***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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Copperhas & continues to be the most widely used material for Earthing .

BS-7430. Code of Practice for Earthing .
Whichstates “ Copper is one of the better & commonly used materials for EarthElectrodes & Underground Conductor’s .

Earthingarrangements’ within buildings in the UK . should conform to BritishStandard – 7671: & 2011.

Forthe sake off . 2391-10 . -&-s Exams . The requirements for “ Erection & Initial Verification of Electrical Installations .

(2 sets of Testing here ) Verification &Periodic Inspection & Testing
i) InitialVerification . 134.2.
ii) Periodic Inspection . 135 . – tofollow 134.2.2.

Appendix 6 . for Certification & Reporting Electrical Installation ConditionReport . that replaces the ( Periodic Inspection Report ) New condition reportincludes a New Inspection Schedule

p/36. Verification : All measures by means of which compliance ofthe Electrical Installation with therelevant requirements of BS-7671 are checked . Comprising
Inspection. Testing & Certification .

134.1.7. Testing – Where necessary for safety purpose. suitable warning signs & / or notices shall be provided .

BS-7671:2011 & GN-3 . go Hand & hand . intesting . & Exams 2391-10 .

313.1. Reminds us . (v) The suitability for the requirements of theinstallation . including the Maximum Demand . 2392-10 .
MaximumDemand . Ring Final Circuit – maximumpermitted sustained load to be drawn by this circuit would . be 32A – 100%

Doesthe device that has to be provided for switching off a bathroom ( Extract Fan ) for mechanical maintenance need to be locatedadjacent to the Fan . ( No )
p/152. Regulation – 537.3.2.4.
Butthe device does need to be placed & marked as to be readily identifiable& convenient for the Intended Use .

2392-10: Installation Circuit Arrangements .

p/46. The Four Regulations under Section 314 of BS-7671:2011 .
Setout the requirements for the circuit arrangements . Essentially . circuits mustbe provided in sufficient number so that danger is prevented . &inconvenience minimised . both under normal & fault conditions &arranged so that operation . Inspection . Maintenance & testing may becarried out in a safe manner .

Itis Important . that a sufficient number of circuits are provided so thatequipment unaffected by a fault condition remains safe & functioning whenanother circuit develops a fault . The designer would need to consider theeffects . in terms of consequential events . of the operation of a singleprotective device .

Regulation314.1.4. calls for each circuit to beelectrical separate & connected individually & detached from all othercircuits where they terminate in a distribution board .
Implicitly: the connection of each circuit Line .Neutral & CPC conductors must follow a logical sequence at theirtermination in the distribution board

Summaryof ( Low
ExistingBS-7671:

 

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Summaryof ( Low – voltage ) fuse standardchanges for first amendment . p/295 .

ExistingBS-7671:2008 fuse. BS-88.2.2. : BS-7671:2011 fuse . BS-88-2 . ( Bolted ) type fuse is recognised ( Fusesystem E )
ExistingBS-7671:2008 fuse. BS-88-6 : BS-7671:2011 fuse . BS-88-2 . “ ( Clip in ) type fuse is recognised ( Fusesystem G )
ExistingBS-7671:2008 fuse. BS-1361 : BS-7671:2011 fuse . BS-88-3 . “ ( Cartridge ) type fuse is recognised ( Fusesystem C )

 

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RCBOs . BS-7671:2008 . Functional Earth Wire Connection Requirement . ??

Eaton– RCBO Functional Earth Wire Connection Requirements ...

 

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Ambient Temperature Correction Factor .

The measured Loop Impedance given . O.S.G. p/120 . Table B8
Thevalues assume that the maximum operating temperature of the insulation is ( 70°C ) & the Ambient Temperature whencarrying out the test is at ( 10°C ) AtAmbient Temperatures other than this . Correction Factors . should be applied .

Table B8 p/120 . The correction factor is given by :
(1 + 0.004 – ambient temp – 10 )
Where( 0.004 ) is the temperature coefficient per ( °C ) at 20°C for copper &aluminium .

If the ambient temp is ( 25°C - 1.06 ) the measured impedance of the circuit protected by a ( 32A type MCB ) should not exceed ( 1.16 x 1.06 = 1.23Ω )

 

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SomethingKnock-up . 2392-10 .

□ Measurementof Prospective Fault Current - Ipf - ( PFC ) & ( PSCC )

For the sake of -&-s )- This test is made with an Earth Fault Loop Impedance Tester set to Amps . -&-s– BS-EN-611557-3.

The ( PFC ) which is how much current will flow in the event of a fault .
isdivided into two parts .

Prospective Earth Fault Current )- Line to Earth .
Prospective Short Circuit Current )- Fault between Liveconductors ! L/N

The ( PFC ) test is made at the Origin of theInstallation . & its value ( Obtained in kA )
(PFC ) & ( PSCC ) tests ( Higher ofthe Two Values is Recoded )

□ How do we Do this Test . for -&-s sake .
BS-EN-611557-3. – GN-3 ◄

AnEarth Fault Loop Impedance Tester .the valueof Earth Fault Loop Impedance ( Zs ) maybe determined by . !!

i) Direct measurement of ( Zs ) at thefurthest point in the circuit .
ii)Direct measurement of ( Ze ) at the Origin of the circuit &adding to the “ Value “ of ( R[SUP]1[/SUP]+ R[SUP]2[/SUP] ) point to NOTE : measured during Continuity Tests .
iii) Obtained the “ Value “ of ( Ze ) from theElectricity Supplier & adding to this “ Value “ of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) as above .

(Ze ) is the Loop Impedance “ Value “ External to the Source of the Circuit(s) Supply .

 

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□ DirectMeasurement of ( Zs )

Directmeasurement of Earth Fault LoopImpedance . is achieved by use of an . Earth Fault Loop Impedance Tester .
TheInstrument operates from the main supply & therefore can only be used ona ( LiveInstallation ) connected directlyto the ( Furthest Point ) of the circuit .

Note : ( Parallel Paths) will be present which will ( affect ) the true circuit(s) Earth Loop ImpedanceReading(s)

□ Measurementof ( Ze )
(Ze ) can be measured using an . Earth Fault Loop ImpedanceTester . at the ( Origin )
Connectedusing approved leads between the ( Live Terminals ≈ ) ofthe supply & means of Earthing with the main switch closed .

Note : to Remove the possibility of ( Parallel Paths) the means of Earthing must bedisconnected from the Main Protective Bonding . conductors for the duration of the Test.

“ Verification “ of Earth Loop Impedance Test Results .
Valuesof Earth Loop Impedance obtained ( Zs ) should be compared with one of thefollowing . 41.3.: 41.4. : 41.5. :

EarthFault Loop Impedance ( Zs )
• This is a Live Test .
Canbe obtained direct measurement using an “ Earth Loop ImpedanceTester “ Or by adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) obtained earlier to ( Ze )

Obtaining( Ze ) External Loop Impedance .
• This is a Live Test .
ByEnquiry ( Must test to ensure Earth ispresent )

Direct measurement of ( Zs ) can only be made on a . Live Installation. No earthing conductors aredisconnected for this purposes of the test & this may result in readingsobtained which are lower than the value of . Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) This is due to the parallelearth paths presented within the installation .

□ Whattype of Earthing System are there .

Thereare Three types listed in BS-7671:2011 . p/45

TN-S. system
TN-C-S. ( PME ) system .
TT. System .

2392-10: Testing point of View .
Continuity of protective conductors is clearly important as are the Tests for ( Insulation Résistance : Loop Impedance : Operation of RCDs )

 

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Don’t forget “ Lads“ Please show your appreciation with the " THANKS " button !!! :svengo:

 

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(1 ) -

InstantaneousTrip Currents . x In .

MCBs : Icu - ( rated ultimate / breaking capacity )
MCBs : Ics - ( rated service / breaking capacity )

Thedifference between . BS-EN-60898 “ MAY be used insteadof CALCULATION “ / BS-3871 formula. To beUsed :
BS-3871– are still out there .

MiniatureCircuit Breakers “ conforming to BS-EN-60898 are suitable for Isolation ◄
Miniaturecircuit breakers ( MCBs ) manufacturedto earlier standards . such as . BS-3871 : are unlikely to be suitable for Isolation. ◄

Note: There is NO type ( A) instantaneous tripping characteristic to ( Avoidconfusion ) with the ( A ) abbreviation for Amperes . B : C : D : - MCBS

Determinationof Maximum Earth – Loop Impedance ( Zs )
Themaximum value of Earth Fault Loop Impedance maybe found in the . Wiring Regulations . BS-7671:2011 . details’ published bythe Manufactures . ◄◄

 

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B: C : D : - Table 41.3 . BS-EN-60898 . ( For instantaneous operation givingcompliance with the ( 0.4s ) Disconnection time )

B) 3 ( In) to 5 ( In )
C) 5 ( In) to 10 ( In )
D) 10 ( In) to 20 ( In )

B / Curve.
Themain characteristic of the ( B ) curve is Instantaneous trigger for currentsbetween ( 3 to 5 times) the rated current . Therefore .
Theyare mainly applied for the protection of circuits with ( resistive characteristics ) or involvingsignificant cable distance . Incandescent lamps . showers. . etc .

{ B means the fast magnetic trip will operatebetween ( 3 to 5 times ) nominal setting }
p/25 . Circuit Breaker. Abnormal currents such as Short Circuit Currents}

Note : THE valuesspecified in Table 41.3. for the types& ratings of Overcurrent devices listed “ MAY be used insteadof CALCULATION “ p/55 . ◄◄◄◄

Circuitbreakers are going to be used for protection . disconnection times willautomatic conform to the requirements provided that the circuit(s) meet the ( Zs ) …. 41.3.
MCBs. BS-EN -60898 .

TypeB – 3 & 5 times . its rating passed through it .
TypeC – 5 & 10 times .
TypeD – 10 & 20 times .

Tablesfor ( Zs ) specific value of current is required . ( Worst case is Used )

OhmsLaw : to the supply voltage ( 230V ) & ( Ia ) to obtain a ( Zs) value for the device . Regulation411.4.5. – ( Zs x Ia ≤ Uo )

TypeB . – Zs for a 20A can be calculated . 5x 20 = 100 . 230 ÷ 100 = 2.3Ω …… ( Worst case is Used ) ◄◄◄
TypeC . – Zs for a 20A can be calculated . 10 x 20 = 200 . 230 ÷ 200 =1.15Ω
TypeD . – Zs for a 20A can be calculated . 20 x 20 = 400 . 230 ÷ 400 =0.57Ω

□ Switch disconnectors. it function is Only to disconnect electrical circuits with currents of up to 100A . Singlepole . “ Doublepole “ . Triple pole . Four pole .
MainLoad Disconnector Switch – Isolator .

 

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(2 )

TypeB . – Zs for a 20A can be calculated . 5x 20 = 100 . 230 ÷ 100 = 2.3Ω …… ( Worst case is Used ) ◄◄◄

Regulations’. table 41.3 . ( Look it UP )◄◄

Rating20A – Zs . is 2.30Ω .

TypeC . – Zs for a 20A can be calculated . 10 x 20 = 200 . 230 ÷ 200 = 1.15Ω
TypeD . – Zs for a 20A can be calculated . 20 x 20 = 400 . 230 ÷ 400 = 0.57Ω

 

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(3 )

For. BS-3871 )- Types 1 , 2 , 3 , & 4 ,

Themaximum value of . Earth Fault LoopImpedance ( May be Calculated ) &using the Manufactures Tripping Characteristic .

formula.O.S.G. p/72 . Table 7.2.7. (ii) - ( b ) . Now withdrawn )

Thesetypes of circuit breakers are identified by the use of numbers . 16[SUP]th[/SUP] Edition . still in Use .

BS-3871 - formula. To be Used :

1 . 2.7 / 4 – ( In ) …. BS-3871
2 . 4 / 7 – ( In ) ….
3 . 7 / 10 – ( In ) ….
4 . 10 / 50 – ( In ) ….

TypeB )- 3 to 5 ( In ) …. BS-EN-60898 .
TypeC )- 5 to 10 – ( In ) ….
TypeD )- 10 to 20 – ( In ) ….

Circuitbreakers . …. BS-3871

Type( 1 ) … Multiplier ( 4 ) .. In
Type( 2 ) … Multiplier ( 7 ) .. In
Type( 3 ) … Multiplier ( 10 ) .. In
Type( 4 ) … Multiplier ( 50 ) .. In

Zs) value for a 20A type ( 1 ) – BS-3871. ( 4 x20 = 80 ) ( 230÷ 80 = 2.87Ω )

 

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(4 )

Short Circuit Capacity according to BS- 3871 )- now obsolete .
Was( Expressed as an ( M ) value .

M 1– 1000A
M –1.5 . 1500A
M 3– 3000A .
M 4.5– 4500A .
M6 – 6000A .
M9 – 9000A

 

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-&-s. Any circuit or equipment vulnerable to a particular test should beindentified by . ?
p/117- 514.9.1. The provision of a Legible diagram . chart ortable prior to testing .
2392-10: The purpose of the Inspection conducted prior to Testing an installation isto verify that . ?
p/189- 611.2. (iii) “ equipment ” is not damaged or defective so as to impairsafety .
2392-10: No alteration shall be made to an existing installation unless the ?
p/20- 132.16 . it is established that the alteration will notimpair the safety of the existing installation .

2392-10: The Inspecting & Testing required duringa Periodic Inspection should be recorded on a Electrical Installation Condition Report . & be carried out by .
p/195- 621.5. Competent Person .

2391-10: Q) prior to an Inspection in accordance with BS-7671:2011 , The competentperson carrying out the work shall normally . ?
p/189- 611.1.
A) Inspection shall ( Precede Testing ) & shall normally bedone with that part of the installation under Inspection disconnected from thesupply .

2391-10: Q) Installations should be arranged so as to avoid hazards in the event ofa fault . & to facilitate safe operation inspection . testing & maintenance . .? Onemethod of complying with this is to .
p/46- 314.1.
A) divide the installation into circuits .

 

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Reasons) ( IR ) Testing . 2392-10 .

InsulationRésistance . Details of such equipmentshould be recorded on the Schedule of Test Results . “ Inspector “ TestResults . so that the Inspector carrying out ( Routine ) Periodic Testing in thefuture is aware of the presence of such equipment .

□ “ Generic Scheduleof Test Results . “ p/402 . Apprentices .

Aswith the 17[SUP]th[/SUP] Edition 2008 - “ Schedule of TestResults . “ ( Test Results – ► Functional Testing ) RCD time 13 / Other 14 .

Withthe 2011 : the Wording has gone . ( RCD ) – ( mS ) 1 x / 5x / Testbutton operation . ( Same thing -Functional Testing )

Apprentices.
612.13. – p/194 .

The Effectiveness of ANY Test Facility

 

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2392-10: for -&-s . they will work into 2011 .

Keychange is to the “ Schedule of Inspections “ That is to be used when carrying out a ( PeriodicInspection )

“ Now “ a Condition Report. will need to have a “ Schedule of Inspections “ relevant to thePeriodic Inspection . workcarried Out .

BS-7671:2008

Previously . Schedule of Inspections was ► ( Generic ) ◄ & used for both the (Periodic Inspection Report ) & ( Electrical Installation Certificate )

Thisis were -&-s will trip you Up .2392-10 ▲

134.2.2. : The designer of the Installation shall make arecommendation for the interval to the ( First ) Periodic Inspection & Test. as detailed in Part 6 . 2011