minimum cable size based on continuous current carrying capacity 3) Determine the minimum cable size based on voltage drop considerations 4) Determine the 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. Step 1 Determine if the highest ambient temperature a conductor is subjected to exceeds 30 degrees Celsius. 0000010392 00000 n Not every installation method is provided in BS 7671, as there are too many permutations. British Cables Company introduces new cables to its range. 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. % Copyright 2023 by myElectrical Engineering Limited. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. 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. Table 4C6 of BS 7671:2018+A1:2020 provides rating factors for cables enclosed in concrete floor troughs. F/T 183 issued by the ERA. However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. 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). , #gc6aa5 xref Z Table 4: Cable surrounded by thermal insulation length in insulation mm derating factor 50 0.89 100 0.81 200 0.68 Appendix 4 of BS 7671 by Mark Coles Appendix4,Current-carrying capacity and voltage drop for cables and flexible cords,hasseensignificant . <<95D84A24FD5A1F4C8152C1D91F51EC80>]>> Up to six cables can be bunched together without derating. The reports are still available and can be purchased here. 0000007414 00000 n The Institution of Engineering and Technology is registered as a Charity in England & Wales (no 211014) and Scotland (no SC038698). For more details on BS 7671 voltage drop calculations, see. DE-RATING FACTORS Our Company Genesis & Evolution Why Us KEI Power Gallery Beyond Business Certifications Downloads Clients Testimonials Reach Us Locate Us CALL (112) 681-8840 Follow Follow Toggle navigation Products & Solutions Extra High Voltage Cables High Voltage Cables Low Voltage Cables Control Cables House Wire HomeCab-FR BanFire-ZHFR Transformer full load current is calculated by: Ifull-load = 12.5 106 / 1.73 20 103 = 361 A. Don't forget derating factors. stream *Eng-Tips's functionality depends on members receiving e-mail. Determine the application. *NOTE: The third harmonic content expressed as total harmonic distortion. 0000001701 00000 n Both the load factor and the RHO value of the backfill also play large roles in determining the potential derating of the conductors in the duct bank. << /Length 5 0 R /Filter /FlateDecode >> Please read our. Myth Busters #7 - Out with the old, in with the new. 0000008621 00000 n 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 %PDF-1.3 Got the answer from BS 7671, but still got another question on the previous attachment. Don't worry though, you'll be sent straight back to the community after completing the registration. IEC 60502. Equally loaded just means that that's what they've assumed when calculating the numbers in that table (i.e. 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. 0000078800 00000 n 0000011053 00000 n Even then couldn't group more than 4 power circuits. trailer Thanks. 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 table below provides derating guidelines for 200 0 C rated Teflon (type PTFE) wire. 0 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. 1. These are related to the line voltage for three phase circuits and phase voltage for single phase circuits. Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. I have attached a cable verification sheet made in Amtech software. Cable Derating (Factors) Cable Sizing Input Data Checklist. 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. Fictitious Dimensions. The assumed values for each publication are identified in Table 1 below, the main influencing factor is the soil thermal resistivity. Reference method D of BS 7671:2018+A1:2020 should be applied for cables buried in the ground in and around buildings. 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. k2-3,Kw#`nu>+LKYgT Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 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. Others, of course, may disagree. The correction factor is justified as the current carrying capacity is capable of limitation by additional external factors, e.g. Cable current capacity calculations in BS 761 are based on the derating factor method, seeCable Derating (Factors). % 4 0 obj But on a steel ship for example, power cables are run in raceways and cable sheaths are used for HOFR (Heat . Thermal resistivity of soil is different to soil resistance. 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. Login. I ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc for the RFC circuits. 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 . factor to obtain the current - carrying capacity I required for the cable . There are consultancies that specialize in this type of work. MV Cable Derating Factors NF C 13-200 [France] MV Cable Derating Factors NF C 13-200 [France] Mothafukin Morrissey. 0000004990 00000 n 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. BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. 0000015597 00000 n (No. Cable Sizing - derating factors - Wiring and the Regulations BS 7671 - IET EngX - IET EngX This site uses cookies. 0000007209 00000 n xNf(@-c]D$t7:z)Q In the first example, a 4,000-amp duct bank with a design load of 3,600 amps is simulated based on an earth RHO factor of 90, dirt RHO factor of 90 and a load factor of 100 . The user of ERA is particularly popular amongst DNO (district network operators) and supply authorities. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. The installation method takes into account assumed parameters, such as ambient ground temperature (Ca), soil thermal resistivity (Cs), depth of laying (Cd) and spacing factor (Cg), the correction factors for which can be found in Tables 4B2, 4B3, 4B4 and 4C2 respectively. Don't worry though, you'll be sent straight back to the community after completing the registration. It was not until the Seventeenth Edition of the IEE Wiring Regulations in 2008 that tabulated values were reintroduced as Table 4D4A (thermoplastic) and Table 4E4A (thermosetting). 5;b^VL477/8:m}*lXIw{%;YOol*V5@r,;VkYNM|&Q@VVGC`i(c cB&0s!|8~%q$sJ(2% cL*qOX_Q>H+i.3@qhJ The ERA was commissioned to produce a series of reports on the current-carrying capacities of cables. The tables give the voltage drop in mV/A/m for various installation conditions. 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. 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. Reply to Paul651975 OP LeeH - Esteemed Arms Already a Member? IEC 60502 is an International Electrotechnical Commission standard, which gives current ratings for medium voltage cables. 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. Do you need to include all cables fixed to a cable tray when calculating grouping factors. 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). 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