-
Please checkout the new poll we will be pushing hard, and want some good stories to come out of this
result are public - you can change your vote over time, which might genuinely be the case from time to time.
Discuss ***Useful Information For The Working Sparky*** in the Australia area at ElectriciansForums.net
OP
amberleaf
Sorry about my Spell Checker , it was Made in Scotland
Broken my Glass , wearing my Wife’s Glasses , PS I like the word Résistance from Halo Halo
British Version ↔ Resistance )
When you mention about the Test Meter you open a can of Worms !!!!! do you take a Proving Unit Every time you use you Test Meter on Mains ?
Ps you never Know HSE may come up with that yet ???? Thank you Amberleaf
Doomed keep up the good work Mate ,
Why Inspect & Test
Inspection & Testing of Electrical Installations
The Electricity at Work Regulations 1989 is a Statutory Document :
It is a Legal Requirement that Statutory Regulations are Complied with ,
Not to Comply is a Criminal Offence and Could Result in a Heavy Fine and Evan Imprisonment to Extreme Cases ,
These Regulations to Ensure that Places of Work Provide a Safe , Well-Maintained Electrical Systems ,
A Simple way to Provide this is to Ensure that Newly Installed Circuits & Existing Installations are Tested on a Regular Basis ,
Electrical Test Certificates are Used to Record what has been Done and Confirm that the Installation Meets the Required Standard ,
British Standard for Electrical Installations is BS-7671
The Requirement for Electrical Installations , within this Standard , Regulation 610.1 States that “ Every Installation “ shall ,
During Erection and on Completion before being put into Service be Inspected & Tested to Verify , so far as Reasonably Practicable ,
That the Requirements of the Regulations have been Met “
Regulation 610.1 States that “ where Required , Periodic Inspection & Testing of Every Electrical Installation shall be Carried out in
Accordance with Regulations ( 621.2 to 621.5 ) in Order to Determine as far as is Reasonably Practicable, whether the Installation
Is in a Satisfactory Condition for Continued Service “ ,
Document P of the Building Regulations 2000 for Electrical Safety came into Effect on 1 Jan : 2005 And was Amended in April 2006 ,
The Purpose of this Document is to Ensure Electrical Safety in Domestic Electrical Installations ,
General ,
This States that Electrical work must Comply with The Electricity at Work Regulations 1989 and that any Installation or
Alteration to the Main Supply must be Agreed with the Electricity Distributor ,
Protection Against Flooding
The Distributor must Install the Supply the Supply Cut-Out in a Safe Place and Take into Account the Risk of Flooding ,
Compliance with The Electricity Safety , Quality and Continuity Regulations 2002 is Required , its Law
For the Apprentice
This is all got to do with Testing ( this is a Start , all you need to know, ive broke it down )
“ Useful Piece of Equipment “
( R1 = R2 ) Socket Adapter
Socket -Tester ( Measure the Effectiveness of the Earth ) the Earth Fault Loop Impedance ,
This will Not Only be Useful for the Safe Isolation of Socket-Outlets ,
It can also be Used for Ring-Circuit Testing and the ( R1 = R2 )
Testing of Ring-Circuit / Radial-Circuit , Without having to Remove them from the Wall ,
Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Rn Neutral
HSE “ GS-38 Leads “ should be :
Flexile and Long Enough , but Not to Long ,
Isolated to Suit the Voltage at which they are to be Used ,
Coloured where it is Necessary to Identify One Lead from the Other ,
Undamaged and Sheathed to Protect them Against Mechanical Damage ,
Measurement Equipment Used by Electricians when Working on or Investigating Power Circuits with a Rated Voltage Not Exceeding 650Volts ,
Heath & Safety ( GS-38 ) Approval Mains Voltage Indictor , ( Maintain Output Voltage for Extended Testing )
GS-38 Test Lamp Fused ( Range 80 / 500 Volts ( 230v / 15watt Pygmy Lamp )
“ The Probes should “
Have a Maximum of 4mm Exposed Tip ( Preferably 2mm )
Be HRC Fused at 500mA or have Current Limiting Resistors ,
Have Finger Guards ( to Stop Finger Slipping on Live Terminals )
Be Colour Identified ,
“ Locking Devices “ Padlock / and other Locking off Devices for MCBs ,
( Warning Notices )
( Live Circuit Warning )
( Danger Do Not Switch On )
Proving Units
Battery Powered Proving Unit , Essential for Safe Use of Voltage Indicators & Test Lamps ,
● Proving Unit Check : all Neon Lamps Located within the Testing Device illuminate for Duration of ( PROOF TEST )
Regulation 4(3) of the Electricity at Work Regulations 1989 Recommends that the Following Procedure be Adopted so that the Device Itself is ( Proved ) –
● Connect the Test Device to the Supply Which is to be Isolated ; this should Indicate Mains Voltage ,
● Isolated the Supply and Observe that the Test Device Now read ( 0V )
● Connect the Test Device to Another Source of Supply to “ Prove that the Device is Still Working Correctly ,
● Lock-Off the Supply and Place Warning Notices “ Only then should Work Commence on the Dead Supply ,
( EAWR ) Regulation 12
Means for Cutting off the Supply and for Isolation :
( EAWR ) Regulation 13
Precautions for Work on Equipment Made Dead :
You must make Absolutely Certain that you and you Alone are in Control of the Circuit to be Worked on
Proving the Circuit is Live you can Proceed as Follows ,
Step 1 , Ensure Voltage Indicator / Test Lamp is Working Correctly , ( Voltage Lights Lit )
Step 2 , Test Between “ All “ Live Conductors and Live Conductors and Earth ,
Using Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Voltage Lights Lit )
Step 3 , Locate the Point of Isolate , Isolate and Lock Off , ( Warning Notices )
Step 4 , Test Circuit to Prove that it is the Correct Circuit that you have Isolated , ( No Voltage Lights Lit )
Using Test-Socket-Adaptor ( Test Between “ All “ Live Conductors and Live Conductors and Earth ) L/N/E ,
Step 5 , Check that the Voltage Indicator is Working by Testing it on a Proving Unit or Know Live Supply , ( Voltage Lights Lit )
Most GS-38 Test Lamps will Trip an RCD when Testing Between Live & Earth ,
Better to Use an Approved Voltage Indicator to GS-38 as most of these do Not Trip RCDs ,
Broken my Glass , wearing my Wife’s Glasses , PS I like the word Résistance from Halo Halo
British Version ↔ Resistance )
When you mention about the Test Meter you open a can of Worms !!!!! do you take a Proving Unit Every time you use you Test Meter on Mains ?
Ps you never Know HSE may come up with that yet ???? Thank you Amberleaf
Doomed keep up the good work Mate ,
Why Inspect & Test
Inspection & Testing of Electrical Installations
The Electricity at Work Regulations 1989 is a Statutory Document :
It is a Legal Requirement that Statutory Regulations are Complied with ,
Not to Comply is a Criminal Offence and Could Result in a Heavy Fine and Evan Imprisonment to Extreme Cases ,
These Regulations to Ensure that Places of Work Provide a Safe , Well-Maintained Electrical Systems ,
A Simple way to Provide this is to Ensure that Newly Installed Circuits & Existing Installations are Tested on a Regular Basis ,
Electrical Test Certificates are Used to Record what has been Done and Confirm that the Installation Meets the Required Standard ,
British Standard for Electrical Installations is BS-7671
The Requirement for Electrical Installations , within this Standard , Regulation 610.1 States that “ Every Installation “ shall ,
During Erection and on Completion before being put into Service be Inspected & Tested to Verify , so far as Reasonably Practicable ,
That the Requirements of the Regulations have been Met “
Regulation 610.1 States that “ where Required , Periodic Inspection & Testing of Every Electrical Installation shall be Carried out in
Accordance with Regulations ( 621.2 to 621.5 ) in Order to Determine as far as is Reasonably Practicable, whether the Installation
Is in a Satisfactory Condition for Continued Service “ ,
Document P of the Building Regulations 2000 for Electrical Safety came into Effect on 1 Jan : 2005 And was Amended in April 2006 ,
The Purpose of this Document is to Ensure Electrical Safety in Domestic Electrical Installations ,
General ,
This States that Electrical work must Comply with The Electricity at Work Regulations 1989 and that any Installation or
Alteration to the Main Supply must be Agreed with the Electricity Distributor ,
Protection Against Flooding
The Distributor must Install the Supply the Supply Cut-Out in a Safe Place and Take into Account the Risk of Flooding ,
Compliance with The Electricity Safety , Quality and Continuity Regulations 2002 is Required , its Law
For the Apprentice
This is all got to do with Testing ( this is a Start , all you need to know, ive broke it down )
“ Useful Piece of Equipment “
( R1 = R2 ) Socket Adapter
Socket -Tester ( Measure the Effectiveness of the Earth ) the Earth Fault Loop Impedance ,
This will Not Only be Useful for the Safe Isolation of Socket-Outlets ,
It can also be Used for Ring-Circuit Testing and the ( R1 = R2 )
Testing of Ring-Circuit / Radial-Circuit , Without having to Remove them from the Wall ,
Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Rn Neutral
HSE “ GS-38 Leads “ should be :
Flexile and Long Enough , but Not to Long ,
Isolated to Suit the Voltage at which they are to be Used ,
Coloured where it is Necessary to Identify One Lead from the Other ,
Undamaged and Sheathed to Protect them Against Mechanical Damage ,
Measurement Equipment Used by Electricians when Working on or Investigating Power Circuits with a Rated Voltage Not Exceeding 650Volts ,
Heath & Safety ( GS-38 ) Approval Mains Voltage Indictor , ( Maintain Output Voltage for Extended Testing )
GS-38 Test Lamp Fused ( Range 80 / 500 Volts ( 230v / 15watt Pygmy Lamp )
“ The Probes should “
Have a Maximum of 4mm Exposed Tip ( Preferably 2mm )
Be HRC Fused at 500mA or have Current Limiting Resistors ,
Have Finger Guards ( to Stop Finger Slipping on Live Terminals )
Be Colour Identified ,
“ Locking Devices “ Padlock / and other Locking off Devices for MCBs ,
( Warning Notices )
( Live Circuit Warning )
( Danger Do Not Switch On )
Proving Units
Battery Powered Proving Unit , Essential for Safe Use of Voltage Indicators & Test Lamps ,
● Proving Unit Check : all Neon Lamps Located within the Testing Device illuminate for Duration of ( PROOF TEST )
Regulation 4(3) of the Electricity at Work Regulations 1989 Recommends that the Following Procedure be Adopted so that the Device Itself is ( Proved ) –
● Connect the Test Device to the Supply Which is to be Isolated ; this should Indicate Mains Voltage ,
● Isolated the Supply and Observe that the Test Device Now read ( 0V )
● Connect the Test Device to Another Source of Supply to “ Prove that the Device is Still Working Correctly ,
● Lock-Off the Supply and Place Warning Notices “ Only then should Work Commence on the Dead Supply ,
( EAWR ) Regulation 12
Means for Cutting off the Supply and for Isolation :
( EAWR ) Regulation 13
Precautions for Work on Equipment Made Dead :
You must make Absolutely Certain that you and you Alone are in Control of the Circuit to be Worked on
Proving the Circuit is Live you can Proceed as Follows ,
Step 1 , Ensure Voltage Indicator / Test Lamp is Working Correctly , ( Voltage Lights Lit )
Step 2 , Test Between “ All “ Live Conductors and Live Conductors and Earth ,
Using Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Voltage Lights Lit )
Step 3 , Locate the Point of Isolate , Isolate and Lock Off , ( Warning Notices )
Step 4 , Test Circuit to Prove that it is the Correct Circuit that you have Isolated , ( No Voltage Lights Lit )
Using Test-Socket-Adaptor ( Test Between “ All “ Live Conductors and Live Conductors and Earth ) L/N/E ,
Step 5 , Check that the Voltage Indicator is Working by Testing it on a Proving Unit or Know Live Supply , ( Voltage Lights Lit )
Most GS-38 Test Lamps will Trip an RCD when Testing Between Live & Earth ,
Better to Use an Approved Voltage Indicator to GS-38 as most of these do Not Trip RCDs ,
Last edited by a moderator:
OP
iceman
thats very helpfull amberleaf but how does one remember all that for the 2391 holy grail exam? lol wot areas do you think i should mainly concentrate on regarding regs and gn3? i knw all the test equitment scales and voltages, certificates for periodic and miner works eic etc testing ring final ciruits insulation resistence polarity ze zs rcd pfc functional testing any help would be great cheers
Please posts your question in the main forums. Thanks.
Please posts your question in the main forums. Thanks.
Last edited by a moderator:
OP
amberleaf
Supplementary Protective Bonding Conductors ( Where Required )
Supplementary Bonding is Required where Circuit Disconnection Times Cannot be Met ( Regulation 411.3.2.6 ) or
Where there is an Increased Risk of Electric Shock ,
Those Areas would be in Bathrooms , Swimming Pools & Other Special Locations ,
Where Disconnection Times Cannot be Met and the Effectiveness of Supplementary Bonding is Required to be Checked
( Regulation 415.2.2 ) a Simple Test is Required ,
Automatic Disconnection is by a Protective Device , Regulations give a Formulae -
( R ≤ 50V / Ia ) if the Circuit is Protected by an RCD , the Formulae Becomes ( R ≤ 50V / I∆n )
When this Formulae is Used , it will Ensure that Any Touch Voltage in the Bonded Area will Not Rise above ( 50 Volts a.c. )
Before the Protective Device Operates ,
The Formulae where a Protective Device is in Place for Automatic Disconnection of Supply ( ADS )
Step 1 , find ( Ia ) for a 5 seconds Disconnection Time ,
Device 32Amp BS- 88 fuse
Appendix 3 / BS-7671 fig 3.3A
32A Device a Current of 125 Amp is Required to Operate the Fuse ,
This Value Can also be Found by Using the Maximum ( Zs ) Value Found Table 41.4 ( 1.84Ω )
Calculation : Ia = Uo ÷ Zs ( Ia = 230 ÷ 1.84 = Ia = 125A
This Method Can be Used for all Protective Devices :
Now the Values Can be Used to Verify that the Area does or does Not Require Supplementary bonding to be Installed ,
( R ≤ 50V ÷ Ia ( 50 ÷ 125A = 0.4Ω ) is the Maximum Value Permitted between Exposed or Extraneous Conductive Parts ,
If when Measured it is found that the Résistance is Higher than 0.4Ω then Supplementary bonding will be Required
The Values of Résistance will Not be the Same for Different Ratings or Type of Protective Devices ,
Where an RCD is Installed to Protect the Circuit the Calculation to find out if Supplementary bonding is Required ,
R = 50v ÷ I∆n ( R = 50v ÷ 0.03 R = 1666Ω , ( 50v ÷ 30mA = 1.666Ω
Bonding is Not well-Understood by Joe Public ,
You have Travelled 20/30 Miles to Fit Kitchen / Completed Everything to Comply with Required Regulations ,
A few days later, however, and before you have been paid for the Work ,
You Receive Phone Call from your Customer Informing you that his Next door Neighbour has Spotted that you
Have Not Bonded the Sink , of Course your Customer will Believe that his Neighbour is Right and you have Forgotten Something ,
The Choice is your / Do you Try and Convince your Customer that his Neighbour is Wrong ,
Do You Travel back to the Job to Carry Out the Bonding to Ensure Big Bucks ,
Just Put a Couple of Earth Clamp and a Short Length of 4mm2 Earthing Round the Pipes ,
( Cheaper just to Use the Supplementary Protective Bonding in the First Place )
For the Apprentice :
2.5mm2 / 1.5mm2 / Twin & Earth Cable 22meters long ,
OSG 9A ( Résistance of Copper ) 2.5mm2 / Copper : 7.41
The Résistance / Phase Conductor , ( R1 )
R1 - 7.41 x 22m ÷ 1000 = 0.163Ω *
Divide the Largest Conductor by the Smallest to find the Ratio of Conductors ,
( how much Bigger is the Largest Conductor , ( 2.5 ÷ 1.5 = 1.67
2.5mm2 Conductor is 1.67 x Larger than 1.5mm2 Conductor , therefore , it must have 1.67 x less Résistance than 1.5mm2 Conductor ,
0.163Ω * x 1.67 = 0.27Ω ( this is the Resistance of 1.5mm2 Conductor ,
OSG 9A ( Résistance of 1.5mm2 Copper : 12.10mΩ ( 22meters of 1.5mm2 Copper ,
22 x 12.10 ÷ 1000 = 0.266Ω
Final Check : OSG 9A
Résistance 2.5mm2 / 1.5mm2 Cable , we will See that it has a Résistance ( 19 51mΩ ) per meter
22 meters of it will have a Résistance of ( 22 x 19.51 ÷ 1000 = 0.429Ω
The Résistance Value of 2.5mm2 ( 0.163Ω ) and the Résistance Value of the 1.5mm2 is ( 0.266Ω )
Add them Together : ( 0.163Ω + 0.266Ω = 0.429Ω ( Finally , 0.429Ω is the Résistance of our 2.5mm2 / 1.5mm2 -
Measured as One Cable ,
This beats tons of paper work ,
“ Insulation Résistance “
This is a Test that can be Carried Out on a Complete Installation , or Single Circuit
For This Case ,
Domestic , ( Single Circuit or Ring ) New Installation ,
The Test is Necessary to find Out if there is Likely to be any Leakage of Current Through the Insulated Parts of the Installation ,
A Leakage could Occur for Various Reasons ,
Good Way to Think of this Test is to Relate it to a Pressure -Test
We Know that Voltage is the Pressure where the Current is Located in a Cable ,
On a Low Voltage Circuit , the Expected Voltage would be around 230v a.c the Voltage Used in an Installation Test on a 230V -
Circuit is 500v d.c , Which is More than Double the Normal Circuit Voltage , therefore , it can be Seen as a Pressure Test Similar
To a Plumber Pressure Testing the Central Heating Pipes ,
Circuits between 0V – 50v a.c
Required Test Voltage , ( 250v d.c. )
17th Edition : ( 0.5MΩ )
Circuits between 50V a.c – 500v a.c
Required Test Voltage , ( 500V d.c. )
17th Edition : ( 1MΩ )
Circuits between 500V & 1000V a.c.
Required Test Voltage , ( 1000V d.c. )
17th Edition : ( 1MΩ )
Domestic Installations ,
Remember that Testing should be Carried Out from the Day the Installation Commences ( Regulation 610.1 )
“ Insulation Résistance “
If for Some Reason , there is a Piece of Equipment Connected to the System that Cannot be Isolated from the Circuit Under Test ,
Do Not Carry Out the Test Between Line Conductors – Only Test Between live Conductor & Earth
This is to Avoid Poor Readings and Possible Damage to Equipment , this Test should Only be Carried Out on Individual Circuits ,
Not the Whole Installations , as it is Important to Test as Much of the Installation as Possible ,
Three Phase Sub-Mains is Tested the Results are :
L1 to Earth is 130MΩ
L2 to Earth is 80MΩ
L3 to Earth is 50MΩ
N to Earth is 100MΩ
If these Conductors were now Joined and Tested to Earth the Value would be as Given ,
Calculation ,
1 1 1 1 1
--- + --- + --- + --- + ---
R1 R2 R3 R4 Rt / N
( 1 1 1 1 1 )
--- + --- + --- + --- + --- = 19.92MΩ
130 80 50 100 0.05
Enter it this way into a Calculator : ( Remember the Button 1/X )
130X-1 + 80X-1 + 50X-1 + 100X-1 = X-1 = 19.92MΩ
This Value is Still Acceptable but Lower because the Conductors are in Parallel ,
Iceman , this is what you can face ,
Swindon Massive , send email to Kev , 20 pounds C/D It’s a Must
A Ring Circuit is Protected by a 30A BS-3036 Semi-Enclosed Rewirable Fuse
Measured ( Zs ) 0.96Ω
( Final Circuits Not Exceeding 32A )
This is a Ring Final Circuit , Disconnection time has to be 0.4sec ( table 41.2 BS-7671
Maximum ( Zs ) / 30A Rewirable Fuse – 1.04Ω
Eighty per Cent of this Value must Now be Calculated , this can be Achieved by Multiplying it by ( 0.80. )
1.04 x 0.80 = 0.83Ω
The Measured Value for the Circuit must now be Lower than the Corrected Value if it is to Comply : BS-7671
Measured Value 0.96Ω
Corrected Value 0.83Ω
The Measured Value of ( Zs ) is Higher , therefore , the Circuit will Not Comply ,
Option one is the Preferred Method because it will give an Accurate Value whereas the Test in -
Option two will Include Parallel Paths and because of this will Often give Lower Readings ,
Option one should Always be Used for an Initial Verification as the First Reading will be Used as a Benchmark -
To be Compared with Results taken in Future Periodic Tests ,
On a Periodic Inspection Using Option two , a Higher Test Results is Obtained than on the Initial Verification ,
This would Indicate that the Circuit is Deteriorating and that Further Investigation would be Required ,
The Methods Described here must be Fully Understood by Anyone who is Intending to sit the ---- & ------
---- Exam on Inspection & Testing of Electrical Installations ,
For the Apprentice
BS 7671 lists Five Types of Earthing System :
TN-S, TN-C-S, TT, TN-C, and IT.
T = Earth (from the French word Terre)
N = Neutral
S = Separate
C = Combined
I = Isolated ( The source of an IT system is either )
Connected to Earth through a Deliberately Introduced Earthing Impedance or is Isolated from Earth. All Exposed-Conductive-Parts of an Installation are Connected to an Earth Electrode. )
When Designing an Electrical Installation, One of the First things to Determine is the Type of Earthing system.
The Distributor will be Able to Provide this Information.
The System will Either be TN-S, TN-C-S (PME) or TT for a Low Voltage Supply given in Accordance with the
Electricity Safety, Quality and Continuity Regulations2002. Appendix 2 This is because TN-C Requires an Exemption
from the Electricity Safety, Quality and Continuity Regulations, and an IT system is Not Permitted for a
Low Voltage Public Supply in the UK because the Source is Not Directly Earthed. Therefore TN-C and IT
Systems are both Very Uncommon in the UK.
Supplementary Bonding is Required where Circuit Disconnection Times Cannot be Met ( Regulation 411.3.2.6 ) or
Where there is an Increased Risk of Electric Shock ,
Those Areas would be in Bathrooms , Swimming Pools & Other Special Locations ,
Where Disconnection Times Cannot be Met and the Effectiveness of Supplementary Bonding is Required to be Checked
( Regulation 415.2.2 ) a Simple Test is Required ,
Automatic Disconnection is by a Protective Device , Regulations give a Formulae -
( R ≤ 50V / Ia ) if the Circuit is Protected by an RCD , the Formulae Becomes ( R ≤ 50V / I∆n )
When this Formulae is Used , it will Ensure that Any Touch Voltage in the Bonded Area will Not Rise above ( 50 Volts a.c. )
Before the Protective Device Operates ,
The Formulae where a Protective Device is in Place for Automatic Disconnection of Supply ( ADS )
Step 1 , find ( Ia ) for a 5 seconds Disconnection Time ,
Device 32Amp BS- 88 fuse
Appendix 3 / BS-7671 fig 3.3A
32A Device a Current of 125 Amp is Required to Operate the Fuse ,
This Value Can also be Found by Using the Maximum ( Zs ) Value Found Table 41.4 ( 1.84Ω )
Calculation : Ia = Uo ÷ Zs ( Ia = 230 ÷ 1.84 = Ia = 125A
This Method Can be Used for all Protective Devices :
Now the Values Can be Used to Verify that the Area does or does Not Require Supplementary bonding to be Installed ,
( R ≤ 50V ÷ Ia ( 50 ÷ 125A = 0.4Ω ) is the Maximum Value Permitted between Exposed or Extraneous Conductive Parts ,
If when Measured it is found that the Résistance is Higher than 0.4Ω then Supplementary bonding will be Required
The Values of Résistance will Not be the Same for Different Ratings or Type of Protective Devices ,
Where an RCD is Installed to Protect the Circuit the Calculation to find out if Supplementary bonding is Required ,
R = 50v ÷ I∆n ( R = 50v ÷ 0.03 R = 1666Ω , ( 50v ÷ 30mA = 1.666Ω
Bonding is Not well-Understood by Joe Public ,
You have Travelled 20/30 Miles to Fit Kitchen / Completed Everything to Comply with Required Regulations ,
A few days later, however, and before you have been paid for the Work ,
You Receive Phone Call from your Customer Informing you that his Next door Neighbour has Spotted that you
Have Not Bonded the Sink , of Course your Customer will Believe that his Neighbour is Right and you have Forgotten Something ,
The Choice is your / Do you Try and Convince your Customer that his Neighbour is Wrong ,
Do You Travel back to the Job to Carry Out the Bonding to Ensure Big Bucks ,
Just Put a Couple of Earth Clamp and a Short Length of 4mm2 Earthing Round the Pipes ,
( Cheaper just to Use the Supplementary Protective Bonding in the First Place )
For the Apprentice :
2.5mm2 / 1.5mm2 / Twin & Earth Cable 22meters long ,
OSG 9A ( Résistance of Copper ) 2.5mm2 / Copper : 7.41
The Résistance / Phase Conductor , ( R1 )
R1 - 7.41 x 22m ÷ 1000 = 0.163Ω *
Divide the Largest Conductor by the Smallest to find the Ratio of Conductors ,
( how much Bigger is the Largest Conductor , ( 2.5 ÷ 1.5 = 1.67
2.5mm2 Conductor is 1.67 x Larger than 1.5mm2 Conductor , therefore , it must have 1.67 x less Résistance than 1.5mm2 Conductor ,
0.163Ω * x 1.67 = 0.27Ω ( this is the Resistance of 1.5mm2 Conductor ,
OSG 9A ( Résistance of 1.5mm2 Copper : 12.10mΩ ( 22meters of 1.5mm2 Copper ,
22 x 12.10 ÷ 1000 = 0.266Ω
Final Check : OSG 9A
Résistance 2.5mm2 / 1.5mm2 Cable , we will See that it has a Résistance ( 19 51mΩ ) per meter
22 meters of it will have a Résistance of ( 22 x 19.51 ÷ 1000 = 0.429Ω
The Résistance Value of 2.5mm2 ( 0.163Ω ) and the Résistance Value of the 1.5mm2 is ( 0.266Ω )
Add them Together : ( 0.163Ω + 0.266Ω = 0.429Ω ( Finally , 0.429Ω is the Résistance of our 2.5mm2 / 1.5mm2 -
Measured as One Cable ,
This beats tons of paper work ,
“ Insulation Résistance “
This is a Test that can be Carried Out on a Complete Installation , or Single Circuit
For This Case ,
Domestic , ( Single Circuit or Ring ) New Installation ,
The Test is Necessary to find Out if there is Likely to be any Leakage of Current Through the Insulated Parts of the Installation ,
A Leakage could Occur for Various Reasons ,
Good Way to Think of this Test is to Relate it to a Pressure -Test
We Know that Voltage is the Pressure where the Current is Located in a Cable ,
On a Low Voltage Circuit , the Expected Voltage would be around 230v a.c the Voltage Used in an Installation Test on a 230V -
Circuit is 500v d.c , Which is More than Double the Normal Circuit Voltage , therefore , it can be Seen as a Pressure Test Similar
To a Plumber Pressure Testing the Central Heating Pipes ,
Circuits between 0V – 50v a.c
Required Test Voltage , ( 250v d.c. )
17th Edition : ( 0.5MΩ )
Circuits between 50V a.c – 500v a.c
Required Test Voltage , ( 500V d.c. )
17th Edition : ( 1MΩ )
Circuits between 500V & 1000V a.c.
Required Test Voltage , ( 1000V d.c. )
17th Edition : ( 1MΩ )
Domestic Installations ,
Remember that Testing should be Carried Out from the Day the Installation Commences ( Regulation 610.1 )
“ Insulation Résistance “
If for Some Reason , there is a Piece of Equipment Connected to the System that Cannot be Isolated from the Circuit Under Test ,
Do Not Carry Out the Test Between Line Conductors – Only Test Between live Conductor & Earth
This is to Avoid Poor Readings and Possible Damage to Equipment , this Test should Only be Carried Out on Individual Circuits ,
Not the Whole Installations , as it is Important to Test as Much of the Installation as Possible ,
Three Phase Sub-Mains is Tested the Results are :
L1 to Earth is 130MΩ
L2 to Earth is 80MΩ
L3 to Earth is 50MΩ
N to Earth is 100MΩ
If these Conductors were now Joined and Tested to Earth the Value would be as Given ,
Calculation ,
1 1 1 1 1
--- + --- + --- + --- + ---
R1 R2 R3 R4 Rt / N
( 1 1 1 1 1 )
--- + --- + --- + --- + --- = 19.92MΩ
130 80 50 100 0.05
Enter it this way into a Calculator : ( Remember the Button 1/X )
130X-1 + 80X-1 + 50X-1 + 100X-1 = X-1 = 19.92MΩ
This Value is Still Acceptable but Lower because the Conductors are in Parallel ,
Iceman , this is what you can face ,
Swindon Massive , send email to Kev , 20 pounds C/D It’s a Must
A Ring Circuit is Protected by a 30A BS-3036 Semi-Enclosed Rewirable Fuse
Measured ( Zs ) 0.96Ω
( Final Circuits Not Exceeding 32A )
This is a Ring Final Circuit , Disconnection time has to be 0.4sec ( table 41.2 BS-7671
Maximum ( Zs ) / 30A Rewirable Fuse – 1.04Ω
Eighty per Cent of this Value must Now be Calculated , this can be Achieved by Multiplying it by ( 0.80. )
1.04 x 0.80 = 0.83Ω
The Measured Value for the Circuit must now be Lower than the Corrected Value if it is to Comply : BS-7671
Measured Value 0.96Ω
Corrected Value 0.83Ω
The Measured Value of ( Zs ) is Higher , therefore , the Circuit will Not Comply ,
Option one is the Preferred Method because it will give an Accurate Value whereas the Test in -
Option two will Include Parallel Paths and because of this will Often give Lower Readings ,
Option one should Always be Used for an Initial Verification as the First Reading will be Used as a Benchmark -
To be Compared with Results taken in Future Periodic Tests ,
On a Periodic Inspection Using Option two , a Higher Test Results is Obtained than on the Initial Verification ,
This would Indicate that the Circuit is Deteriorating and that Further Investigation would be Required ,
The Methods Described here must be Fully Understood by Anyone who is Intending to sit the ---- & ------
---- Exam on Inspection & Testing of Electrical Installations ,
For the Apprentice
BS 7671 lists Five Types of Earthing System :
TN-S, TN-C-S, TT, TN-C, and IT.
T = Earth (from the French word Terre)
N = Neutral
S = Separate
C = Combined
I = Isolated ( The source of an IT system is either )
Connected to Earth through a Deliberately Introduced Earthing Impedance or is Isolated from Earth. All Exposed-Conductive-Parts of an Installation are Connected to an Earth Electrode. )
When Designing an Electrical Installation, One of the First things to Determine is the Type of Earthing system.
The Distributor will be Able to Provide this Information.
The System will Either be TN-S, TN-C-S (PME) or TT for a Low Voltage Supply given in Accordance with the
Electricity Safety, Quality and Continuity Regulations2002. Appendix 2 This is because TN-C Requires an Exemption
from the Electricity Safety, Quality and Continuity Regulations, and an IT system is Not Permitted for a
Low Voltage Public Supply in the UK because the Source is Not Directly Earthed. Therefore TN-C and IT
Systems are both Very Uncommon in the UK.
Last edited by a moderator:
OP
amberleaf
Regs : 4E4A :
3 - Core Swa ( 3 x 95 Csa = 285mm2 Clipped Direct 289 Amp ( 300mm2 )
3 - Core Swa ( 3 x 70 Csa = 210mm2 Clipped Direct 238 Amp ( 300mm2 )
4 - Core Swa ( 4 x 70 Csa = 280mm2 Clipped Direct 238 Amp
2391 / 2392-10 my advice is to look through most of the Notes ive Downloaded / 1 / 5 pages ,
This may help you to Jog your Memory , Ps – Put them all together and you have most of the Answers, like this ,
2391 will do a Lot off writing ,
BS 7671 Electrical forms
● Electrical Installation Certificate ( 3 Signatures )
Approved Contractor Issuing the Certificate has Not been Responsible for the Design – or the Inspection & Testing Off the Electrical Work ,
Certification of the three Persons must be Carried Out Separately Using ,
(1) Designer , (2) Constructor , (3) Inspector ,
● Electrical Installation Certificate ( 1 Signature ) 2392-10
( One Person is Responsible for the Design )
The Electrical Installation Certificates is to be used only for the Initial Certification of New
Installation or For an Addition or Alteration to an Existing Installation “
where NEW circuits have been Introduced “
The "Original" Certificate is to be given to the person ordering the work ( Regulation 632.1 ) A duplicate should be retained by the Contractor.
● Electrical Installation Certificate 2382-10 ( New Work Only
This Certificate is only Valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test Results.
● EIC Schedule of Inspections ( Schedule of Circuit Details Continuation Sheet )
● EIC Schedule of Test Results ( Continuation Sheet )
● Minor Electrical Installation works Certificate
Twenty Short Questions , 2391 old Questions
Your working to this Principle , somewhere along the Line ,
(1) three Single Sockets have been added to a Ring Final Circuit : State
(a) Inspection & Testing Certificate that will need to be Completed ,
(b) Title in Law Given to the Inspection
(c) Legal Status of the Inspection
(2) an Engineering Works 18 years Old and is Due for Inspection and Test : State the
(a) Type of Inspection and Test Required ,
(b) Documents that must Accompany the Completed Certificate ,
(c) Circumstances under which the Type of Inspection and Test in (a) above may Not be Required ,
(3) State the Legal Status of the following
(a) BS-7671 : 2008
(b) Guidance Note 3
(c) HSE , GS-38
(4) Give One Example of Each of the Following
(a) an Exposed Conductive Part
(b) an Extraneous Conductive Part
(c) Direct Contact
(5) State Three Methods of Protection Against Indirect Contact
(6) State the Earthing Systems that Use the Following as Return Path
(a) Pen Conductor
(b) Cable Sheath
(c) General Mass of Earth
612.9
Methods of Calculation of Earth Fault Loop Impedance from Given Data and Measurement of Conductor Résistance
The External Earth Fault Loop Impedance ( Ze ) can be Calculated Using the Supply Voltage & the Prospective Earth Fault
Current Value Measured at the Supply ,
( Ze ) = Supply Voltage ( Prospective Earth Fault Current )
Final Circuit Earth Loop Impedance ( Ze ) can be Calculated by Adding the External Earth Fault Loop Impedance ( Ze )
( to the R1 + R2 Value of the Circuit ,
General Rule of Thumb is to Multiply Tabulated Values by 0.8 before Comparing the Test Values Obtained During Test ,
Requirements of Regulation 411.4.5 or 411.5.4 ,
411.4.5 ( Zs x Ia ≤ Uo ) 230 ÷ 0.57Ω = 403A Earth Fault Conditions
( Zs ) Should Not Exceed 0.8 Times , Appendix 14
( Zs = Uo ÷ Ia , 230 ÷ 403 = 0.5 Ω
Earth Fault Loop Impedance Exceeds 0.8 / Uo / Ia ,
A More Precise Assessment of Compliance with Regulation 411.4.5 or 411.5.4 as Appropriate , may be Made (i) (ii) (iii) (iv) (v)
Note : Other Methods are Not Precluded ,
p-249 fig 3.4 Type B, MCB to BS-EN 60898 / RCBOs BS-EN 61009-1 , Overcurrent , 32Amp / 160A ( Zs ) 41.3
Ief / Zs ≤ Uo ÷ Ia ( Zs ≤ 230 ÷ 160A = ( Zs ≤ 1.437Ω
Max Loop Impedance , 32A – I 160A required ( 41.3 ( 32 / Zs 1.44Ω
RCBO , BS-EN 61009-1 Appendix 3 p-243
Zs = Uo ÷ Ia ( 230 ÷ 160 = 7.18
411.3.2 Specifies Max Disconnection Times for Circuits ,
Conditions for Automatic Disconnections Cannot be Fulfilled by Overcurrent Device ,
“ Fault Protection ”
Fault Protection can be Met by Meeting the Disconnection times Regs , 411.3.2
This is Achieved by Limiting Earth Fault Loop Impedance ( 41.2 41.3 41.4 )
411.3 Requirements for Fault Protection :
(1) 411.3.1.1
(2) 411.3.1.2
(3) 411.3.2
BS-88-22 80A ÷ 740A = 0.1sec ( PSSC ) Fig , 3.3a 80A 740A / 0.4sec ;
BS-88-22 - BS-88-6 : 41.4 - 40A / Zs / 1.35Ω ( Uo ÷ Zs = 170A / 230 ÷ 1.35 Ω = 170A ) 170A – 5sec Fig , 3.3b
40 ÷ 170A = 0.2 sec ( PSSC )
PS off to the Mother Land , 5 Days ,
Jason you have 5 Days Holiday , hit the 24-Pack ? , Amberleaf
3 - Core Swa ( 3 x 95 Csa = 285mm2 Clipped Direct 289 Amp ( 300mm2 )
3 - Core Swa ( 3 x 70 Csa = 210mm2 Clipped Direct 238 Amp ( 300mm2 )
4 - Core Swa ( 4 x 70 Csa = 280mm2 Clipped Direct 238 Amp
2391 / 2392-10 my advice is to look through most of the Notes ive Downloaded / 1 / 5 pages ,
This may help you to Jog your Memory , Ps – Put them all together and you have most of the Answers, like this ,
2391 will do a Lot off writing ,
BS 7671 Electrical forms
● Electrical Installation Certificate ( 3 Signatures )
Approved Contractor Issuing the Certificate has Not been Responsible for the Design – or the Inspection & Testing Off the Electrical Work ,
Certification of the three Persons must be Carried Out Separately Using ,
(1) Designer , (2) Constructor , (3) Inspector ,
● Electrical Installation Certificate ( 1 Signature ) 2392-10
( One Person is Responsible for the Design )
The Electrical Installation Certificates is to be used only for the Initial Certification of New
Installation or For an Addition or Alteration to an Existing Installation “
where NEW circuits have been Introduced “
The "Original" Certificate is to be given to the person ordering the work ( Regulation 632.1 ) A duplicate should be retained by the Contractor.
● Electrical Installation Certificate 2382-10 ( New Work Only
This Certificate is only Valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test Results.
● EIC Schedule of Inspections ( Schedule of Circuit Details Continuation Sheet )
● EIC Schedule of Test Results ( Continuation Sheet )
● Minor Electrical Installation works Certificate
Twenty Short Questions , 2391 old Questions
Your working to this Principle , somewhere along the Line ,
(1) three Single Sockets have been added to a Ring Final Circuit : State
(a) Inspection & Testing Certificate that will need to be Completed ,
(b) Title in Law Given to the Inspection
(c) Legal Status of the Inspection
(2) an Engineering Works 18 years Old and is Due for Inspection and Test : State the
(a) Type of Inspection and Test Required ,
(b) Documents that must Accompany the Completed Certificate ,
(c) Circumstances under which the Type of Inspection and Test in (a) above may Not be Required ,
(3) State the Legal Status of the following
(a) BS-7671 : 2008
(b) Guidance Note 3
(c) HSE , GS-38
(4) Give One Example of Each of the Following
(a) an Exposed Conductive Part
(b) an Extraneous Conductive Part
(c) Direct Contact
(5) State Three Methods of Protection Against Indirect Contact
(6) State the Earthing Systems that Use the Following as Return Path
(a) Pen Conductor
(b) Cable Sheath
(c) General Mass of Earth
612.9
Methods of Calculation of Earth Fault Loop Impedance from Given Data and Measurement of Conductor Résistance
The External Earth Fault Loop Impedance ( Ze ) can be Calculated Using the Supply Voltage & the Prospective Earth Fault
Current Value Measured at the Supply ,
( Ze ) = Supply Voltage ( Prospective Earth Fault Current )
Final Circuit Earth Loop Impedance ( Ze ) can be Calculated by Adding the External Earth Fault Loop Impedance ( Ze )
( to the R1 + R2 Value of the Circuit ,
General Rule of Thumb is to Multiply Tabulated Values by 0.8 before Comparing the Test Values Obtained During Test ,
Requirements of Regulation 411.4.5 or 411.5.4 ,
411.4.5 ( Zs x Ia ≤ Uo ) 230 ÷ 0.57Ω = 403A Earth Fault Conditions
( Zs ) Should Not Exceed 0.8 Times , Appendix 14
( Zs = Uo ÷ Ia , 230 ÷ 403 = 0.5 Ω
Earth Fault Loop Impedance Exceeds 0.8 / Uo / Ia ,
A More Precise Assessment of Compliance with Regulation 411.4.5 or 411.5.4 as Appropriate , may be Made (i) (ii) (iii) (iv) (v)
Note : Other Methods are Not Precluded ,
p-249 fig 3.4 Type B, MCB to BS-EN 60898 / RCBOs BS-EN 61009-1 , Overcurrent , 32Amp / 160A ( Zs ) 41.3
Ief / Zs ≤ Uo ÷ Ia ( Zs ≤ 230 ÷ 160A = ( Zs ≤ 1.437Ω
Max Loop Impedance , 32A – I 160A required ( 41.3 ( 32 / Zs 1.44Ω
RCBO , BS-EN 61009-1 Appendix 3 p-243
Zs = Uo ÷ Ia ( 230 ÷ 160 = 7.18
411.3.2 Specifies Max Disconnection Times for Circuits ,
Conditions for Automatic Disconnections Cannot be Fulfilled by Overcurrent Device ,
“ Fault Protection ”
Fault Protection can be Met by Meeting the Disconnection times Regs , 411.3.2
This is Achieved by Limiting Earth Fault Loop Impedance ( 41.2 41.3 41.4 )
411.3 Requirements for Fault Protection :
(1) 411.3.1.1
(2) 411.3.1.2
(3) 411.3.2
BS-88-22 80A ÷ 740A = 0.1sec ( PSSC ) Fig , 3.3a 80A 740A / 0.4sec ;
BS-88-22 - BS-88-6 : 41.4 - 40A / Zs / 1.35Ω ( Uo ÷ Zs = 170A / 230 ÷ 1.35 Ω = 170A ) 170A – 5sec Fig , 3.3b
40 ÷ 170A = 0.2 sec ( PSSC )
PS off to the Mother Land , 5 Days ,
Jason you have 5 Days Holiday , hit the 24-Pack ? , Amberleaf
Last edited by a moderator:
OP
amberleaf
Old Notes some Revision : 2391 “ Iceman “
9A / OSG ( R1+R2 )
10mm2 / 4mm2 ( 6.44mΩ/M
( R1+R2 ) : 6.44 x 14.75 = 0.095Ω
( Zs ) Circuit - 0.095Ω + 0.7 = 0.795 ( 0.8 ) Ω
Max : ( Zs ) 45A BS-3036 : 3.2B ( 41.4 ) 5sec – 1.59Ω
C/f ( t ) 1.59 x 0.8 = 1.27Ω
As the Actual ( Zs ) is Lower
9A / OSG : 4mm2 Cooper Conductors ,
Résistance / 4.61mΩ / M
( R1+R2 ) Phase & CPC / 4mm2 – 9.22mΩ / M
( R1+R2 ) : 9.22 x 67 ÷ 1000 = 0.061Ω ( 0.61Ω ),
As it is a Ring ( 0.61 ÷ 4 = 0.15Ω ,
( R1+R2 ) Value 0.15Ω ,
( Zs = Ze+ R1+R2 ) 0.63 + 0.15 = 0.78Ω
As Max : permissible ( Zs ) is given 0.9 from OSG , “ No ( t ) ( Ci )
Sub / ( Ze ) from the actual ( Zs ) to find Max : permissible ( R1+R2 ) Value ,
( R1+R2 ) = 0.9 – 0.63 = 0.27Ω
Now Sub : actual ( R1+R2 ) Value from Max : permissible Value , ( 0.27 -0.15 = 0.12Ω )
Max : Résistance that our Spur could have ( 0.12Ω )
Length / transpose / Calculation :
( mV x Length ÷ 1000 = R )
Find Length transpose to : ( R x 1000 ÷ mV / Length )
Therefore : ( Length = 0.12 x 1000 ÷ 9.22 = 13meters ) :
2.5mm2 / 1.5mm2 ( Résistance 19.51m/Ω per meter .
( 5.8 meters of the Cable have ( Résistance 5.8 x 19.51 ÷ 1000 = 0.113
0.113 is ( Résistance of the Additional Cable , ( R1+R2 ) for this Circuit will now be ( 0.2 + 0.1133 = 0.313Ω )
9A / OSG ( 10mm2 Copper / Résistance 1.83mΩ x 22 ÷ 1000 = 0.4Ω ) *
By Calculation ↔ ( Zs = Ze+ R1+R2 ) or Use a Low Current Test Instrument , *
1/50 + 1/80 + 1/60 + 1/50 = 0.069 ( R = 1 / 0.069 = 14.45Ω ) *
Determining Touch Voltage : ( Ze ) x Rated mA - I∆n / RCD
TT / ( Ze ) = 200Ω ( Main RCD is Rated at 100mA
200Ω x 100mA ÷ 1000 = ( 20V )
For Circuit(s) having Conductors of up to 25mm2 Operating at Normal Frequency ( 50Hz ) Inductance may be Ignored
And it is Acceptable to Determine ( Zs ) Using the Formula
Rather than by Measurement Using an Earth Fault Loop Impedance Test Instrument , Zs = Ze+ R1+R2
Popular Question is “ When can ( Zs ) “ be Less than ( Ze ) given that ( Zs = Ze+ R1+R2 ) ( 239- ) ←
Testing and Measuring it ( Ze ) at Origin and ( Zs ) at the Furthest Point ( 239- ) ←
( Zs ) Test : Check the Continuity of the Earth
Earth Loop Impendence Test ,
( Ze ) is Part of the Earth Fault Loop Impendence External to the Installation ( the Impendence of the Supply )
( R1 ) is the Résistance of the Consumers Phase Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,
( R2 ) is the Résistance of the Consumers Protective Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,
( Zs = Ze+ R1+R2 )
( R1 ) is the Résistance of the Live Conductor :
( R2 ) is the Résistance of CPC
( Zs = Ze ) will give you ( R1+R2 ) approx ,
Therefore to find ( R2 ) in Isolation you need to know the Value of ( R1 ) and Subtract this from the Above or just Measure it Directly with a Meter ,
> ( Ze ) is the External Impedance Measured at the
> Incoming Point of the Supply at the Premises , it is
> the Résistance of the Phase Cable and the Return to
> the Transformer ,
( Zs = Ze+ R1+R2 ) is Measurable Via Method ( 2 ) Long Lead : ( Zs = Ze+ R1+R2 ) : ( R2 ) is a Measure of Résistance of CPC only Via Long-Lead ( Method ( 2 ) ( Ra ) is the Résistance of the Earthing Conductor :
( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor
V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )
TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,
( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor
V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )
TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,
( R1+R2 ) is the Résistance of the Circuit Phase Conductor & the Résistance or the Circuit Protective Conductor ,
One of the Dead Test i.e. Pre-Energization
Connect the Circuit Phase Conductor to Earth Rail , Either by Removing it from the MCB or by Using a Short-Linking Wire ,
At the Furthest Most Point of the Circuit Measure the Résistance between Phase & Earth ( CPC )
Using a Low Resistance Ohms Meter , this is your ( R1+R2 ) Value
The ( R1+R2 ) for Ring Final Circuit is Done Slightly Differently ,
( Ze ) is the External Earth Fault Loop Impedance to the Installation ( it is Measured in Isolation ) i.e. You need to Isolate the Supply ,
Disconnect the Earthing Conductor from the ( MET ) and Measure the Impedance between Phase and the Earthing Conductor using -
An Earth Fault Loop Impedance Tester ,
Once you have Completed the Test , Remember to Reconnect the Earthing Conductor before you Re-Energize !!1
( Zs ) is the Total Loop Impedance of the Circuit , it can be Done by Measurement at the Furthest Most Point of the Circuit or by -
( Zs = Ze+ R1+R2 )
( PFC ) is Basically the Maximum Current which can Flow in the System,
It needs to be Conducted at the Origin , for this you need to Conduct a ( PSSC ) Prospective Short Circuit Current Test :
Which is between Each Phase & Neutral / or Phase – Phase if 3 Phase )
( PEFC ) is between Each Phase & Earth -
The Highest Value is the Prospective Fault Current ( PFC ) ( Ze ) is the ( Z ) at the External Part of the Installation , that is Immediately after the Meters as Far as Practicable
( Ze ) Power Off , at your Mains ( or Only ) Isolator with all Bonds Disconnected ( also Check the Prospective current here ,
With Bonds Connected then Check Prospective Current Again ( it is Usually Higher Due to ( Parallel Paths ) -
This Highest Reading is the ( PFC )
Check ( R1+R2 ) on each Circuit Add to ( Ze ) then this gives the Calculated ( Zs )
When Energised ( With Bonds Reconnected of Course ) then Recheck that ( Zs = Ze+ R1+R2 ) or Less than Due to ( Parallel Paths ) -
This Confirms ( Zs ) Actually Does Exist ,
Also PH-PH in 3-Phase for a ( PFC ) or Double the Single Phase Readings ,
( Zs = Zdb+ R1+R2 )
Where the Distribution Board is at the Origin of the Installation , ( 239- )
2391 / this is a Written Exam , Use some off the Wording ,
9A / OSG ( R1+R2 )
10mm2 / 4mm2 ( 6.44mΩ/M
( R1+R2 ) : 6.44 x 14.75 = 0.095Ω
( Zs ) Circuit - 0.095Ω + 0.7 = 0.795 ( 0.8 ) Ω
Max : ( Zs ) 45A BS-3036 : 3.2B ( 41.4 ) 5sec – 1.59Ω
C/f ( t ) 1.59 x 0.8 = 1.27Ω
As the Actual ( Zs ) is Lower
9A / OSG : 4mm2 Cooper Conductors ,
Résistance / 4.61mΩ / M
( R1+R2 ) Phase & CPC / 4mm2 – 9.22mΩ / M
( R1+R2 ) : 9.22 x 67 ÷ 1000 = 0.061Ω ( 0.61Ω ),
As it is a Ring ( 0.61 ÷ 4 = 0.15Ω ,
( R1+R2 ) Value 0.15Ω ,
( Zs = Ze+ R1+R2 ) 0.63 + 0.15 = 0.78Ω
As Max : permissible ( Zs ) is given 0.9 from OSG , “ No ( t ) ( Ci )
Sub / ( Ze ) from the actual ( Zs ) to find Max : permissible ( R1+R2 ) Value ,
( R1+R2 ) = 0.9 – 0.63 = 0.27Ω
Now Sub : actual ( R1+R2 ) Value from Max : permissible Value , ( 0.27 -0.15 = 0.12Ω )
Max : Résistance that our Spur could have ( 0.12Ω )
Length / transpose / Calculation :
( mV x Length ÷ 1000 = R )
Find Length transpose to : ( R x 1000 ÷ mV / Length )
Therefore : ( Length = 0.12 x 1000 ÷ 9.22 = 13meters ) :
2.5mm2 / 1.5mm2 ( Résistance 19.51m/Ω per meter .
( 5.8 meters of the Cable have ( Résistance 5.8 x 19.51 ÷ 1000 = 0.113
0.113 is ( Résistance of the Additional Cable , ( R1+R2 ) for this Circuit will now be ( 0.2 + 0.1133 = 0.313Ω )
9A / OSG ( 10mm2 Copper / Résistance 1.83mΩ x 22 ÷ 1000 = 0.4Ω ) *
By Calculation ↔ ( Zs = Ze+ R1+R2 ) or Use a Low Current Test Instrument , *
1/50 + 1/80 + 1/60 + 1/50 = 0.069 ( R = 1 / 0.069 = 14.45Ω ) *
Determining Touch Voltage : ( Ze ) x Rated mA - I∆n / RCD
TT / ( Ze ) = 200Ω ( Main RCD is Rated at 100mA
200Ω x 100mA ÷ 1000 = ( 20V )
For Circuit(s) having Conductors of up to 25mm2 Operating at Normal Frequency ( 50Hz ) Inductance may be Ignored
And it is Acceptable to Determine ( Zs ) Using the Formula
Rather than by Measurement Using an Earth Fault Loop Impedance Test Instrument , Zs = Ze+ R1+R2
Popular Question is “ When can ( Zs ) “ be Less than ( Ze ) given that ( Zs = Ze+ R1+R2 ) ( 239- ) ←
Testing and Measuring it ( Ze ) at Origin and ( Zs ) at the Furthest Point ( 239- ) ←
( Zs ) Test : Check the Continuity of the Earth
Earth Loop Impendence Test ,
( Ze ) is Part of the Earth Fault Loop Impendence External to the Installation ( the Impendence of the Supply )
( R1 ) is the Résistance of the Consumers Phase Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,
( R2 ) is the Résistance of the Consumers Protective Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,
( Zs = Ze+ R1+R2 )
( R1 ) is the Résistance of the Live Conductor :
( R2 ) is the Résistance of CPC
( Zs = Ze ) will give you ( R1+R2 ) approx ,
Therefore to find ( R2 ) in Isolation you need to know the Value of ( R1 ) and Subtract this from the Above or just Measure it Directly with a Meter ,
> ( Ze ) is the External Impedance Measured at the
> Incoming Point of the Supply at the Premises , it is
> the Résistance of the Phase Cable and the Return to
> the Transformer ,
( Zs = Ze+ R1+R2 ) is Measurable Via Method ( 2 ) Long Lead : ( Zs = Ze+ R1+R2 ) : ( R2 ) is a Measure of Résistance of CPC only Via Long-Lead ( Method ( 2 ) ( Ra ) is the Résistance of the Earthing Conductor :
( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor
V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )
TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,
( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor
V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )
TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,
( R1+R2 ) is the Résistance of the Circuit Phase Conductor & the Résistance or the Circuit Protective Conductor ,
One of the Dead Test i.e. Pre-Energization
Connect the Circuit Phase Conductor to Earth Rail , Either by Removing it from the MCB or by Using a Short-Linking Wire ,
At the Furthest Most Point of the Circuit Measure the Résistance between Phase & Earth ( CPC )
Using a Low Resistance Ohms Meter , this is your ( R1+R2 ) Value
The ( R1+R2 ) for Ring Final Circuit is Done Slightly Differently ,
( Ze ) is the External Earth Fault Loop Impedance to the Installation ( it is Measured in Isolation ) i.e. You need to Isolate the Supply ,
Disconnect the Earthing Conductor from the ( MET ) and Measure the Impedance between Phase and the Earthing Conductor using -
An Earth Fault Loop Impedance Tester ,
Once you have Completed the Test , Remember to Reconnect the Earthing Conductor before you Re-Energize !!1
( Zs ) is the Total Loop Impedance of the Circuit , it can be Done by Measurement at the Furthest Most Point of the Circuit or by -
( Zs = Ze+ R1+R2 )
( PFC ) is Basically the Maximum Current which can Flow in the System,
It needs to be Conducted at the Origin , for this you need to Conduct a ( PSSC ) Prospective Short Circuit Current Test :
Which is between Each Phase & Neutral / or Phase – Phase if 3 Phase )
( PEFC ) is between Each Phase & Earth -
The Highest Value is the Prospective Fault Current ( PFC ) ( Ze ) is the ( Z ) at the External Part of the Installation , that is Immediately after the Meters as Far as Practicable
( Ze ) Power Off , at your Mains ( or Only ) Isolator with all Bonds Disconnected ( also Check the Prospective current here ,
With Bonds Connected then Check Prospective Current Again ( it is Usually Higher Due to ( Parallel Paths ) -
This Highest Reading is the ( PFC )
Check ( R1+R2 ) on each Circuit Add to ( Ze ) then this gives the Calculated ( Zs )
When Energised ( With Bonds Reconnected of Course ) then Recheck that ( Zs = Ze+ R1+R2 ) or Less than Due to ( Parallel Paths ) -
This Confirms ( Zs ) Actually Does Exist ,
Also PH-PH in 3-Phase for a ( PFC ) or Double the Single Phase Readings ,
( Zs = Zdb+ R1+R2 )
Where the Distribution Board is at the Origin of the Installation , ( 239- )
2391 / this is a Written Exam , Use some off the Wording ,
Last edited by a moderator:
OP
amberleaf
239x “ Wording “ Iceman
The Insulation Resistance should be above 2MΩ
If it is Less than Further Investigation must be Carried Out as ( a Latent Defect may Exist ) *
In any Exam it is Vital that the Question is Read Carefully , Often it is better to Read a Question Several Times
To try and Understand what is being Asked
If the Question asks for a Fully Labelled Diagram , then Marks are Awarded for the Diagram and the Labelling ,
Where the Question Asks “ Explain with the Aid of a Diagram “ then a Diagram and a Written Explanation is Required ,
When the Question ask for a List then you will be Expected to List a Sequence of Events in the Correct Order , -
( Just a List with No Explanation ) if you are Required to State Something then a Statement is Required in No Particular Order ,
List the Sequence of Dead Tests :
(a) Continuity of Protective Conductors’ ( Including Main & Supplementary Equipotential Bonding : Test
(b) Continuity of Ring Final Circuit Conductors : Test
(c) Insulation Résistance : Test ( Remember the Wording , Use in the Right Contents )
State Three Statutory Documents Relating the Inspecting & Testing ( of Electrical Installations )
(a) The Electricity at Work Regulations 1989 ( No more No Less )
(b) The Health & Safety at Work Act 1974
(c)
Always try to Answer the Questions in “ FULL “ using the Correct Terminology :
For Example : if Asked “ Which is the Type of Inspection to be Carried Out on a New Installation”
The Answer must be : An Initial Verification ,
For the Document Required for Moving a Switch or Adding a Socket the Answer must be :
An Electrical Installation Minor Works Certificate , ( Not Just Minor Works )
The Initial Verification of an Installation or Circuit is Very Important and it must be Carried Out Correctly :
The Documentation for this Serves two Purposes ,
Firstly , it is a Certificate which should be Provided to Show that the Installation has been Installed Correctly and that it is Safe to Use
This Certification should Not be Issued Until the Installation has been Tested & the Results have been Verified as being Satisfactory ,
It would be a Pointless Exercise to just Inspect & Test an Electrical Installation when it is Completed – it is Vital that the
Installation is Inspected Regularly During the Installation and Before any Cables are Finally Covered Up ,
Remember ↔ that , When you Sign the Electrical Installation Certificate ,
You are Taking Responsibility for Every Part of the Installation that you Sign for
This should Not be Taken Lightly because , if an Accident Occurs Due too an Unsafe Installation ;
The Person who has Carried Out the Inspection & Test May Well be Held Responsible ,
( Remember Your Arse is on the Firing Line )
In Many Ways , Initial Verification Should be Easier than Carrying Out a Periodic Inspection on an Existing Installation
As the Person Carrying Out the Test should know their Way around it ,
Because they would have seen it as it was being Installed ,
PS : Use the Correct Terminology ←←←←
Insulation Résistance Test Instrument : ( NOT Megger )
Low Reading Ohms Meter ( Not Continuity Tester or millli Ohms Meter )
Electrical Installation Certificate / or ( EIC ) NOT Electrical Installation Report
Schedule of Test Results – ( NOT Schedule of Test or Schedule of Results )
Testing ( 3-Phase Induction Motor )
There are Many Types of 3-Phase Motors but far the Most Common is the Induction Motor ,
It is Quite Useful to be Able to Test them for Serviceability
Before Carrying Out Electrical Tests it is Good Idea to Ensure that the Rotor Turns Freely
This may Involve Disconnecting any Mechanical Loads . The Rotor should Rotate Easily and you should Not be Able to hear any Rumbling from the Motor Bearings , if the Motor has a Fan on the Outside of it , Check that it is Clear of any Debris which may
Have been Sucked in to it , Also Check that any Air Vents into the Motor are Not Blocked ,
Generally : if the Motor Windings are Burnt Out there will be an Unmistakable Smell of Burnt Varnish
It is still a Good Idea to Test the Windings as the Smell could be from the Motor being Overloaded
Three Phase Motors are Made up of Three Separate Windings / in the Terminal box there will be ( Six Terminals ) as Each Motor Winding will have Two Ends , The Ends of the Motor Windings will Usually be Indentified as -
( W1 , W2 ; U1 , U2 ; or V1 , V2 ) The First Part of the Test is Carried Out Using a Low-Résistance Ohms Meter ,
Test Each Windings End – End ( W1 to W2 , U1 to U2 , and V1 to V2 ) The Résistance of Each Winding should be Approximately
The Same and the Résistance Value Will Depend on the Size of the Motor ,
If the Résistance Values are Different then the Motor will Not be Electrically Balanced and it should be Sent for Rewinding , if
Résistance Values are the Same , then the Next Test is Carried Out Using an ( Insulation Résistance Tester ) MΩ
Join W1 and W2 Together , U1 and U2 Together , and V1 and V2 Together ,
Carry Out an Insulation Résistance Test between the Joined Ends , i.e. W to U then W to V and then between U and V , -
Repeat the Test between Joined Ends and the Case , or the Earthing Terminal of the Motor ↔
( these Tests can be in any Order to Suit you )
Providing the Insulation Résistance is ( 2MΩ ) or Greater then the Motor is Fine , if the Insulation Résistance is above ( 0.5MΩ )
This Could be Due to Dampness and it is Often a Good Idea to run the Motor for a While before Carrying Out the Insulation Test -
Again as the Motor may Dry Out with Use :
To Reconnect the Motor Windings in Star : Join W2 , U2 and V2 Together and Connect the 3-Phase Motor Supply to -
W1 , U1 and V1 , if the Motor Rotates in the Wrong Direction , Swap Two of the Phase of the Motor Supply
To Reconnect the Motor Windings in Delta , Join W1 to U2 , U1 to V2 and V1 to W2 and then Connect the 3-Phase Motor -
Supply One to Each of the Joined Ends ,
If the Motor Rotates in the Wrong Direction , Swap Two-Phases of the Motor Supply ,
Test Instruments’
Guidance Note GS-38
GS-38 is for Electrical Test Equipment Used by Electricians and Gives Guidance to Electrically Competent Persons Involved in
Electrical Testing , Diagnosis and Repair , Electrically Competent Persons :
Electricians , Electrical Contractors , Technicians , Mangers or Appliance Repairers
Voltage Indicating Devices
Instruments Used Solely for Detecting a Voltage Fall into Two Categories :
Detectors that Rely on an Illuminated Lamp :
Lamps are Fitted with a 15Watt Lamp , and Should Not give Rise to Danger if the Lamp is Broken , a Guard should also Protect it ,
Detectors that Use Two or more Independent Indicating Systems / One of Which May be Audible /
And Limit Energy input to the Detector by the Circuitry Used , Two-Pole Voltage Detector
i.e. a Detector Unit with an Integral Probe , an Interconnecting Lead and a Second Probe
These Detectors are Designed and Constructed to Limit the Current and Energy that can Flow into the Detector
This Limitation is Usually Provided by Combination of the Circuit Design Using the Concept of Protective Impedance , and
Current- Limiting Resistors built into the Probe , the Detectors are also Provided with in Features to Check the Functioning
Of the Detector before and After Use , The Interconnecting Lead and Second Probes are Not Detachable Components ,
These Type of Detectors’ do Not Require Additional-Limiting Resistors or Fuses to be Fitted Provided that are Made
To an Acceptable Standard and the Contact Electrodes are Shrouded
Voltage Indicating Devices :
Guidance Note GS-38
Lamps and Voltage Indicators are Recommended to be Clearly Marked with the Maximum Voltage which may be Tested by the
Device and any Short Time Rating for the Device if Applicable ,
This Rating is Recommended Maximum Current that should Pass-Through the Device for a Few Seconds
As these Devices are Generally Not Designed to be Connected for more than a Few Seconds ,
The Insulation Resistance should be above 2MΩ
If it is Less than Further Investigation must be Carried Out as ( a Latent Defect may Exist ) *
In any Exam it is Vital that the Question is Read Carefully , Often it is better to Read a Question Several Times
To try and Understand what is being Asked
If the Question asks for a Fully Labelled Diagram , then Marks are Awarded for the Diagram and the Labelling ,
Where the Question Asks “ Explain with the Aid of a Diagram “ then a Diagram and a Written Explanation is Required ,
When the Question ask for a List then you will be Expected to List a Sequence of Events in the Correct Order , -
( Just a List with No Explanation ) if you are Required to State Something then a Statement is Required in No Particular Order ,
List the Sequence of Dead Tests :
(a) Continuity of Protective Conductors’ ( Including Main & Supplementary Equipotential Bonding : Test
(b) Continuity of Ring Final Circuit Conductors : Test
(c) Insulation Résistance : Test ( Remember the Wording , Use in the Right Contents )
State Three Statutory Documents Relating the Inspecting & Testing ( of Electrical Installations )
(a) The Electricity at Work Regulations 1989 ( No more No Less )
(b) The Health & Safety at Work Act 1974
(c)
Always try to Answer the Questions in “ FULL “ using the Correct Terminology :
For Example : if Asked “ Which is the Type of Inspection to be Carried Out on a New Installation”
The Answer must be : An Initial Verification ,
For the Document Required for Moving a Switch or Adding a Socket the Answer must be :
An Electrical Installation Minor Works Certificate , ( Not Just Minor Works )
The Initial Verification of an Installation or Circuit is Very Important and it must be Carried Out Correctly :
The Documentation for this Serves two Purposes ,
Firstly , it is a Certificate which should be Provided to Show that the Installation has been Installed Correctly and that it is Safe to Use
This Certification should Not be Issued Until the Installation has been Tested & the Results have been Verified as being Satisfactory ,
It would be a Pointless Exercise to just Inspect & Test an Electrical Installation when it is Completed – it is Vital that the
Installation is Inspected Regularly During the Installation and Before any Cables are Finally Covered Up ,
Remember ↔ that , When you Sign the Electrical Installation Certificate ,
You are Taking Responsibility for Every Part of the Installation that you Sign for
This should Not be Taken Lightly because , if an Accident Occurs Due too an Unsafe Installation ;
The Person who has Carried Out the Inspection & Test May Well be Held Responsible ,
( Remember Your Arse is on the Firing Line )
In Many Ways , Initial Verification Should be Easier than Carrying Out a Periodic Inspection on an Existing Installation
As the Person Carrying Out the Test should know their Way around it ,
Because they would have seen it as it was being Installed ,
PS : Use the Correct Terminology ←←←←
Insulation Résistance Test Instrument : ( NOT Megger )
Low Reading Ohms Meter ( Not Continuity Tester or millli Ohms Meter )
Electrical Installation Certificate / or ( EIC ) NOT Electrical Installation Report
Schedule of Test Results – ( NOT Schedule of Test or Schedule of Results )
Testing ( 3-Phase Induction Motor )
There are Many Types of 3-Phase Motors but far the Most Common is the Induction Motor ,
It is Quite Useful to be Able to Test them for Serviceability
Before Carrying Out Electrical Tests it is Good Idea to Ensure that the Rotor Turns Freely
This may Involve Disconnecting any Mechanical Loads . The Rotor should Rotate Easily and you should Not be Able to hear any Rumbling from the Motor Bearings , if the Motor has a Fan on the Outside of it , Check that it is Clear of any Debris which may
Have been Sucked in to it , Also Check that any Air Vents into the Motor are Not Blocked ,
Generally : if the Motor Windings are Burnt Out there will be an Unmistakable Smell of Burnt Varnish
It is still a Good Idea to Test the Windings as the Smell could be from the Motor being Overloaded
Three Phase Motors are Made up of Three Separate Windings / in the Terminal box there will be ( Six Terminals ) as Each Motor Winding will have Two Ends , The Ends of the Motor Windings will Usually be Indentified as -
( W1 , W2 ; U1 , U2 ; or V1 , V2 ) The First Part of the Test is Carried Out Using a Low-Résistance Ohms Meter ,
Test Each Windings End – End ( W1 to W2 , U1 to U2 , and V1 to V2 ) The Résistance of Each Winding should be Approximately
The Same and the Résistance Value Will Depend on the Size of the Motor ,
If the Résistance Values are Different then the Motor will Not be Electrically Balanced and it should be Sent for Rewinding , if
Résistance Values are the Same , then the Next Test is Carried Out Using an ( Insulation Résistance Tester ) MΩ
Join W1 and W2 Together , U1 and U2 Together , and V1 and V2 Together ,
Carry Out an Insulation Résistance Test between the Joined Ends , i.e. W to U then W to V and then between U and V , -
Repeat the Test between Joined Ends and the Case , or the Earthing Terminal of the Motor ↔
( these Tests can be in any Order to Suit you )
Providing the Insulation Résistance is ( 2MΩ ) or Greater then the Motor is Fine , if the Insulation Résistance is above ( 0.5MΩ )
This Could be Due to Dampness and it is Often a Good Idea to run the Motor for a While before Carrying Out the Insulation Test -
Again as the Motor may Dry Out with Use :
To Reconnect the Motor Windings in Star : Join W2 , U2 and V2 Together and Connect the 3-Phase Motor Supply to -
W1 , U1 and V1 , if the Motor Rotates in the Wrong Direction , Swap Two of the Phase of the Motor Supply
To Reconnect the Motor Windings in Delta , Join W1 to U2 , U1 to V2 and V1 to W2 and then Connect the 3-Phase Motor -
Supply One to Each of the Joined Ends ,
If the Motor Rotates in the Wrong Direction , Swap Two-Phases of the Motor Supply ,
Test Instruments’
Guidance Note GS-38
GS-38 is for Electrical Test Equipment Used by Electricians and Gives Guidance to Electrically Competent Persons Involved in
Electrical Testing , Diagnosis and Repair , Electrically Competent Persons :
Electricians , Electrical Contractors , Technicians , Mangers or Appliance Repairers
Voltage Indicating Devices
Instruments Used Solely for Detecting a Voltage Fall into Two Categories :
Detectors that Rely on an Illuminated Lamp :
Lamps are Fitted with a 15Watt Lamp , and Should Not give Rise to Danger if the Lamp is Broken , a Guard should also Protect it ,
Detectors that Use Two or more Independent Indicating Systems / One of Which May be Audible /
And Limit Energy input to the Detector by the Circuitry Used , Two-Pole Voltage Detector
i.e. a Detector Unit with an Integral Probe , an Interconnecting Lead and a Second Probe
These Detectors are Designed and Constructed to Limit the Current and Energy that can Flow into the Detector
This Limitation is Usually Provided by Combination of the Circuit Design Using the Concept of Protective Impedance , and
Current- Limiting Resistors built into the Probe , the Detectors are also Provided with in Features to Check the Functioning
Of the Detector before and After Use , The Interconnecting Lead and Second Probes are Not Detachable Components ,
These Type of Detectors’ do Not Require Additional-Limiting Resistors or Fuses to be Fitted Provided that are Made
To an Acceptable Standard and the Contact Electrodes are Shrouded
Voltage Indicating Devices :
Guidance Note GS-38
Lamps and Voltage Indicators are Recommended to be Clearly Marked with the Maximum Voltage which may be Tested by the
Device and any Short Time Rating for the Device if Applicable ,
This Rating is Recommended Maximum Current that should Pass-Through the Device for a Few Seconds
As these Devices are Generally Not Designed to be Connected for more than a Few Seconds ,
Last edited by a moderator:
OP
amberleaf
239- Calculation of the Maximum ( Zs ) of the Circuit Breakers’
It is Often Useful to be able to Calculate the Maximum ( Zs ) Value for Circuit Breakers without the Use of Tables ,
BS-EN 60898 Devices : ( 20A / BS-EN 60898 Device )
Type B / MCB Must Operate within 3 to 5 Times its Rating ,
( Worst Case Scenario Therefore ) we must Assume that the Device will Not Operate until a Current Equal to ( 5 ) times -
Its Rating Flows Through it ( Ia ) for a 20A Type B / MCB this will be ( 5 x 20A = 100A )
If we Use a Supply Voltage of 230volts – which is the Assumed Open Circuit Voltage ( Uo ) of the Supply -
Ohm’s Law can be Used to Calculate the Maximum ( Zs )
( Zs ) = Uo ÷ 100 = ( Zs ) = 230 ÷ 100 = 2.3Ω
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type B / MCB = 2.3Ω
( 20A / BS-EN 60898 Device ) Type C / MCB Must Operate at a Maximum of 10 times its Rating ( In )
( 10 x 20 = 200A ( 230 ÷ 200 = 1.15Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type C / MCB = 1.15Ω
Type D / MCB with a Nominal Operating Current ( In ) Must Operate at a Maximum of 20 times its Rating : -
( 20 x 20 = 400A ( 230 ÷ 400 = 0.57Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type D / MCB = 0.57Ω
The Maximum ( Zs ) Values for a Type C are 50% of the ( Zs ) Value :
The Maximum ( Zs ) Values for a Type D are 50% of the ( Zs ) Value : of a Type C MCB ,
Maximum Earth Loop Impedance ( Zs ) for Fuses :
Fuses have to Operate at 0.4 or 5 sec Depending on the Type of Circuit which they are Protecting ,
To find the Maximum Permissible ( Zs ) Value for a Fuse , the Current Curves in Appendix 3 / Fig : 3.1
Find the Maximum Permissible ( Zs ) for a BS-1361 Fuse with a Rating of 20Amp with a Required Disconnection Time of 0.4 sec
( Look in Appendix 3 / Fig : 3.1 , the Left-Hand side of the Grid Represents the Disconnection Time )
From the Bottom Left-Hand Corner , follow the Line Upwards Until the Horizontal Line Representing 0.4 sec is Found
Follow the Horizontal Line across to the Right Until the Bold Line for a 20Amp Fuse is Found ,
From where the Horizontal Line Touches the Bold Line move Vertically Down the Page Until you meet the Bottom Line of the Grid ,
The Bottom Line Represents the Automatic Operating Current for the Fuse , it can be Seen that the Current Required is Around 130Amps
( The Table in the Right-Hand top Corner of the Page will Show this Value to be 135Amps )
( Zs ) = Uo ÷ Ia / ( Zs ) = 230 ÷ 135 = 1.7Ω
To Check this look : BS-7671 / 41.2 / ( Zs ) BS-1361 / 20A = 1.7Ω
( Do not Forget to Correct this Value for the Conductor Operating Temperature & Ambient Temperature : if Required ,
This Calculation can be Used for any Type of Protective Device :
Remember that the Disconnection Time for a Circuit Breaker will always need to be 0.1 sec
Comparing Maximum ( Zs ) & Measured ( Zs )
Unfortunately we Cannot Compare this Value Directly to any Measured ( Zs ) Values that we have :
This is because the Values given in BS-7671 for ( Zs ) are for when the Circuit Conductors’ are at their Operating Temperature -
( Generally 70ºC )
Assume that we have a Circuit Protected by 32A BS-EN 60898 Type B :
Measured ( Zs ) is 0.98Ω
5 x 32 = 160A ( 230 ÷ 160 = 1.44Ω )
The Measured ( Zs ) at 70ºC for the Circuit is 1.44Ω )
To find ¾ of 1.5 we can Multiply it by 0.8 ( 1.5 x 0.8 = 1.2Ω )
1.2Ω now becomes our Maximum Value : and we Compare our Measured Value Directly to it without having to Consider the Ambient Temperature or the Conductor Value :
In this Case it is , and the 32Amp Type B Device would be Safe to Use ,
Calculation of the Maximum ( Zs ) of the Circuit Breakers’ It is Often Useful to be able to Calculate the Maximum ( Zs ) Value for Circuit Breakers without the Use of Tables ,
BS-EN 60898 Devices : ( 20A / BS-EN 60898 Device )
Type B / MCB Must Operate within 3 to 5 Times its Rating ,
( Worst Case Scenario Therefore ) we must Assume that the Device will Not Operate until a Current Equal to ( 5 ) times -
Its Rating Flows Through it ( Ia ) for a 20A Type B / MCB this will be ( 5 x 20A = 100A )
If we Use a Supply Voltage of 230volts – which is the Assumed Open Circuit Voltage ( Uo ) of the Supply -
Ohm’s Law can be Used to Calculate the Maximum ( Zs )
( Zs ) = Uo ÷ 100 = ( Zs ) = 230 ÷ 100 = 2.3Ω
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type B / MCB = 2.3Ω
( 20A / BS-EN 60898 Device ) Type C / MCB Must Operate at a Maximum of 10 times its Rating ( In )
( 10 x 20 = 200A ( 230 ÷ 200 = 1.15Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type C / MCB = 1.15Ω
Type D / MCB with a Nominal Operating Current ( In ) Must Operate at a Maximum of 20 times its Rating : -
( 20 x 20 = 400A ( 230 ÷ 400 = 0.57Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type D / MCB = 0.57Ω
The Maximum ( Zs ) Values for a Type C are 50% of the ( Zs ) Value :
The Maximum ( Zs ) Values for a Type D are 50% of the ( Zs ) Value : of a Type C MCB ,
Maximum Earth Loop Impedance ( Zs ) for Fuses :
Fuses have to Operate at 0.4 or 5 sec Depending on the Type of Circuit which they are Protecting ,
To find the Maximum Permissible ( Zs ) Value for a Fuse , the Current Curves in Appendix 3 / Fig : 3.1
Find the Maximum Permissible ( Zs ) for a BS-1361 Fuse with a Rating of 20Amp with a Required Disconnection Time of 0.4 sec
( Look in Appendix 3 / Fig : 3.1 , the Left-Hand side of the Grid Represents the Disconnection Time )
From the Bottom Left-Hand Corner , follow the Line Upwards Until the Horizontal Line Representing 0.4 sec is Found
Follow the Horizontal Line across to the Right Until the Bold Line for a 20Amp Fuse is Found ,
From where the Horizontal Line Touches the Bold Line move Vertically Down the Page Until you meet the Bottom Line of the Grid ,
The Bottom Line Represents the Automatic Operating Current for the Fuse , it can be Seen that the Current Required is Around 130Amps
( The Table in the Right-Hand top Corner of the Page will Show this Value to be 135Amps )
( Zs ) = Uo ÷ Ia / ( Zs ) = 230 ÷ 135 = 1.7Ω
To Check this look : BS-7671 / 41.2 / ( Zs ) BS-1361 / 20A = 1.7Ω
( Do not Forget to Correct this Value for the Conductor Operating Temperature & Ambient Temperature : if Required ,
This Calculation can be Used for any Type of Protective Device :
Remember that the Disconnection Time for a Circuit Breaker will always need to be 0.1 sec
Comparing Maximum ( Zs ) & Measured ( Zs )
Unfortunately we Cannot Compare this Value Directly to any Measured ( Zs ) Values that we have :
This is because the Values given in BS-7671 for ( Zs ) are for when the Circuit Conductors’ are at their Operating Temperature -
( Generally 70ºC )
Assume that we have a Circuit Protected by 32A BS-EN 60898 Type B :
Measured ( Zs ) is 0.98Ω
5 x 32 = 160A ( 230 ÷ 160 = 1.44Ω )
The Measured ( Zs ) at 70ºC for the Circuit is 1.44Ω )
To find ¾ of 1.5 we can Multiply it by 0.8 ( 1.5 x 0.8 = 1.2Ω )
1.2Ω now becomes our Maximum Value : and we Compare our Measured Value Directly to it without having to Consider the Ambient Temperature or the Conductor Value :
In this Case it is , and the 32Amp Type B Device would be Safe to Use ,
OP
amberleaf
RCBO : Double Pole ,
“ Earth Leakage “
“ Overload Protection “
“ Short Circuit Protection “
“ Over Voltage & Surge Voltage Protection “
“ Switch Line & Neutral for Increased Safety “
“ Will Replace Existing Earth Leakage Devices “
239-
Why do we Need to Confirm Correct Polarity ?
Incorrect Polarity can Give rise to Danger in a Number of Ways :
(i) Parts of the Installation May Remain Connected to the Line Conductor when Switched off by a Single-Pole Device but , for all Intents and Purposes , will Appear to be Dead :
(ii) in the Event of an Overload , the Circuit-Breaker or Fuse Protecting that Part of the Installation would Disconnect the Neutral of the Circuit , Leaving the Load at Full Line Voltage ,
(iii) An Earth Fault Current Might Remain Undetected by Overcurrent Protective Devices
Re-Cap :
Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions to Existing Installations ,
Domestic Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions Existing Installations , in a Single Dwelling ( House or Individual Flat )
Minor Electrical Installation Works Certificate -
Intended for Minor Installation Work that Does Not Include the Provision of a New Circuit ,
Periodic Inspection Report : for an Electrical Installation -
Intended for Reporting on the Condition of an Existing Installation ,
Nature of Supply Parameters :
Provision is Made to Record the Supply Parameters which Comprise ,
Normal Voltage(s) U ( Line to Line ) : Uo ( Line to Earth ) ( in Volts )
This Parameter can Generally be Determined Only by Enquiry ,
For Public Supplies in the UK , U / 400V and Uo 230V – Two Phase / Three-Phase Supplies ,
And U – Uo are 230V – Single-Phase Supplies
Nominal Frequency , ( f ) / Hz
This Parameter can Generally be Determined Only by Enquire , ( in UK Nominal Frequency ; Invariably ( 50 Hz )
For the Apprentice What is GS-38 "IEE Guidance Note 3: Inspection and Testing ,
Guidance Note GS38, published by the Health and Safety Executive ( HSE ), sets out in clear and concise terms the features that any instruments and meters should have if they are to be used to carry out electrical tests in accordance with BS 7671. In order to comply with the Electricity at Work Regulations 1989 it is critical that any competent person carries out electrical testing safely, and this guidance note draws attention to the risks of using test instruments that do not meet the GS38 standard. In brief, some of the requirements for test instruments include:
• The test probes should have finger guards, ideally 2mm or 4mm of exposed conductive tip (to prevent the user accidentally making contact with either the probes or live conductors under test) and should be fitted with a High Breaking Capacity inline fuse or fuse-and-resistor combination with a low current rating (to prevent the probes rupturing under high short-circuit currents and/or damaging the test instrument if incorrect range settings are used, typically drawing more than 500mA ).
• The test leads should be adequately insulated to suit the environment in which they’re being used, are coloured differently from each other so as to be distinguishable, are flexible, are capable of handling the maximum current range of the test instrument and are shrouded or sheathed to protect against mechanical damage, securely connect the leads to the test instrument and safeguard against the possibility of direct contact with live parts.
GS38 also Identifies Three Categories of Test Instruments, namely those that:
• Test for the presence of a voltage ( voltage detection )
• Measure Voltages
• Measure current and resistance ( as well as, in some cases, Inductance and Capacitance )
• Look at the test instrument, probes, leads and connectors for any obvious signs of physical damage. Have you stored the test instrument properly? Did you lend it out to someone that didn’t look after it ? Are there knots, kinks or cuts in the leads ? Is the case cracked ? Are the connections loose ?
• Look at the ratings on the test instruments, probes, leads and connectors to make sure they’re suitable for the job you’re asking them to do. Do you know what range you need to be using ?
• Does the test instrument have a calibration date on it? If you don’t know when the instrument was last calibrated, how can you be sure you’re getting the right readings ?
Before carrying out any actual tests, make sure you know all the procedures involved in carrying out safe isolation on the circuit(s) you intend to work on.
To sum up, GS38 has been designed both to keep both you and others safe and to try and define a clear standard that manufacturers can work towards to make sure electrical testing is carried out sensibly and safely. Although high-quality test instruments can be costly one-off purchases, keep in mind the cost of your own safety ! As with any tools, good quality instruments and meters pay for themselves many times over and being skilled in their use is a true measure of a Qualified and Competent Electrician .
For the Apprentice : some Revision ,
A 6A BS-EN-61009-1 RCBO with a Maximum Value of Earth Fault Loop Impedance of ( 1.92Ω is Type D )
( Part 4 : Protection for Safety , Regulation 411.4.7 ( 41.3 )
The Maximum Disconnection Time for a Circuit Supplied by a Reduce Low Voltage System Using a 110V Midpoint Earthed
Transformer is ( 5sec ) Part 4 : Protection for Safety , Regulation 411.8.3
Where Basic Protection and / or Fault Protection is Provided , Certain External Influences may Required Additional Protection
Provided by ( Use of 30mA RCDs ) Part 4 : Protection for Safety , Regulation 415.1.1
The Horizontal Top Surface of a Barrier or Enclose which is Readily Accessible shall Provide a Degree of Protection of at Least
( IPXXD or IP4X ) Top of CU : Part 4 : Protection for Safety , Regulation 416.2.2
The Symbol Used to Show that a BS-88 Device has a Motor Circuit Application is ( gM ) Symbols Used in the Regulations p-35 - 411.4.6
The Effectiveness of Protective Measures should be Considered with Regard to ( Maintainability ) -
Party 3 : Assessment of General Characteristics , Regulation 341.1
The Measure of Automatic Disconnection of Supply is Employed for a Circuit Supplying 13A Socket-Outlet Intended
For General Use by Ordinary Persons , which of the Following does “ NOT “ Contribute to the Provision of Fault Protection ,
( Reinforced Insulation ) Part 4 : Protection for Safety , Regulation 411.1 (ii)
(a) Protective Earthing (b) Main Protective Bonding Conductor (c) Additional Protection by RCD ( d) Reinforced Insulation ) ←←
Basic Protection may be Provided by : Basic and Enclosures to IPXXB or IP2X (Part 4 : Protection for Safety , Regulation 416.2.1 ,
Which of the Following need “ Not “ be Tested Under Fire Conditions to Ensure Compliance with Non-Flame Propagating Requirements :
( a) Cables : ( b) Protective Devices ←←← : (c) Conduit Systems : (d) Trunking Systems : Part 4 : Protection for Safety , Regulation 422.2.1
In the Event of an Earth Fault on the HV side of a Substation the LV Installation may be Affected by :
( Uf ) Part 4 : Protection for Safety , Regulation 442.2
A Cable Concealed in a Wall Outside the Prescribed Zone at a Depth of Less than 50mm Must :
( be Enclosed in Earthed Metallic Conduit ) Part 5 : Section & Erection of Equipment , Regulation 522.6.6
239- this may come up in the Future ,
“ Client Demand for a Continuous Supply “
Where the Client Does Not want Any Interruption in the Supply and it is Not Possible to Work on Effected Area during Normal Working Hours ;
Arrangements should be Made for a Planned Maintenance or Shut Down in Order for the Repair to be Carried Out Safely
“ Earth Leakage “
“ Overload Protection “
“ Short Circuit Protection “
“ Over Voltage & Surge Voltage Protection “
“ Switch Line & Neutral for Increased Safety “
“ Will Replace Existing Earth Leakage Devices “
239-
Why do we Need to Confirm Correct Polarity ?
Incorrect Polarity can Give rise to Danger in a Number of Ways :
(i) Parts of the Installation May Remain Connected to the Line Conductor when Switched off by a Single-Pole Device but , for all Intents and Purposes , will Appear to be Dead :
(ii) in the Event of an Overload , the Circuit-Breaker or Fuse Protecting that Part of the Installation would Disconnect the Neutral of the Circuit , Leaving the Load at Full Line Voltage ,
(iii) An Earth Fault Current Might Remain Undetected by Overcurrent Protective Devices
Re-Cap :
Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions to Existing Installations ,
Domestic Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions Existing Installations , in a Single Dwelling ( House or Individual Flat )
Minor Electrical Installation Works Certificate -
Intended for Minor Installation Work that Does Not Include the Provision of a New Circuit ,
Periodic Inspection Report : for an Electrical Installation -
Intended for Reporting on the Condition of an Existing Installation ,
Nature of Supply Parameters :
Provision is Made to Record the Supply Parameters which Comprise ,
Normal Voltage(s) U ( Line to Line ) : Uo ( Line to Earth ) ( in Volts )
This Parameter can Generally be Determined Only by Enquiry ,
For Public Supplies in the UK , U / 400V and Uo 230V – Two Phase / Three-Phase Supplies ,
And U – Uo are 230V – Single-Phase Supplies
Nominal Frequency , ( f ) / Hz
This Parameter can Generally be Determined Only by Enquire , ( in UK Nominal Frequency ; Invariably ( 50 Hz )
For the Apprentice
What is GS-38 "IEE Guidance Note 3: Inspection and Testing ,Guidance Note GS38, published by the Health and Safety Executive ( HSE ), sets out in clear and concise terms the features that any instruments and meters should have if they are to be used to carry out electrical tests in accordance with BS 7671. In order to comply with the Electricity at Work Regulations 1989 it is critical that any competent person carries out electrical testing safely, and this guidance note draws attention to the risks of using test instruments that do not meet the GS38 standard. In brief, some of the requirements for test instruments include:
• The test probes should have finger guards, ideally 2mm or 4mm of exposed conductive tip (to prevent the user accidentally making contact with either the probes or live conductors under test) and should be fitted with a High Breaking Capacity inline fuse or fuse-and-resistor combination with a low current rating (to prevent the probes rupturing under high short-circuit currents and/or damaging the test instrument if incorrect range settings are used, typically drawing more than 500mA ).
• The test leads should be adequately insulated to suit the environment in which they’re being used, are coloured differently from each other so as to be distinguishable, are flexible, are capable of handling the maximum current range of the test instrument and are shrouded or sheathed to protect against mechanical damage, securely connect the leads to the test instrument and safeguard against the possibility of direct contact with live parts.
GS38 also Identifies Three Categories of Test Instruments, namely those that:
• Test for the presence of a voltage ( voltage detection )
• Measure Voltages
• Measure current and resistance ( as well as, in some cases, Inductance and Capacitance )
• Look at the test instrument, probes, leads and connectors for any obvious signs of physical damage. Have you stored the test instrument properly? Did you lend it out to someone that didn’t look after it ? Are there knots, kinks or cuts in the leads ? Is the case cracked ? Are the connections loose ?
• Look at the ratings on the test instruments, probes, leads and connectors to make sure they’re suitable for the job you’re asking them to do. Do you know what range you need to be using ?
• Does the test instrument have a calibration date on it? If you don’t know when the instrument was last calibrated, how can you be sure you’re getting the right readings ?
Before carrying out any actual tests, make sure you know all the procedures involved in carrying out safe isolation on the circuit(s) you intend to work on.
To sum up, GS38 has been designed both to keep both you and others safe and to try and define a clear standard that manufacturers can work towards to make sure electrical testing is carried out sensibly and safely. Although high-quality test instruments can be costly one-off purchases, keep in mind the cost of your own safety ! As with any tools, good quality instruments and meters pay for themselves many times over and being skilled in their use is a true measure of a Qualified and Competent Electrician .
For the Apprentice : some Revision ,
A 6A BS-EN-61009-1 RCBO with a Maximum Value of Earth Fault Loop Impedance of ( 1.92Ω is Type D )
( Part 4 : Protection for Safety , Regulation 411.4.7 ( 41.3 )
The Maximum Disconnection Time for a Circuit Supplied by a Reduce Low Voltage System Using a 110V Midpoint Earthed
Transformer is ( 5sec ) Part 4 : Protection for Safety , Regulation 411.8.3
Where Basic Protection and / or Fault Protection is Provided , Certain External Influences may Required Additional Protection
Provided by ( Use of 30mA RCDs ) Part 4 : Protection for Safety , Regulation 415.1.1
The Horizontal Top Surface of a Barrier or Enclose which is Readily Accessible shall Provide a Degree of Protection of at Least
( IPXXD or IP4X ) Top of CU : Part 4 : Protection for Safety , Regulation 416.2.2
The Symbol Used to Show that a BS-88 Device has a Motor Circuit Application is ( gM ) Symbols Used in the Regulations p-35 - 411.4.6
The Effectiveness of Protective Measures should be Considered with Regard to ( Maintainability ) -
Party 3 : Assessment of General Characteristics , Regulation 341.1
The Measure of Automatic Disconnection of Supply is Employed for a Circuit Supplying 13A Socket-Outlet Intended
For General Use by Ordinary Persons , which of the Following does “ NOT “ Contribute to the Provision of Fault Protection ,
( Reinforced Insulation ) Part 4 : Protection for Safety , Regulation 411.1 (ii)
(a) Protective Earthing (b) Main Protective Bonding Conductor (c) Additional Protection by RCD ( d) Reinforced Insulation ) ←←
Basic Protection may be Provided by : Basic and Enclosures to IPXXB or IP2X (Part 4 : Protection for Safety , Regulation 416.2.1 ,
Which of the Following need “ Not “ be Tested Under Fire Conditions to Ensure Compliance with Non-Flame Propagating Requirements :
( a) Cables : ( b) Protective Devices ←←← : (c) Conduit Systems : (d) Trunking Systems : Part 4 : Protection for Safety , Regulation 422.2.1
In the Event of an Earth Fault on the HV side of a Substation the LV Installation may be Affected by :
( Uf ) Part 4 : Protection for Safety , Regulation 442.2
A Cable Concealed in a Wall Outside the Prescribed Zone at a Depth of Less than 50mm Must :
( be Enclosed in Earthed Metallic Conduit ) Part 5 : Section & Erection of Equipment , Regulation 522.6.6
239-
this may come up in the Future ,“ Client Demand for a Continuous Supply “
Where the Client Does Not want Any Interruption in the Supply and it is Not Possible to Work on Effected Area during Normal Working Hours ;
Arrangements should be Made for a Planned Maintenance or Shut Down in Order for the Repair to be Carried Out Safely
Last edited by a moderator:
OP
amberleaf
2392 - Measurement of Prospective Fault Current Using a Two-Lead Instrument : ( Set , Loop – 20kA )
Take Particular Care During the Test Process ;as Fault Conditions are Most Severe at the Origin of an Installation ,
Where this Test is being Preformed ,
The Prospective Short-Circuit and Prospective Earth Fault Current are to be Measured ( or Determined by an Alternative Method )
At the Origin and at Other Relevant Points in the Installation ,
Note that a Measurement made at a Point in the Installation such as an Item of Switchgear fed by a Distribution Circuit would not be the Maximum for the Installation
The Earthing Conductor , Main Equipotential Bonding Conductors and Circuit Protective Conductors should all be Connected
During these Tests , because the Presence of these and any Other Parallel-Paths to Earth May Reduce the Impedance of the Fault Loop and so Increase the Prospective Fault Current , ( PFC )
The Instrument to be Used is an Earth Fault Loop Impedance Test Instrument , with or Without a Prospective Fault Current Range ,
A Set of Test Leads is Required , having Two or Three Probes to Suit the Requirements of the Particular Test Instrument ,
A Two-Lead Test Instrument Connected Across the ( Line and Neutral ) of an Incoming Supply ,Not that for Measuring a Line to Earth Value ,
The Instrument Must be Connected Across the Line and Main Earthing Terminal
Measurement of Prospective Fault Current Using a Three-Lead Instrument : ( Set , Loop – 20kA )
Three-Lead Instrument Connected Across the Line, Neutral and Earth of an Incoming Supply ,
Procedure :
Check that the Test Instrument , Leads , Probes and Crocodile Clips ; are Suitable for the Purpose ,
Select the Appropriate Range and Scale ( Prospective Fault Current 20 kA )
Observing all Precautions for Safety , Connect the Instrument to the Incoming Energised Supply to Measure a ( Line to Neutral Value )
Check the Polarity Indictor “ if Any “ on the Instrument for Correct Connection ,
Press the Button :
Record the Reading :
Repeat the above Steps ; as Appropriate , with the Instrument Connected for Measurement of the ( Line to Earth Value )
If the Test Instrument does Not have a ( Prospective Fault Current Range ) the Readings given by the above Procedure are
( Fault Loop Impedance in Ohms )
To Convert each of these Readings into a Prospective Fault Current ,
( Divide them into the Measured Value of Line to Neutral Voltage )
Measured Voltage : 230V / Measured Value of Fault Loop Impedance between ( Line & Neutral ) at the Origin = 0.05Ω
Maximum Prospective Short-Circuit Current ( Line to Neutral ) 230 ÷ 0.05 = 4600A / or 4.6kA
( This Value would have been Given Directly if the Instrument had a ( Prospective Fault Current Range )
The Same Procedure is Now Repeated , Taking Readings between ( Line and Earth ) to Determine the Maximum Prospective Earth Fault Current ,
The Higher of the Two Prospective Fault Current ( Line to Neutral or Line to Earth ) should be Recorded on the Certificate or Report ;
“ Warning “ Do-Not Test Between Lines with 230V Instrument :
Three Phase Supplies
Unless a Test Instrument Designed to Operate at 400V :
It will be Necessary to Calculate the Prospective Fault Current between ( Lines )
Where an Installation is Supplied by Two or More Phases , the Maximum Prospective Fault Current is Likely to be between ( Line Conductors )
The Prospective Fault Current Between Line can be Determined by Using the Measured Value of the Line to Neutral ( PFC )
Complex Relationship between the Line to Neutral and the Line / Line Values of Prospective Fault Current,
( tends to err on the Safe Side )
The Prospective Fault Current ( Line to Neutral )
( Line to Neutral Prospective Fault Current Multiplied by Two :
4.6kA x 2 = 9.2 kA
A Circuit-Breaker to BS-3871 will have an ( M ) Number Marked on it :
This Indicates its Short-Circuit Capacity in kA
M4 Denotes 4000A ( 4 kA ) M9 Denotes 9000A ( 9 kA )
Fuses are Not so Straightforward :
BS-3036 - 1 kA to 4 kA ( Depending on Duty Rating )
BS-1361 – 16.5 kA
BS- 88 – 40 kA to 80 kA ( Depending on Duty )
Overcurrent Protective Devices having a Rated Current up to 50A Incorporated in a Consumer Unit Conforming to part 3 of
BS-EN60439 : 1991 ( Annex ZA of Corrigendum June 2006 )
Are Considered Adequate for a Prospective Fault Current of up to 16 kA ,
Provided the Consumer Unit is Fed by a Service Cut-Out having an ( HBC Fuse ) to BS-1361 Type II ,
Rated at Not More than 100A , on a Single-Phase Supply of Nominal Voltage up to 250V
Schedule of Works Required for “ FIRE PROTECTION in a 2-Storey Semi-Detached / Terraced House
“ To Provide Adequate Means of Escape in Case of Fire “
Provide and Fix a Half-Hour Door ( FD ) FD-30S to any Room Other than a Bathroom or Water Closet ( WC ) which Opens onto the Ground Floor
Hallway or First floor Landing , Conforming to British Standards ( BS ) BS 476: Parts 22,23 / 31.1 Installation to BS-8214:1990
This will Normally Include the Ground , Floor Kitchen , Ground Floor / Lounge / Dining Room & the Fist Floor Bedrooms ,
These should be Hung on Three Hinges , which Comply with BS-EN 1935 ( European Notation ) to Leave Gaps Not Greater than 4mm ( Millimetres )
To the Head and Stiles and Not More than 8mm at the Bottom ,
If a Production Size Fire Door will Not Provide a Minimum Overall Gap of 4mm & 8mm Respectively the Either :-
(a) a Single Strip of Hardwood Lipping may be Glued and Pinned to the Door Edges :
(b) a BS-476 Fire Door Blank May be Cut to Size and the Vertical Edges Finished with Hardwood Lipping as Above :
1.2 insert a Combined Intumescent Strip / Smoke Seal to Routed Edges of the Stiles and Top Rail of the Door ,
Alternatively the Strip can be Fitted to the Jambs and Head of the Frame or Lining ,
1.3 Door Stops Do Not Need to be Changed Providing they are Sufficient to Retain the Door , if New-Planted Stops are Fitted they Must be
Fixed by 38mm No 10 Screw at 230mm Centres
1.4 Provide and Fix the Following Ironmongery :
1 . Self Closing Device of an Approved Type ( Perko , Briton , Dorma or Similar )
Garden Gate Type Springs and Rising Butt Hinges are NOT Acceptable :
2 . Latch – Mortice Latch , Tubular Mortice Latch , Mortice Sash Lock , all Complete with Suitable Knob or Lever Furniture ,
Or Cylinder Rim Night latch , we Would Recommend the Fitting of a Combined and Latch Unit , This is Lockable from the Outside
With the Use of a Key , and on the Room Side bt Means of a Thumb Turn ,
Note : Locks Do Not have to be Provided on Internal Doors , However if they are Fitted they Must Meet the Above Specification :
1.5 Exit Doors which are Required to be Fastened During Occupation of the Premises must be Made to Open Easily and
Immediately from the Inside , without the Use of a Key ,
( Fire Signs )
2.1 Provide and Fix to all Doors, a Sign Stating ” FIRE DOOR KEEP SHUT “ in Minimum Lettering of 5mm
2.2 Provide and Fix to any Understairs Cupboard Door , or Cupboard Door Situated off the Ground Floor Hallway or Fist Floor Landing ,
A Sign Stating “ FIRE DOOR KEEP LOCKED “ In Minimum Lettering of 5mm
2.3 All Fire Safety Signs should Comply with BS-5499 : Part 1:1990
2.4 Fire Safety Check List Notices ( as Enclosed ) should be Provided and Sited on the Inner Faces of all the Doors ,
Measurement of Prospective Fault Current Using a Two-Lead Instrument : ( Set , Loop – 20kA ) Take Particular Care During the Test Process ;as Fault Conditions are Most Severe at the Origin of an Installation ,
Where this Test is being Preformed ,
The Prospective Short-Circuit and Prospective Earth Fault Current are to be Measured ( or Determined by an Alternative Method )
At the Origin and at Other Relevant Points in the Installation ,
Note that a Measurement made at a Point in the Installation such as an Item of Switchgear fed by a Distribution Circuit would not be the Maximum for the Installation
The Earthing Conductor , Main Equipotential Bonding Conductors and Circuit Protective Conductors should all be Connected
During these Tests , because the Presence of these and any Other Parallel-Paths to Earth May Reduce the Impedance of the Fault Loop and so Increase the Prospective Fault Current , ( PFC )
The Instrument to be Used is an Earth Fault Loop Impedance Test Instrument , with or Without a Prospective Fault Current Range ,
A Set of Test Leads is Required , having Two or Three Probes to Suit the Requirements of the Particular Test Instrument ,
A Two-Lead Test Instrument Connected Across the ( Line and Neutral ) of an Incoming Supply ,Not that for Measuring a Line to Earth Value ,
The Instrument Must be Connected Across the Line and Main Earthing Terminal
Measurement of Prospective Fault Current Using a Three-Lead Instrument : ( Set , Loop – 20kA )
Three-Lead Instrument Connected Across the Line, Neutral and Earth of an Incoming Supply ,
Procedure :
Check that the Test Instrument , Leads , Probes and Crocodile Clips ; are Suitable for the Purpose ,
Select the Appropriate Range and Scale ( Prospective Fault Current 20 kA )
Observing all Precautions for Safety , Connect the Instrument to the Incoming Energised Supply to Measure a ( Line to Neutral Value )
Check the Polarity Indictor “ if Any “ on the Instrument for Correct Connection ,
Press the Button :
Record the Reading :
Repeat the above Steps ; as Appropriate , with the Instrument Connected for Measurement of the ( Line to Earth Value )
If the Test Instrument does Not have a ( Prospective Fault Current Range ) the Readings given by the above Procedure are
( Fault Loop Impedance in Ohms )
To Convert each of these Readings into a Prospective Fault Current ,
( Divide them into the Measured Value of Line to Neutral Voltage )
Measured Voltage : 230V / Measured Value of Fault Loop Impedance between ( Line & Neutral ) at the Origin = 0.05Ω
Maximum Prospective Short-Circuit Current ( Line to Neutral ) 230 ÷ 0.05 = 4600A / or 4.6kA
( This Value would have been Given Directly if the Instrument had a ( Prospective Fault Current Range )
The Same Procedure is Now Repeated , Taking Readings between ( Line and Earth ) to Determine the Maximum Prospective Earth Fault Current ,
The Higher of the Two Prospective Fault Current ( Line to Neutral or Line to Earth ) should be Recorded on the Certificate or Report ;
“ Warning “ Do-Not Test Between Lines with 230V Instrument :
Three Phase Supplies
Unless a Test Instrument Designed to Operate at 400V :
It will be Necessary to Calculate the Prospective Fault Current between ( Lines )
Where an Installation is Supplied by Two or More Phases , the Maximum Prospective Fault Current is Likely to be between ( Line Conductors )
The Prospective Fault Current Between Line can be Determined by Using the Measured Value of the Line to Neutral ( PFC )
Complex Relationship between the Line to Neutral and the Line / Line Values of Prospective Fault Current,
( tends to err on the Safe Side )
The Prospective Fault Current ( Line to Neutral )
( Line to Neutral Prospective Fault Current Multiplied by Two :
4.6kA x 2 = 9.2 kA
A Circuit-Breaker to BS-3871 will have an ( M ) Number Marked on it :
This Indicates its Short-Circuit Capacity in kA
M4 Denotes 4000A ( 4 kA ) M9 Denotes 9000A ( 9 kA )
Fuses are Not so Straightforward :
BS-3036 - 1 kA to 4 kA ( Depending on Duty Rating )
BS-1361 – 16.5 kA
BS- 88 – 40 kA to 80 kA ( Depending on Duty )
Overcurrent Protective Devices having a Rated Current up to 50A Incorporated in a Consumer Unit Conforming to part 3 of
BS-EN60439 : 1991 ( Annex ZA of Corrigendum June 2006 )
Are Considered Adequate for a Prospective Fault Current of up to 16 kA ,
Provided the Consumer Unit is Fed by a Service Cut-Out having an ( HBC Fuse ) to BS-1361 Type II ,
Rated at Not More than 100A , on a Single-Phase Supply of Nominal Voltage up to 250V
Schedule of Works Required for “ FIRE PROTECTION in a 2-Storey Semi-Detached / Terraced House
“ To Provide Adequate Means of Escape in Case of Fire “
Provide and Fix a Half-Hour Door ( FD ) FD-30S to any Room Other than a Bathroom or Water Closet ( WC ) which Opens onto the Ground Floor
Hallway or First floor Landing , Conforming to British Standards ( BS ) BS 476: Parts 22,23 / 31.1 Installation to BS-8214:1990
This will Normally Include the Ground , Floor Kitchen , Ground Floor / Lounge / Dining Room & the Fist Floor Bedrooms ,
These should be Hung on Three Hinges , which Comply with BS-EN 1935 ( European Notation ) to Leave Gaps Not Greater than 4mm ( Millimetres )
To the Head and Stiles and Not More than 8mm at the Bottom ,
If a Production Size Fire Door will Not Provide a Minimum Overall Gap of 4mm & 8mm Respectively the Either :-
(a) a Single Strip of Hardwood Lipping may be Glued and Pinned to the Door Edges :
(b) a BS-476 Fire Door Blank May be Cut to Size and the Vertical Edges Finished with Hardwood Lipping as Above :
1.2 insert a Combined Intumescent Strip / Smoke Seal to Routed Edges of the Stiles and Top Rail of the Door ,
Alternatively the Strip can be Fitted to the Jambs and Head of the Frame or Lining ,
1.3 Door Stops Do Not Need to be Changed Providing they are Sufficient to Retain the Door , if New-Planted Stops are Fitted they Must be
Fixed by 38mm No 10 Screw at 230mm Centres
1.4 Provide and Fix the Following Ironmongery :
1 . Self Closing Device of an Approved Type ( Perko , Briton , Dorma or Similar )
Garden Gate Type Springs and Rising Butt Hinges are NOT Acceptable :
2 . Latch – Mortice Latch , Tubular Mortice Latch , Mortice Sash Lock , all Complete with Suitable Knob or Lever Furniture ,
Or Cylinder Rim Night latch , we Would Recommend the Fitting of a Combined and Latch Unit , This is Lockable from the Outside
With the Use of a Key , and on the Room Side bt Means of a Thumb Turn ,
Note : Locks Do Not have to be Provided on Internal Doors , However if they are Fitted they Must Meet the Above Specification :
1.5 Exit Doors which are Required to be Fastened During Occupation of the Premises must be Made to Open Easily and
Immediately from the Inside , without the Use of a Key ,
( Fire Signs )
2.1 Provide and Fix to all Doors, a Sign Stating ” FIRE DOOR KEEP SHUT “ in Minimum Lettering of 5mm
2.2 Provide and Fix to any Understairs Cupboard Door , or Cupboard Door Situated off the Ground Floor Hallway or Fist Floor Landing ,
A Sign Stating “ FIRE DOOR KEEP LOCKED “ In Minimum Lettering of 5mm
2.3 All Fire Safety Signs should Comply with BS-5499 : Part 1:1990
2.4 Fire Safety Check List Notices ( as Enclosed ) should be Provided and Sited on the Inner Faces of all the Doors ,
Last edited by a moderator:
Reply to ***Useful Information For The Working Sparky*** in the Australia area at ElectriciansForums.net
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