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The F is a great plane to get started with about air combat in DCS world. BS has further requirements for underfloor heating in Regulation Every installation must be inspected and tested during erection and on completion before being put into service to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met. Precautions must be taken to avoid danger to persons and to avoid damage to property and installed equipment during inspection and testing.
If the inspection and tests are satisfactory, a signed Electrical Installation Certificate together with a Schedule of Inspections and a Schedule of Test Results as in Appendix 7 are to be given to the person ordering the work.
Inspection must precede testing and must normally be done with that part of the installation under inspection disconnected from the supply. The purpose of the inspection is to verify that equipment is: When a test shows a failure to comply, the installation must be corrected.
Where appropriate during this measurement, line and neutral conductors may be connected together polarity: Electrical testing involves danger. It is t h e test operative's duty to ensure his or her o w n safety, and t h e safety of others, in the performance of t h e test procedures. W h e n using test instruments, this is best achieved by precautions such as: S o m e test instrument manufacturers advise that their instruments be used in conjunction w i t h fused test leads and probes.
Others advise the use of non-fused leads and probes w h e n t h e instrument has in-built electrical protection, but it should be noted that such electrical protection does not extend to the probes and leads.
The advice given does not preclude other test methods. Tests should be carried out in t h e following sequence. Results obtained during the various tests should be recorded on the Schedule of Test Results Appendix 7 for future reference and checked for acceptability against prescribed criteria.
Test p r o c e d u r e s Continuity of circuit proteetiwe conductors and protective bonding conductors for ring final circuits see Test methods 1 and 2 are alternative ways of testing the continuity of protective conductors. Every protective conductor, including circuit protective conductors, the earthing conductor, main and supplementary bonding conductors, should be tested to verify that the conductors are electrically sound and correctly connected.
Use an ohmmeter capable of measuring a low resistance for these tests. Such installations should be inspected for soundness of construction and test method 1 or 2 used to prove continuity. Bridge the line conductor to the protective conductor at the distribution board so as to include all the circuit. Then test between line and earth terminals at each point in the circuit. If the instrument does not include an 'auto-null' facility, or this is not used, the resistance of the test leads should be measured and deducted from the resistance readings obtained.
Figure Connections for testing continuity of circuit protective conductors using test method 1. Connect one terminal of the test instrument to a long test lead and connect this to the installation main earthing terminal. Connect the other terminal of the instrument to another test lead and use this to make contact with the protective conductor at various points on the circuit, such as luminaires, switches, spur outlets, etc.
Continuity test method 2 For main bonding, connect one terminal of the test instrument to a long test lead and connect this to the installation main earthing terminal. Connect the other terminal of the instrument to another test lead and use this to make contact with the protective bonding conductor at its further end, such as at its connection to the incoming metal water, gas or oil service.
The connection verified boxes on the Electrical Installation Certificate should be ticked if the continuity of the earthing conductor and of each main bonding conductor is satisfactory, and the details of the material and the cross-sectional areas of the conductors recorded. A three-step test is required to verify the continuity of the line, neutral and protective conductors and the correct wiring of a ring final circuit.
The test results show if the ring has been interconnected to create an apparently continuous ring circuit which is in fact broken, or wrongly wired. Use a low-resistance ohmmeter for this test.
These resistances are n, r n and r 2 respectively. A finite reading confirms that there is no open circuit on the ring conductors under test.
The resistance values obtained should be the same within 0. If the protective conductor has a reduced csa the resistance r 2 of the protective conductor loop will be proportionally higher than that of the line and neutral loops e. If these relationships are not achieved then either the conductors are incorrectly identified or there is something w r o n g at one or more of the accessories.
Figure The end-to-end resistances of the line, neutral and protective conductors are measured separately. Step 2 The line and neutral conductors are then connected together at the distribution board so that the outgoing line conductor is connected to the returning neutral conductor and vice versa see Figure The resistance between line and neutral conductors is measured at each socket-outlet.
The readings at each of the sockets wired into the ring will be substantially the same and the value will be approximately one-quarter of the resistance of the line plus the neutral loop resistances, i. Any sockets wired as spurs will have a higher resistance value due to the resistance of the spur conductors. Where single-core cables are used, care should be taken to verify that the line and neutral conductors of opposite ends of the ring circuit are connected together.
An error in this respect will be apparent f r o m the readings taken at the socket-outlets, progressively increasing in value as readings are taken towards the midpoint of the ring, then decreasing again towards the other end of the ring. The line and neutral conductors are cross-connected and the resistance measured at each socket-outlet. Step 3 The above step is then repeated, this time with the line and cpc cross-connected see Figure The resistance between line and earth is measured at each socket.
The readings obtained at each of the sockets wired into the ring will be substantially the same and the value will be approximately one-quarter of the resistance of the line plus cpc loop resistances, i.
As before, a higher resistance value will be recorded at any sockets wired as spurs. The value can be used to determine the earth fault loop impedance Zs of the circuit to verify compliance with the loop impedance requirements of BS see Step 3: The line and cpc conductors are cross-connected and the resistance measured at each socket-outlet. Tests should be carried out using the appropriate d.
The tests should be made at the distribution board with the main switch off, all fuses in place, switches and circuit-breakers closed, lamps removed and other current-using equipment disconnected. Where a circuit contains two-way switching, the two-way switches must be operated one at a time and further insulation resistance tests carried out to ensure that all the circuit wiring is tested.
Table Insulation resistance measurements are usually much higher than those of Table More stringent requirements are applicable for the wiring of fire alarm systems in buildings, see BS In these circumstances, each circuit should then be tested separately. Where surge protective devices SPDs or other equipment such as electronic devices or RCDs with amplifiers are likely to influence the results of the test or may suffer damage from the test voltage, such equipment must be disconnected before carrying out the insulation resistance test.
Where it is not reasonably practicable to disconnect such equipment, the test voltage for the particular circuit may be reduced to V d. Where the circuit includes electronic devices which are likely to influence the results or be damaged, only a measurement between the live conductors connected together and earth should be made and the value should be not less than the value stated in Table Resistance readings obtained should be not less than the minimum value referred to in Table For a circuit containing two-way switching or two-way and intermediate switching,.
Three-phase Test to earth from all live conductors including the neutral connected together. Where disconnecting all equipment. The method of test prior to connecting the supply is the same as test method 1 for checking the continuity of protective conductors which should have already been carried out see For ring final circuits a visual check may be required see It is important to confirm that: After connection of the supply, polarity must be checked using a voltage indicator or a test lamp in either case with leads complying with the recommendations of HSE Guidance Note GS This impedance reading is treated as the electrode resistance and is then added to the resistance of the protective conductor for the protected circuits.
The test should be carried out before energising the remainder of the installation. The measured resistance should meet the following criteria and those of For TT systems, the value of the earth electrode resistance RA in ohms multiplied by the operating current in amperes of the protective device lAn should not exceed 50 V. The effectiveness of the distributor's earth must be confirmed by a test. The external impedance Z e may be measured using a line-earth loop impedance tester.
The main switch is opened and made secure to isolate the installation from the source of supply. The earthing conductor is disconnected from the main earthing terminal and the measurement made between line and earth of the supply. Direct measurement of Z s can only be made on a live installation. Neither the connection with earth nor bonding conductors are disconnected.
This must be taken into account when comparing the results with design data. Care should be taken to avoid any shock hazard to the testing personnel and to other persons on site during the tests. The value of Z s determined for each circuit should not exceed the value given in Appendix 2 for the particular overcurrent device and cable. This test should be carried out before energising other parts of the system. For further information on the measurement of earth fault loop impedance, refer to Guidance Note 3 Inspection and Testing.
Designs should be based on the maximum fault current provided by the distributor see 7. If it is desired to measure prospective fault levels this should be done with all main bonding in place. Measurements are made at the distribution board between live conductors and between line conductors and earth. For three-phase supplies, the maximum possible fault level will be approximately twice the single-phase to neutral value. For three-phase to earth faults, neutral and earth path impedances have no influence.
Switchgear, controls, etc. Verification of voltage drop is not normally required during initial verification. A new requirement has been introduced into BS that, where required, it should be verified that voltage drop does not exceed the limits stated in relevant product standards of installed equipment.
Where no such limits are stated, voltage drop should be such that it does not impair the proper and safe functioning of installed equipment. Typically, voltage drop will be evaluated using the measured circuit impedance. The requirements for voltage drop are deemed to be met where the voltage drop between the origin and the relevant piece of equipment does not exceed the values stated in Appendix 12 of BS It should be remembered that voltage drop may exceed the values stated in Appendix 12 in situations such as motor starting periods and where equipment has a high inrush current where such events remain within the limits specified in the relevant product standard or reasonable recommendation by a manufacturer.
Residual current device RCD is the generic term for a device that operates when the residual current in the circuit reaches a predetermined value. An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between the line and neutral conductors. In the case of a single-phase circuit, the device monitors the difference in currents between the line and neutral conductors. In a healthy circuit, where there is no earth fault current or protective conductor current, the sum of the currents in the line and neutral conductors is zero.
If a line to earth fault develops, a portion of the line conductor current will not return through the neutral conductor. The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current l An. The tests are made on the load side of the RCD, as near as practicable to its point of installation and between the line conductor of the protected circuit and the associated circuit protective conductor.
The load supplied should be disconnected during the test. With a leakage current flowing equivalent to 50 per cent of the rated tripping current, the device should not open. With a leakage current flowing equivalent to per cent of the rated tripping current of the RCD, the device should open in less than ms. With a leakage current flowing equivalent to per cent of the rated tripping current of the RCD, the device should open in less than ms unless it is of Type S' or selective which incorporates an intentional time delay.
In this case, it should trip within a time range from ms to ms. The maximum test time must not be longer than 40 ms, unless the protective conductor potential rises by less than 50 V. The instrument supplier will advise on compliance. An integral test device is incorporated in each RCD.
This device enables the electrical and mechanical parts of the RCD to be verified, by pressing the button marked T or 'Test' Figure Operation of the integral test device does not provide a means of checking: The test button will only operate the RCD if the device is energised.
Confirm that the notice to test RCDs quarterly by pressing the test button is fixed in a prominent position see 6. In Figure In a healthy circuit, w h e r e there is no earth fault current or protective conductor current, t h e s u m of t h e currents in t h e line and neutral conductors is zero.
If a line to earth fault develops, a portion of t h e line conductor current will not return through t h e neutral conductor. The device monitors this difference, operates and disconnects t h e circuit w h e n the residual current reaches a preset limit, t h e residual operating current l A n.
This appendix provides information on the determination of the maximum demand for an installation and includes the current demand to be assumed for commonly used equipment. It also includes some notes on the application of allowances for diversity.
The information and values given in this appendix are intended only for guidance because it is impossible to specify the appropriate allowances for diversity for every type of installation and such allowances call for special knowledge and experience. The values given in Table 1B, therefore, may be increased or decreased as decided by the installation designer concerned. No guidance is given for blocks of residential dwellings, large hotels, industrial and large commercial premises; such installations should be assessed on a case-by-case basis.
The current demand of a final circuit is determined by adding the current demands of all points of utilisation and equipment in the circuit and, where appropriate, making an allowance for diversity. Typical current demands to be used for this addition are given in Table 1A. The current demand of an installation consisting of a number of final circuits may be assessed by using the allowances for diversity given in Table 1B which are applied to the total current demand of all the equipment supplied by the installation.
The current demand of the installation should not be assessed by adding the current demands of the individual final circuits obtained as outlined above. In Table 1B the allowances are expressed either as percentages of the current demand or, where followed by the letters f. The current demand for any final circuit which is a standard circuit arrangement complying with Appendix 8 is the rated current of the overcurrent protective device of that circuit.
An alternative method of assessing the current demand of an installation supplying a number of final circuits is to add the diversified current demands of the individual circuits and then apply a further allowance for diversity. In this method the allowances given in Table 1B should not be used, the values to be chosen being the responsibility of the installation designer.
Appendix The use of other methods of determining maximum demand is not precluded where specified by the installation designer. After the design currents for all the circuits have been determined, enabling the conductor sizes to be chosen, it is necessary to check that the limitation on voltage drop is met.
At least 0.
Final circuits for discharge lighting must be arranged so as to be capable of carrying the total steady current, viz. Where m o r e exact information is not available, t h e d e m a n d in volt-amperes is taken as the rated lamp watts multiplied by not less than 1. This multiplier is based upon the assumption that the circuit is corrected to a power factor of not less than 0. Notes to Table I B: L of remaining appliances O. L of remaining appliances No diversity allowablet No diversity allowablet No diversity allowablet o X c rt X.
L of remaining appliances o. L of remaining appliances. The tables in this appendix provide m a x i m u m permissible measured earth fault loop impedances Z s for compliance with BS where the standard final circuits of Table 7. The values are those that must not be exceeded in the tests carried out under Table 2E provides correction factors for other ambient temperatures.
Where the cables to be used are to Table 4, 7 or 8 of BS 6 0 0 4 or Table 3, 5, 6 or 7 of BS or are other thermoplastic PVC or thermosetting low smoke halogen-free LSHF cables to these British Standards, and the cable loading is such that the m a x i m u m operating temperature is 7 0 C, then Tables 2 A - 2 C give the m a x i m u m earth fault loop impedances for circuits with: For each type of fuse, t w o tables are given: The tabulated values apply only w h e n the nominal voltage to Earth U 0 is 2 3 0 V.
Appendix Note: The impedances tabulated in this appendix are lower than those in Tables The correction factor divisor used is 1. For smaller section cables the impedance may also be limited by the adiabatic equation of Regulation A value of k of from Table Table 2A Semi-enclosed fuses. Maximum measured earth fault loop impedance in ohms at ambient temperature where the overcurrent protective device is a semi-enclosed fuse to BS NP means that the combination of the protective conductor and the fuse is Not Permitted.
Appendix Table 2B BS 88 fuses. Maximum measured earth fault loop impedance in ohms at ambient temperature where the overcurrent protective device is a fuse to BS Appendix Table 2C BS fuses. The values below are for energy limiting class 3, type B and C devices only. For other device types and ratings or higher fault levels, consult manufacturer's data.
See Regulation. Ambient temperature correction factors Correction factor from 10 C notes 1 and 2 0. The correction factor is given by: The ambient correction factor of Table 2E is applied to the earth fault loop impedances of Tables 2 A - D if the ambient temperature is other than 10 C.
For example, if the ambient temperature is 25 C the measured earth fault loop impedance of a circuit protected by a 32 A type B circuit-breaker to BS EN should not exceed 1. Appendix Selection of types of cable and flexible cord for particular uses and external influences. For compliance with the requirements of Chapter 52 for the selection and erection of wiring systems in relation to risks of mechanical damage and corrosion, this lists, in two tables, types of cable and flexible cord suitable for the uses indicated.
These tables are not intended to be exhaustive and other limitations may be imposed by the relevant regulations of BS , in particular those concerning maximum permissible operating temperatures. Information is also included in this appendix on protection against corrosion of exposed metalwork of wiring systems. Intermediate support may be required on long vertical runs 70 C maximum conductor temperature for normal wiring grades including thermosetting types note 4 Cables run in PVC conduit should not operate with a conductor temperature greater than 70 C note 4.
For general indoor use in dry or damp locations. May be embedded in plaster For use on exterior surface walls, boundary walls and the like For use as overhead wiring between buildings For use underground in conduits or pipes For use in building voids or ducts formed in-situ.
Additional mechanical protection may be necessary where exposed to mechanical stresses Protection from direct sunlight may be necessary. Black sheath colour is better for cables exposed to sunlight May need to be hard drawn HD copper conductors for overhead wiring note 6 Unsuitable for embedding directly in concrete.
Ml cables should have overall PVC covering where exposed to the weather or risk of corrosion, or where installed underground, or in concrete ducts Additional protection may be necessary where exposed to mechanical stresses Protection from direct sunlight may be necessary.
Black sheath colour is better for cables exposed to sunlight.
Route marker tape should also be installed, buried just below ground level. Cables should be buried at a sufficient depth. Where they are to be installed during a period of low temperature, precautions should be taken to avoid risk of mechanical damage during handling.
A minimum ambient temperature of 5 C is advised in BS This must be limited to 70 C where drawn into a conduit, etc. Additional advice is given in BS A catenary support is usual but hard drawn copper types may be used.
Electric cables. Mineral insulated cables and their t e r m i n a t i o n s w i t h a rated voltage not exceeding V. LSHF, cables, must be including thermosetting from insulated with separated expanded polystyrene. Grommets Natural rubber grommets can be softened by contact w i t h thermoplastic PVC. Appendix Wood preservatives Thermoplastic PVC sheathed cables should be covered to prevent contact with preservative fluids during application. After the solvent has evaporated good ventilation is necessary the preservative has no effect.
Creosote Creosote should not be applied to thermoplastic PVC sheathed cables because it causes decomposition, solution, swelling and loss of pliability.
Table 3B. Uses Indoors in household or commercial premises in dry situations, for light duty Indoors in household or commercial premises, including damp situations, for medium duty For cooking and heating appliances where not in contact with hot parts For outdoor use other than in agricultural or industrial applications For electrically powered hand tools.
Indoors in household or commercial premises where subject only to low mechanical stresses Indoors in household or commercial premises where subject only to low mechanical stresses For occasional use outdoors For electrically powered hand tools. For general use, unless subject to severe mechanical stresses For use in fixed installations where protected by conduit or other enclosure.
General, including hot situations, e. The length of the flexible cable or cord must be such that will permit correct operation of the protective device. At such inlet points it may be necessary to use a device which ensures that the cable is not bent to an internal radius below that given in the appropriate part of Table 4 of BS Strain relief, clamping devices or cord guards should not damage the cord.
Flexible cables and cords should not be placed where there is a risk of damage from traffic passing over them, unless suitably protected. Appendix zinc alloys complying with BS , iron or steel protected against corrosion by galvanizing, sherardizing, etc.
Contact between bare aluminium sheaths or aluminium conduits and any parts made of brass or other metal having a high copper content should be especially avoided in damp situations, unless the parts are suitably plated. If such contact is unavoidable, the joint should be completely protected against ingress of moisture. Wiped joints in aluminium sheathed cables should always be protected against moisture by a suitable paint, by an impervious tape, or by embedding in bitumen.
This appendix describes examples of methods of support for cables, conductors and wiring systems which should satisfy the relevant requirements of Chapter 52 of BS The use of other methods is not precluded where specified by a suitably qualified electrical engineer.
Cables generally Items 1 to 8 below are generally applicable to supports on structures which are subject only to vibration of low severity and a low risk of mechanical impact. For cables of any type, installation in ducting or trunking without further fixing of the cables, vertical runs not exceeding 5 m in length without intermediate support. For cables of any type, resting without fixing in horizontal runs of ducts, conduits, cable ducting or trunking.
For sheathed-and-armoured cables in vertical runs which are inaccessible and unlikely to be disturbed, supported at the top of the run by a clip and a rounded support of a radius not less than the appropriate value stated in Table 4E. For sheathed cables without armour in vertical runs which are inaccessible and unlikely to be disturbed, supported by the method described in Item 6 above; the length of run without intermediate support not exceeding 5 m for a thermosetting or thermoplastic sheathed cable.
Appendix 8 For thermosetting or thermoplastic PVC sheathed cables, installation in conduit without further fixing of the cables, any vertical runs being in conduit of suitable size and not exceeding 5 m in length. Particular applications 9 In caravans, for sheathed cables in inaccessible spaces such as ceiling, wall and floor spaces, support at intervals not exceeding 0.
Owerhead waring 13 For cables sheathed with thermosetting or thermoplastic material, supported by a separate catenary wire, either continuously bound up with the cable or attached thereto at intervals, the intervals not exceeding those stated in column 2 of Table 4A. Appendix Conduit and cable trunking 18 19 20 21 Rigid conduit supported in accordance with Table 4C. Cable trunking supported in accordance with Table 4D.
Conduit embedded in the material of the building. Pliable conduit embedded in the material of the building or in the ground, or supported in accordance with Table 4C.
For the spacing of supports for cables having an overall diameter exceeding 40 mm, the manufacturer's recommendations should be observed. The spacings stated for horizontal runs may be applied also to runs at an angle of more than 30 from the vertical.
For runs at an angle of 30 or less from the vertical, the vertical spacings are applicable. Appendix Table 4B Maximum lengths of span and m i n i m u m heights above ground for overhead wiring between buildings, etc. Mmmrnm height of span above ground m f. Cables sheathed with thermoplastic PVC or having an oil-resisting and flame-retardant or HOFR sheath, in heavy gauge steel conduit of diameter not less than 20 mm and not jointed in its span.
Thermoplastic PVC covered overhead lines on insulators without intermediate support. Bare overhead lines on insulators without intermediate support. Aerial cables incorporating a catenary wire. A bare or insulated overhead line for distribution between buildings and structures must be installed to the standard required by the Electricity Safety, Quality and Continuity Regulations In some special cases, such as where cranes are present, it will be necessary to increase the minimum height of span above ground.
It is preferable to use underground cables in such locations. They assume that the conduit is not exposed to other mechanical stress. A flexible conduit should be of such length that it does not need to be supported in its run.
They assume that the trunking is not exposed to other mechanical stress. Supports should be positioned within mm of bends or fittings. Thermosetting or thermoplastic PVC circular, or circular stranded copper or aluminium conductors.
Thermosetting or thermoplastic PVC solid aluminium or shaped copper conductors Mineral. For flat cables the diameter refers to the major axis. The value in brackets relates to single-core circular conductors of stranded construction installed in conduit, ducting or trunking.
Mineral insulated cables may be bent to a radius not less than three times'the cable diameter over the copper sheath, provided that the bend is not reworked, i.
A number of variable factors affect any attempt to arrive at a standard method of assessing the capacity of conduit or trunking. Some of these are: The following tables can only give guidance on the maximum number of cables which should be drawn in.
The sizes should ensure an easy pull with low risk of damage to the cables. Only the ease of drawing-in is taken into account. The electrical effects of grouping are not.
As the number of circuits increases the installed current-carrying capacity of the cable decreases. Cable sizes have to be increased with consequent increase in cost of cable and conduit. It may sometimes be more attractive economically to divide the circuits concerned between two or more enclosures.
If thermosetting cables are installed in the same conduit or trunking as thermoplastic PVC insulated cables, the conductor operating temperature of any of the cables must not exceed that for thermoplastic PVC , i.
The following three cases are dealt with. Single-core thermoplastic PVC insulated cables in: Appendix i Single-core thermoplastic PVC insulated cables in straight runs of conduit not exceeding 3 m in length. For each cable it is intended to use, obtain the appropriate factor from Table 5A.
Add the cable factors together and compare the total with the conduit factors given in Table 5B. The minimum conduit size is that having a factor equal to or greater than the sum of the cable factors. Table 5A Cable factors for use in conduit in short straight runs Table 5B Conduit factors for use in short straight runs. Single-core thermoplastic PVC insulated cables in straight runs of conduit exceeding 3 m in length, or in runs of any length incorporating bends or sets.
For each cable it is intended to use, obtain the appropriate factor from Table 5C. Add the cable factors together and compare the total with the conduit factors given in Table 5D, taking into account the length of run it is intended to use and the number of bends and sets in that run. The minimum conduit size is that size having a factor equal to or greater than the sum of the cable factors. For the larger sizes of conduit, multiplication factors are given relating them to 32 mm diameter conduit.
The inner radius of a conduit bend should be not less than 2. Additional factors: Appendix iii Single-core thermoplastic PVC insulated cables in trunking For each cable it is intended to use, obtain the appropriate factor from Table 5E.
Add the cable factors together and compare the total with the factors for trunking given in Table 5F. The minimum size of trunking is that size having a factor equal to or greater than the sum of the cable factors. Cable factors for trunking Conductor cross-sectional area mm 2 1.
These factors are for metal trunking and may be optimistic for plastic trunking, w h e r e the crosssectional area available may be significantly reduced f r o m t h e nominal by t h e thickness of the wall material. The provision of spare space is advisable; however, any circuits added at a later date must take into account grouping, Regulation Other sizes and types of cable or trunking For sizes and types of cable or trunking other than those given in Tables 5E and 5F, the number of cables installed should be such that the resulting space factor does not exceed 45 per cent of the net internal cross-sectional area.
Space factor is the ratio expressed as a percentage of the sum of the overall cross-sectional areas of cables including insulation and any sheath to the internal cross-sectional area of the trunking or other cable enclosure in which they are installed. The effective overall cross-sectional area of a non-circular cable is taken as that of a circle of diameter equal to the major axis of the cable.
Care should be taken to use trunking bends etc which do not impose bending radii on cables less than those required by Table 4E. Appendix Current-carrying capacities and voltage drop for copper conductors Current-carrying capacity device provides both fault current and overload current protection. Procedure 1 2 The overcurrent device rating ln is then selected so that l n is greater than or equal The design current lb of the circuit must first be established.
The various rating factors are identified as follows: C a for ambient temperature, see Table 6A C is a rating factor to be applied where the installation conditions differ from those for. Appendix Cc for the type of protective device or installation condition, i. The requirements of BS are deemed to be satisfied if the voltage drop between the origin of the installation and a lighting point does not exceed 3 per cent of the nominal voltage 6. Table 6A Rating factors for ambient air temperatures other than 30 C to be applied to the current-carrying capacities for cables in free air.
Insulation Mineral Thermoplastic covered or bare and exposed to touch 70 C 1. Appendix Thermal insulation Where a cable is to be run in a space to which thermal insulation is likely to be applied, the cable should, wherever practicable, be fixed in a position such that it will not be covered by the thermal insulation.
Where fixing in such a position is impracticable, the cross-sectional area of the cable must be increased appropriately. For a cable installed in thermal insulation as described in Tables 6D1, 6E1 and 6F no correction is required. Reference methods , and require the cable to be in contact with the plasterboard or the joists, see Tables 7.
For a single cable likely to be totally surrounded by thermally insulating material over a length of more than 0. Where a cable is totally surrounded by thermal insulation for less than 0. The derating factors in Table 6B are appropriate to conductor sizes up to 10 mm 2 in thermal insulation having a thermal conductivity X greater than 0. Rating factors for one circuit or one multicore cable or for a group of circuits, or a group of multicore cables to be used with the current-carrying capacities of Tables 6D1, 6E1 and 6F.
Bunched in air, 1. Where horizontal clearances between adjacent cables exceed twice their overall diameter, no rating factor need be applied. Tables for two loaded conductors for the two-core cables, and to the Tables for three loaded conductors for the three-core cables.
For some installations and for other methods not provided for in the above table, it may be appropriate to use factors calculated for specific cases, see for example.
When cables having differing conductor operating temperature are grouped together, the current rating is to be based upon the lowest operating temperature of any For example, a group of N loaded cables would normally require a group rating factor of Cg.