Zs - Ze = R1 + R2.. Is this right ??

[castlon11]

When doing electrical tests i've always been told the way to get R1 + R2 is to minus your Ze reading from all your Zs readings, is this allowed ?or do all dead tests have to be done, considering the results are almost identical everytime whichever way you do it ????

 

[Mac]

When doing electrical tests i've always been told the way to get R1 + R2 is to minus your Ze reading from all your Zs readings, is this allowed ?or do all dead tests have to be done, considering the results are almost identical everytime whichever way you do it ????

Are you sure you're not an inspectorI used to work for a spark that had software to work out most of the calcs.The bloke i worked with did the basic tests and the rest were done on the computer.Not good in my opinion,but what do you say to the bloke that pays your wages

 

[castlon11]

No im not read my last couple of posts and you'll see . Anyway thanks for the answer but not sure if i can use anyhing from it.

 

[Mac]

No im not read my last couple of posts and you'll see . Anyway thanks for the answer but not sure if i can use anyhing from it.

What do you want to use the info for.Just curious mate

 

[castlon11]

Well this is the way i have been taught to do the tests and everyone in my company does the same but we have been told that it is not allowed and doesn't always give the same results. So is there anything that says you cant do this or is it just not practical.

 

[saveloy]

An R1 + R2 dead test should be carried out to prove that you have continuity of cpc throughout the circuit that you are testing. This will also ensure that when you perform an IR test ,that you are testing all conductors for IR. Also an R1 + R2 test is used to prove correct polarity, and also that line conductors are switched in lighting circuits.

 

[castlon11]

Well this is the way i have been taught to do the tests and everyone in my company does the same but we have been told that it is not allowed and doesn't always give the same results. So is there anything that says you cant do this or is it just not practical.

Thanks but i know what the tests are for and how to test them but wondering does anyone know if this is just an inpractical way of doing this or it is infact not allowed

 

[jim_uk85]

I know where your're coming from on that one, I am unsure myself if it is correct or not. I was taught to use that method only when doing periodic inspections so you can spend a bit extra time doing visual checks such as routing of cables etc. On a new installation certificate i would do the test itself rather than just work out the calculation

 

[castlon11]

Thanks..Yes sorry i forgot to mention that this question was about PIR and EIC ect tests, anyone else know about these methods ?

 

[Des 56]

The way I see it
If you take the Zs and deduct the Ze you cant be sure that the R2 bit is the cpc or is some parralell paths giving you the same readings

The Zs could be taken this week and the R1+R2 calculated and next week a copper water pipe is changed to alcathene and bang goes your earth path

I think either a R1+R2 should be taken or an R2 as well as a Zs

 

[xraytek]

considering the results are almost identical everytime whichever way you do it ????

Is that true?
I would have thought Zs by calculation would be higher then live measurements due to bonding

 

[castlon11]

well this is what i want to get a clear picture of, as every-time I've played about with these tests the results are surprisingly similar, which although taking all your comments on board i believe it could be a sufficient way of testing... I would say to try the two different ways for yourself then let me know what your results are.

 

[Guest123]

Always, always measure R1+R2!

Using the Ze-Zs calculation is NOT an accurate way of obtaining the R1+R2 value due to parallell paths that exist.

As has been said R1+R2 confirms polarity and continuity and should always be measured.

 

[castlon11]

O.k thanks but how about the other way around ? do your R1+ R2 tests then add Ze to get your Zs results ? (sometimes i do this when the rcd starts tripping and giving ridiculously high readings)

 

[Guest123]

That is a more common practice and indeed will give an accurate result as you are eliminating those parallell paths that exist via pipework, structural steel etc, when measuring Zs with a meter, as the result of the calculation will concern that circuit only. Indeed a lot of chaps only use the calculation method for obtaining Zs.

There again when the cover is back on the DB the Zs of the circuit will be different because all the bonding conductors will be connected anyway.

Myself I always test Zs and then compare to the calculation, overkill I know but lets face it a calc only takes a few seconds to do.