***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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EarthFault Loop Impedance .

i) Electrical Earth Fault on a circuitcurrent flows from the Line conductor throughthe Fault . down the CPC.
Alongthe Earthing Conductor provided by the Electricity Company for . TN-S & TN.C.S. or through the EarthElectrode . for a TT System .

ii)The Circuit ( Loop ) then is the Transformers winding ( Impedance )
theSupply Company Line conductor in theInstallation & return Earth conductor ( Résistance )

iii)This Complete Circuit is called the ( Earth Fault Loop) & the ( Earth Fault Loop Impedance ) isthe value in Ohms . Measured

EarthFault Protection for an Electrical Installation .
- Thesupply must have ( One Pole connected to Earth at the Supply Transformer . (Single-Phase ) This creates what is known as a TN- System .
- ( Overcurrent ProtectiveDevice ) MCB . in the Line Conductorwill operate under Earth Fault Conditions provided that enough current flows .

Icant . Stress this Enough .
An“ RCD “ is for . 17[SUP]th[/SUP] Edition / Additional Protection “ Only “ :earmuffs:
433.1. Every Circuit shall be designed so that aSmall Overload of long duration is Unlikely to Occur .

Soif your Earth Fault Path is not good enough to allow sufficient current to flowto operate the MCB . Then you must Install a RCD . :17:

Apprentices:
Electricitytakes the path of Least Résistance . if the path of Least Résistance happens tobe Earth .

EarthElectrode Résistance TT .
The Electrode is the point where the Earth isconnected to Earth .
Measuringthis shows how well the System is connected to Earth . if the Résistance is to High then there is a chance that a Fault will find anEasier Path .

Why’s(- Measuring the Earth Electrode Résistanceshows how good the Earth is & whether it will Work .
EarthRésistance of the Fault Loop Impedance . ifthe Fault Loop Impedance in the Earth Conductor is to Highthen the Current may not rise to a Sufficient Level to cause the MCB to trip inthe Required Time .

 

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Prospective Short Circuit Current -( PSCC )
Thisis the Current you might get if you have a “ ShortCircuit “ in your Supply .

 

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O.S.G. . p/33 - Isolation :46:

Isolating & Switching :

Requirement( Means of Isolation should be Provided. 132.15.1. Every fixed Electric ( Motors ) Etc.

537.1.4.
Atthe Origin of the Installation .
Amain liked switch or Circuit Breaker should beprovided as a Means of Isolation & of Interruptingthe supply on Load.

ForSingle-phase household & similar supplies that may be Operated by UnskilledPersons . A Double - Poledevice must be Used for both TT& TN- Systems .

Fora Three-phase supply to an Installation forming part of a TT System . An Isolator must Interrupt the Line & NeutralConductors . ( DP ) in a TN-S or TN-C-SSystem only the Line Conductors need be Interrupted.

ForEvery Circuit : 537.2.1.1.
Otherthan at the Origin of the Installation . Every Circuit or Group of Circuits thatmay have to be Isolated without Interrupting the Supply to other circuitsshould be provided with its OWN Isolating device. The device must SWITCH all Live conductors . in a TT System & all Lineconductors in a TT System.

Apprentices.
TTSystem & all Line conductors in a TT System
►► Line conductors(s) ( Line & Neutral ) BothLive conductors . -&-s L/N

Asthe Regulation tells Us . p/118 : Isolation .

537.2.Note : Isolation is a “ Function “ intended tomake DEAD for reasons of Safety all or adiscrete section of the Electrical Installations by separating the ElectricalInstallation or Section from Every Source of Electric Energy .

 

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Loop Impedance Testing :

A “ Loop“ in NOT the same as aCircuit . :svengo:
A “ Circuit “ conforms to a Design :hurray:

A Loop may define itself byIncluding Unsuspected Elements where current has found Parallel Paths to Earth .

An Earth Loop determines the Effectiveness of the Protective Device

 

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Prospective Short Circuit Current ( PSCC ) this is theMaximum Short Circuit Current . That could flow in a Event of aFault . It is NecessaryInformation for the Correctsizing of Protective Devices .

The Maximum point of Test for ( PSCC ) is at the Service Entrance . 2392-10
Impedance is best Tested at the Farthest Point from theIncoming Supply .

 

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A “ Circuit “ conformsto a Design . Example :

The Job am on . Wants RCBOs – Only :svengo:

O.S.G. . p/19
Type of Protective Device .
The Consumer Unit ( or DistributionBoard ) ( DB ) containsdevices for the Protection of the Final Circuit . AGAINST

i) Overload - 433.Regulations .
ii) Short – Circuit -434. Regulations .
iii) Earth Fault . 434. Regulations.

Function (i) & (ii) are carried out usually by One Device . Circuit Breaker .
Function (iii) may beCarried out by the CircuitBreaker provided for function (i) & (ii) . or by an RCD .

An RCBO . being a Combined – Circuit Breaker& RCD . Will carry out Functions .(i) – (ii) & (iii) ◄◄ :hurray:

Conforms to a Design . BritishStandards – 2008 :20:

 

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2392-10 : some Revision . :icon_bs:

Prospective Fault Current ( PFC ) is the ►►Highest of the ►► ( PEFC ) & ( PSCC ) ◄◄
it is the Greater of these Two . Prospective Fault Currents . :uhoh2:

Remember the Difference in wording between ( Guidance ) & ( Regulation ) :dots:

O.S.G. 10.2.2. – States . That with the Supply Connected .
i) Check polarity withthe Supply Connected . Using an approved voltage indicator .
ii) Earth Electrode résistanceusing a Loop Impedance tester
GN-3 . p/48 .
Switch OFF Supply before Disconnecting the Earth .
A Loop Impedance tester is connected between the Line conductor at the Source of the TT Installation & the Earth Electrode . & a test performed . The Impedancereading taken is Treated as the Earth Electrode résistance BS-7671:2008 . Ra - I∆n ≤ 50V.
iii) Earth Fault Loop Impedance .
i) GN-3 . p/49 . Toverify that there is an Earth Connection .

iv) Prospective Fault Current Measurement . if not determined by Enquiry of the Distributor .
Prospective Fault Current ( PFC ) is the ►►Highest of the ►► ( PEFC ) & ( PSCC ) ◄◄

GN-3 . p/52
Prospective Fault Current .
Regulation 612.11. requires that the Prospective Fault Current (Ipf ) under both Short-Circuit & Earth Fault Conditions . be Measured . Calculatedor Determined by another method . At the Origin & at other relevant pointsin the Installation .

GN-3 . 434.5.1. States that the Breaking capacity rating of Each Protective Device shallbe NOT Less than the Prospective Fault Currentat its point of Installation
The “ TERM “ Prospective Fault Current “ includes “ the Prospective Short-Circuit Current & the Prospective Earth Fault Current . it is the Greater ofthese Two Prospective Fault Currents . Which should be Determined & Compared with the breaking capacity of the Device .

v) Functional Testing . including RCDs & Switchgear

-&-s : 2392-10 .
As Testers . Sorry “ Inspectors “
On a NEW Installation you Must Not Carry Out Live Tests until you have ( Verified ◄◄ ) the Earth Continuity ◄◄ & Other Dead Tests – “ Polarity “

 

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2392-10 : Calculationsare Great . – But nothing is Gooduntil Proven . :38:

 

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Chapter 61 : p/155 .2392-10

Initial Verification . ( Inspection & Testing ) Two different Words . :icon_bs:

611 – Inspection .
612 – Testing .

 

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2392-10 . ( T ) Some times when you see it written . You get a better Picture . Yeah . Amber . :icon_bs: :uhoh2:


610.1. Every Installation shall . during its Erection& on Completion before beingput into Service . be Inspected & Tested to Verify . as far as is reasonably Practicable . that the requirementsof the Regulations have been met .

610.2. Sections . 131 .311 to 313 & 514.9.1. ( for information required for a Fundament Principles )
610.3. The Verification shall include comparison of the “ Results “ with the relevant criteria to Confirm that therequirements of the Regulations have been Met .
610.4. For an Addition orAlteration to an Existing Installation . it shall be Verified that the Addition or Alteration complies with the Regulations .& does not Impair the Safety of the Existing Installation .

610.5 – The Verification shall be Made by A Competent Person .
610.6. On Completion ofthe Verification .According to Regulations . 610.1. to 610.5. a Certificate orCertificates . shall be Prepared .

Section 611 – Inspection :
611.1. – The Inspection shall procedure Testing & shallnormally done with that part of the InstallationUnder Inspection . ( Disconnected ◄◄ ) from theSupply .

611.2. – The Inspection shall be made to Verify that theInstalled Electrical Equipment is .
In Compliance withSection 511 – This may be Ascertained byMark or be Certification furnished bythe Installer or by the Manufacturer ) &

Correctly selected & erected in Accordance with theRegulations . &

Not Visibly damaged orDefective . so as to Impair Safety .

612 – Testing : ▼▼
The tests of the Regulation 612.2. to 612.13 . Where relevant . Shall be carried Out & theresults compared with the relevant criteria .

612 – Testing : ▼▼ PAGE– 157 . -&-s big time
The tests of Regulation 612.2. to 612.6. . Where relevantshall be carried Out ( in that Order ◄◄ ) before TheInstallation is Energised .

Where the Installation incorporates an Earth Electrode . Thetest of Regulation 612.7. shall also becarried out ( Before ◄◄ ) TheInstallation is Energised .

612 – Testing : ▼▼ PAGE– 157 . -&-s big time .
If any Test Indicates aFailure to comply . that Test . & any preceding tests . The results of whichmay have been Influenced by the Fault has been Rectified .


Chapsplease hit the Thank you Button . I don’t know if you want any more of thisStuff . ???????????? Amber :dots:

 

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What the Regulations Requires -

612.12. Check of Phase Sequence .
For Multi – Phase circuits there is a Requirement to ( Verify ) ThatPhase Sequence is ( Maintained ) :icon_bs:

 

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2392-10 : We use this Dayin Day out . Yeah . “ ConsumerUnit “ :icon_bs:
Section 514 : Identification& Notices .

514.8. – Identification of the Protective Device .
Circuit Protective Devices are required to be Arranged & Identifiedso that the Circuit Protected may be Easily Recognised .

 

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Workingmy why around 17[SUP]th[/SUP] Edition :hurray:

Making you Aware .

538.4. Residual Current Monitor ( RCM )

An– RCM permanently monitors any leakage current . in the downstreamInstallation or part of it . such a device is NOT intended to provide protection against Electric Shock

538.4.1.
InSupply Systems . RCMs may be installed toreduced the risk of operation of the protective device in the event of excessiveleakage current of the Installation or the connected appliances .

The RCM is intended toalert the User of the Installation before the protective device isactivated .

Wherean RCM is installed Upstream of the RCM . it is recommended that the RCM has arated residual operating current . NOT EXCEEDINGa THIRD of that of the RCD

 

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Short Circuit :- Two or more Live conductors touching each other . :svengo:

Evaluation of Thermal Constraints .
Fault current ( I )is found from .

( I ) = Uo / Zs .

Where:
Uo = nominal Line voltageto Earth .
Zs = Calculated value of Loop Impedance .

( I ) = 230 ÷ 0.53 = 434A

 

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Part1 : Fundamental Principles . :6:

Regulation– 132.13 . Documentation for the Electrical Installation.
Requiresthat documentation . required by regulation – 514.9. & part 6 . isprovided for Every Electrical Installation .

Regulation– 134.1.1. Erection & InitialVerification of Electrical Installations .
Requiresthat good workmanship shall beundertaken by Competent Persons & further requires the “ ManufacturesInstructions shall be followed . Etc .