O.S.G.. The use of other methods’ of determining Maximum Demand is Not Precludedwhere Specified by the Installation Designer
FirstlyI make no Apologies for the Way am Writing on any Matters . it can be a first day Apprentice or some one Needing aJog of Memory . Sowe are all in the Same Boat . “ To Learn “
For the Apprentices . The Day we stop learning is the Day we hang Upour Tool-Bag
CookerDesign Current Calculations
Thefirst thing you have to do is get Your Head around the Calculations !!
(From a Design point of View ) 2392-10
DomesticInstallation Oven(s) & Hob(s) are to be Calculated upon their MAXIMUM LOADING Startwith a simple Calculation ( An Oven has a rating of 2kW ) 2000
(I = P/V ) Formula … I = 2000 ÷ 230V = 8.70A …. Weare Using the Unit Amps
-Controlled via a CookerSwitch with a Socket outlet .
Asa Designer . we’ll have to Apply Diversity ??
Important )- Diversity allowance to be Applied to the FULL LOAD CURRENT for CookingAppliances .
TheO.S.G. is telling us . Purpose of the Final Circuit fed from theConductors ) O.S.G.Table 1B p/97 – column (3) Cooking Appliances → At the Top of the Page Note : Type ofPremises ( 2392-10 → Household Installations ) Domestic Installation(s)
DomesticInstallation(s) Only O.S.G. - 10A + 30% f.l – Full Load ) of connected Cooking Appliances in the Excess of 10A+ 5A if a socket-outlet is incorporated in the Control Unit . ( C.C.U. ) – 45A + 13A Socket Switched with Neon .
Fromyour point of View ( The First 10A ofthe rated current plus 30% of the reminder ( Plus) 5A if the Control Unit incorporates s Socket.
Calculations)- You bank “ Hold OFF“ the first 10 Amps of the Maximum Load Current ) The10A will be used at the End of the Calculations’
-So your Work out the Total Power Rating & then calculate the Full Load Current
Calculations)- Power = ( 2 x 1 ) + ( 2 x 1.5 ) + ( 2+ 3 ) = 10kW
I= 10000 ÷ 230V = 43.48A … round it up to the first four numbers43.47826087 ( 48 ) 43.48A
The adequacy of the existing installation is thereforerequired to be Assessed in Three - Areas . ◄◄
i) Existing equipment – including that of the supply : whichmay have to carry Increased Loads .
it is necessary to establish that the rating &condition of all appropriate equipment within an installation – Such asOvercurrent protective devices . Final & Distribution circuit conductors .Switchgear & Distribution boards . is capable of supporting the planned Addition or Alteration . The condition of the existingequipment should be Assessed for its ability tocarry any Increased Load . & where appropriate . Inrush & Startingcurrents . & for Defects. Omissions . Damage . & minor deterioration . any inadequaciesin the Existing Installation that would resultin a reduced level of safety in the new work – That is a level of safety lessthan afforded by compliance with BS-7671 – must be corrected before the newwork is put into service .
( The electricity distributorsequipment may have to carry Additional Load - & Inrush & Startingcurrents . & its suitability & condition must be Assessed . Thedistributor should be Assessed . The distributor should beRequested to upgrade the supply . ( WhereRequired )
ii) Earthing & Bonding arrangements .
Assessing the adequacy & suitability of the Existing Earthing & Bondingarrangements . • Establishingthe suitability of means of Earthing in respect of its Type . such as a ( PME ) Earthingterminal or an earth rod . & condition – is it Corrodedor Damaged or Inaccessible. ?????? “ Verification “ of themeans of Earthing by determination of the external earth fault loop impedance (Ze ) See regulation 313.1. if ( Ze ) is determinedby enquiry or calculation. it is necessary also to obtain a Measured Valueto verify that the intended means of earthing is both present & of theexpected value . ( Determination of external earthfault loop impedance at the Origin of the Installation )
• Ascertaining that the Earthingconductor is of Adequate Cross-sectional area ( C.S.A.)
Establishing . determining or confirming the presence &adequacy of circuit protective conductors for both the final circuit(s) &any distribution circuit(s) forming part of the Additionor Alteration .
Where the protective measure against electric shock isAutomatic Disconnection of supply ( ADS ) the adequacy of the exitng bondingmust be established . it is an essential requirement for safety that mainprotective bonding is provided
iii) Certain Additional considerations .
Additional considerations relating to the existing installation orany effects that the Addition or Alteration may have upon it . such as those mentioned inregulations ( 131.8.) but are covered by other requirements of BS-7671:2008 .& are therefore Applicable .
Grouping Effects . The Rating of all Cables in the Wiring System. both existing & proposed additional cables . must be assessed to take accountof any additional Heat Generated by the larger grouping . & be derated asnecessary . if the existing cables would not be adequate when derated . Then oneoption would be to install the new cables separately from the existing groups
Upgrading of an existing Installation . where Necessary . :waving:
When an existing installation is not adequate to support aproposed Addition or Alterationsafely the work must NOT proceed . &
• The client must be Advisedimmediately & preferably in writing . • The necessary upgrading workshould be recommended to the client . • When the clients consent has beengiven . the upgrade work should be completed before the Addition or Alteration is put intoService .
Amechanical switching device or association of devices intended to cause theopening of the contacts when the residual current attains a given value underspecified conditions .
ResidualCurrent : Algebraicsum of the currents in the Live conductors of acircuit at a point in the electrical installation .
ResidualOperating Current residualcurrent which causes the RCD to operate under specified conditions .
General Requirements 410.3.2. The followingspecification of voltage is intended unless otherwise stated .
-A.C. ≈ Voltages are r.m.s. :waving:
Chapter41 of BS-7671:2008 specifies essentialrequirements regarding protection against ElectricShock . including Basic protection & Fault protection . Regulation 410.3.2. states that a Protective measure shall consist of .
i) An appropriate combination of a provision forBasic protection & an Independent provision for Faultprotection . or ii)An enhanced protective provision which provides both Basicprotection & Fault protection .
TheTerm(s) Basic protection & Fault protection & gives brief details of themeasures of protection recognized by BS-7671:2008
AdditionalProtection . can be provided by use of an RCD - Residual Current Device .
Itis generally NOT acceptable to install a SingleRCD to provide Additional Protection at the Origin of an Installation whichsupplies more than one circuit . Where .
• A fault causing theoperation of the sole device would also disconnect Healthy Circuits .& may result in hazards or inconvenience to the USER of the installation –Regulation 314.1. & • Protective conductor current may be expectedto Occur during normal operation of the connectedLoad(s) which may cause the Unwanted operationof the RCD – Regulation . 531.2.4.
Table- 4D2B Column(1) - 1.0mm Sq . Soif ( Ib ) design current were 10 Amps . Length( 10Mtrs ) mV/A/m is ( 44 ) fromTable .
Voltdrop formula is ( mV/A/m x Ib x L ) ÷ 1000 So( VD ) = 44 x 10 x 10 ÷ 1000 - VD = 4.4 Volts dropped .
Signs. of ( mV/A/m ) are because the Units following are representingOne of each of ( A ) & ( m )
ElectricalInstallation Calculation(s) Apprentices
Thefollowing factors are NOT needed .
i)The type & nominal current rating of the associated Overcurrent Protective Device. ii)The Ambient Temperature . iii)Whether the circuit is run singly or grouped with other circuits iv)The power factor of the Load .
ForD.C. circuitsusing conductors of any cross-sectional area . & for A.C. circuits usingconductors of ( 16mm[SUP]2[/SUP] or less cross-sectionalarea ) Voltagedrop = tabulated ( mV/A/m ) x Ib x Lvolts / 1000
For A.C. circuits usingconductors of ( 25mm[SUP]2[/SUP] or less cross-sectionalarea ) Voltagedrop = tabulated ( mV/A/m ) Z x Ibx L volts / 1000
Note: that the tabulated ( mV/A/m )[SUP]z [/SUP]Value will be found in the Colum appropriate to the methodof installation & type of circuit but the sub-column headed ( Z ) it should also be Notedthat in all cases it is admissible to calculate the voltage drop using ( Ib ) & not ( In )
Inthe voltage drop tables of Appendix 4 ofBS-7671 the heading used is “ Voltage drop per Ampereper Metre “ & the tabulated valuesare given in ( millivolts ) This approach does not lead to any misunderstanding& . as indicated by the two formulae above . one can readily determine thevoltage drop of whatever type of circuit using the appropriate tabulated value .
However. it can be argued that these tabulated ( mV/A/m ) values are strictly inmilliohms / m . Additionto their use in determining the voltage drop of a circuit . they can also beused . equally directly . to determine the résistance per metre of a circuitconductor . Therésistance per metre ( in milliohms / m ) of a particular conductor in a single-phase orD.C. circuit is simply the tabulated (mV/A/m ) value dived by ( 2 ) or . Ina Three-phase circuit . its tabulated ( mV/A/m ) value divided by ( √3 )
A. D.C.circuit is wired in Single-core 70°C pvc-insulated non-sheathed cable to BS-6004 .having copper conductors of ( 10mm[SUP]2[/SUP] ) C.S.A. If - Ib = 40A & L = 33m . what is thevoltage drop .
Table4D1B . column 2 the ( mV/A/m ) is found to be ( 4.4. milliohms/m ) The voltage drop is . - 4.4. x 40 x 33 ÷ 1000 = 5.8V
CalculateVoltage Drop .
:17: ( mV/A/m ) is milivolts ↔ per Amp per Metre . mV (- foreach ( Amp ) when calculating using later formula You will be multiplying .
then… for Each Metre – Multiplying again .
The( A ) & ( m ) for mV/A/m are assumed to be Unitof One . So as it is divided by One & then Again …it ends up as the First Figure .
Thisis commonly achieved by switching off an Isolation device . within thedistribution board . Regulation – 537.2.2.1.requires that the device shall Isolate all LiveConductors . subject to the provisions of Regulation - 537.1.2.
TheNeutral Conductor is also a Live Conductor . ina TN-S or TN-C-S Installation . however. Regulation – 537.1.2. allows the Neutral Conductor to NOTbe isolated where it is reliably connected to Earth.
Ifthe supply complies with the Electrical Safety . Quality & ContinuityRegulation 2002 . A Three-pole isolating device is sufficient for a Three-phasesupply .
Regulation537.2.1.7. however . says that there should be some provision for disconnecting theNeutral . for Example . by using a Bolted Link . ( Can only be disconnected by means of a Tool )
Three-phase( TT Supplies ) will require disconnection of the Neutral . So a ( Four-pole Isolation device is Needed )
2392-10:- For a Single-phase supply where the Main Switch will be Used by “ Ordinary Persons “ The Insolating Switch mustInterrupt both Live Conductor(s) :13:
Designer& Installers . must select a wiring system that avoids damage to the sheath& insulation of cable during installation . use & maintenance
Wherecables enter a distribution board from trunking . The cables must be protectedfrom any Sharp Edges in order to comply with Regulation – 522.8.1. Commonmethods of complying include deburring edges & using grommet strips ormanufactured spacers .
Regulation526.9. requires that the cores of Unsheathed Cables from which the Sheath has beenremoved & non-sheathed cables at the termination of the trunking . areEnclosed .
Protectionagainst Electric Shock needs to be provided by offering both “ Basic protection“ & “ Fault protection “
Basic protection includes the insulation ofLive parts & Barriers or enclosures such as distribution boards . Appropriatedevices or “ Blanks “must be fitted to ( Maintain IP2X or IPXXB) if the Top of the horizontal surfaceis readily accessible then the level of protection there should be IP4X orIPXXD .
Automaticdisconnection of the supply will usually provide fault protection . This involvesProtective Earthing . Main Protective bondingConductor. & the automatic disconnection of a device if there is an Earth Fault . The designer will normally need toensure co-ordination of protective devices & Earth Fault Loop Impedances sothat disconnection will occur within the maximum times given in – 411.3.2.2. –411.3.2.3. or 411.3.2.4.
Anadditional requirement for the protection against Electric Shock . is tospecify RCDs where they are needed – 415.1.1. . recognises that RCDs with a ratedresidual operating current ( I∆n ) up to30mA & an operating time NOT exceeding ( 40mS) at a residual current of ( 5 I∆n ) provides additional protection for A.C. systems . if the Basic or Fault protection fails . or against Carelessness bythe End User .
Chapter56 of BS-7671 covers Fire Detection & AlarmCircuits . Regulation 560.7.1. States that these Safety Services must be “ Independent of OtherCircuits “
Requirementsof BS-5839 Fire Detection & Fire AlarmSystems for buildings. Clause 25.2. states thatthe “ Mains Supply “ to the Fire Alarm System should be from the “Load Side “ of the main Isolating device for the building& have its “Own “ Isolating Protective Device . Circuit Breaker .
Thecircuit should also be from a point in the Electrical Distribution System .that is close to the Main Isolating Device for the Building .
InAddition . every protective device that can Isolate the supply to the FireAlarm System . Other than the Main Isolator for the building . Should beclearly labelled . FIRE ALARM . DO NOT SWITCH OFF . – in a durable & fade resistant material .
Thecolours were chosen so that Even “ Colour – Blind People “ could tell them apart . :leaving:
Domestic- Wiring a Plug . Line – Neutral – Earth . ( Green with Yellow Stripes )
UsefulJunk . Two things about the Earth Cable. i)The Earth cable only does anything if there isa Fault . Otherwiseit’s not involved in the circuit at all . ii)The Earth cable is there to help the “ RCD “ To isolate the Appliance / or Equipment fromthe Line Conductor .
Theproblem with ( MCB ) is that it’s Not very good at Protecting youfrom Electric Shock . RCDswork by comparing the Line & Neutral currents - & tripping out if they are different .
SinglePhase & Line to Line loop testing on circuits that are [ NOT ] protected byRCD . ◄◄◄ :6:
Option 1 . ( 2-wire lead set ) Green lead:- LO/L2 – Green - port . Red + port . Option 2 . ( MainsPlug test lead ) Plug . bottom right port .
Setthe Instrument to the [ HI ] loop test range
Highcurrent Line to Earth loopimpedance measurement ( at a power socket ) Testlead set :- Option 2 .
i)Insert the plug into an Installation socket . ii)Supply voltage & polarity are displayed iii)The test will “ bleep “ & automatically start when voltage is detected iv)Measured loop value is displayed - ifdesired the test can be repeated by pressing the YellowTest Button .
Thereare Two-Ways three phase can be connected to form a working system . Star ( Y ) Delta ( ∆)
Industry– Three-phase is mainly used to power Electric Motors . because .
• Three-phase motors have greater Output fortheir physical Size . • Three-phase motors have more UniformedStarting Torque . • Three-phase systems require Less Copper inconductors to transmit the power . i.e. ( P = VI & if the voltage is 400V less current is needed to make the same poweras 230V . Less current means smaller conductor(s)
Example.
Three-phasevoltage is produced with a device called an Alternator . TheAlternator has Three sets of Windings . Mechanically fixed ( 120 Electrical Degree ) to each other which when passed ( Rotated ) through a fixed magnetic field & the speedthat the windings pass through the field .
Thecurrent available from the Alternator is limited by the Cross-sectional area . (Size ) ofthe conductor in the Alternators windings . Becausethere are Separate voltages . each one can be used as a Single Phase power sourceprovided a Neutral connection is available .
Alternator(s) . AnElectrical Generator is a machine which converts “ MechanicalEnergy “ by electromagneticinduction . A Generatorwhich produces alternating current isreferred to an A.C. Generator .
Combinationof the “ Words “ Alternating & Generator . Theword “ Alternator “ has come into widespread use .
Themajor difference between an “ Alternator “ & D.C. Generator is the method of connection to the External Circuit. “ Alternator “ is connected to the External Circuit by Slip-rings “ D.C.Generator “ is connected by a commutator.
RCD . 40mS– 0.04 of a second . ( NOT – 0.4secs ) Example . Fault conditions . havea duration of any longer than ( 0.4 of asecond )
Withinhealthy system . long before the extended use of RCDs . Automatic Disconnection of Supply is guaranteed within ( 0.4 of a second & with an RCD0.04 of asecond )
Aftercompletion of an installation or an alteration to an installation . the Work must be inspected & tested toensure . as far as reasonably practicable . that Fundamental Requirements for Safety has beenmet .
• Before adding to or Alteringan installation . ensure that such work Will not impair any part of theexisting installation & that the exisiting is in a safe condition toaccommodate the Addition .
• All Motorsmust have a readily accessible means of disconnection.
CoP : ▼ :gettree:
• In UK legislation . which legaldocument relates to Inspection & Testing of Electrical Equipment . ( The . EAWR –1989 ) • What would a ( 230V ) hair dryer be definedas . According to the . EAWR – 1989 ( An ElectricalSystem ) :banghead: • What is the Title . in Law .given to a person carrying out Inspection & Testing of electrical equipment . ( ADuty Holder )
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