***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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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

If you Know → Need to know. Yeah

Volts÷ Ohm’s → Need to know =Amps
Volts÷ Amps → Need toknow = Ohm’s
Voltsx Amps → Need toknow = Watts
Watts÷ Amps → Need toknow = Volts
Watts÷ Volts → Need toknow = Amps
Ampsx Ohm’s → Need toknow = Volts

Resistanceof the Length of Cable ….. Ohm’s x Current Drawn….. Amps = Volt Drop … Vd

FlexibleCables ?

Ifwe are “ Overloading “ a Cable : Keep inmind that the cable . Has a running current . by using more it will get Hot& eventually Melt the PVC coating . ( Plain English – Use the Right Size )
TheRegulations . my be a pain in the But !!There for a reason some kind person sitting at a desk has done the Work for us

Definitions/ p24 – Flexible Cord . A flexible cable in which the Cross-sectional area ofEach Conductor does Not Exceed 4.0mm[SUP]2[/SUP] ( PS. You will get this on CoP -&- ) 2011

BritishStandard BS-7671 : is set of Electrical Standards published by the IET in the UK .
TheStandards are NOT a LEGAL REQUIREMENT but a set of Standards which will ensurea Safe & Proper Electrical Installation

Aswe Say in the Trade ?? Some Contracts Specify that the Electrical Equipment ofthe “ Installation “ will CONFORM to BS-7671 & so at this Point they become( LEGALLY BINDING on the INSTALLER )

Fora Designer point of View .

Definition)- MechanicalProtection

522.6.5.(v) A cable installed under a floor or above a ceiling shall be run in such a positionthat it is NOT liable to be Damaged by contact with the floor or ceiling ortheir fixings .
PlainEnglish ) Be mechanically protectedagainst Damage . Prevent penetration of the Cable by Nails & Screws . & Like ( Keep Cables Out of Harms Way )

2392-10. We will use this on Part P . also

iii)&& (v) require Conduit & Trunking to be Earthed

• Whatis Mechanical Protection !!

Example : FP-200 is Fire Résistance? say 30 mins

Pyro: Mechanical Protection & Fire Résistance (2/1 )
i)Protection of cables against Mechanical Protection
ii)Protection of cables against Damage by Fire …( Long history of performing extremelywell in Fire(s) - Beyond the duration necessary to ensure theObjectives !!

MostDesigners specify either MICS → ( Pyro ) orProprietary Fire-resisting Cable(s)
Asa young Designer . ?? What would you Use .

?Mechanical Protection – running the cables on Cable Tray .

CableTypes ??
Twomost Important thing about Cable(s)

i)Insulation Properties’ are One of the Most Important things to consider whenselecting a Cable for a Circuit .
(if the Insulation is not rated for the Environment the circuit is installed intit can have a number of Detrimental Effects on its operation & Safety )

ii)Mechanical Protection . for cables is probably as Equally as Important as itsInsulation if the circuit with limited Mechanical Strength .
( Installedin an Environment where there is a risk of it coming into contact with Heavy Objects. as for our point of view ? )

522.6.5.(v) A cable installed under a floor or above a ceiling shall be run in such a positionthat it is NOT liable to be Damaged by contact with the floor or ceiling ortheir fixings .
PlainEnglish ) Be mechanically protectedagainst Damage . Prevent penetration of the Cable by Nails& Screws . & Like ( Keep Cables Out of Harms Way )

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

SeparatedExtra Low Voltage ( SELV )
Isthe most common method of providing protection . ElectricalSeparation ( Which means NO Electricalconnection between the SELV circuit &higher voltage systems )

* BS-7671 . 2392-10 some questions -&- “ Initial Verification “
Asa Tester .

* Regulation 610.1 - Theseare Hand & Glove with Q/As -&-s
Everyinstallation shall during Erection & on Completion before being put into Service. be Inspected & Tested to Verify . So far is reasonably practicable . Thatthe regulations have been met .

( Precautions’shall be taken to avoid Danger to persons . Livestock & to avoid damage toproperty & Installed Equipment during Inspection & Testing )

Certification& Reporting –

* 632.4 . Defects or omissions revealedduring Inspection & Testing of the Installation Work covered by theCertificate shall be made good before the Certificate is issued .

YoungApprentices !! InsulationRésistance Testing . ( IR)

Why we REMOVE LAMPS .

TheCOIL that is that is the LAMP FILAMENT is Effectively creating a Short Circuit between the Line& Neutral conductors

Let’slook at it in an other way - The bulb is only Designed to operate with 230V ( by applying 500V? would we do Damage )

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

All cable(s) have Electrical Résistance. So !

Therewill be Heat loss ( Energy loss ) when they Carry Current . This loss appearsas Heat & the Temperatureof the cable rises.
i)The rate of Heat loss is a function of the difference in Temperature between the Conductor & thesurroundings .
ii)“ Making it “ As the conductor Temperature rises – so does its rate of Heat Loss

Backon to Cable(s) .
Cablesare designed to be able to withstand a certain amount of Heat
Copperis a very good Electrical Conductor ( 300mm[SUP]2[/SUP])
Thismeans that the Résistance of a length of Copper Cable is relatively low .

Aluminiumcable would have Nearly Twice the Résistance of Copper Cables with the sameDimensions . ( 500mm[SUP]2[/SUP])
That’sthe reason why we stop using them / partly Cost

- Therésistance of the cable )- A higher résistancecable will get hotter at a given Current .
-The Insulation on the cable )- This will tend to keep it warm like a quilt .
- TheEnvironment of the cable )- were it is situated .

DesignCurrent ( Ib )

i)The first stage of the Design Current is to determine how much current will flowin the Circuit .
ii)This Current is known as the Design Current & is the FULL LOAD CURRENT of the CIRCUIT.
iii)Depending on Load ????

Singlephase . 230V resistive .
I= P/V . at this stage you areCalculating the Design Current )- I = 2000 ÷ 230V = 8.70A

Three-phaseInductive Load . power consumption of 30.000Watts – 30kW
Powerfactor – 0.95

atthis stage you are Calculating the Design Current )- I = P --- √3 x V cos Ø

I= 30000 --- √3 x 400 x 0.95 = 45.58A

[ √3x 400 x 0.95 ] = 658.1793069
30000 ÷ 658.1793069 = 45.58028441
Roundoff . = 45.58A

UsefulJunk . Ambient Temperature( Ci )
RememberCables must give off Heat … ( Surroundings’ ofthe cable . the more difficult it is for the cable to get rid of Heat )

Tables 4B1 & 4B2 – 17[SUP]th[/SUP] Edition . Note 30°C– 4B1 … Note 20°C – 4B2. & The O.S.G.

Wording C.C.C. - We will see itas sometimes as ?? Tabulated C.C.C. / Iz– de-rated C.C.C. ( Current Carrying Capacity )

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

Polarity:
Correct polarity is achieved by the correct termination of conductors’ to the terminals of all Equipment .

Polarity:
Is either Correct or Incorrect– There nothing in between .

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

Example. “ it still forms part of Designing “

Cable Calculations ( The Whys & How’s ) it’s a Start

- Workout the design current ( Ib ) … I = P/V
-Select the Protective Device size ( Ib ≤ In )
- if we need to . Obtain all correction factors . Ca .Cc . Cg . Ci .
-Calculate ( Iz ) … Iz = In ----- Ca x Ci x Cg x Cc
-Select Conductor sizes . With ( Iz ) use the tables Appendix 4 & choose . ( Iz ≤ It )
-Calculate Volt-drop . Use design current ( mV/A/m ) value from cable table .The circuit length then ÷ 1000 [ Volt-drop Ib x ( mV / A / m ) x L --- 1000
-Calculate ( R1 + R2 ) Using table ( 9A / 9B & 9C ) find the mΩ/m value ÷1000 then apply multipliers . ▼
(R1 + R2 ) = 9A --- 1000 x 9B x 9C = Ω
- Calculate( Zs ) ……. ( Zs = Ze + R1 + R2 ) = Ω
-Verify ( Zs ) values with BS-7671 – using the tables in section 41 ensure calculatedvalues is less than the Tabulated values . ETC
- Calculatethe Fault Current .. Using nominal voltage & ( Zs ) . I = Uo/Zs = A . PS – Usefuljunk Regulations p/35 . Symbols (If ) fault current ( A ) 442.2.1
-Establish the disconnection time . Usingthe fault current . device type & time / current graphs in Appendix 3 obtainthe Expected Disconnection Time .
- Calculateminimum size of CPC . Using the Adiabatic formula . Input all values ( Including k factor ) & work out minimum size ofCPC . Then compare with our chosen CPC size .

HiBruce

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

559.6.1.5. Fixing of the Luminaries.

Thevast majority of light fittings are installed above head height . so clearly itis Important that the fittings are secure BS-7671 requires that the fixing for somethingas Light as a Pendent Set has to be capable ofsupporting a Mass of 5kg .

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

SorryI have to break this into two parts .

Firstlyyou should be aware there are 3 Methods / Consumer Units available . [ I will try & open the Examples for you]

Knowledgeis the greatest arsenal we have .

Thereare Single Load – RCD .
Split Load RCD & RCBO

► Just a Point to Note here . The RCD is not just a Manually OperatedInsolating Switch – Sensitive Safety Device which cuts OFFin fraction of a second if it Senses an Earth Fault.
► Question ? it is NotPractical to fit One RCD to protect the Whole House . !! Why Tripping .
Ido want to open a mine field here . “ Division of Installation “
314.Every Installation shall be divided into Circuits . as necessary to ? (i) Avoidhazards & minimize inconvenience in the event of a Fault . “ So “ One RCDat the Main incoming does not meet this criteria . ( iv)

Example)- 8 – Way 30mA DPRCD … ( 1 x RCD) IP2X .
BS-EN 60439-3……(British Standards )The country hasStandards for & reasonNOT made in China
100 Amp .
Example)- 6A ( SP) type B / MCB …. 40A ( SP ) type B / MCB → This could be used for a Shower& Power Circuit
( SP ) meaning -Single – Pole ( Line Only )
( DP ) meaning -Double – Pole ( Line& Neutral Only ) with ( L & N – Earth must be Added )

Asa Young Designer this must seem daunting . Don’t Worry
gointo the Forum& Ask Questions . We wereApprentices at one Time . Yeah .

Meaning!! BS-EN 60439-3
Regulation530.3.4. ( Consumer’s Controlgear ) Learning Curve .
Foran Installation with a 230V Single phase supplyrated up to 100A that is under the control of Ordinary Persons . Switchgear & Controlgearassemblies shall either comply with BS-EN 60439-3& Regulation 432.1. or be a Consumer Unit incorporating components &Protective devices specified by the Manufacturer complying with BS-EN 60439-3 . including the conditional Short-circuit testdescribed in Annex ZA of BS-EN 60439-3 .

Asa young Designer . if we look in O.S.G. p/17 – 2.2.5
Consumer’sControlgear
AConsumer Unit ( to BS-EN 60439-3- Annex ZA ) is for use on Single-phase Installation’s up to ( 100A ) itincludes . 530.3.4
•A Double pole isolator .
Fuses. circuit breakers or RCBOs for protection against Overload & Faultcurrents . &
•RCDs for Additional Protection against Electric Shock . ( Anything that moves . RCD it & Earth it )RCD / RCBO – remember that an RCBO is RCD/MCB .

Designer/ Electrician :
Whenspecifying Enclosures & their Accessories . it is Important to bear in mindExisting Standards to which the Products are Manufactured&/or Tested .
TheStandards are Written to Ensure CONFORMITY .Integration with other Products & Safety ofPersons & Equipment.

Thisto keep in Mind -
Overload.
ShortCircuit ↔ ( Fault Current )
EarthFault .
Wewill go there an other day { PS am not asking you to take this in all in One .am opening your eyes to things as a Young Designer }

IP4X . Rating’s on Consumer Units . “ Meaning “
RedCover - The Only Requirement of the Regulations ( BS-7671:2008) – 416.2.2. forthe Initiated ↔ ( is the TOP SURFACE of theEnclose ) IP4X/ IPXXD
(with Apertures Intended to exclude Particles of Greater than ( 1mm diameter ) To stop Dirt falling into the Enclosure

IP2X . Rating’s on Consumer Units . “ Meaning “
TheBottom & Sides ofthe Enclosures Only need to be IPXXB or IP2X ( The Testis made with a Metallic British Standard finger Test – 12.5mm diameter .
“Plain English “ FullPenetration into the Enclosure is NOT Allowed . Let ask you this ??

[Both Joints of the finger may be Bent through 90° degrees with respect to theAxis of the Finger but in ONE & the SAME direction ]
AmUsing the Wording - Finger is PushedWithout UNDUEFORCE . So there you have it . in One
Young Apprentices this is Only Guidance

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

ConsumerUnit(s)
MCBs/ RCBOs are sitting on the bottom off Buzz Bar “ Copper Bar “ Feeds Mainspower to MCBs / RCBOs
MCBs/ RCBOs are Clipped onto a DIN rail

Justa point to Note :
Wecan get – MCBs Colour coded dolly’s allow quick Visual Identification of Ratings .now – BS-EN 60898

Whatis a Split Load .
100A Main Isolator → outgoingways ?? MCB / RCBOs ( 4) Non-RCD side
RCD30mA – 80A → MCBs ( 4 ) RCD side - ( Additional Protection ) 30mA RCD Basic Protection / Touching Live Parts . ARCD is a Fixed Equipment
RCD30mA – 80A → MCBs ( 4 ) RCD side

TestingRCD buttons – Do Not Hold the button more than 2 seconds [ You are crating aFault in the RCD for Testing Purposes]

RCDs- 0° & 180° deg ( ½ - 1x – 5x )times ( This sign is for Alternating Current ≈ A.C. ) Marked on the RCD - 230V . SinglePhase

Donot Overlook – as a Tester that ( When all the Tests are Complete the Testbutton to Ensure this Functions Correctly )

Pointto Note . The 17[SUP]th[/SUP] Edition tells usto test the Button on an RCD “ But Not “Before or After Testing RCD .

Megger1552 )- an RCD Tester is an ElectronicDevice which draws current from the Supply for it’s Operation .
Thiscurrent is usually of the Order of a few mA s which is taken from Line & Neutral of the Supply under Test(s) Single-phase

For-&-s Purposes Exams’ ?? TestingResidual Current Devices ( RCD )

-&-s– i) BS-200mS ……………….. Older
-&-s– ii) BS-EN 300mS

RCDto Achieve Automatic Disconnection in the case of a Fault . ( If )

411.3.2.1.
Requires. “ in most cases “ that a Protective Device ( MCB ) shall Interrupt the Supply to a Line Conductor of a Circuit or Equipment in the eventof a Fault of Negligible Impedance between / Line Conductor& part or a Protective Conductor for the Circuit or Equipment within theAppropriate Required Disconnection Time .

“Plain English “
2392-10- TN- 0.4 seconds 41.1 – 411.3.2.2. tells us The maximum Disconnection – 41.1. shallb e applied to final circuits NOT EXCEEDING 32A [Domestic Installation(s) ]

 

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Re: ***Cont../ Useful Information for Electricians’ & Apprentices***

Working my way Around the 17[SUP]th[/SUP] Edition :

555)- Transformers .

Thereare Only three Regulation(s) . 555.1.1. to 555.1.3. relating to Transformers asItems of Equipment .
Throughtheir Installation . subject to the generality of BS-7671:2008

Thefirst > Autotransformers & Step-up-Transformers
Autotransformers& requires where such transformer is employed & is connected to acircuit with a Neutral conductor that conductormust be connected to the common terminal of the Winding

Regulation555.1.2. Precludes .
Theconnection of Step-up Autotransformers to an ( IT ) system . in all cases wherea Step-up Transformer is used - Regulation555.1.3.calls for a Linked Switch to disconnectall Live Conductor(s) Line & Neutral – Simultaneously fromthe Supply ( DP )

 

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Working my way around the 17[SUP]th[/SUP] Edition .

Principal Requirements for Devices for General Emergency Switching

Regulation537.4.2.3.
( Requirement )- Where practical . non-automatic device
Regulation537.4.1.2.
( Requirement )- Switching of all the live conductors( Except the Neutral where excused by Regulation 537.1.2. ) is required if there is a Risk of Electric Shock
Regulation537.4.2.1.
( Requirement )- Capableof Switching Load Current .
Regulation537.4.2.1.
( Requirement )- In the case of Motor(s) . Must be capable of switching stalled-rotor current .
Regulation537.4.1.3.
( Requirement )- To be Single-ActionDevice .
Regulation537.4.2.7.
( Requirement )- Identified as to purpose ( Appropriately Labelled )
Regulation537.4.1.3.
( Requirement )- Device to act as directly as Possible onCircuit concerned
Regulation537.4.2.5.
( Requirement )- Suitably Located
Regulation537.4.2.3.
( Requirement )- If device is used to operatecontactor controlling the circuit . Switching is requiredto de-energize coil . or another technique of suitable reliability mustbe used
Regulation537.4.2.6.
( Requirement )- If Push Button. must be the Latching OFF TYPE
Regulation537.4.2.8.
( Requirement )- Plug &Socket-outletNOTACCEPTABLE
Regulation537.4.2.4.
( Requirement )- Operating Knob . Lever or Button . PERFERABLY Colour RED .

I have shorted some stuff in wording .

 

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Young Apprentices .

Wording– Two Words in different contents ( EmergencyStopping ) as opposed to ( Emergency Switching )

 

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LearningCurve Here .

Emergency Switching )- devices must “ Regulation 537.4.2.1. “ must be capable of Interrupting the Supply ON LOAD
Plain English – The Full Load Current )

Emergency Switching )- requirements apply to ALL EQUIPMENT where a HAZARD may be EXPECTED in NORMAL USE.
Plain English – Located in a ReadilyAccessible Position & Operator is not put in DANGR - that could be you one day

 

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Difference in Wording

Regulation 537.4.1.3. – Demands that an Emergency Switch Arrangement is such that onesingle action will Interrupt the appropriate supply .
Regulation 537.4.1.3. – Means for Emergency Switching shall act as directly as possible onthe appropriate supply conductors .

 

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Regulation(s)Table 53.2 ( Restriction on Use as Isolator ) Note 3 bottom of page – read

Fused ConnectionUnit : ( FCU ) Yes / Note 3
Whatthe Regs are saying – Suitable for OFF LOAD operation Only You will be . Isolationof current using equipment . ( Fuse in Pocket ????? )

2392-10)- keep in mind you may have a TT System Except where Neutral requiresIsolation .
PS – I have been known to use lock off Spurs Unit / padlock

 

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Testing

IsolationRequirements relating to System Types

TN-C ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only
TN-C ( Number ofPhases – Three – Phase ↔ ( Isolationrequired for ) Three Line(s) Only

TN-C–S ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only
TN-C–S ( Number of Phases – Three – Phase ↔ ( Isolation required for ) Three Line(s) Only

TN-S ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only
TN-S ( Number of Phases – Three – Phase ↔ ( Isolation required for ) Three Line(s) Only

TT( Number of Phases – Single – Phase ↔ (Isolation required for ) Line & Neutral
TT( Number of Phases – Three – Phase ↔ (Isolation required for ) Three Line(s) & Neutral

IT( Number of Phases – Single – Phase ↔ (Isolation required for ) Line& Neutral
IT( Number of Phases – Three – Phase ↔ (Isolation required for ) Three Line(s) & Neutral