***Cont../ Useful Information for Electricians & Apprentices***

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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


2392-10/ Domestic Installation Oven(s)

Ovenhas 4 Rings ( 2 x 1kW ) & ( 2 x 1.5kW ) & Grill ( 2kW ) & Oven (3kW )

-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

UsingDiversity allowance stated ↑↑ ( 43.48A sub 10A = 33.48A )

I= 33.48 x 30 ÷ 100 = 10.04A

Youradding the ( 5A ) for Socket outlet . I = 10A + 10.04 + 5A = 25.04A )- Asa Designer this is your Expected Current Demand .

Remember )- Supply Cables Rated to suit DesignCurrent ( Iz )

 

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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 . The distributor 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

 

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Additions & Alterations to anInstallation .

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 .

 

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RCD:

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.

 

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Taking from Old Notes : ◄◄◄ :13:

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 .
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( 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 .

 

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Isolation & Switching . :leaving:

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:

 

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Cable Entry .

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 .

 

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Protectionagainst Electric Shock . :speechless:

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 .

 

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FireDetection & Alarm Circuits :

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 .

 

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UsefulJunk .

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 .

 

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Justone off many Faults you may Encounter . :13:

Fault - between N & E . ( Trips the RCD / RCBO ) had one today – out off . 20 – it wasthe twelve socket

M3.5 Screws has sliced theinsulation on the Neutral Wire is a back box .

 

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Megger1552 –

HighCurrent Loop – Testing [ HI ] :39:

SinglePhase & Line to Line loop testing on circuits that are [ NOT ] protected by RCD . ◄◄◄ :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 .

 

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Apprentices’.

Typesof Three phase connections : :smilewinkgrin:

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.

 

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:smilewinkgrin:Useful Junk

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 RCD 0.04 of asecond )

MaximumDisconnection Times . – Table 41.1
TN- 0.4 sec .
TT- 0.2 sec .

 

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FundamentalRequirements for Safety .

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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Manufactures Instructions are mandatory & BS-7671 are Non-mandatory . :43:

RCBOs:
Tripping time ( t )
(In ) = 1.13 – In .. Notrip current . ( < 1hr )
(In ) = 1.45 – In .. Tripcurrent . ( ≤ 1 hr )

 

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RCBOs:

EarthFault Current sensitivity - 30mA - I∆n
Tripping principles employed:- Electronic detection & Actuationfor Residual Current :43:

 

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RCBOs:
Withthe RCBO you have provided Additional Protection . :toetap05:

MCBs.

Requirementsfor Automatic disconnection – maximum disconnection times . Table 41A
411.3.2. – Automatic disconnection in “ Case “ of a “ Fault “

Normalcable ratings relate to continuous service under specified installationconditions .
Cableswill . of course . Carry Higher Currents – for Short Time without suffering permanent damage . Type –B . C . circuit breakers can generally be selected to achieve tripping timesthat will protect the circuit conductors against normal surge currents in accordancewith . BS-7671 .

Thisis more difficult to achieve with type D. devices . :43:
Whichmay “ Require a Lower earth Loop Impedance ( Zs ) to achieve the Operating Times required by Regulation. 411.3.2. – Automatic disconnection in “ Case “ of a “ Fault “

 

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FusedConnection Unit : ( Accessories ) :26:
A fusedconnection unit is defined in BS 7671 as a deviceassociated with the fixed wiring of an installation by which appliances may beconnected, and having provision for a replaceable cartridge fuse link. Fusedconnection units manufactured to BS 1363-4 haveprovision for a BS 1362 cartridge fuse-link andare available with or without an integral switch.
Fusedconnection units have a nominal voltage rating not exceeding 250 V a.c. at afrequency of 50 Hz, and a current rating not exceeding 13 A. Fusedconnection units are classified as: • switched or unswitched • flush, surface or panel-mounting • with or without provision for an outgoing flexible cableor cord • with or without indicator lamp. Fusedconnection units should, amongst other things, be marked with: • number of the British Standard, that is BS 1363• rated current; that is 13 A• rated voltage; that is a.c. not greater than 250 V• nature of supply; a.c. only• incoming (in or supply) terminals• outgoing (out or load) terminals • symbols to identify whichterminals are line, neutral and earth.Theincoming (supply) line and neutral terminals of fused connection units aredesigned for the connection, without special preparation, such as twisting, ofup to three 2.5 mm2 solid or stranded copperconductors, or up to two 4 mm[SUP]2[/SUP] strandedcopper conductors. Theincoming earthing terminal is designed to permit the connection, withoutspecial preparation, of up to three 1.5 mm2 or 2.5 mm2 solid or stranded copper conductors, or of up to two 4 mm2 stranded copper conductors. Theoutgoing (load) line, neutral and earth terminals are each designed for theconnection, without special preparation, of one 1.5 mm2or 2.5 mm2 solid or stranded copper conductor. Whereprovision is made by the connection unit for the fitting of a flexible cord,one copper conductor having a nominal cross-sectional area of 0.5 mm2 up to and including 1.5 mm2 may beused. InstallationThedepth of accessory box should be such that the cables or conductors do notsuffer damage or cause stress to the terminals, (Regulations 522.8.1and 522.8.3refer). BS 1363-4 recommends that the depth of thebox should be such that there is a adequate wiring space. Fusedconnection units are supplied with a cord anchorage to enable the installer toprevent stress and strain on connections, as required by Regulation 522.8.5. SwitchingFusedconnection units are not designed for d.c.supplies and may only switch an a.c. supply. Aswitch fused connection unit is a double-pole device and may therefore be usedwhere it is necessary to switch both the line and neutral conductors, such asmight be the case where a step-up transformer is used (Regulation 555.1.3refers). Anunswitched fused connection unit is not a double-pole deviceand may not be used as such.Table53.2 of BS 7671 permits all fused connection unitsto be used as a means of isolation for TN systems by means of the removal of thefuse-link. Removal of the fuse-link of an unswitched fused connection unit,however, is not suitable for emergency switching or functional switching. The relevant aspects ofTable 53.2

 

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RCBO designated type AC . is an RCBO for which tripping is ensuredfor residual sinusoidal alternating currents . :yesnod:
Whethersuddenly applied or slowly rising . an RCBO designated type ( A ) is an RCBOfor which tripping is ensured both for residual sinusoidal alternating currentsand residual pulsating direct currents . whether suddenlyapplied or slowly rising .

ConventionalTripping Current .
TheConventional Tripping Current of a circuit – breaker is a characteristicrelating to protection of the circuit againstoverload current . it is a specified value of circuit which causes the deviceto trip within a specified time [ known as the conventional time ] at the specified reference temperature . conventional tripping current isusually expressed as a multiple of the rated [ or nominal ] current ( In ) of the circuit breaker .

Residualcurrent breakers conforming to – BS-EN 61009 .all have a conventional tripping current of ( 1.45. In ) The related conventional time is ( 1 Hour ) forcircuit – breakers of rated currents ( In ) up to & including ( 63A ) . & ( 2 Hours ) for circuit – breakers of rated currentsgreater than ( 63A )

Thesymbol generally used for conventional tripping current is ( I[SUP]2[/SUP] ) rather than ( It )as is used in circuit – breakers standards . such as – BS-EN 61009 .
Thisis because “ conventional tripping current “ Means the same as the Term “ Current causing effective operation of theoverload protective device “ used in – BS-7671
Inwhich the symbol ( I[SUP]2[/SUP]) is Used .

 

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UsefulJunk .
( I[SUP]2[/SUP]t ) Characteristics . :carolers:

( I[SUP]2[/SUP]t ) ( Joule integral or “ Energy let-through )
The ( I[SUP]2[/SUP]t ) (Joule integral . also more commonly knownas the energy let-through ) of an RCBO is equal to the integral of the square of the FaultCurrent ( I ) over a given time interval ( t )