Calculated Zs on an EICR

[TJC1]

Got asked to carry out and EICR on a doctors surgery (NHS)

On the previous inspection done 5 years ago, they stated under limitations.. The Zs reading of each circuit has been calculated.

In theory if you have a Ze + R1 + R2 then yes you would get the result, but isn't it still good practice to do your Zs test?

 

[buzzlightyear]

testing is now in order to see if it compliances, with the value of the mcb .

 

[Sintra]

Personally speaking I always prefer to measure Zs as this is the only test that confirms the complete circuit including protective devices. There’s always a possibility that you can have a high resistance accross a device that would result in a high impedance at the end of the circuit. This will never be found by calculation.

 

[TJC1]

testing is now in order to see if it compiles .

??

 

[buzzlightyear]

??

read GN note 3

 

[TJC1]

Most circuits that are not protected by an RCD are buried in the wall less than 50mm. Would you make a note of this C3 for every circuit?

 

[buzzlightyear]

Most circuits that are not protected by an RCD are buried in the wall less than 50mm. Would you make a note of this C3 for every circuit

yes .

 

[Risteard]

Most circuits that are not protected by an RCD are buried in the wall less than 50mm. Would you make a note of this C3 for every circuit?

Why not make a general observation rather than repeating it for each circuit?

 

[Ian1981]

Why not make a general observation rather than repeating it for each circuit?

Very true, otherwise you could have numerous codes related to the same thing

 

[cliffed]

Got asked to carry out and EICR on a doctors surgery (NHS)

On the previous inspection done 5 years ago, they stated under limitations.. The Zs reading of each circuit has been calculated.

In theory if you have a Ze + R1 + R2 then yes you would get the result, but isn't it still good practice to do your Zs test?

Why wouldn’t you do a zs test.

 

[Blissof89]

GN3 states that calculating you Zs is perfectly acceptable. Almost seems to advise it over live testing.

 

[telectrix]

GN3 states that calculating you Zs is perfectly acceptable. Almost seems to advise it over live testing.

written by suits at a desk, instead of us poor sods in the real world.

 

[Ian1981]

The regulations also state that zs can be obtained by other methods than direct measurement so technically it’s not against regulations if you don’t do a direct measurement.
As it’s an EICR I do direct measurement and don’t bother with the R1+R2 method
I use a wander lead connected to the MET and connect to exposed conductive parts(lights and the like) to verify they are connected to earth

 

[Blaspark]

Most circuits that are not protected by an RCD are buried in the wall less than 50mm. Would you make a note of this C3 for every circuit?

C2 according to napit codebreakers book. Their opinion not mine.

 

[Blaspark]

written by suits at a desk, instead of us poor sods in the real world.

Is it not actually better for various reasons. You can't do a live test for zs without bonding connected which will give you a lower value. However building works may permanently remove that parallel path.
If you use ze + r1 + r2 you get the highest possible value which will be more resilient.
No?

 

[westward10]

C2 according to napit codebreakers book. Their opinion not mine.

You not got a recycling bin for waste paper.

 

[telectrix]

it's a C3 all day long. only way you could justify a C2 is potential danger from a numpty nailing or screwing the cable.if it's within prescribed zones, then numpty deserves whatever he gets.

 

[Blaspark]

You not got a recycling bin for waste paper.

Why so harsh on the book. It's very difficult to decide what to put on the eicr personally I like to avoid that bs and defer to an "authoritive source"

 

[westward10]

It isn't an authoritative source though Code designation should be judged from knowledge, experience and any factors which are present on the day. You should not need a guide to steer you through an EICR and if you do maybe you need to question your competence for the task you are undertaking.

 

[Ian1981]

The code breaker book advises a C2 code for tails that are not the minimum required 25mm.
I mean where in bs7671 states that tails must be 25mm?
What if you have 16mm tails? Why is that a C2 if they are acceptable for the load they are connected to and satisfy the requirements for fault protection?

 

[Blaspark]

The code breaker book advises a C2 code for tails that are not the minimum required 25mm.
I mean where in bs7671 states that tails must be 25mm?
What if you have 16mm tails? Why is that a C2 if they are acceptable for the load they are connected to and satisfy the requirements for fault protection?

I'm not sure. Why is 25mm specified at all?

I agree that example seems counter intuitive

 

[Ian1981]

I'm not sure. Why is 25mm specified at all?

That’s my point.

 

[Blaspark]

That’s my point.

Maybe it would be good to know why the 25mm is specified, if we understood that we might understand why the c2 is in the book.
The iet do have a phone number. If they can't give a straight answer I might think they are talking sh*t but if you don't ask you won't know

 

[Blaspark]

Is it not actually better for various reasons. You can't do a live test for zs without bonding connected which will give you a lower value. However building works may permanently remove that parallel path.
If you use ze + r1 + r2 you get the highest possible value which will be more resilient.
No?

Anybody going to contradict this?

 

[Blaspark]

Personally speaking I always prefer to measure Zs as this is the only test that confirms the complete circuit including protective devices. There’s always a possibility that you can have a high resistance accross a device that would result in a high impedance at the end of the circuit. This will never be found by calculation.

I think that what you're saying is reasonable however we always test sockets with a plug, at least I do, so that covers that. Then you have lights, switches and other devices which are tested at the terminals to test the connection not the device.
So ze + r1+r2 is still best because it prevents parallel earth paths.

 

[cliffed]

GN3 states that calculating you Zs is perfectly acceptable. Almost seems to advise it over live testing.

Agree but to get your r1 + r2 reading-the curcuit needs to be switched off,so why not a zs test

 

[Blaspark]

Agree but to get your r1 + r2 reading-the curcuit needs to be switched off,so why not a zs test

Zs test is a live test. It also includes parallel paths which might be removed. There can be parallel which shouldn't be removed and there's a procedure for managing them.
Live tests are discouraged for obvious reasons as should be taking Zs values that include paths that may be removed.

 

[Ian1981]

Maybe it would be good to know why the 25mm is specified, if we understood that we might understand why the c2 is in the book.
The iet do have a phone number. If they can't give a straight answer I might think they are talking sh*t but if you don't ask you won't know

Dno on our new build sites stipulate 25mm conductors with a 16mm earthing conductor as they fit a 100amp fuse.

 

[cliffed]

Zs test is a live test. It also includes parallel paths which might be removed. There can be parallel which shouldn't be removed and there's a procedure for managing them.
Live tests are discouraged for obvious reasons as should be taking Zs values that include paths that may be removed.

It’s also an eicr zs should take place,leaving all Main bonding connected,how are you suppose to get the pfc & ze measured @ origin

 

[Blaspark]

Dno on our new build sites stipulate 25mm conductors with a 16mm earthing conductor as they fit a 100amp fuse.

In that case the c2 seems wrong.
Could it be that the codebreakers codes are only for installations done to the bs 7671 that the codebreakers book is for.
My codebreakers book for the 18th edition its codes probably may only make sense on an 18th edition installation.
However rcd for protection against shock is a general thing and it's ratings on that may apply retrospectively. I'd have to think about it.

 

[Blaspark]

It’s also an eicr zs should take place,leaving all Main bonding connected,how are you suppose to get the pfc & ze measured @ origin

Pfc/pscc are measured with bonding connected. Ze isn't. Zs is best always calculated.
I think so at least

 

[Blaspark]

If you can't switch off supply to take a Ze correctly maybe that should be a limitation on a eicr. Otherwise people might wonder why the Ze has dropped since the eic though it'd be obvious to the old hands here.

 

[cliffed]

Pfc/pscc are measured with bonding connected. Ze isn't. Zs is best always calculated.
I think so at least

Agree on the Ze,Zs can be cakculated this usually happens @ the design stage.
Are we actually saying no live testing.

 

[westward10]

I maybe incorrect but the calculated Zs test which seems to be coming prevalent is due to the possible risk of exposed live parts. This begs the question how Ze will be performed which is a required test and exposes the individual to similar exposed live parts.

 

[Ian1981]

I maybe incorrect but the calculated Zs test which seems to be coming prevalent is due to the possible risk of exposed live parts. This begs the question how Ze will be performed which is a required test and exposes the individual to similar exposed live parts.

That’s the likes of the Niceic sticking their beak in and quoting the EAWR for live working which is nonsense in my opinion

 

[cliffed]

On the Eicr tests we do,it’s a live test,with necessary risk assessments.
I’m getting confused here,waithing for the Eng v Wales match to begin,bbq at local pub.
Its hot,& in Uk ha ha
,

 

[Blaspark]

That’s the likes of the Niceic sticking their beak in and quoting the EAWR for live working which is nonsense in my opinion

Eawr allows live working.

 

[Ian1981]

Live testing is impossible to avoid.
Even if you obtain the Ze measurement from the dno, you should still verify it’s connection to earth externally by live testing

 

[cliffed]

Live testing is impossible to avoid.
Even if you obtain the Ze measurement from the dno, you should still verify it’s connection to earth externally by live testing

Defo

 

[Blaspark]

On the Eicr tests we do,it’s a live test,with necessary risk assessments.
I’m getting confused here,waithing for the Eng v Wales match to begin,bbq at local pub.
Its hot,& in Uk ha ha
,

Ok so you Zs live but how do you do Ir test?

Live testing is impossible to avoid.
Even if you obtain the Ze measurement from the dno, you should still verify it’s connection to earth externally by live testing

Yes you should and if you can't that's a limitation. To do so requires disconnected bonding which requires power off

 

[Blaspark]

I maybe incorrect but the calculated Zs test which seems to be coming prevalent is due to the possible risk of exposed live parts. This begs the question how Ze will be performed which is a required test and exposes the individual to similar exposed live parts.

Similar =/= same. Is the dB on the ceiling? Is the light on the ceiling?
Is Ze a necessary and unavoidable live test? Is Zs at light fitting an unavoidable live test?
And still... Parallel paths and consistent test reports. You don't want the eicr different to the eic and you don't want the eicr done differently each time a different company shows up.

 

[TJ Anderson]

Live working and live testing are two different things.

Also in my opinion (and we can all have them as Inspectors)....

Calculating Ze + R1 + R2 to give you recorded Zs value is not satisfactory and should only be used during initial verification of new install or changes to a circuit to give you a predicted value of Zs which you then confirm by measurement. By doing both tests, you also can highlight parallel earth paths just for you own sanity. Yes, sometimes Zs will be considerably less than Ze + R1 + R2, so what, if you understand parallel paths. When you do and R1 + R2 test you are making temporary changes to install (a link) and after it is put back it should be confirmed by a measured Zs. If only an R1 + R2 test is carried out then added to Ze and recorded as Zs, this creates the possible scenario that an installation gets left less safe following a EICR than when it started if a cpc was to be broken and not noticed.

Zs only is perfectly suitable for EICR as the system has already been commissioned and is operating.

 

[Blaspark]

Live working and live testing are two different things.

Also in my opinion (and we can all have them as Inspectors)....

Calculating Ze + R1 + R2 to give you recorded Zs value is not satisfactory and should only be used during initial verification of new install or changes to a circuit to give you a predicted value of Zs which you then confirm by measurement. By doing both tests, you also can highlight parallel earth paths just for you own sanity. Yes, sometimes Zs will be considerably less than Ze + R1 + R2, so what, if you understand parallel paths. When you do and R1 + R2 test you are making temporary changes to install (a link) and after it is put back it should be confirmed by a measured Zs. If only an R1 + R2 test is carried out then added to Ze and recorded as Zs, this creates the possible scenario that an installation gets left less safe following a EICR than when it started if a cpc was to be broken and not noticed.

Zs only is perfectly suitable for EICR as the system has already been commissioned and is operating.

"after it is put back it should be confirmed by a measured Zs."
Visual inspection is fine for that according to the rules.

"Calculating Ze + R1 + R2 to give you recorded Zs value is not satisfactory"
Every inspector can have his opinion. My opinion is that that statement is false.

"By doing both tests, you also can highlight parallel earth paths just for you own sanity."
If you want pal

"Zs only is perfectly suitable for EICR as the system has already been commissioned and is operating."
Do it differently each time and you don't get to see how the system changes over time, which is very valuable info.

You shouldn't do live tests if they aren't needed. You need to Ir test the circuit therefore you need to switch it off. Therefore you can do your r1+r2 at the same time.

If you can switch the whole dB off you can take a Ze if not its a limitation.

I'm repeating myself. It's boring

 

[westward10]

I think you are over complicating an EICR. The Zs reading whether there are parallel paths or not is the realistic value of the circuit in service. I understand on an IV you need to verify protective conductors and polarity before energizing the circuit but not on an EICR.

 

[Blaspark]

I think you are over complicating an EICR. The Zs reading whether there are parallel paths or not is the realistic value of the circuit in service. I understand on an IV you need to verify protective conductors and polarity before energizing the circuit but not on an EICR.

It's only complicated if you think about it. If you just do it the way is recommended by me and others you get all the benefits I seem to have to repeatedly state

 

[westward10]

I often do two readings at something like a water heater or boiler and have found on a couple of occasions no continuity of the cpc when disconnected but aside from that on an EICR I am not complicating matters after all I have 100 circuits a day to do

 

[Blaspark]

You guys seem so determined to do it live. I highly suspect that you do eicr on business that don't organise scheduled maintenance properly and don't understand the benefits and how easy it can be.
Are you guys doing eicr without ever switching anything off and with tons of limitations? It's how it seems.
I have no problem with live work when it's sensible

Doing 100 tests a day instead of 50 good ones is fine for earning cash but not good for the clients if they were half way wise

 

[westward10]

The 100 circuits was a joke. If you are removing all parallel paths what is your opinion of a circuit which has had supplementary bonding deliberately connected to it with the aim of reducing the Zs value so fault protection is maintained because this has effectively become part of the circuits fault path.

 

[Blaspark]

The 100 circuits was a joke. If you are removing all parallel paths what is your opinion of a circuit which has had supplementary bonding deliberately connected to it with the aim of reducing the Zs value so fault protection is maintained because this has effectively become part of the circuits fault path.

I think that's quite dodgy but allowed. I remember something specified like there has to be documentation for the duty holder so he/she is aware of the risks and isn't going to have it removed during building modifications and such. I suppose in such a case you can't use calculated values, which are deliberately worst case (a worst case building management is preventing happening) and should document it on your certs since on going management of that risk is necessary

 

[Blaspark]

Do you know where I find out about that in the regs or legislation? I can't remember right now