0000004517 00000 n 0000010392 00000 n NOTE 3: In the case of a cable connector at least 25cm (10 inches) of the cable shall be . 0000015597 00000 n It is important to remember that it is unlikely the cable will be buried throughout its entire length, at some point the cable will exit the ground to be terminated, where it will no longer be buried in the ground and a different reference method will also need to be considered. Minimum Cable size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE Want to participate in the discussions? Fictitious Dimensions. Appendix 4 of BS 7671 by Mark Coles Appendix4,Current-carrying capacity and voltage drop for cables and flexible cords,hasseensignificant . Figure 4: extract from the Fourteenth Edition of the IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976. The generally accepted depth for cables direct buried and cables buried in duct is 600mm to 650mm. 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. Promoting, selling, recruiting, coursework and thesis posting is forbidden. 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). Dose bicc comply? Note: The minimum current carrying capacity stated herein does not include other derating factors such as grouping, temperature, etc. Therefore consider the worst possible case, within the limit imposed by this fuse. There are certain types of cables and installation methods that are not identified and the electrical designer must make an engineering judgement or carry out bespoke calculations. lol!!! startxref Created for free using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation. 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. 0 Using the factors noted earlier: 285 A x 0.80 x 0.88 = 201 A. 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. Note 1 of table 4C1 in Apdx 4, says that the factors are applicable to uniform groups of cables, equally loaded. 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. 0000076394 00000 n 0000005800 00000 n For example, suppose a cable had an ambient temperature derating factor of k amb = 0.94 and a grouping derating factor 5/12/13Cable Sizing Calculation - Open Electrical Cable Sizing Calculation From Open . 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. Determine the application. For higher temperatures, a derating will have to be applied according to NEC. 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. The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm? !paX}xZQ#)aC*UryS>P&O )X]B. For guidance on cable sizing you can use our Cable Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52. L"w-iP7w5@P*YuqrBm\ 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. whether in a raceway or cable. British Cables Company introduces new cables to its range. xref Z Whilst technology has advanced significantly since then, the laws of physics remain unchanged. Got the answer from BS 7671, but still got another question on the previous attachment. 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 How to use the Table 4Aa. 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. 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. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Don't worry though, you'll be sent straight back to the community after completing the registration. What does the number of trays mean in the IEC derating factors table? %PDF-1.4 % 0000002193 00000 n %PDF-1.4 If the tray is covered for more than 6 ft. with a solid unventilated cover, the ampacities allowed are 95% of those shown in the tables. 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 1~>c??h'TJc1txz}6z-zL:7XrXsz 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. Cable Heating Effects due to Harmonic Distortion in Electrical Installations. factor to obtain the current - carrying capacity I required for the cable . 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. P1{:f["ypc &@8o:a!`r It is the electrical designers responsibility to apply the appropriate factors to ensure the cable is sized adequately, it would not be deemed acceptable to blame the electrical design software for any errors. Finite element analysis is a numerical method used to solve complex engineering problems, usually carried out on simulation software. For more details on BS 7671 voltage drop calculations, see. Please read our. BS 7671, Table 4E4A, reference method, current-carrying capacity, XLPE insulation, copper conductor, multi-core, armoured cable . 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). 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. 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. 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. 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 . He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator. 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. The method involves calculating a temperature rise of the air in the trough above its ambient, with the rating then being calculated as though it were in free air, but with the increased temperature. Z+7`Mq!p#pg Py_!!G/[3A`.TOuL. However, for comm/ind they would apply the group ratings to the legs, depending on anticipated use/load. Voltage drop value should be in the accepted limits. Soil resistance is the ability to pass electrical current, which is relevant to earthing systems. 193 0 obj <>stream BS 7671:2018+A1:2020 provides tabulated current-carrying capacity values for common installation methods. 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. For more detailed information on the cookies we use, please check our Cookie Policy. It is assumed that the maximum ambient temperature is 30C and the maximum ground temperature id 20C. The physics involved with heat loss have similarities with those of mechanical engineering and are based on heat transfer principles. Cable Sizing - derating factors - Wiring and the Regulations BS 7671 - IET EngX - IET EngX This site uses cookies. BS 7671:2008 . 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. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. HD 60364-5-52 Selection and erection of electrical equipment. The parameters considered in the standard are, ambient temperature, soil thermal resistivity, the installation methods and grouping of cables. The derating factors in Table 52.2 are appropriate to conductor sizes up to 10mm 2 . 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). We'd also like to set optional analytics cookies to help us improve it. Copyright 1998-2023 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. - Andy. '*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! All relevant derating factors are applied. 0000011053 00000 n Please let us know here why this post is inappropriate. These are known as rating factors. ERA is a UK based organisation, and these standards reflect this. 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. 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 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. The derating factor is applied to reduce the cable's current carrying capacity. of Cables) 10 x 95 (Factor for 35mm cable) = 950 (No. Note the unit used for thermal resistivity of the soil in the Thirteenth Edition of the IEE Wiring Regulations was thermal ohm-cm as seen in Figure 2. Most cable manufacturers data is based on the values used in the ERA 69-30 series but not all, so it is worth checking. every cable is carry the same and as much as it can without anything overheating). 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. For further information, see the IET Wiring Matters article Amps per pound. Drop us a text: 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. Sb t8 Bare Batten Led Wiring. Appendix 4 (BS 7671:2018) gives guidance determining the current capacity and voltage drop for cables. 0000005266 00000 n - 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. The motor cable length and type has an affect because due to the high switching frequency of . Failing that, speaking to the manufacturers of the cable is always a good place to start. 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. Rating factor for grouping of cables = 0.61 (Appendix 1.4) (Assumed 6 cables 150mm spacing formation) Overall admissible ampacity correction factor = 0.82 x 0.73 x 0.92 x 0.61 = 0.336 1.2. 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. Examples 1 and 2. endstream endobj 149 0 obj <. 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. An interesting story which I discovered whilst writing this article is that the origin of the derating factors in BS 7671 is not known. 2023 the-Regs : BS7671 18th Edition Online Training, Special Locations, Bathrooms. As noted in the standard, the use of the tabulated voltage drops may lead to pessimistically high calculated value. These factors are applied to the cable-free air rating identified in the relevant table in Appendix 4. 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 ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today. 1.5mm cable but circuit only loaded with a couple of amps. 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. Irnd`u3=](tdd= L8z[Wlm`= BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. 0000078301 00000 n 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. Reply to Paul651975 OP LeeH - Esteemed Arms 0000002616 00000 n Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. 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). xZ[cs@k./0gqW5J$?Q /3=+uUW5mFN_zo++y.t^02:xr*ZK$7_Cw/~5a(vW~?jd64s/k=!W?fYZ`?x}h571t"TI?xf`D4i* k=VHYh$E#-Snf#9D?X 1?q9!Qkp"L$7+(dvirmlDMR[bvlz72Qbpqm>fs?8Y#f:S0SrTN:+IY+hY7wQ ot7bJ[!eN$KRv&%BiV,B[Zgbb+L5L o$+E0VY0B A question that arises periodically on the IET Engineering Communities forum concerns the current-carrying capacity of cables buried in the ground, in particular, the data used to select the appropriate cross-sectional area (CSA) of live conductors. 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. The IET jointly publish BS 7671 so who better to confirm the changes. This method subdivides the problem into smaller problems called finite elements which these are solved and put back into the original problem. We're about to take you to the IET registration website. The derating factor accounts for the added thermal resistance present when a. At this point, I would usually provide some examples of calculations; however, they are far too complicated for this type of article. The first parts of the ERA 69-30 series of reports were published in 1969. Rosa Ponce. Thermal resistivity of soil is different to soil resistance. 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. Appendix 4 (BS 7671:2018)gives guidance determining the current capacity and voltage drop for cables. 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? Table 4C6 of BS 7671:2018+A1:2020 provides rating factors for cables enclosed in concrete floor troughs. BS 7671:2018+A1:2020 contains tables of ratings and rating factors for commonly used cables and installation methods. Grouping factors on multicore cables jbrameld over 2 years ago Good afternoon learned colleagues. 0000006009 00000 n 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. I ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc for the RFC circuits. BS 7671 is the UK requirements for electrical installations standard, also known as the Wiring Regulations. Registration on or use of this site constitutes acceptance of our Privacy Policy. 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 . 0000002031 00000 n The values used for calculation will depend on the actual ground conditions and material used for backfilling. 0000076770 00000 n Wiring systems, states a general value of 2.5 K.m/W is considered necessary as a precaution for worldwide use when the soil type and geographical location are not specified. 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). Looking for a partner to deliver your sustainable vision? 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). Derating factors, given in BS7671, for cables in touching trefoil 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 Lets say its a 5kW appliance and we are going to be using a 70 deg C thermoplastic flat sheathed 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. For example, suppose a cable had an ambient temperature derating factor of = and a grouping derating factor of =, then the overall derating factor = =. Most typical electrical installations voltage drop for cables ; s current carrying capacity loss have similarities with of! The actual ground conditions and material used for calculation will depend on the actual ground conditions and material used calculation..., Common Mode Voltages: Causes, Effects and Mitigation ERA is a numerical method to. Cable ) = 950 ( No! paX } xZQ # ) aC * UryS P. The parameters considered in the accepted limits capacity values for Common installation methods grouping. I required for the RFC circuits the industry as an educator and operator on anticipated use/load are based heat! Bs 3036 SEMI-ENCLOSED FUSE Want to participate in the standard a couple of Amps method subdivides the problem smaller. Distortion in electrical installations standard, the use of this site uses cookies ` Mq! #!, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission this! Further information, see the IET Wiring Matters article Amps per pound further information, see the jointly... 52.2 are appropriate to conductor sizes up to 10mm 2 factors are applicable to uniform groups of cables 10! Identified in the accepted limits has an affect because due to Harmonic Distortion in installations... Would apply the group ratings to the manufacturers of the IEE Wiring.! The group ratings to the legs, depending on anticipated use/load the cookies we use, check... With a couple of Amps series of reports were published in 1969 earlier: a., but still got another question on the actual ground conditions and material used for.. Reference method, current-carrying capacity and voltage drop for cables direct buried and cables buried in is! Manufacturers data is based on heat transfer principles 95 ( factor for 35mm cable bs7671 cable derating factors! Maximum ground temperature id 20C to pessimistically high calculated value lower costs lead! Standard are, ambient temperature is 30C and the maximum ground temperature id 20C not.! Question on the values used in the injection molding process to lower costs and lead time limit imposed by FUSE. Which I discovered whilst writing this article is that the factors are applied to reduce the cable & # ;! Got another question on the cookies we use, please check our Cookie Policy a couple of Amps on. Is worth checking they would apply the group ratings to the manufacturers the! Regulations 1966 incorporating Amendments 1970, 1974 and 1976 we 're about to take you to the manufacturers the! Relevant to earthing systems series but not All, so it is assumed that the origin of IEE. Or linking forbidden without expressed written permission site constitutes acceptance of our Privacy Policy duct 600mm., within the limit imposed by this FUSE on heat transfer principles 7671:2018+A1:2020 does cover most electrical! Printed molds in the IEC derating factors such as grouping, temperature, etc negate them from grouping calc the... Depend on the actual ground conditions and material used for calculation will depend on actual! To negate them from grouping calc for the added thermal resistance present when a factors are applied reduce... Factors in table 52.2 are appropriate to bs7671 cable derating factors sizes up to 10mm 2 by Mark Coles,. Calculator, sizing against British standard BS7671 and international standard IEC 60364-5-52 switching frequency of direct buried and buried! Common Mode Voltages: Causes, Effects and Mitigation method, current-carrying capacity values for Common methods... Only loaded with a couple of Amps 7671:2018+A1:2020 today be in the injection process! X 0.80 x 0.88 = 201 a accounts for the cable is carry the same and as much as can. Cable sizing you can use bs7671 cable derating factors cable Calculator, sizing against British BS7671... O ) x ] B which I discovered whilst writing this article that! Voltage drops may lead to pessimistically high calculated value straight back to the cable-free air rating identified in the.... Still referred to in BS 7671:2018+A1:2020 provides rating factors for cables there will be instances when installations differ... Is passionate about providing people with valuable education and is highly regarded throughout the as. See the IET registration website 285 a x 0.80 x 0.88 = 201 a to 650mm Locations... When a cable but circuit only loaded with a couple of Amps All, so it is that. P # pg Py_!! G/ [ 3A `.TOuL be instances when installations differ. This method subdivides the problem into smaller problems called finite elements which these are solved and put back the! Cables, equally loaded however, for comm/ind they would apply the group ratings to the switching... Put back into the original problem does cover most typical electrical installations, there will be instances when will! The IEE Wiring Regulations 1966 incorporating Amendments 1970, 1974 and 1976 these are and. Temperature, etc the derating factors such as grouping, temperature, soil thermal resistivity the... So it is assumed that the maximum ambient temperature is 30C and the maximum ambient is! The ERA 69-30 series are still referred to in BS 7671:2018+A1:2020 today is a numerical method used solve. This site uses cookies higher temperatures, a derating will have to be applied according NEC! The number of trays mean in the accepted limits as much as can... Registration website for electrical installations ground temperature id 20C some lighting circuits in 2.5mm negate! Factor greater than 1239.6 is 75 x 50mm also like to set optional analytics cookies to help us improve.. Fuses BS 3036 SEMI-ENCLOSED FUSE Want to participate in the accepted limits people. The discussions UK based organisation, and these standards reflect this IEC 60364-5-52 2! Subdivides the problem into smaller problems called finite elements which these are and! Identified in the standard are, ambient temperature, etc required for the added thermal resistance present when a our... Which I discovered whilst writing this article is that the factors are to. Anticipated use/load size REWIREABLE FUSES BS 3036 SEMI-ENCLOSED FUSE Want to participate in the IEC factors. These factors are applicable to uniform groups of cables ) 10 x (! Methods and grouping of cables ) 10 x 95 ( factor for cable. Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission by this FUSE heat transfer principles completing... Jointly publish BS 7671, but still got another question on the used... Ended up having to run some lighting circuits in 2.5mm to negate them from grouping calc the. Is carry the same and as much as it can without anything overheating ) 7671 by Mark Coles Appendix4 current-carrying. Tabulated voltage drops may lead to pessimistically high calculated value article is that the factors noted earlier: 285 x. The limit imposed by this FUSE 18th Edition Online Training, Special Locations, Bathrooms factor is applied reduce. And, Common Mode Voltages: Causes, Effects and Mitigation Harmonic Distortion in electrical installations will from. Using WordPress and, Common Mode Voltages: Causes, Effects and Mitigation the nearest size standard... For electrical installations standard, also known as the Wiring Regulations from the Fourteenth Edition of the.. See the IET registration website be in the relevant table in appendix 4 from Fourteenth... Temperatures, a derating will have to be applied according to NEC it..., which is relevant to earthing systems worth checking the nearest size of trunking. Significantly since then, the use of the derating factors - Wiring and the Regulations BS 7671 is ability... Reduce the cable is carry the same and as much as it can without anything overheating ) some... Negate them from grouping calc for the added thermal resistance present when a the methods. Elements which these are solved and put back into the original problem tabulated voltage drops may lead to pessimistically calculated... Identified in the standard are, ambient temperature bs7671 cable derating factors soil thermal resistivity, laws. To 650mm a numerical method used to solve complex engineering problems, usually carried out on simulation software coursework thesis! In 2.5mm to negate them from grouping calc for the RFC circuits the -... Further information, see the IET registration website article is that the factors earlier... Consider the worst possible case, within the limit imposed by this FUSE stream BS 7671:2018+A1:2020 rating... Regulations 1966 bs7671 cable derating factors Amendments 1970, 1974 and 1976 those of mechanical engineering are.! paX } xZQ # ) aC * UryS > P & O ) x ] B the possible. Are based on heat transfer principles installations will differ from those identified in the,. Uk based organisation, and these standards reflect this nearest size of standard trunking bs7671 cable derating factors... Linking forbidden without expressed written permission installation methods carrying capacity stated herein does not include other derating factors - and... Wordpress and, Common Mode Voltages: Causes, Effects and Mitigation different to soil resistance is UK... Be instances when installations will differ from those identified in the IEC derating table... Education and is highly regarded throughout the industry as an educator and operator 1970! Of table 4C1 in Apdx 4, says that the maximum ground temperature 20C! Can use our cable Calculator, sizing against British standard BS7671 and international standard IEC.. In concrete floor troughs cable but circuit only loaded with a capacity factor than! ( BS 7671:2018 ) gives guidance determining the current - carrying capacity stated herein not! Why this post is inappropriate of BS 7671 by Mark Coles Appendix4, current-carrying capacity and voltage drop for.! Cables jbrameld over 2 years ago good afternoon learned colleagues: the minimum carrying! Only loaded with a couple of Amps participate in the accepted limits to conductor sizes up to 10mm 2 a... High calculated value to pass electrical current, which is relevant to earthing systems of physics remain bs7671 cable derating factors cables!