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S

SKY

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Hi Gents.

What a lovely day - 27c in my living room!! Will need the fan tonight.

When ZE testing do you take the main earth out from the CU or the MET?

If you take it out of the CU would I get bad readings due as the earthing to the gas and water services?

Thanks
 
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Strima

-
Arms
Esteemed
Isolate and disconnect the earth to avoid parallel paths...

If you still have the bonding connected you wouldn't necessarily get a 'bad' reading but it would not be an accurate one.
 
S

SKY

  • Thread Starter Thread Starter
  • #3
Thanks Strima

Do I disconenct from the CU or MET?
 
S

SirKit Breaker

  • Thread Starter Thread Starter
  • #4
As long as you disconnect it from the installation you will be fine, usually from the earth block next to the cu or from the earth bar in the cu.

Cheers...........Howard
 

Amp David

-
Mentor
Arms
Disconnect from the DB/CU, this way you are verifying that the earth from any earth block to the CU is intact.

If bonding is connected to the earth block, then disconnect but if its into the CU earth bar no need, as you will have already removed the earth from said bar.

Hope it makes sense
 

Jimmy Boy

-
Arms
Where ever the main distributors earth goes to ? if it goes to the MET disconnect from there, if in CU from there, I am not being funny so don't take it so but do you actually know what 'Ze' is and the purpose for which you are obtaining the measurement ? if you don't I suggest you don't try and obtain it, understand what you are doing, why you are doing it, before you try and do it !..or risk an accident.

ATB J
 

Des 56

-
Arms
Esteemed
Hi Gents.

What a lovely day - 27c in my living room!! Will need the fan tonight.


Thanks
You surely must be talking about the south east of England

I don't think most people who live in that area realise that they have a completely different climate to just about everywhere else in Britain


Its a lovely day here where I live,except the clouds have blocked out all of the sunshine for all of the daylight hours and they seem to have an endless quantity of the wet stuff oozing out from them,as usual
You sure are spoilt,again, as usual :74:

Please just think of your rain drenched countrymen when gloating :sad_smile:
 
S

SKY

  • Thread Starter Thread Starter
  • #9
Where ever the main distributors earth goes to ? if it goes to the MET disconnect from there, if in CU from there, I am not being funny so don't take it so but do you actually know what 'Ze' is and the purpose for which you are obtaining the measurement ? if you don't I suggest you don't try and obtain it, understand what you are doing, why you are doing it, before you try and do it !..or risk an accident.

ATB J
Hi - Understand the reason for taking the ZE and adding the R1 + R2s to get ZS.
Just need refreshing - finished college a 18 months ago and TBH have not done much since so i'm just refreshing myself in prep for my Elecsa test next month.

Thanks All
 
O

oldtimer

  • Thread Starter Thread Starter
  • #11
It depends how the earths are run ie if you have a MET and the gas and water is connected along with the main DNO earth then disconnect the main earth and then test Ze once you have done this then reconnect. As long as you are measuring the main DNO earth only with no other earth connected then you have a proper reading ie no P paths and no borrowed earths
 
Sky, I would strongly recommend the IET GN3 book on I&T. It explains everything you will need to know, in a very easy-to-read way. The Elecsa assessor will like it if you have it in your library also.
Don't forget to isolate any installation which you are removing the earthing from.
 

Jimmy Boy

-
Arms
You will deffo need GN3 mate all though to be fair it's in the OSG you will need to get the live tests right

Good luck

J
 
S

SKY

  • Thread Starter Thread Starter
  • #14
Cheers:

Have New Green OSG, BGB GN3 (Yellow Cover) and NICEIC testing and inspecting book.
Need to have a good read.

Thanks All
 

Strima

-
Arms
Esteemed
Consider myself spanked by Mr Guitarist.
That's not a spank, that's a gentle tap on the bum to point you in the right direction... :lol:
 
Hi Gents.

What a lovely day - 27c in my living room!! Will need the fan tonight.

When ZE testing do you take the main earth out from the CU or the MET?

If you take it out of the CU would I get bad readings due as the earthing to the gas and water services?

Thanks
Sky please tell me that you're kidding. It's a pretty fundamental test and the reasons for it are not that hard to understand
 

Jimmy Boy

-
Arms
Top of the class so why do we measure for an impedance as opposed to a resistance ? R1 & R2 aren't impedance it might be worth exploring this to educate a little not for me lol !

J
 
Top of the class so why do we measure for an impedance as opposed to a resistance ? R1 & R2 aren't impedance it might be worth exploring this to educate a little not for me lol !

J
You really want to discuss impedance on a scorching hot Sunday morning??
And I thought I was a nerd... :)
 

Des 56

-
Arms
Esteemed
You really want to discuss impedance on a scorching hot Sunday morning??
And I thought I was a nerd... :)
Its not so scorching if you live in one of the UK rain forests
These dark water filled filled clouds covering the whole of the sky tend to put the dampers on such dreams
I'm trying to remember how many months since I last saw that shining thing that is rumoured to be up there
 
Its not so scorching if you live in one of the UK rain forests
These dark water filled filled clouds covering the whole of the sky tend to put the dampers on such dreams
I'm trying to remember how many months since I last saw that shining thing that is rumoured to be up there
Been several days of 30ish degrees here, and the sun is just burning everyone to a crisp who doesn't put factor 50 on. Very hard to sleep at night.
You are so lucky to have it cool and cloudy.....




Only kidding. It's bloody luvly :)
 

Strima

-
Arms
Esteemed
So all that dancing done by men with bells has paid off in Norfolk... :lol:
 
G

Guest123

  • Thread Starter Thread Starter
  • #29
Impedance can be said to be the total opposition to current flow in an AC circuit which is why when it comes to ohms law for AC circuits, we should be using Z (as it contains both inductance & capacitance) not R as R is only true for DC.
 

Jimmy Boy

-
Arms
^ This was my understanding also,however I assumed you could only measure (Z) on an energised circuit,so as to take account of Inductance and Capacitance as with a Ze test or a live Zs, however this leaves me with a niggle in my mind, if you can get Zs by adding R1+R2 (Pure Resistance) to Ze (Impedance) how can it be a true Z (s) measurement ?

J
 
A

amberleaf

  • Thread Starter Thread Starter
  • #31
Idon’t . as a rule
Idon’t . as a rule download onto the main forum .

Lenny. I do ask for your Indulges .



Thismatter is intended for 2394:



Pointsto remember : 2394 : ( Ze & ( Zs )



Earth-Fault-Loop-Impedance Testing



When Measuring ( Ze )the means of ( Earthing )

Earthing-Conductor must be disconnected from the Installation for the duration of the test. To remove parallel-paths .

- External-Loop-Impedance- ( Ze )



Measuring ( Zs ) neither the means of Earthing or theBonding-conductors must be disconnected to Retainthe ( Parallel-Path ) Lower ReadingsΩ .

- Circuit-Loop-Impedance( Zs )




- - - Updated - - -

Ido request the Members indulges . Thankyou .

Calculationsfor earth fault loop impedance

Earth-Fault-Loop-Impedance.

The. Earth-fault-loop-impedance is given by .

(Zs = Ze + R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Thevalue of ( Zs ) can be found by .

i). Measuring the . earth-fault-loop-impedance - ( Zs ) at the furthest-point .
ii). Measuring the . earth-fault-loop-impedance - ( Ze ) at the Origin of theInstallation ( at the Incoming-supply& adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

iii). Taking the . earth-fault-loop-impedance - ( Ze ) provided by the DNO . &adding - ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Pointto Note : Obtaining the value of ( Zs )Measurement of ( Zs )
Readings obtained using this method will be ( Less-than ) Ze + (R[SUP]1[/SUP] + R[SUP]2[/SUP] ) because of .Parallel-Earth-Paths .

(Zs ) Plug-in - Instrument Loop-setting . will give you . Earth-Loop-Impedancevalue . 0.3Ω

Earth-Fault-Loop-Impedance. Test on a circuit - ( Zs )
Live-Test : ≈

Thereason for this Test . is to ensure the . Earth-Fault-Loop-Impedance ( Zs ) isLow enough to ensure that enough current can flow through the circuit to operate the protective-device in therequired-time .

Thissocket-outlet is protected by an RCD .
ToCarry out this Test . Instrument that will use a Low-current to carry out this Test .

Note - The Socket-Outletis Switch OFF .
Instrument: Megger - LTW325 : ( Loop) Set it to No-Trip . Plug in into theSocket-outlet . “ switch it On “ Your reading - 0.35Ω

Compareit directly to the O.S.G. - Table B6 - p.119
(32A ) type B . protective-device .

Useyour chart . go down Left-hand column (B ) along the Top ( 32A ) three-down .where the linesmeet these a value of ( 1.24Ω ) 1.24is higher than 0.35Ω
0.35Ω being lower . more current will flow throughthe system than required to operate the circuit-protective-device .

 
A

amberleaf

  • Thread Starter Thread Starter
  • #32
(Ze ) That part of the . Earth-Fault-Loop-Impedance . which is external to theInstallation .
External-Impedance.

Live-Test : ≈
ForSafety-Reasons : it is Essential that the entire installation is Isolated fromthe supply - Before the ( Earthing-Conductor isdisconnected )

Switchoff the Main Switch - 100A .
(Incoming Protective-Conductor ) 2394 :You are Disconnect the Earthing-Conductor from the . Main-earthing-termnal inside your Consumer unit . .

Instrumentam using - Megger - 1552
Connectyour GS-38 . Black-lead with crocodile-clip . on to the disconnected- Earthing-Conductor .
Setyour . megger to Hi-loop .
( Your Instrument is On - stand-by )

Connectyour GS-38 . Red-lead with insulating-tip . onto the main incoming Line-conductor
(Your megger will automatically start when you put the Otherprobe onto the Line-conductor ) Schedule of Test-Results. reading 0.28Ω .

Insulating-tip- 2mm isfor Live-Testing . Finger’s Etc .
Dead-Testing. by removing it your have 4mm - probe .

For Obvious Reasons
The- Earthing-Conductor . must be reconnected ( Before- re-energising ) the supply to the Installation . -&-s for Safety-Reasons. Exams

2394; for Initial-Verification . we take it toobe Norm .

The- ( Earthing-Conductor ) must be disconnected from the ( MET )main-earthing-terminal .
( Inside theconsumer-unit ) Or
(Outside the consumer-unit )
-Brass-Earth-Block . ( MET )
-Chrome-Earth-Block . ( MET ) “ 4-way or 8-way “
 
A

amberleaf

  • Thread Starter Thread Starter
  • #33
SomethingI knocked up .

ThisQualification 2394: was introduced as aprogression or “ Interim “ Qualification to help those who wanted to go on tocomplete the 2395 .

2394: Your . Emphasis is on AchievingSuccess . What you put ( In ) you will get ( Out ) . Yeah . No Quick-Fix here. Study . Closed-book . multiple-choice & Practical
Everythinghas a Knock-on-Effect .
ThePractical-part of this course assumes ( No )prior knowledge of Inspection & Testing . 2394 : Your are practicing-Electricians .

2394: - Inspection & Testing

Inspection& Testing : which will fall into your category of Certificate &Reporting .
P.29 . Inspection . Examination of an electrical-installation using all the senses asappropriate .
p.36 : Testing . Implementation of ( Measuring ) to assess an electrical-installation by means of which its effectiveness is proved . This includes ascertaining (Value ) by means of appropriate measuring-Instrument(s) where measured values are not detectable byInspection .
p.36 : Verification . All ( Measures) by means of which compliance of theelectrical-installation . with the relevant requirements of BS-7671:2011: arechecked . comprising . 2394 : Yourreason(s) . Inspection . Testing &Certificate .
p.31 : Origin of an Installation : The position at which electrical-energyis delivered to an electrical-installation .

Firstly: On the Test-boards / Demonstration-boards . Simulating . an Electrical-Installation . in Theory .
Secondly: Your first line of defence is . “Visual - Inspection . the Question youare asking you’re self . has it been. Visually - Inspected ??

Bearingin mind the Type of Inspection . ?? Domestic - Installation ( EIC) Electrical-Installation-Certificate .
Opportunity to perform an Initial -Verification . Inspecting & Testindividually . on the Day .

Therequired-Testing which has been Specially-designed.
TheWording which am using carefully . Specially-designed ◄►Resistors . Insideappliances . there will be Faults . Socket-outlets . Spurs . Lighting ??

Inorder to perform the Tests . you are using a Range of Test-Instrument(s) .
GN-3. p82 : the Instrument used for Low-résistance tests . may . Continuity-range ofan Insulation - & - Continuity-tester .
Weall know we all use . Multifunction - Testers .
•Using Test equipment correctly .

Certificate& Reporting : Schedule of Test Results .
p.389 - (viii ) : Schedule of Inspection& Schedules of Test-results as required by. Part-6 . should be issued with the associated ( EIC - New) or ( EICR - Existing )
Whatdoes Certification tell us . Reportingon Condition(s) on Existing or Initial -Verification .

p.392 . ( EIC ) point to Note. You are Issuing “ Safety-Certificate “ you are complying withBS-76717:2011: You are in the eyesof British-Standards Competent Person .

p.25 : Competent Person .
Aperson who possesses sufficienttechnical knowledge . relevant practical skills Etc . you are proving yourSelf to be an Inspector .
p.389 . Informative . “ My-Reason “
(i) the ( EIC) required by part-6 . should be makeout & signed or otherwise authenticated by a ( Competent Person ) or persons in respect of the design .construction . Inspection & Testing
(v) the ( EIC) Where Design . Construction .Inspection & Testing are the ( Responsibility of One-Person ) a Certificate with a ( Single-signature ) Declaration

Testing. fall into Two-Categories . Dead-Testing . Live-Testing .
Therequirements for . Inspection & Testing a New-Installation ( Initial -Verification ) including . Visual-inspection . Dead-tests . Live-tests . & Completion of the( Associated-documentation)

2394: Points to Watch for .
GN-3. p84 : RCD testers - BS-EN-61557-7 . Tocheck RCD-operating & to minimise ( Danger ) duringthe Test . the Test-current should beapplied for no longer than ( 2s ) -&-s
GN-3. p83 : Earth-fault-loop-impedance - BS-EN-61557-3 . This means that theinstrument should cut-off the test current after ( 40mS ) -&-s .



 

Des 56

-
Arms
Esteemed
^ This was my understanding also,however I assumed you could only measure (Z) on an energised circuit,so as to take account of Inductance and Capacitance as with a Ze test or a live Zs, however this leaves me with a niggle in my mind, if you can get Zs by adding R1+R2 (Pure Resistance) to Ze (Impedance) how can it be a true Z (s) measurement ?

J
I think you make a good point and it appears to me initially that it is indeed an untrue Zs (when the external impedance and the resistance only is used)

It also seems to me that the impedance of the circuit would mainly only be affected when there is an applied load and that for all intents and purposes, the Ze +(R1+R2) would be the same value as the circuit impedance, when the circuit load is just the test meter

At least that's my take on it
 
A

amberleaf

  • Thread Starter Thread Starter
  • #35
GN-3. p.53
2394:point to Note . ( Ze at the Origin ) for Domestic-Installation in our case .

GN-3. reminds us .
ForLarger-installations with consumer-units . or distribution-boards - ( Not at the Origin ) therecan arise . confusion over the “ Term “ External-earth-loop-impedance( Ze ) & some prefer to Write orNote the . earth-fault-loop-impedance at the . ( distribution-board as Zdb ) as . Strictly-speaking . this value is not . External to the installation. Thus . the formula is denoted . ( Zs = Zdb + R[SUP]1[/SUP]+ R[SUP]2[/SUP] )

GN-3 - p.52.” Verification “
(Ze ) is the part of the . Earth-Fault--Impedance . External to the circuit - concerned .( Ze ) can be anywhere you choose to referit ( To)
Inthis case .

(Zdb ) Earth-fault-loop-impedance . at a ?. Distribution-board or Consumer-units . which is ( Not-directly-connected tothe Origin of an Installation)

 

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