Require help with testing figures

Hello everybody, I'm new to this forum and require some help.
I'm an apprentice electrician studying in my 3rd year of college and have currently just passed my test and inspection exams. However I am struggling on 1 thing. Don't get me wrong, I know how to test and carry out all procedures correctly, but need help knowing where to look to verify my readings. I have the BS7671 17th Amendment book and the OSG, but where exactly am I looking to verify;
r1
r2
rn
(R1+R2) / R2

I know where to find Max Zs & RCD Trip times, and insulation resistance is simple enough. But I'm just a little rocky on finding the above max readings.

Any help would be appreciated.

there is no values given for max. resistances in bs7671 like there is for max. ZS's. if the Zs readings are within limits, then you know that the resistance values are OK. if you look at tables for 0hms/m for different cable sizes, multiply by ther estimated length of a cable, then you will have an idea of what the resistance should be.

telectrix said:

there is no values given for max. resistances in bs7671 like there is for max. ZS's. if the Zs readings are within limits, then you know that the resistance values are OK. if you look at tables for 0hms/m for different cable sizes, multiply by ther estimated length of a cable, then you will have an idea of what the resistance should be.

Click to expand...

Do you mean this table?
(Sorry for crappy quality, I'm using my cheap tablet )

View attachment 35589

Thats the one, then the next page gives you an adjustment for the t.

Hi,do not forget that these figures are theoretical,and will not take in to account,anomalies in conductor size or possible additional resistance,at every connection point,say at socket outlets.

This is where doing as much testing as possible,even when not required,will build up a mental picture of what's going on,and allow effective fault finding. For instance,two legs of a RFC,may both give a slightly different figure than what you estimate the circuits length to show,but,are equal.
If the two legs gave a reading closer to the expected length,but were somewhat uneven,this may point to increased resistance,at connections.

The figures in your books,are guides for expected values,but are certainly no substitute,for real-time assessment.

There are situations,IR testing springs to mind, where your testing will reveal a certain "fail",according to the guides,but you would NOT be replacing the item tested Wax on,Wax off...