Who does just a Zs when carrying out a periodic on a lighting circuit

[nickblake]

Just answered a question on another post ,and it dawned on me , yippee the brain kicked into gear , i have read on loads of posts that people say doing an inspection just calculate the R1R2 by doing a Zs and taking away the Ze , i have never liked this method and heres a reason why , supplimentary bonding !!!!! you go into a house you do an R1R2 test you get a reading if there are any open circuits it shows up and it can be rectified , so what happens if the install is up to 16th edition all supplimentary bonding is in place ,3/4 the way through the lighting circuit there is a bathroom with an electric shower , you find the last on the run bedroom next to the bathroom quick Zs all ok , heres the scinario , the cpc's have have been cut off at the first light switch , metal clad switches and light fittings , so you test the last on the run get a good Zs reading fill in the sheet calculate the R1R2 and walk away ,so what if the supplimentary bonding has been installed between the shower and the light as it was in the 16th edition ,you then will have a reading which is false and potentially leave the entire un earthed circuit thinking its ok , so the moral of the thread is R1R2 Insulation and Zs simples easy to see the supplimentary bonding and and not put 2 and 2 together , thank you malcom for kicking my brain into gear on this one just a comment he made made me think :devilish:

 

[Sparky Ninja]

R1&R2 should never be calculated from Zs and Ze. It can only be calculated from resistivity, factors and length.
I believe that it's never been written down as an acceptable method, if it has I would like to see it.

 

[DurhamSparky]

got my arse kicked by Elecsa when i calculated on my first assessment ZS-ZE... never did it since and luckily i never got reassessed as it went down as observation only!

 

[nickblake]

Totally agree widdler but you see posts on here saying just do a Zs when inspecting , and my post is just there to high light why it should never be done , yes to calculate the Zs but not to back calculate ,

 

[IQ Electrical]

Totally agree widdler but you see posts on here saying just do a Zs when inspecting , and my post is just there to high light why it should never be done , yes to calculate the Zs but not to back calculate ,

Ha, let them try it in a decent sized industrial installation, you can almost end up with a negative R1+R2 once the parallels have taken effect!

 

[Spudnik]

On a new or altered installation there is no excuse not to carry out the dead test as well as live tests.

On a PIR..... well......errrrr....

 

[Sparky Ninja]

Totally agree widdler but you see posts on here saying just do a Zs when inspecting , and my post is just there to high light why it should never be done , yes to calculate the Zs but not to back calculate ,

If you see any of them pop up again mate can you refer them to this thread, that is advise we have to eliminate from here.

 

[nickblake]

yep i see what you are saying jason , one i will remeber did a R1R2 on a lighting circuit tested out ok , but the was something not quite right , found out that half way though the circuit the polarity changed then changed back again , 4 lights had an incorrect polarity so now i do tend to do an R1R2 at every lighting point

 

[Deleted member 26818]

I don't generaly measure or record R1+R2 on PIRs, unless the power is off.
I just conduct a Zs test at each fitting to prove continuity, and operate the associated switch to prove polarity.

 

[nickblake]

If you see any of them pop up again mate can you refer them to this thread, that is advise we have to eliminate from here.

yes mate i most certainly will

 

[IQ Electrical]

I don't generaly measure or record R1+R2 on PIRs, unless the power is off.
I just conduct a Zs test at each fitting to prove continuity, and operate the associated switch to prove polarity.

The test is 'continuity of protective conductors' and there is no requirement to have a value, only to prove continuity.

If your 'buzzer set' meets the requirements for continuity testing (current and voltage) then you're there.

Using EFLI only as a continuity of protective conductors test will probably open up a few more pages of debate....

 

[Sparky Ninja]

I don't generaly measure or record R1+R2 on PIRs, unless the power is off.
I just conduct a Zs test at each fitting to prove continuity, and operate the associated switch to prove polarity.

The key thing there being that you don't record calculated values.
I take it you don't do verification of voltage drop then?

 

[Deleted member 9648]

Totally agree widdler but you see posts on here saying just do a Zs when inspecting , and my post is just there to high light why it should never be done , yes to calculate the Zs but not to back calculate ,

There are two instances on a PIR where it IS acceptable to omit R1+R2 and just carry out a Zs.

1. Where a previous full schedule of test results is available to the inspector it is permitted to carry out a Zs test and compare to previous recorded results. If the measured Zs is the same or very close to the previous recorded Zs it is reasonable to assume the R1+R2 will also be the same and omit that test, if the results were not substantially the same the R1+R2 would need to be verified.

2. Where it is agreed with the client that an R1+R2 test should not be carried out in order to minimise disruption to essential supplies.

In both instances it should be stated on the extent and limitations section that R1+R2 tests were not carried out and the reasons why.

It is quite wrong to state that an R1+R2 test should always be carried out on a PIR

 

[nickblake]

i have to on a PIR software goes nuts if i dont fill it in , i do like to see what the readings are on an R1R2 test then i can get an approximate idea of what the Zs reading should be and take into account of parralell earth paths etc , if i dont do it the testing just doesnt feel right i know it sounds daft when you use a method for so many years , like changing from a manual gear box to an automatic i suppose

 

[Deleted member 9648]

i have to on a PIR software goes nuts if i dont fill it in , i do like to see what the readings are on an R1R2 test then i can get an approximate idea of what the Zs reading should be and take into account of parralell earth paths etc , if i dont do it the testing just doesnt feel right i know it sounds daft when you use a method for so many years , like changing from a manual gear box to an automatic i suppose

I know what you are saying,but there are plenty of situations when doing a PIR when it just isnt practical,or entirely neccessary. Technically the DB should be isolated when R1+R2 testing...which can take a considerable time on a large DB with multiple circuits.....it just may not be feasible in a typical working environment.