***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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• Surge current Or Inrush current . the maximum .instantaneous input current drawn by an electrical device when first turned on.

• BS-7671:2011 . put specific responsibility onthe Installer . 510.3 . requires that the Installer takes intoAccount the Manufacture’s Instruction’s .

 

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Faultcurrents to be considered include faults between Line conductors & Earth .Line conductors & Neutral . & Line to Line conductors .
most domestic installations the ( PFC ) the value canexceed until 6kA . up to which value the ( Icn & Ics ) values are the same.
highestfault currents will arise with Three-phase Line conductors shorting together & to Earth .

 

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Just a reminder .

So where does this [ 0V ] or[ Zero ] potential come from . The Earth .
p/26 . Earth .
The conductive mass of the . Earth .whose electricalpotential at any point is conventionally taken as [ Zero ]

 

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Just a reminder . 2392-10 .
Earthing matters will come up in Exams .-&-s

Conductors used in such connections . are called “ Protective Conductors “ . & theycan be . subdivided .

Domestic Installations - Circuit protective conductors . CPC. For connectingexposed-conductive-parts to the [ MET ]
Domestic Installations - Main protective bonding conductors . for [ Bonding] together main incoming services .

 

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• Whencompleting Additions to a circuit such as an extra socket

a. state the type of Certificate to be issued
b. list three items of information that need to be entered on the form
c. state to who the form should be given.

Solution

a. A Minor Electrical Installation Works Certificate.
b. (i)- Details of the existing installation . (ii)- Description of the minorworks . (iii)- Essential Tests / Test results.
c. The person ordering the work.

Q/As . it’s all you need to know to passyou on your Exams . 2392-10 . :banghead:

 

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( MEIWC )
Minor ElectricalInstallation Works Certificate . are used for . “ Minor Works “ Only .

It come under this . Certification & Reporting : Regulation aretelling you the [ Answer’s ] :13:

Notes p/394 :
Minor WorksCertificate is intended to be Used for . Additions & Alterations .to aninstallation that Do Not Extendto the provision of a New Circuit .

Minor ElectricalInstallation Works Certificate. Q) Inspecting & Testing shouldalways be carried out . A) Irrespective of the extentof the work undertaken .


Let’s open it Up . Q/As -&-s .

Q) state to who theform should be given. A) The personordering the work . 2392-10 :

P/394 : ( To be appended to theCertificate )

2392-10 . You : should havereceived an “ Original “ certificate & the contractor should have retained a ( Duplicate )
if you were the person ordering the Work .

►► “ BUT “ not the Owner of the installation . “ You “ should pass this Certificate . Or a copy of it . to the “ Owner “

Point to NOTE here . MinorElectrical Installation Works Certificate.

2392-10 . -&-s are looking for . The right Certification& Reporting : for the Job .

This Certificate isNOT appropriate if yourequested the “ Contractor “ to undertake more [ Extensive Installation Work ]
For which youshould have received an [ Electrical InstallationCertificate ] EIC .

Regulations . are saying that ? you cannot use a Minor Certificate for Major Work . Etc .

Minor ElectricalInstallation Works Certificate. Notes . : are used for “ Minor Work “ that Do Not Extend to a New Circuit .

p/394 . Regulation aretelling you the [ Answer’s ]

□ The addition of a socket outlet to an “ Existing Circuit “
□ The addition of a Lighting point to an “ Existing Circuit “
□ Relocation of a light switch .
□ Can also be used for the replacement ofaccessories & luminaries .

□ NOT : for the replacement of distribution boards Or similar items .

 

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Part 4: Declaration

I/We CERTIFY that the said works do not impair the safety of the Existing Installation, that the said works have been designed, constructed, inspected and tested in accordance with BS 7671:2011…(IET Wiring Regulations), amended to……………………(date) and that said works, to the best of my/our knowledge and belief, at the time of my/our inspection, complied with BS 7671 except as detailed in Part 1.

( MEIWC)

 

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Inspection& Testing : 2392-10 : 2011 . -&-s . “ InitialVerification “

Ifthe Inspection & Tests . are Satisfactory . a signed ( EIC ) 631.4 . together with a . Schedule of Inspections .& a Schedule of Test Results . 632.1 .
( Asin Appendix G ) are to be given to the person ordering thework . 632.3.

▲ (EIC ) p/391 . Bottom page . Regulations are telling you the Answers. 2392-10 .
Schedules : The attached Schedules are part of this document & thisCertificate is valid only when they are attached to it .
………….. Schedules ofInspections & ………… Schedules of Test Results are attached.

 

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InspectionProcess . “ Wording “

VisualInspection . 2392-10 :

Wesee the words : Omission ?? . of appropriate sleving on Lighting Switch conductors &Two-way lighting strappers .

 

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Remember - aLive conductor includes the Neutral also .

2391-10: prepare for taking the Exam .

Studentmust be aware of the correct use of Terminology when Answering Questions .Marks will be lost for Incorrect Use . “Nil Pwa“ - No points

Using: Completion Certificate “ instead of . ( EIC) Electrical InstallationCertificate .
Using: Electrical Inspection Certificate “ instead of . ( EIC ) Electrical Installation Certificate .
Using: Initial Inspection Certificate “ instead of . ( EIC) Electrical InstallationCertificate .
Using: Minor Work Certificate “ instead of . ( MEIWC ) Minor ElectricalInstallation Works Certificate . ◄► This is myFull Tile . Exams

2392-10:
Thisdocument is made up of Three-parts : ( 1. EIC ) 2 . Schedule of Inspections : 3. Schedule of Test Results : Exams .

( EIC ) ThisCertificate must be issued for a completely new Installation .
( EIC ) must beaccompanied by a Schedule of Test Results & a Schedule of Inspection .Without these two documents . the ( EIC ) is notValid . p/392– ( 2) ****

An Inspection & Test which is carried out ona [ New Installation ] to prove compliance is called an [ InitialVerification ]
p/395: Schedule ofInspections – ( forNew Installation work Only )

[ Initial Verification Inspection]
Thisdocumentation which should be completed is the . Electrical InstallationCertificate . ( EIC ) this must be accompanied by a Schedule ofTest Results & a Schedule ofInspection .

Thecertificate issued for an Initial Verification must be accompanied by aschedule of : ????
a.Test results only .
b.Inspections only .
c.Tests & schedules of inspections .
d.Schedule of inspections . & Schedules of test results . “ take your best Shot “ :icon_bs:

“ Facts“
▲ (EIC ) p/391 . Bottom page . Regulations are telling you the Answers. 2392-10 .
Schedules : The attached Schedules are part of this document & thisCertificate is valid only when they are attached to it .
………….. Schedules ofInspections & ………… Schedules of Test Results are attached.

 

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Allinformation given by myself on these forums is used at entirely your own riskand is not necessarily the view of www.electriciansforums.net.

Justfor reading “ purposes “

ExtractFans in Bathrooms & Shower rooms .

- Ameans of Isolation to enable the fan to be separated from the source of energybefore gaining access to Live parts .
Themeans of Isolation would be provided by the device at the Origin of the Circuit. MCB – BS- EN 60947-3 Fan Isolatormounted adjacent to the fan

BS-EN 60947-3 . applies to switches . disconnections. switch- disconnections . & fuse-combination units to be used in distribution circuit & motor circuits of which the rated voltage does notexceed 1000V . a.c. or 1500 d.c.

-A means of switching off the fan for the purposes of Mechanical maintenance .cleaning .

BS-EN 60947-3 . fan Isolator mounted adjacent to the fan would fulfil therequirement for switching off for Mechanicalmaintenance . Regulation – 537.3.2.4. .requires the open position of the contacts of such a switch to be clearlyindicated .

-A functional switch to enable the fan to be switched “ On “ & “ OFF “ this functionalswitch may not be required where a . humidistat is used as a means of control .

Any suitable switch in table 53.2. of BS-7671:2011 would fulfil the requirements forthe functional switching . for such rooms without a window the fan is usuallyconnected to the light switch . Or a separate switch provided for rooms with awidow .

□ ExtractFans with a “ Run-on “ timer & / or humidistat .

BS-EN 60947-3 . fan Isolator .
Mountedadjacent to the fan would provide the appropriate means of switching “ OFF “ for Mechanical maintenance . Where theisolator switches both the switch wire & permanent Line conductor this would also provide a meansof [ Local Isolation ] where access to Live parts is required . the isolator should be located adjacent to the fan out with .Zones 0. 1.& 2 in accordance with Section 701of BS-7671:2011

Note; Such isolators also permit the Neutral conductor to be isolated .

□ ExtractFans without a “Run-on “ timer & / or humidistat .

Fanswhich are simply controlled by afunctional switch we would also recommend a BS- EN 60947-3 . fan isolator mounted adjacent to the fan as above. to provide the appropriate means of switching “ OFF “ for Mechanicalmaintenance . & local isolation . this is particularly important ifthe functional switch is mounted outside the room . consequently out with thecontrol of the person working on the fan .

ElectricalFixtures . Building Standards . requires that these fixtures can be Operated Safety .

P/286: BS-EN 60947-3 . – 533.1. 2011 .

 

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Methodsof determining ( Ze )

Threemethods : Calculation . Enquiry . Measurement . must be used todetermine ( Ze )

Thedeclared maximum values of ( Ze ) & ( PSCC ) at the Origin .
230VSingle-phase & 230 / 400V Three-phase .

Characteristic: External Earth Fault Loop Impedance . ( Ze )
TN-S- 0.80Ω .
TN-C-S– PME . 0.35Ω .
TT- 21Ω .
Prospective Short Circuit Current ( Isc ) at theOrigin . [ Single-phase supply - 16.000A ] ……….. ( Isc ) meaning . p/38. A .
Prospective Short Circuit Current ( Isc ) at theOrigin . [ Three-phase supply - 25.000A ]

Themaximum values of ( Ze ) & (Isc ) declared by an electricity distributor are based on opposite suppositionsconcerning the impedance of the supplyto an installation . & cannot therefore be expected to occur at the sametime .
Inparticular . the maximum values of ( Ze) are based on the supply of higherimpedance – such as one employing long runs of low voltage cable & a distributiontransformer of lower ( kVA rating ) & the maximum values of ( Isc ) are based on the supply of lower impedance –such as one employing short runs of low voltage cable & a distribution transformerof higher ( kVA rating )

Thedeclared maximum values of ( Ze ) & (Isc ) can . in this case of a . TN-C-S system . be used to estimate the maximum value of ( Ze ) liable to occur in normal circumstances .& hence to determine the range of the possible values of ( Ze )

Example. Consider a Single-phase supply of nominal voltage . 230V . to aninstallation forming part of a TN-C-S system . where the electricity distributor declares a maximum values of ( Ze ) as 0.35Ω & (Isc ) as 16.000A . By Ohms law . it can estimated that .
When ( Isc ) is at is maximum value of 16.000A . ( Ze ) willbe at its minimum value of . 0.014Ω - givenby 230V ÷ 16.000A . therefore . in this case . the normal range of valuesof ( Ze ) should be taken as [ 0.014Ω to 0.35Ω ] in the absence of better information .

Themethod of estimating the minimum value of ( Ze ) given in the Example .strictly applies only to a TN-C-S system . Although it can generally be usedwith reasonable accuracy for a TN-S system also .

Note: Calculator - 230V ÷ 16000 = 0.014 )

The reason why the method referred to inthis Example strictly applies only to a TN-C-S system . is that it uses the maximum [ prospective short – circuit current ] at the Origin .
Onthe assumption that this is equal to the maximum [ prospective earth – fault current ] at the Origin .
- upon which the minimum value of ( Ze ) really depends . Only for a TN-C-S system is the assumptionfully justified . this is because the short – circuit & earth – fault currents in such a system share a common path in the distribution network . due tothere being a combined protective & neutral ( PEN ) conductorin the network . the assumption is only approximately true for a TN-S system . which uses separate protective & neutral conductors throughout .

Enquiry. like calculation . does not verifythat the intended means of earthling is present or that the value of ( Ze ) iswithin the expected normal range therefore . confirmation of theserequirements by measurement is still required before the installation isEnergized .

 

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Sinks .Domestic : Domestickitchens, bedrooms and cloakrooms (unlike bathrooms and shower rooms) are notincluded amongst the special installations or locations in Part 7 of BS 7671 and are not rooms where the resistance of thebody is likely to be significantly reduced. Therefore, normal precautionsagainst electric shock should be adequate and the general rules of BS 7671 are applicable. However,whilst BS 7671:2011 does not forbid the installation of asocket-outlet or other accessory close to a sink in a domestic kitchen, bedroomor cloakroom, the requirements of Regulation 512.2.1 have to be taken into account. Therequirements of Regulation 512.2.1 mean that ordinary BS 1363socket-outlets and similar accessories are not suitable to be installed soclose to sinks or draining boards that they are likely to be splashed withwater or operated with wet hands. Thepenetration of water into an accessory could have serious effects. Waterentering the terminals and mechanism may lead to corrosion, internal arcing,general degradation and eventually malfunction. Additionally, and moreseriously, water may provide a track for the line voltage to be transmitted tothe front cover of the accessory, giving rise to the risk of electric shock.
512.2.1. ‘Equipment shall be of a design appropriate tothe situation in which it is to be used or its mode of installation shall takeaccount of the conditions likely to be encountered.’
A rule of thumb recommendation for domestic premises, to avoid theeffects of splashing, is that ordinary BS 1363socket-outlets and similar accessories should ideally be mounted not less thanabout 300 mm (ideally not less than about 1000 mm), in the horizontal plane,from the extremity of a sink top or wash basin.

 

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“ Definitions“

A “ wiring system “ & “ Conduit “ are defined in part 2 – 2011 .

Wiringsystem “ p/36.
Anassembly made up of cables or busbars . & parts which secure & . if necessary. enclose the cable or busbars .

Conduit“ p/25 .
Apart of a closed wiring system for cables . in electrical installations . allowing them to be drawn in & / orreplaced . but not inserted laterally .

Steelconduit forms part of a wiring system .

- PEN conductors :

Steelconduit must not be used as a combined protective & neutral ( PEN ) conductor . Regulation 543.2.10 .States .
543.2.10 . – A separate metalenclosure for cable shall not be used asa PEN conductor .

Restrictionson Use .
BS-7671:2011. places restrictions on the use ofSteel Conduit .

LiftShafts .
No cable or conduit is to be run in a lift ( orhoist ) shaft unless it forms part of the lift installationas defined in BS- EN 81-1 – Regulation 528.3.5. refers .
Apermitted exception is equipment relating to the lift installation . such aswell lighting . which commonly utilises conduit.

 

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EarthFault Loop Impedance :

A limiting value of earth fault loop impedance . isspecified in the ( ADS ) requirements for TT system under two circumstances.

Wherean RCD . is used for fault protection .
Wherean Overcurrent device . is used for fault protection .

ProtectiveMeasure ( ADS ) for a TT system.
Asfor other types of electrical system . the magnitude & duration of voltagesbetween “ simultaneously accessible “ Exposed-conductive-parts . & Extraneous--conductive-parts . occurring anywherein a installation during an Earth Fault . ADS , achieves this coordinating thecharacteristics of the protective device for automatic disconnection . the earthing arrangements for the installation& the relevant impedance of the circuit concerned .

BS-7671:2011 . States three fundamental requirements for “ Fault Protective “ by ADS in a TT system .
- Protectiveearthing - Regulation / 411.3.1.1.
- Protective equipotential bonding . - Regulation / 411.3.1.2.
- Automaticdisconnection in case of a Fault . - Regulation/ 411.3.2.

Protectivedevices :

Faultprotection . 411.5.2. requires on ormore of the following types of protective devices shall be used . the “ Former being preferred “
- RCD.
-Overcurrent protective device such as .Fuse or Circuit breaker .