***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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(4 ) from a Testing point of View .

“ Motors lying inStorage “

Point to NOTE )- Check that the ( Insulation Résistance) of the Motor is satisfactory beforeSwitching on the Supply .

Why. ?? . Dampnessmay have been picked up During Storage . (( Bang )) :banghead:

 

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(5 ) Importance ☑

MotorTerminal Block :
Terminalarrangements for a (( Six – terminal )) Motor & the correct winding connections .

A1 – A2 :

B1 – B2 :

C1 – C2:

( Motor Windings ) if the connections to any winding are ( Reversed) the ( Magnetic fields ) will work against each other & a serious ( Overload ) willoccur .

Whenthe ( Starter) changes the Motor to the ( Delta ) configuration .

Never allow )- A2 .to be connected to B2 & A1 to C1 .


Importance )- This “ MUST NOT “ be confused with the ( Reversal of any TWO phases of the Supply ) when Motorrotation needs to be ( Reversed ) :banghead:

 

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(6 )

Frequency of Rotor Currents : :banghead:

Asthe rotating field is an ( Alternating One ) the currents intended in theRotor Cage Bars are also alternating . These are . however . NOT the same frequency as the supply . The frequencyof the rotor currents ( ƒs ) is given by .

( ƒs ) = Slip xsupply frequency .

Therefore: = S x ƒ .

S ) is expressed as a per Unit value . “ Example “ ( for 4% Slip )

S = 4 ÷ 100 = 0.04 .

 

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(7 )

An ( Eight – pole Squirrel – cage InductionMotor ) has a Synchronous speed of ( 12.5 revs/second) & a ( Slip of 2% )

Calculatethe frequency of the ( Rotor Currents )

ƒ = n x p .

= 12.5 x 4 = 50Hz .


ƒs = S x ƒ .

= 2 ÷ 100 x 50 . = 1Hz

 

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(8 )

Three– phase Motors may be ( Reversed ) by changing over any ( Two – phases )

 

[Engineer54]

Re: ***Cont../ Useful Information for Electricians & Apprentices***
(4 ) from a Testing point of View .

“ Motors lying in Storage “

Point to NOTE )- Check that the ( Insulation Résistance) of the Motor is satisfactory before Switching on the Supply .

Why. ?? . Dampness may have been picked up During Storage . (( Bang )) :banghead:

Also, if Motors that have been in storage for extended periods of time, there is a very real chance that flat spots in baring faces have occurred. Motors or any rotary equipment such as generators etc, need baring supported shafts turned on a regular basis to stop this very real problem (and very costly) occurring...

On a job in Libya, the main contractor had purchased and delivered to site 6 No of 750kVA generators then left them covered up (tarp's) on site for 3 years in temperatures approaching 45C!! Every seal, baring and fiber gasket in those 6 generators needed replacing before we could put them eventually into service!! It cost the main contractor more than the original cost of the generators to put them right. lol!!! Thank god they didn't do the same with the 3MVA 10.800KV generator at the main HQ site ...lol!!!

 

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(9 ) Wound – round type . ( Slip ring motor )

Slip:

Themotor of an induction motor cannot travel at ( Synchronous speed) as there would be NO flux cutting& the machine would NOT work .

The ( rotor )is . then . said to “ Slip “ inspeed behind the ( Synchronous speed )

Slip– ( S ) is usually expressed as a percentage & is given by .

Slip– ( % ) = ( N[SUP] S [/SUP]- N[SUP] r[/SUP][SUP] [/SUP][SUP] [/SUP]) / N[SUP] S [/SUP]x 100 .

Where. ( N[SUP] S [/SUP]) [SUP] [/SUP]isthe ( Synchronousspeed )
N[SUP] r[/SUP][SUP] [/SUP][SUP] [/SUP]) is the rotorspeed .

► Six – pole ) . Cage induction motor runs at ( 4% ) Calculate the motor speed if the supplyfrequency is ( 50Hz )

( Synchronous speed ) N[SUP] S [/SUP]= ƒ / p

= 50 ÷ 3 = 16.666 revs / second

Therefore: 4 = ( 16.66 - N[SUP] r[/SUP][SUP] [/SUP][SUP] [/SUP]) 16.66 x 100 .
Therefore: 4 x 16.66 / 100 = ( 16.66 - N[SUP] r[/SUP][SUP] [/SUP][SUP] [/SUP])
Therefore: N[SUP] r[/SUP][SUP] [/SUP][SUP] [/SUP]) = 16.66 – ( 4 x 16.66 / 100 )

= 16.66 .sub 0.66 = 16 revs/seconds

Six – pole- ( 3 ) ◄


● (Synchronous Induction Motor ) :banghead:

Greatadvantage of the ( Synchronous Inductiontype ) is its ability to sustainheavy mechanical “ Overloads “ suchan “ Overload “ pullsthe motor out of ( Synchronism ) but it continues to run as an ( Induction Motor ) until the “ Overload “ is removed . at which time it pulls back into ( Synchronism again )

 

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● Useful Junk . Old Notes ◄

Nowadays the Instruments doit all for Us .

Determinethe power in Watts . & Volts . Amperes .& the power factor of a single –phase circuit . ( Load )

Calculatethe ( kVA ) & the power factor ofthe Load .

Only Example : 8A : 240V : 1.152kW.

kVA = VA / 1000 .

= 8 x 240 ÷ 1000 . = 1.92 kVA

PF. = kW / kVA . = 1.152 ÷ 1.92 = 0.6

 

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Remember this is Only an Analogy ) What a wasteof a Good Bud . !

The ( Beer Analogy)

Thisis a useful way to explain the ( Power Factor )

Wehave a pint beer glass with the main body of beer & the head . Although theglass is ( Full) part of it is useless . & the true amount of beer is ( Less ) than apint .
A ratioof true to ( Apparentbeer ) would indicate how much head there was . So if this ratio ( Pint Factor ) where (1 ) or ( Unity ) there would be NO head . & a ( PF ) of ( 0.5 ) wouldmean half beer & half head . clearly . it is better to have a ( PF ) close to ( Unity )

Apparent pint . Actual or True beer ◄► Head or Useless beer . Pintfactor = True pint / Apparent pint .

 

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-&-s– BS-7671:2008 ( 2011 )

This is an Open Book Assessment . & Learners will be allowed to take in thefollowing permitted reference material .
IET. Wiring books taken into examinations can containthe following .

• Bookmarks ( e.g. . blank post-it-notes orcorners of pages folded )
• Highlighting of text .
• The Corrigendum . issued by the IET as asupplements to the wiring regulations in July 2008 .

IET wiring regulations . books taken into exams cannot contain the following : :32:

• Sample exam questions . answers or diagrams .
• Any writing in the regulations or accompanyingwritten notes .
• Notes . diagrams or any content that may inanyway advantage the candidate in answering questions within the exam .

Itis the ( Responsibility) of any ( Centre ) to ensure the material in the candidate’s . IET Regulations to Electrical Installationscannot unfairly advantage candidates in any way . if there is any doubt overthe suitability of content the publication should NOT be used & replacedwith “ Clean Regulations “

-&-s : - Candidates will also require a ( Non-programmable calculator )

 

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Are any changes beingmade to the 2392 Fundamental inspection, testing and initial verificationqualification ?
The2392 qualification will be migrating to the QCF in late 2011, with very few changes tocontent or the assessments. More details will be released in autumn 2011.

 

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2392-10:

Protectionagainst Sock .

Provethat the following tables provides ( Instantaneous Disconnection ) for a . BS-EN-type 32A. MCB using tables ( 41.3. – App 3 )
Conformsto :

( Zs ≤ Uo / Ia )

17[SUP]th[/SUP] Edition 2008:2011 )- Table – 41.3. End of the Table . !! ( Type –B . 46/In ) ( Type – C . 23/In ) ( Type – D . 11.5/In )

Zs ≤ 230 ÷160 = 1.44Ω .

( Type – B . 46/In ) ► 46 ÷ 32 = 1.44Ω . Maximum ( Zs ) table 41.2

230÷ 46 = 5 . In . multiplier for instdist .

Min. Amps . for inst . dist (Appendix 3 )

Manufacturesdata show ( 3 – 5 * In ) for instantaneous disconnection .

B. > 3 In . ≤ 5.0 In
C > 5In . ≤ 10.0 In
D > 10 In . ≤ 20.0 In

 

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Protection Against Electric Shock .

Protectionprovided by s Residual Current Device ( TN- systems )
Followingcondition applies . Regulation – 411.5.2.
( Zs x IΔn ≤ 50V )

• ( Zs ) = Earth Fault Loop Impedance in Ohms . Ian= rated residual operating current in Amps .

Protectionin ( TT system )

Theuse of Overcurrent Protective Devices are NOTexcluded . although it is preferred to use a ( RCD) with a disconnection time of NOT greater than ( 1 sec ) 411.3.2.4.

R[SUP]A[/SUP] x Ia ≤ 50V .

Regulation– 411.5.3.

R[SUP]A[/SUP] = sum of all the resistances of earth electrode& protective conductors connected to the Exposed – conductive – parts .
I[SUP]A[/SUP] = the current causing automatic operation of theprotective device with ( 1 sec )

Allowancesfrom Table 41.1. :

411.3.2.3.– TN - systems disconnection time < 5 sec for a . distribution circuits .
411.3.2.4.– TT - systems disconnection time < 1 sec for a . distribution circuits .
Not covered by . 4113.2.2. – ( > 32A circuits )
411.3.2.6.– where disconnection times cannot be met then ( Supplementary Bonding ) must beApplied .

 

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In some Applications where the continuity of service is very high .

“ Hospital “ Operating Rooms . as we can’t accept the tripping of Electricity oncean Earth Fault Occurs .
- Areswhere the Explosions risk is High .

• Omission of Protective devices for SafetyReasons . 2008:2011.

433.3.3. .

Used where unexpected disconnection would cause a dangeroussituation .

i) the exciter circuit of a rotating machine .
ii) the supply circuit of a lifting magnet .
iii) the secondary circuit of a currenttransformer .
iv) a circuit supplying a fire extinguishingdevice .
v) a circuit supplying a safety circuit (fire or gas alarm )

vi) a circuit supplying Medical Equipment used for Life – support in specific Medical Locations’ . where an ( IT ) systems . is incorporated .

 

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aswe know . there are Three- Types ofEarthing Systems in the 2011 .

TN-S.
TN-C-S – ( PME ) .
TT.

Fora ( Low-voltage ) supply given in accordance with the .Electricity Safety . Quality & Continuity Regulations . 2002 .

Deleted by BS-7671:2008 – Amendment . No 1 .

IT) & ( PEN ) is withdrawn .

i) - This is because ( TN-C ) requires an ( Exemption ) from the . Electricity Safety . Quality &Continuity Regulations .
ii) - & ( IT ) system is NOT permitted for a ( Low-voltage ) public supply in the UK. Because thesource is NOT directly Earthed .

 

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(1 ) I split this Question up . of the Net.

Whichone of the following ( Test Readings ) for Continuity of CPC. Would satisfy BS-7671:2011 for a 230V A.C.lighting circuit . ( 0.5Ω )

10MΩ.
100Ω .
1MΩ.
0.5Ω

Calculations’: 230V ÷ 0.5Ω = 460A .

460A )- this is Fault Current would easily disconnect the 6A – MCB .protective device within 0.4 seconds (TN- Earthing system ) Why??

p/301– fig . 3A4 . Type B– BS-EN 60898 .

□ MCB . BS-EN – 60898 .
Rating– ( 6A ) . Current - ( 30A )

□ RCBO is / MCB / RCD
Rating– ( 6A ) . Current - ( 30A )

Overcurrent characteristics of RCBO to BS-EN- 61009-1 : MagneticSettings )- 5 x 6A = 30A . ( Zs < 230 ÷ 30A = 7.67Ω ) table – 41.3 - 6A / 7.67ohms )

( 32A )- RCBO toBS-EN- 61009-1 : Domestic Installation. MagneticSettings )- 5 x 32A = 160A. ( Zs < 230 ÷ 160 = 1.4375 – 1.43. table – 41.3 - 32A / 1.44ohms )

(Zs ≤ 230 / 160 = Zs ≤ 1.43Ω )

-&-s. The maximum ( Zs ) for a BS-EN-60898 . 32A . B type circuit breaker protecting a DomesticRing Final Circuit is . table – 41.3. 1.44Ω .

 

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Witha Spilt –Load . Consumer Unit .

Regulation314. (i) Splitthe Circuit(s)

Downstairslights are on the same RCD as the Upstairs sockets . “ Reason “ forthis is that . if the RCD trips & Downstairs lights go OFF . Downstairs’ sockets are ( Still Live ) the User can plug a tablelamp into One of Them .

 

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Regulations522.6.102. p/125 .

Meansthat such ( Additional RCD Protection ) applies alsoto Lighting circuit(s) . to eliminate the risk of both Lighting circuit(s) . going OFF simultaneously because OFF nuisance tripping .

Each“ Lighting circuit on a Separate RCD.

BathroomLighting Circuit . ( Supplementary equipotential Bonding ) may be Omitted within a Bathroom or Shower .where the conditions of Regulation 701.415.2.are Complied with .
Theseconditions include the requirement that all ( Final circuit(s)within the location have ( Additional protection ) by means of a 30mA– RCD

TheBathroom Lighting Circuit is supplied by means of a Separate Circuit.

Regulations522.6.102.

Where Regulation 522.6.101. applies& the installation is NOT intended to be UNDER the supervision of a ( Skilled or Instructedperson ) a cable installed in accordance withRegulation 522.6.101 – (v) & NOT also complying with Regulation . 522.6.101– (i) . ( ii ) . ( iii ) . or ( iv )

☞ Shall be provided with ( Additional protection ) by means of an ( RCD ) having the characteristics specified inRegulation 415.1.1.

522.6.101 . p/124 .

(iv)– be mechanically protected against damage sufficient to prevent penetration ofthe cable by Nails . Screws & the Likes .

 

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531.5. RCDs in an ( IT )

Whereprotection is provided by an RCD & disconnection following a ( First Fault ) is not envisaged . the Non-operating .residual current of the device shall be at least Equal to the current whichcirculates on the ( First Fault ) toEarth of negligible impedance affecting a Line Conductor .

 

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Socketoutlets . 411.3.3. p/54 .
(i) All socket outlets for general use byOrdinary persons Not Exceeding ( 20A ) .should be protected by a . 30mA – RCD .

Plain English )- p/31. Ordinary Person . A person who is neither a skilled person nor an instructedperson .
TheWording is that socket – outlets with a rated current NotExceed 20A . that are for use by ( Ordinary Persons) & are intended for general use areto be protected .
2392-10. Intended to cover all who dwell in . Houses . Flats . Yeah .

PortableEquipment . see ( Mobile ) p/31 .
(ii) All ( Mobile ) equipment foruse Outdoors should be protected by a . 30mA – RCD . Notexceeding 32A . for use Outdoors .

Mobile equipment ( Portable equipment –( deprecated )) .Electrical equipment which is ( Moved ) while in ( Operation ) or which caneasily be moved from one place to another( while Connectedto the Supply )

SpecialLocations .
Allcircuits in a room with fixed bath or shower should be protected by one or more. 30mA – RCD . shower . lighting . Heater . Ventilation .

( T ) Fundament Principles . 132.13. ( Documents for Electrical Installation(s)
514.9.1. & Part 6. - & whereapplicable . Part 7 . is provided for everyElectrical Installation .

Regulation. 134.1.1. Erection & Initial Verification of ElectricalInstallation(s) requires that goodworkmanship shall be undertaken by ( Competent Person(s) & further requires ( ManufacturesInstruments ) shall be followed .

 

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2392-10: if we reposition a ( Pull – cord ) switch in a location containing abath or shower . Would the circuit need to be RCD protected . YES .
Yesbecause the work would be more than a ( Like – for – like - replacement ) Regulation . 701.411.3.3. .

 

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2392-10.

• Fundamental Principles . ( Scope ) p/14.

(vi ) additions &alterations to installations & also parts of the existing installationaffected by an addition & alteration .

 

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Amendment No 1 . 2011 .

16[SUP]th[/SUP] Edition - Which has renamed Periodic Inspection Reports- ( PIRs ) TO.

ElectricalInstallation Condition Reports – ( EICRs )

UsefulJunk .
Underthe existing arrangements . 2011 . the codes will have a Letter “ C “ for code . in front of them .

2392-10: These reports are also used by placesof work to demonstrate ( Compliance ) with the Electricity at Work Regulations 1989 .

Thetypes of properties that typically fall within the ( EICRs ) guidelines .

BS-7671:2011. Scope . p/14 .

2392-10.
110.1.1. . The regulationsapply to the design . erection & “ Verification “ of electricalinstallations such as those of : E.g.
i)residential premises .
ii)commercial premises .
iv)industrial premises .
vi)prefabricated buildings .

xv) medical locations .

p/36. ( T ) “ Verification “ all measures bymeans of which compliance of the electrical installation with the relevant requirementsof BS-7671:2011 . are checked . comprising . Inspection & Testing &Certification .

 

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ElectricalInstallation Condition Report . ( EICR )

PeriodicInspection is an Inspection on the condition of an ExistingElectrical Installation . To . Prioritiseany deficiencies against BS-7671:2011

Oneway of confirming an ( Existing Electrical Installation ) is safe forcontinued use to have the Installation ( Periodically Inspected & Tested ) & a“ Report “ on the Condition ( Issuedto the personOrdering the Work )

Mustmake this clear . 2392-10 : -&-s . TRIP UP ONE

“ Electrical Installation Condition Report “ is asthe title indicates a “ Report “ NOT a CERTIFICATE . ◄◄ -&-s

( Existing Electrical Installation )
Itrelates to an assessment of the . “ in service condition “ of an Electrical Installation . against therequirements of the Current Edition of BS-7671-2011

-&-s )- the “ Report “ is primarilyfor the benefit of the person ordering the Work .

“ Wording . “ 2391-10 – Exams

Electrical Installation Condition Report Certificate . N/A - NO MARKS :banghead:
Electrical Installation Condition Report .

( Periodic Inspection & Testing) of an Electrical Installation is also ( recommended ) atthe end of the ( Period stated ) on the ( ElectricalInstallation Certificate ) Or .the Last ( ElectricalInstallation Condition Report )

Q/As . -&-s .

An ElectricalInstallation Condition Report . shouldinclude details of the ( Extent of the Installation) &
Any( Limitations of the Inspection & Testing )
The( Reasons for any such Limitations )

The ( Main purpose) of having your Electrical Installation checked is therefore to ( Identify ) so far as is reasonably practicable . & ( Report ) on any factors Impairing or likely to impair the safety of the Electrical Installation .

 

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Visual Condition Report :

Thisreport is intended to be issued only for the purpose of reporting on conditionof an “ Existing Electrical Installation “

Ingeneral a ( VisualCondition Report ) is suitableonly where the Installation has been Inspected & Tested within the last twoyears & the results were reported on an ElectricalInstallation Certificate . Or an Electrical Installation Condition Report .

Note . that a “ Visual ConditionReport “ includes ONLYthe findings of the Inspection of an Electrical Installation .
Note . it does NOTinclude the results of any Electrical Testing.

-&-s: just because I’m paranoid doesn’t meanthey’re not out to get ME .

“ Visual ConditionReport “ isreally a “ Electrical Installation Condition Report “ without the Measurement(s) . :13: Yeah .

 

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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 .

 

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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.

 

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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 .

 

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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 ◄

 

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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

 

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ElectricalTesting :

2392-10: There are Three - criteria for Testing .

Tosatisfy the requirements of the Wiring Regulations . 2011 . these are . :juggle:

□ Inspection .
□ Testing .
□ Certificate .

 

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“ 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 .

 

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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

 

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• 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 .

 

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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 .

 

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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

 

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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 .

 

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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

 

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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 .

 

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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. ~