A - General rules of electrical installation designElectrical installation guide 2018 Schneider Electric - all rights reservedA21 MethodologyFor the best results in electrical installation design it is recommended to read and to use all the chapters of this guide in the order in which they are presented.A - General rules of electrical installation design Rules and statutory regulationsRange of low-voltage extends from 0 V to 1000 V in a.c. and from 0 V to 1500 V in d.c. One of the first decision is the selection of type of current between the alternative current which corresponds to the most common type of current through out the world and the direct current. Then designers have to select the most appropriate rated voltage within these ranges of voltages. When connected to a LV public network, the type of current and the rated voltage are already selected and imposed by the Utility.Compliance with national regulations is then the second priority of the designers of electrical installation. Regulations may be based on national or international standards such as the IEC 60364 series.Selection of equipment complying with national or international product standards and appropriate verification of the completed installation is a powerful mean for providing a safe installation with the expected quality. Defining and complying with the verification and testing of the electrical installation at its completion as well as periodic time will guarantee the safety and the quality of this installation all along its life cycle. Conformity of equipment according to the appropriate product standards used within the installation is also of prime importance for the level of safety and quality.Environmental conditions will become more and more stringent and will need to be considered at the design stage of the installation. This may include national or regional regulations considering the material used in the equipment as well as the dismantling of the installation at its end of life.A3 - Installed power loads - CharacteristicsA4 - Power loading of an installationInstalled power loads - CharacteristicsA review of all applications needing to be supplied with electricity is to be done. Any possible extensions or modifications during the whole life of the electrical installation are to be considered. Such a review aimed to estimate the current flowing in each circuit of the installation and the power supplies needed.The total current or power demand can be calculated from the data relative to the location and power of each load, together with the knowledge of the operating modes (steady state demand, starting conditions, non simultaneous operation, etc.)Estimation of the maximum power demand may use various factors depending on the type of application; type of equipment and type of circuits used within the electrical installation.From these data, the power required from the supply source and (where appropriate) the number of sources necessary for an adequate supply to the installation is readily obtained.Local information regarding tariff structures is also required to allow the best choice of connection arrangement to the power-supply network, e.g. at medium voltage or low voltage level.B - Connection to the MV utility distribution networkConnection to the MV public distribution networkWhere this connection is made at the Medium Voltage level a consumer-type substation will have to be studied, built and equipped. This substation may be an outdoor or indoor installation conforming to relevant standards and regulations (the low-voltage section may be studied separately if necessary). Metering at medium-voltage or low-voltage is possible in this case.C - Connection to the LV utility distribution networkConnection to the LV utility distribution networkWhere the connection is made at the Low Voltage level the installation will be connected to the local power network and will (necessarily) be metered according to LV tariffs.D - MV & LV architecture selection guideMV & LV architecture selection guideThe whole electrical system including the MV installation and the LV installation is to be studied as a complete system. The customer expectations and technical parameters will impact the architecture of the system as well as the electrical installation characteristics.Determination of the most suitable architecture of the MV/LV main distribution and LV power distribution level is often the result of optimization and compromise.Neutral earthing arrangements are chosen according to local regulations, constraints related to the power-supply, and to the type of loads.The distribution equipment (panelboards, switchgears, circuit connections, ...) are determined from building plans and from the location and grouping of loads.The type of premises and allocation can influence their immunity to external disturbances.
A - General rules of electrical installation designElectrical installation guide 2018 Schneider Electric - all rights reservedA20Rated Diversity Factor for distribution switchboardsThe standards IEC61439-1 and 2 define in a similar way the Rated Diversity Factor for distribution switchboards (in this case, always y 1).IEC61439-2 also states that, in the absence of an agreement between the assembly manufacturer (panel builder) and user concerning the actual load currents (diversity factors), the assumed loading of the outgoing circuits of the assembly or group of outgoing circuits may be based on the values in Fig. A13.If the circuits are mainly for lighting loads, it is prudent to adopt ks values close to unity.Type of loadAssumed loading factorDistribution - 2 and 3 circuits0.9Distribution - 4 and 5 circuits0.8Distribution - 6 to 9 circuits0.7Distribution - 10 or more circuits0.6Electric actuator0.2Motors y 100 kW0.8Motors > 100 kW1.0Fig. A13 Rated diversity factor for distribution boards (cf IEC61439-2 table 101)Diversity factor according to circuit functionks factors which may be used for circuits supplying commonly-occurring loads, are shown in Fig. A14. It is provided in French practical guide UTE C 15-105.Circuit functionDiversity factor (ks)Lighting1Heating and air conditioning1Socket-outlets0.1 to 0.2 [a]Lifts and catering hoist [b]b For the most powerful motorb For the second most powerful motorb For all motors10.750.60[a] In certain cases, notably in industrial installations, this factor can be higher.[b] The current to take into consideration is equal to the nominal current of the motor, increased by a third of its starting current.Fig. A14 Diversity factor according to circuit function (see UTE C 15-105 table AC)4 Installed power loads - Characteristics
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Electrical installation guide 2018 Schneider Electric - all rights reservedA - General rules of electrical installation designA214.4 Example of application of factors ku and ksAn example in the estimation of actual maximum kVA demands at all levels of an installation, from each load position to the point of supply is given Fig. A15.In this example, the total installed apparent power is 126.6 kVA, which corresponds to an actual (estimated) maximum value at the LV terminals of the MV/LV transformer of 65 kVA only.Note: in order to select cable sizes for the distribution circuits of an installation, the current I (in amps) through a circuit is determined from the equation: Schneider Electric - Electrical installation guide 2005B18B - General design - Regulations -Installed power4.4 Example of application of factors ku and ksAn example in the estimation of actual maximum kVA demands at all levels of aninstallation, from each load position to the point of supply (see Fig. B14oppositepage).In this example, the total installed apparent power is 126.6 kVA, which correspondsto an actual (estimated) maximum value at the LV terminals of the HV/LV transformerof 65 kVA only.Note: in order to select cable sizes for the distribution circuits of an installation, thecurrent I (in amps) through a circuit is determined from the equation:I=kVAU x 10 33where kVA is the actual maximum 3-phase apparent-power value shown on thediagram for the circuit concerned, and U is the phaseto- phase voltage (in volts).4.5 Diversity factorThe term diversity factor, as defined in IEC standards, is identical to the factor ofsimultaneity (ks) used in this guide, as described in 4.3. In some English-speakingcountries however (at the time of writing) diversity factor is the inverse of ks i.e. it isalways u 1.Factor of simultaneity for distribution boardsFigure B12 shows hypothetical values of ks for a distribution board supplying anumber of circuits for which there is no indication of the manner in which the totalload divides between them.If the circuits are mainly for lighting loads, it is prudent to adopt ks values close tounity.Fig. B12 : Factor of simultaneity for distribution boards (IEC 60439)Number ofFactor ofcircuitssimultaneity (ks)Assemblies entirely tested0.92 and 34 and 50.86 to 90.710 and more0.6Assemblies partially tested1.0in every case chooseFactor of simultaneity according to circuit functionKs factors which may be used for circuits supplying commonly-occurring loads, areshown in Figure B13.Circuit functionFactor of simultaneity (ks)Lighting1Heating and air conditioning1Socket-outlets0.1 to 0.2 (1)10 and more0.6Lifts and catering hoist (2)c For the most powerfulmotor1c For the second mostpowerful motor0.75c For all motors0.60(1) In certain cases, notably in industrial installations, this factor can be higher.(2) The current to take into consideration is equal to the nominal current of the motor,oncreased by a third of its starting current.Fig. B13 : Factor of simultaneity according to circuit function4 Power loading of an installationwhere kVA is the actual maximum 3-phase apparent-power value shown on the diagram for the circuit concerned, and U is the phase to- phase voltage (in volts).1DistributionboxWorkshop A50.80.80.80.80.80.855522Lathe1831110.80.411510.62.52.51515Ventilation0.281181121Oven30 fluorescentlampsPedestal-drillWorkshop BCompressorWorkshop Cno. 1no. 2no. 3no. 4no. 1no. 2no. 1no. 2no. 1no. 244441.61.618314.41211112.521815152.5Workshop Adistributionbox0.75PowercircuitPowercircuitPowvercircuitWorkshop BdistributionboxWorkshop CdistributionboxMaingeneraldistributionboardMGDBSocket-ouletsSocket-ouletsSocket-ouletsLightingcircuitLightingcircuitLightingcircuit0.90.90.90.910.63.63124.3115.618.937.8355265LV / MVDistributionbox1110.2110/16 A5 socket-outlets20 fluorescentlamps5 socket-outlets10 fluorescentlamps3 socket-outlets 10/16 A10/16 AUtilizationLevel 1Level 2Level 3Apparentpower(Pa)kVaUtilizationfactormax.Apparentpowerdemandmax. kVADiversityfactorApparentpowerdemandkVADiversityfactorApparentpowerdemandkVADiversityfactorApparentpowerdemandkVADB422003_EN.epsFig. A15 An example in estimating the maximum predicted loading of an installation (the factor values used are for demonstration purposes only)4 Installed power loads - Characteristics 2ff7e9595c
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