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

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RCD– is the Generic Term applied . :20:

RCCB:- Residual Current Breaker .
RCBO:- Residual Current Breaker withOver-current protection .

An RCCB differs from an RCBO in thatthe RCBO will additionally respond to over-current conditions whereas the RCCBwill NOT respond to such conditions .

Apprentices : RCDs

The magnitude of thecurrent flowing to the Load will equal the magnitude ofthe current returning from the Load back to the supply .
Any difference in the current flowing to the Load &returning from the Load is known as a ( Residual Current ) – Dual / Two / Line & Neutral :svengo:

 

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Apprentices : RCDs

Values of Rated ResidualCurrent ( I∆n )

RCDs– can be provided with any value of Residual Current Operating Current ( I∆n ) .
10mA: 30mA : 100mA : 300mA : 500mA : ↔ 704.4.1.1.3.2.1. :20:

30mA : isthe maximum value permissible for additional protection & 300mAis the maximum value permissible for fire protection.
Non-standard values may be Used . BUT the Additional Protection & Fire must NOT beexceeded . :svengo:

 

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Apprentices : RCDs :hurray:

OperatingTimes .

RCDsfall in to two categories in terms of the time taken to respond to & clearResidual Currents’ .

Regulation table - 3A . Appendix 3 – Informative . p/243

General Type :- These RCDs have no specified minimum responsetime but have specified maximum response times as follows .
I∆n ≤ 300mS ↔ Note:- BS-EN
I∆n ≤ 40mS

S Type :- These RCDs have no specifiedminimum response times but have specified maximum response times .
I∆n ≤ 130 – 500mS
5 . I∆n ≤ 50 – 150mS

Delayedresponse ( S – Type ) RCDs are commonly fitted Upstream of general type RCDsbut general type RCDs should never be fitted Upstream of Delayed Types .
The “ Term “ Upstream. refers to proximity to the origin of the Installation & “ Downstream “ refersto proximity to the Load .

 

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Apprentices : RCDs :bulb2:

Maycomprise One or Two poles for use on Single-phase supplies . ( Two currentpaths ) . Three-poles for use on Three-phase supplies . ( Three-current paths ) or
Four-polesfor use on Three-phase & Neutral supplies( Four-current paths )

 

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Inspection& Testing of an installation should be completed by . A competent person

ByDefinition . RCDs :17:

A.C.current comprises of Positive & Negative half cycles with respect to a Zero reference point . & an A.C. fault current canstart to flow to Earth at any point during either half cycle . An A.C. type RCDwill only trip in response to either the Positive &Negative half cycles of the A.C. Earth faultcurrent .
Whereasas ( A ) type RCDwill respond to both half cycles . As the A.C. type RCD is Blind to either the Positive & Negative halfcycles of the A.C. fault current .
Thefault current could flow for up to 10mS before the RCD will see the faultcurrent .

This10mS will be added to the response time of the device .
RCDtesters are usually provided with a button to enable the user to start the flowof the test current at ( 0 degrees / 180degrees ) starting on a Positive goingor a Negative going half cycle respectively .

Bystarting the testing of the RCD at both settings of the test current conductionangle . The user will be able to determine the maximum trip time of the RCD .
Thiscan be done at different test current levels .

 

[shill]

Thank you for all the easy to read info... you made it easy to follow, thank you

 

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Calculationof Earth Fault Loop Impedance :speechless:

The most commonly used measure . Automatic Disconnectionof supply either the Overcurrent protective devices - Which also provideprotection against “ Overload &Short circuit Currents for the circuit Concerned .

ResidualCurrent Devices . RCDs or combined devices RCBOs . Whichever type of device ischosen .

TheEarth Loop Impedance that has to be considered is that which comprises the Impedance of the Source .
TheLine conductor up to the Fault plus the Protective Conductor from the fault to the Source .

Whys& How’s .

Note:- That when an RCD or RCBO is used to provide Automatic Disconnection of thesupply in a ( TN- system ) the calculation of ( Zs ) is normally “ Unnecessary “ provided that “ Continuity“ of the EarthLoop has been Established . ◄◄

Anotherreason for calculating the Earth Loop Impedance is to check that the “ Circuit Protective conductors are adequatelyprotected thermally . & That they comply with the “ Adiabatic Equation givenin Regulation . 543.1.3. – Subject ofChapter 4 .

 

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BS-7671:2008– Bottom of . Table 41.3 – NOTE.

ContainsNO requirements in relation to the Conductor Temperatureat which the Earth Loop Impedance iscalculated .
Note :- The notes to the tables of Maximum Earth FaultLoop Impedance . – Table 41.2. – to 41.4. . States . that the Tabulated Valuesshould NOT be exceeded when the conductors’ are at their Normal Operating Temperature.

ifthe conductors’ are at a different temperature when tested . The reading should be Adjusted Accordingly – Appendix 14.

 

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Current – Carrying Capacity . ofa Conductor . :speechless:

TheMaximum Current which can be carried by aconductor under Specified Conditions without itssteady state temperature exceeding a specified value.

 

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Apprentices.

Namethree types of “ Diagram “used in the Electrical Industry . & explain – ThereUse . :icon_bs:

Anythree from Wiring diagram . Circuit diagram . Block diagram . Layout drawing .Installation drawing . Schematic drawing . Site plan .

A wiringdiagram provides a pictorial representation of an Electrical Circuit . showing arepresentation of the components .
A blockdiagram typically shows the flow of aprocess . each function being represented by a block .
A schematicdiagram uses symbols to show the arrangement of a system clearly .
Whereasa layout diagram shows the physical arrangement of the wires & components .

 

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:45:2392-10: ▼
Q) The main switch in a “ Single – Phase “ domestic Installation interrupt’s how many “ Live Conductors “

-&-s: BS-7671 – Regulation 537.1.4. The main switch should interrupt both LiveConductors on a Single/Phase Supply .

A MainSwitch intended for operation by “ Ordinary Person“ of a Household or similar Installation . shall Interruptboth Live Conductors of a Single-phase supply .

Q) How many poles would the main switch on aThree-phase & Neutral – TN-S supply have .

Threepoles - BS-7671 – Regulation 537.1.2. The Neutral neednot be Switched . ( TN-S or TN-C-S )

2392-10: ▼

Q) State: Two precautions that must be takenbefore carrying out Insulation Résistance Testing .

i) Remove sensitive equipment – Dimmers .Programmers . P.I.R.
ii) Remove equipment that “ GIVES “ falsereadings – Lamps . Neon’s . Motors .
iii)Check it is Safe to continue with the Test . When applying – 250 / 500V .

-&-s: Make sureNo-one else is in contact with any part of the Circuit .

 

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2392-10: ▼

Inrelation to Electrical Installations . :waving:

Whatis meant by Maximum Demand :- This is an Assessment of the current demand of an Installation.
Whatis meant by Discrimination :- The co-ordination ofprotective device(s) so that the device nearest to the load . being of a lowerrating . operates before the device futher up the line . Thereby minimisingloss of supply when a fault occurs .
Whatis meant by Diversity :- An allowance given when calculating maximum demand . due tothe fact that not all of the appliances . will be Used at the Same Time .

 

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2392-10:

FunctionalTesting ?? :waving:

Testing of Switches . Disconnections. Controls . RCDs . to check that they FunctionCorrectly .

 

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2392-10:

ApprovedVoltage Tester . To - GN-38 . :waving:
State:- Three of the requirements for Test Leads .
i) Retractable tips . or not more than ( 4mm) prefer 2mm . Fingers guards . Robustleads . coloured or identified . long enough for the purpose . Fused probes .

State:- the method of Ensuring it is working Effectively .
ii) By the use of an Approved Proving Unit .Testing the voltage tester . Before & After testing the equipment . or Circuit .

 

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Definitions’/ p/23 . EarthingConductor

A protectiveconductor connecting the main Earthing Terminal of an Installation to an EarthElectrode or to other means of Earthing .

Connectsthe main Earthing Terminal to the source of Earth . either an Electrode ( TT ) or means ( TN-S or TN-C-S ) :95:

 

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2392-10: ( T )

Howis Discrimination achieved when Using RCDs . :- Byusing Time-delayed RCDs . :79:

 

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Insight to the working of 17[SUP]TH[/SUP] Edition . “ Examples “

BS-7671:2008. Section 708 – Caravan & Camping Parks .

Thisis accommodated by the provision of suitably placed socket outlets . supplied via distribution circuits .

External Influences .
Equipmentshould have at least the following protection codes .
Impactrésistance . 708.512.2.
IPX4– for the presence of Splashes – ( AD4 ) in accordance with BS-EN 60529.
IP3X– for presence of small objects - ( AE2 ) in accordance with BS-EN 60529.
IK08- for presence of high severity mechanical stress ( AG3) in accordance with BS-EN 62262 .
(The ( IK ) codes are for Impact & ( 0.8 ) is an Impact of ( 5-Joules ) ImpactRésistance .
( Environment – p/324 . AG3 – High Severity . Reinforced Protection . IK08 )

British Standards to whichReference is made in the Regulations . Appendix1 – “ Normative “ p/228 – ( Requirement )

BS-EN 62262:1992 . – 2004 . Specification for degrees’ ofprotection provided by enclosures ( IP Code )
527.2.6.– (i) the system satisfies the test of BS-EN 62262 for ( IP33 )
527.2.6.– (ii) any termination of the system in one of the compartments , separated bythe building construction being penetrated . satisfies the test of BS-EN 62262for ( IP33 )
702.512.2.: External Influences . Electrical equipment shall have at least the following degree of protection according to BS-EN 62262. ( IP ???? )
708.512.2.- (i) & (ii)
708.553.1.8.each socket-outlet & its enclosure forming part of a caravan pitch electricalsupply equipment shall comply with ( BS-EN 60309-2 ) & meet the degree of protection of at least( IP44 ) accordance with BS-EN 60529 .
A721.55.6.- p/218. Terminal blocks .
A721.55.10.- p/218. External lights .

Note : Section 721 : tells us . p/209 – Wording . Yeah :96:
Inorder not to ►► MIX ◄◄ Regulationson different Subjects such as those for Electrical Installation ofcaravan parks with those for Electrical InstallationINSIDE caravans .
Section– 708 . concerns Electrical Installations ( IN ) caravanparks . camping parks & similar locations & . Outside.
Section– 721 . concerns Electrical Installations ( IN ) caravans& motor caravans . Inside

WiringSystems .
Thedistribution circuits are erected either Underground or Overhead .
708.521.1.1.- i) Underground cable ( Preferred )should be suitably protected against Mechanical damage . tent pegs . steelspikes . & at a depth of NO less than ( 0.6m )
708.521.1.2.- ii) Overhead . if overhead . Then ( 6m) above ground where there is Vehicle movement ( 3.5m ) elsewhere .

Switchgear& Socket outlets .
708.530.3.- Supply equipment should be adjacent to . or within ( 20m ) of the pitch .
708.553.1.8.– Socket-outlets should be :- BS-EN 60309-2– ( IP44 )
708.553.1.9.- at between ( 0.5m to 1.5m ) aboveground .
708.553.1.10.- rated not less than ( 16A )
708.553.1.13.– each socket-outlet shall be protected individual by an ( 30mA ) RCD protection. ( The device shall disconnect all LIVE CONDUCTORS including the NEUTRAL.
708.553.1.14.– if the supply is ( TN-C-S ) the protective conductor of each socket-outletneeds to be connected to an ( Earth Rod ) Regulation – 411.5. TT System .

 

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AdditionalProtection . :hurray:

703.411.3.3.Sauna heater .
Allcircuits in the location should have “ Additional Protection “ against shock by30mA RCD .
Except Sauna heater circuits unless Recommended by the Manufacturer . :svengo:

 

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External :- Earth Fault Impedance . ( Ze )

The Importance of this Test . To establish that a good Earthexists at the installation in order for the Remainingtests to go ahead . :svengo:

 

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Additions & Alterations to anInstallation . :waving:

General :

Many existing electrical installations require one or moreAdditions or Alterations during their lifetime . An Addition or Alteration maybe minor ( such as the Addition of a point to a final circuit . or therepositioning of a point ) or major ( such as the Addition of a new finalcircuits . distribution circuits . distribution boards & an upgrade to thesupply .

Where an Addition or Alteration ( which temporary or permanent) is to be made to an installation . the relevant requirements of BS-7671 .have to be met such that both the Addition or Alteration is Safe . & thesafety of the Existing Installation is not Impaired.

In order to be meet the requirements of BS-7671 . Followingmust be undertaken .

• Assessment ofthe existing installation to establish that the parts upon which the Additionor Alteration will rely for safety are both present & suitable for thealtered circumstances . & will continue to be so . & that the supply issuitable .
• Upgrading of parts of the existing installation . where foundnecessary to safely accommodate the Addition or Alteration . as a result of theabove Assessment .
The electricity distributor will need to upgrade thesupply . if Necessary .
• Design & construction of the Addition or Alteration inaccordance with the requirements of BS-7671 .
(T) • Inspection &Testing of any upgrading of the existing installation . & of the Addition or Alteration . as requiredby chapter 63 of BS-7671:2008
• Certification of any upgrading of the existing installation . & of the Addition or Alteration . as requiredby chapter 63 of BS-7671:2008

Assessment of an Existing Installation .
Regulation ( 131.8.) requires an Assessmentto be made of the relevant parts of an existing installation which is tobe Added to or Altered of the Supply .

Regulation ( 131.8.) No Addition orAlteration . temporaryor permanent shall be made to an existing installation . unless it has been ascertained thatthe rating & the condition of any existing equipment . including that ofthe distributor . will be Adequate for the Altered circumstances . furthermore . The Earthing & Bonding arrangements . if necessary for theprotective measured applied for the safety of the Addition or Alteration . shall beAdequate .

 

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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 )

 

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VoltageRating :
:17:
TheVoltage rating of the Overcurrent Protective Devicemust be at least Equal to or Greater than the circuit Voltage .

Voltagerating of an Overcurrent Protective Device is afunction of its capability to open a circuit under an Overcurrent condition .
Thevoltage rating determines the Ability of the OvercurrentProtective Device to “ Suppress “ & “ Extinguish “ the internal arcing that occurs during the openingof an Overcurrent condition .

Ifan Overcurrent ProtectiveDevice is used with a voltage rating lower than the circuit voltage . arcsuppression & the ability to Extinguish the arc will be Impaired & .under some Overcurrent conditions . The OvercurrentProtective Device may NOT clear the OvercurrentSafely .
Thevoltage rating is required to be marked on all OvercurrentProtective Device .

 

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RCBO is RCD+ MCB - ( RCBOs combines the functions of an MCB &RCD in One Unit )

RCD do Nothave Overload Protection . it needs a separate MCB t o backupprotect it . So an RCBO is formed :17:

Residual Current Breaker with Overload Protection

 

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ExposedConductive Parts : :juggle2:

Thesesare Metallic Parts of an Electrical System .which can be touched & which are not normally Live .
Thesecan become Live under Fault Conditions .

Metalcasings of “ Appliances“ ( Kettles . Ovens . )
Wiringcontainment systems such as Metal Conduit . Cable Tray & Trunking .

ExtraneousConductive Parts : :juggle2:

Theseare Metallic Parts within a Building . which do not frompart of the Electrical System . but canalso become Live under Fault Conditions .

Water & Gas Pipes .
AirConditioning .
Boilers .
AirDucting System .
StructuralSteel Work of the Building .

Purposeof Earthing .
Byconnecting to Earth all Metalwork not intended to carry current . a path is provided for leakage currentwhich can be detected & interrupted by RCDs . MCBs

CleanEarth return path from the Consumers Earth to the Supply Earth .

TheEarth Fault Loop.
Theconnection at the consumers Earth can be by means of either an Earth Electrodeat the building were the Earth isrequired or may be in the form of acable which runs back to the Generatoror Transformer & is then connected to an EarthPoint .

Generatoror Transformer at the point of supply always has an Earthpoint . a circuit is formed when Earth – Fault currents are flowing .
Ifthese Fault Currents are large enough they will operate the protective device . thereby isolating the circuit .

The “ Star point“ of the secondary winding in a Three phase - Four – wire distribution transformer is connectedto the Earth to maintain the ( Neutral at Earth Potential )

 

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OverloadCurrent :
Occursin a circuit which is Electrical Sound . p/27 -

FaultCurrent :
Isthe level of current flowing at a level up to & including the ( Prospective Short Circuit Current ) being the Maximum Current that the SupplyTransformer is capable of delivering .

Prospective Short Circuit Current ) must also be taken into account whenselecting the Type of Overcurrent Deviceto be installed .

FaultOccurs at the point between Line Conductors of negligible Impedance or betweena Live Conductor & an Exposed Conductive Part . [ it ismore serous than an Overload Current ]

Wherethe Earth Fault Loop Impedance for a circuit exceeds the maximum ( Zs ) for theOvercurrent device . is it permissibleto use an RCD .
Yes:- Regulation – 411.4.4. – 411.5.2.

Asthe Designer of an Installation . am I allowed to rely on the “ RCD element of an RCBO :49:“ to provide for Fault Protection in order toallow for Loop Impedance values greater than in table 41.3.

Yes:- so long as all the other ApplicableRequirements of the 17[SUP]th[/SUP] Edition ( asAmended ) are met . includingthose for Protection against Overload & Short Circuit .

Stillworking on an Electrical Installation that was designed before “ Amendment 1“ to BS-7671:2008 came into full Effect on ( 31 December 2011 ) to which requirements should theinstallation be ( Inspected . Tested . Verified & Certificated)

AnInstallation Designed before ( 31 December 2011 ) should be ( Inspected . Tested . Verified & Certificated) to BS-7671:2008 .That is to the Origin Version prior to the “ Amendment “

 

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MotorWindings : :49:

A Motorcan be manufactured with the Windings Internally Connected. if this is the case & there are Three Terminal Connections in the Terminal Block labelled .
( U . V .& W . ) you wouldexpect the Motor Windings to be connected in ( Delta Configuration)

MotorWindings with Delta Connection :
Theremay be four connections in the Terminal box labelled ( U. V . W . & N ) if this is the case . The Windings would bearranged to give a ( Star Configuration)

MotorWindings with Four Connections :

Alternatively. the Terminal block may contain Six Connections . ( U1. U2 . V1 . V2 . W1 & W2 . ) This is used where both Star & DeltaConfigurations are required .
TheTerminal connections can then be reconfigured for either Star or Delta .

MotorWindings with Six Connections :

• U1 . U2
• V1 . W2 .
• W1 . V2 .

 

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Cable Selection – Overview .

Requirements .

● The cable supplying the Load should be able to carry the current to the Load safety . After taking into account Diversity . without the cable overheating – ( 523 . App – 4 )
● Protective Devices should be able to provide protection for the cable from excess current ( 432.433. )
● The Length of the cable is Limited to ensure adequate voltage supplies the Load . ( 525 )
● Maximum Loop Impedance of a circuit is Low enough to ensure Disconnection within times specified by Table – 41.1.

● 0.4 – ( TN- ) 0.2 – ( TT ) for all circuits < 32A
5 sec . Disconnection time for Sub-mains distribution circuits

 

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612.7. Earthelectrode résistance .

Wherethe earthing system incorporates an earth electrode as part of the installation. the electrode résistance to Earth shall be measured .

NOTE : Where a measurement of( Ra ) is NOT practicable the measured value ofexternal earth fault loop impedance may be Met . :13:

 

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612.13. Functional testing :

Wherefault protection and/or additional protection is to be provided by RCD . theeffectiveness of any test facility incorporated in the device shall be verified.

612.13.2. Equipment . such as switchgear and controlgear assemblies . drivers . controls and interlocks. shall be subjected to a functional test to show that it is properly mounted .adjusted and installed in accordance with the relevant requirements of theseRegulations . :13:

 

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2392-10-

612.14. Verification of voltage drop .

Whererequired to verify compliance with Section 525 . the following options may beused .

(i)The voltage drop may be evaluated by measuring the circuit impedance .
(ii)The voltage drop may be evaluated by using calculations . for example . bydiagrams or graphs showing maximum cable length v load current for differentconductor cross-sectional areas with different percentage voltage drops forspecific nominal voltages . conductor temperatures and wiring systems .

NOTE : Verification of voltage drop is not normally requiredduring initial verification . – Still the Same :13:

 

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Certification& Reporting :

631.1.

Upon completion of the verification of a new installation orchanges to an existing installation . an Electrical Installation Certificate .based on the model given in Appendix 6 . shall be provided . Such documentationshall include details of the extent of the installation covered by theCertificate . together with a record of the inspection . the results of testingand a recommendation for the interval until the first periodic inspection . :rockon: