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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 )
My point of View .
Note that a VisualCondition Report is not a ( British Standard ) formand may not satisfy the requirement for absolute compliance with a relevant British Standard
VisualCondition Report . ( VCR )
The Domestic Visual Condition Report provides an assessment of the condition of the ElectricalInstallation ( from your point view - taking into account the Limitations of a Visual ONLYInspection )
An N----C . Visual Condition Report . is Not a substitute for a Full Condition Report . & does not include items that can Only be checked with ( TestInstruments ) such as adequacy of Earthing Arrangements .
Whatare the 5 items that an Electrical Installation Condition Report must include .
Example. only
Fivemain aims of a ConditionReport ARE to .
i) Record the results of the Inspection & testingto make sure the electrical installation is safe to used . until the next inspection : following any work needed to make it safe
ii) Find any damage & wear & tear thatmight affect safety . & report it .
iii) Find any part of the electrical installationthat do not meet the IET Wiring Regulations . BS-7671:2011
iv) Help find anything that may cause electrical shocks& high temperatures . which couldlead to serious injuries . burns . fires & other injuries .
v) Provide an important record of theinstallation at the time of the inspection . & for inspection & testing in the future .
□ ElectricalInstallation Condition Report . &Associated Documents . Handover of the “ Condition Report “ tothe client with appropriate information & guidance regarding Actions to be Taken.
There’sDifference in Wording between . Guidance & Regulation .
Polarityof the Incoming Supply needs to be Confirmed which can only be a Live Test .
LivePolarity test . Only needs confirming atthe source of the supply – Once it is connected .
Polarity)- is both a Dead & Live Test . : 2392-10. for the sake of the Regulations .your test is Dead Test . 612.6.
( PFC ) - PSCC .& PEFC . shall be Measured . ( That means Tested )
Youcannot determine which is ( Higher ) Unless you test BOTH. - ( Highest ◄► reading is you ► PFC )
► GN-3 :
Whichever is ( Greater ) of the ( PSCC ) & the ( PEFC ) obtainedshould be recorded on the Schedule of Test Results .
► GN-3 : ( PFC ) Regulation 612.11.
Requiresthat the ( Prospective Fault Current – Ipƒ ) under both . SHORT-CIRCUIT & EARTHFAULT CONDITIONS . be Measured ◄◄◄ Wording Chaps .
► GN-3 : Tells Us - (( PEFC )) may be obtained with the same Instrument .
► GN-3 : Tells Us .
Fora Three-phase system . the ( PSCC ) current . will always be ( Larger ) thanthe ( PEFC ) current .
RCD. testing forms part of the functional tests .
O.S.G. - 612.13. ( vii ) functional testing . including .
► Testing of RCDs .
► Operation of all Switchgear .
Switchesmay be Manually Operated .
Thismay come Up on your Exams . 2391-10 . Wording .
p/51. GN-3 : Residual Current Devices .
thetest ( Measuring) current of ► ( Earth Fault Loop Impedance Testers ) ◄► maytrip any RCD . protecting the ( Circuit )
thereare Two common techniques .
i)Testing at limited current . ******
someinstruments limit test current to below 15mA. this should mean that RCDs with a rated residual operating current of 30mA& greater will Not Trip .
ii) d.c. biasing the RCD .
looptesters using a ( D.C. ) biasing technique saturate the core of the RCD priorto testing . so that the test current is not detected . this technique canusually be expected to be effective for both type A & AC types .
Justa Reminder – 2392-10 . O.S.G. . P/87. ►► TestingChecklist . ◄◄
Q) What are the First Three Live test’s carried out on a New Installationwhen the System is a ( TT System )
612.7. ( iv - O.S.G. ) Earth Electrode . ( Not with your Megger ??? with an Earth Fault Loop Impedance Tester )
p/46– GN-3 . After connection ofthe ( Supply / Polarity )should be confirmed using an ( Approved Voltage Indicator ) ….. ( LIVETEST )
SorryChaps . using GN-3 . 2008. Waiting for my 2012 . GN-3 ◄
what causes Power Factor to change .
Inductive loads causethe AMPS to lag behind the VOLTS. The wave forms of VOLTS and AMPS are then"out of phase" with each other. The more out of phase they becomethen the lower the Power Factor. Power Factor is usually expressed as Cos Phi.(Ø)
In 3 phase power supplies the "power" can bemeasured as a triangle.
• ACTIVEPower is the base line and is the real usable power measured in kW.
• REACTIVEpower is the vertical or that part of the supply which causes the inductiveload. The reactive power in is measured in kVAr (kilo volt-amperes reactive).
• APPARENTPower is the hypotenuse. This is the resultant of the other two components andis measured in kVA.
The effects of power factor
Consider a canal boat being pulled by a horse. If the horse could walk on waterthen the angle (Phi) Ø would be zero and COSINE Ø=1. Meaning all the horsepower is being used to pull the load.
However the relative position of the horse influences the power. As the horsegets closer to the barge, angle Ø1 increases and power is wasted, but, as thehorse is positioned further away, then angle Ø2 gets closer to zero and lesspower is wasted
ElectricalTesting :
2392-10: There are Three - criteria for Testing .
Tosatisfy the requirements of the Wiring Regulations . 2011 . these are . :juggle:
□ Inspection .
□ Testing .
□ Certificate .
“ RCDs “
• State :
a) why a test on a RCD . must not be conducted before a loop impedance test .
b) the reason for afunctional test on an RCD .
c) the maximum test current that needs to beapplied to a 100mA RCD . -&-s .2392-10 .
RCD tests .
a) Loopimpedance test determines that an earth fault loop path exists .
b) functional test determinesthat the RCD will actually operate in the event of a fault . Electro – mechanical test using the “ T “ button . see regulation . 514.12.2.
c) Maximum test current for100mA RCD is ( 100mA ) -&-s . 2392-10 .
2392-10 : “ Limitations “ RCD will ONLY operateunder earth fault conditions & will NOT clear a short circuit or overload .
• RCDs . comes in many forms. ( layman’s terms ) :banghead:
Both types are accepted byBritish Standards
● Non-latching or Active RCD Sockets ) ones will trip when they loose supply volts . or loose Neutral .
● latching or Passive RCD Sockets ) one will remain onuntil an earth fault occurs .
“ latching “ RCDs do notsuffer this problem as they “ remember “ whatstate they were in prior to the power being switched off . the RCD does notneed to be re-set .
Example . RCDs sockets & Spur’s
MK . 13Amp 1 Gang singleor 2 Gang . Weatherproof RCD Socket –IP56 . we all use then .
RCD “ Latches Off “ when tripped or in the event ofa power failure . ( Manual re-set ) ***
Example .
Twin Gang 13A switched RCDSocket “ Passive“ Contacts remain “ Latched “ when power supply is temporarily lost .
Example . 2392-10 / We mustkeep this in mind . Yeah
13 Amp RCD Spur 30mA . “ latching “ RCD will remain set in the event of a loss ofpower supply ( Just because itis an RCD don’t presume that it is Dead ) ifyour working on the other End . ***
13A RCD Adaptor . “ Non-latched “ prevents unexpected start ups .
● “ Latched “ versions will carry on protecting even if the Neutral is lost .
● “ Non-latching “ versions will trip in the event of a lostNeutral .
http://www.******************/Technical/Accessories/RcdSockets/RcdSockets.htm Hope thishelps
• RCD trip when Neural & Earth touch .??
An MCB is a single switch . youare only isolating the Line conductor . all theNeutrals are connected together at the consumer unit . When you touch Neutralto Earth on the load side of the RCD . you provided a parallel path back to thesub-station for all of the Neutral currents of the other still connected &energized circuits . this would cause the total Neutral current to split downthe two paths & un - balance the current flow through the RCD .
Certification .
Regulation – 610.4. requires that compliance with BS-7671 is verified for every addition or alteration. Chapter 63 . contains requirements for certification & reporting ofElectrical Installations .
Regulation 631.1.& 631.3. which requires an . ( EIC ) Electrical Installation Certificate . orMinor Electrical Installation Works Certificate . giving details of the extent of theinstallation covered by the certificatetogether with a record [ schedule ] of the inspection & the results . [schedule ] of testing . be issued following the verification of theinstallation [ new or changes to anexisting installation ] required byChapter 61 of BS-2011 .
The Domestic Electrical Installation Certificate . maybe used . under appropriate conditions . as an alternative to the . ( EIC ) ElectricalInstallation Certificate .
Where Minor Electrical Installation Work . does not include the provision of a newcircuit . a Minor ElectricalInstallation Works Certificate . may be issued for each circuit to which anaddition or alteration is made . instead of an ( EIC ) Electrical Installation Certificate . or a Domestic Electrical Installation Certificate . regulation 631.3.
□ The DomesticElectrical Installation Certificate . may be used . under appropriateconditions . as an alternative to the . ( EIC ) Electrical InstallationCertificate .
All work of the additions or alterations is to becovered by the certificate issued & all requirements of Regulation Groups631 & 632 . for the issue of an (EIC ) Electrical Installation Certificate . or a Minor Electrical Installation WorksCertificate . including those referred to previously . are applicable . Regulation 633.1.
Any defects or omissions found in the existinginstallation during the course of an addition or alteration which do not affectthe safety of the new work must be recorded on the Electrical Installation Certificate or the Minor Electrical InstallationWorks Certificate . Regulation 633.2. & a recommendation made to the clientthat the necessary remedial work be undertake without delay .
We had all learned the hard way that matters in Exams. is putting down the Answers’ the Examiners expect & nothing else .
□ State : Three measurements you would normally undertake at the origin of aninstallation with regards to the characteristics of the supply . 313.1. Supplies .
External impedance Ze .
Prospective short circuitcurrent .
Prospective earth faultcurrent .
2392-10 )- PFC is a generic term & can be either( PSCC ) or ( PEFC ) - Both. at the origin of an installation . “ Measurement “
External LoopImpedance Ze :
The value of Ze .is measured at the origin of the installation on the supply side with the meansof earthing disconnected . To avoid parallel paths.
This is carried out by connecting an Earth LoopImpedance Tester . between the Line conductor & the Main Earthing Terminal at the intake position with the Main Protective Bonding conductor disconnected .
This ensures that parallel résistance paths will not affect the reading .
The installation has to be Energized . & probeswith clips are used . to make contact .
Exams . is putting down the Answers’the Examiners expect & nothing else .
-&-s ) as an Inspector .
i) . The installation has to be Energized . The installationis not Earthed for the duration of the test. ( Possible Danger Aspect here )
ii) . When the test is completed reconnect the Mainprotective bonding conductor .
State : At whichpoint within an installation & between which conductors would the followingtests be made :
All tests made at the Origin .
External loop impedance - Ze .
Ze between Line& Earth . Main protective bonding conductor / OFF.
Prospective Short Circuit Current .
( Ipf ) .Between Line & Neutral .
Prospective Earth Fault Current .
( If ) . BetweenLine & Earth . Main protective bonding conductor / OFF .
State : theelectrical units in which EACH of the following test results would be expressed.
Insulation résistance . MΩ
External loop impedance . Ω
Tripping time of an RCD . mS
Useful Junk . “ Isolationof Earth “
( IT ) The source earthing arrangement are indicatedby the first letter . ( I ) denotesthat all live parts are isolated from earth or that the source of energy isconnected to earth through a deliberately introduced earthing impedance , “ I “ stands for Isolation.
Upgrading of an existing installation . where necessary.
When an existing installation is not adequate tosupport a proposed addition or alteration safety the work must NOT proceed . &
i) The clientmust be advised immediately & preferably in writing . &
ii) Thenecessary upgrading work should be recommended to the client . &
iii) When theclient’s consent has been given . the upgrading work should be completed beforethe addition or alteration is put into service .
□ Design & Construction of the Addition orAlteration .
The addition or alteration is required to meet allrelevant requirements of BS-2011 . including appropriate . the specialrequirements contained in part 7 .Special Installations or Locations . the addition or alteration must not impair the safety of the existinginstallation . Regulation – 610.4.
Inspection & Testing .
Chapter 61 –BS-7671:2011 . contains the requirements for Initial Verification . Inspection& testing must be performed to confirm the adequacy & suitability of .
• The relevantparts of the existing installation to support the changed requirements . &
• The upgradingof the existing installation necessary to support the addition or alteration . &
• The additionor alteration itself .
Where the device is intended to provide …. It means that there is a primary protectiondevice either upstream or downstream . etc .
16[SUP]th[/SUP] Edition . TT system . 2001 / 2004 . ◄ The Why’s
Often served with a 100mA . time/delayed RCD .
The idea being to give discrimationbetween RCDs by a factor of Three & a delay to circuitsrequiring additional protection . ( 3:1 ) 3 x 30mA / 90mA = 100mA
Residual current detection is complementary toovercurrent detection .
Residual current detection cannot provide protectionfor overload or short circuit currents . “ Exceptions “ Short circuit from Line to Earth . Not Lineto Neutral .
What protection must be Achieved . “ RCDs “
Additional Protection : with a rated residual currentof [ IΔn ≤ 30mA / 40mS ] these RCDs are intended toprovide Additional protection against electric shock in case of a failure ofother basic protective measures . & or in the event of carelessness by theUser .
Fault Protection : with a rated residual current of [ IΔn ≤ 30mA]
For an RCD being used for fault protection . it mustverified by test that the device would operate within the relevant maximumdisconnection time permitted by the 17[SUP]th[/SUP] Edition . if an earth fault occurred in the circuitprotected by the device .
Maximum disconnection times permitted by the 17[SUP]th[/SUP]Edition . for A.C. circuits of nominal voltage [ Uo/230V to Earth ] are 0.2 :0.4 : 1s : 5s :
0.4s being themost common in TN-systems . 0.2s in TT- systems .
Additional Protection : Use by ordinary persons . General use . 411.3.3.
As /Additional Protection : 30mA/ 40mS – 5 x IΔn . failure of the provision for Basic protection / provision Fault protection – Carelessness by User . 415.1.1.
Fire Protection : with a rated residual current of [ IΔn ≤ 300mA ] Installation exposed to Fire hazards .
High Load Currents : results of high load currents [ ≥ 6 x In ] Motors . Medical– 2012 . medical equipment CT machines or X ray equipment .
“ RCD “
i) Basic protection : these may only be used as additionalprotection . operating current of 30mA or less . operating time of 40mS or lessat residual current of 5 x IΔn .
ii) Fault protection : used where the loop impedance requirementscannot be met .
• Earthing : Main protective bonding conductor & Automaticdisconnection of supply . “ Fault protection “
The most common method in useRelies on the co-ordination of thecharacteristics of the earthing . impedance of circuits . & operation ofprotective devices . such that no danger is caused by earth fault occurringanywhere in the installation .
Auto Ramp : IΔn. to measure the trip out current on the RCD . ~
PFC or PSCC Test : determined by diving measured mains voltage by measured loop [ L – PE ] résistance or Line [ L – N ] résistance .
Measurement : Insulation Résistance . [ IR ] Test voltage . 50V – 1 mA : 250V - 1 mA : 500V – 1 mA : 1000V - 1 mA : 612.5.2.(iii)
Continuity Testing : 612.2.1. Open circuit voltage 4V : Test current 200mA .
□ The circuitunder test must be switched OFF . de-energised& isolated before test connections are made when carrying out Insulationrésistance & Continuity tests .
□ Continuity ofprotective conductors & earthed mainprotective bonding conductor . of new or modified installation(s) be verified before carrying out an Earth Loopimpedance test . or RCD test .
GS-38 : Leads : Competent Persons .
Megger 1552 . User’s - Reminder H&S requires them to carry out [ Valid Risk Assessment ] of all Electrical Work so as to identifypotential sourees of Electrical Danger& risk of Electrical injury such as inadvertent Short Circuit .
[ Valid Risk Assessment] Where the assessments at the risk issignificant then the use of [ Fused Test Leads ] constructed in accordance with H&S Guidance Note GS-38 “ Electrical Test Equipment forElectricians’ “ should be Used .
S – Time delay . Or Selective
Time Delayed [ Selective ] RCDs “ Megger 1552/3 “
The selective RCD testing is enabled by a [ Long press on theBlue degree Button ]
As selective RCD test mode is enabled the [ MFT ] will emit a long [ Bleep ] & display will show the exclamationmark [ ! ] symbol
Once the selective RCD mode is chosen . testing of theRCDs can be performed in the same way as normal RCD .
To disable selective RCD mode press the degree Button .
RCD Type’s
G – General . No delay .
S – Time delay . Or Selective
A – Responds to pulsed signal .
AC – Responds to A.C. ~
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