Loop Impedance reading

[EddieB]

I would put my bets on RCD uplift as @telectrix suggested, I had some BG ones a while ago that made some circuits wildly high Zs.
If you can do a bypassed Zs on the circuit that will prove it one way or another. To do this I isolate the supply then put a R1+R2 link cable in between live and earth at the furthest point on the circuit in question. Then put the tester on high loop and place between the outgoing circuit feed and the non isolated incoming live, this will give you a non uplifted reading to compare with your current one!
Be very careful when doing this test!

Thank you for replying, funny enough these are BG RCD's, If it is the RCD I can bypass it by feeding a spare MCB from the incoming feed block the neutrals from the mains
and then test the ring.
I would appreciate a sketch showing the process you describe , you can either email it to me or put it on here whatever is the easiest if you wouldn't mind.

you could have errors caused by RCD or MCB. worst i ever saw was a Ze of 0.2 but measured on the outgoing terminals of the rCD it was 341.

Telectrix, thanks for reply, I appreciate it.

 

[telectrix]

here is a method.you turn off the RCD and/or MCB. short L-E at point you want to measure. them MFT on hi current Zs setting (2 leads).bridge to RCD.MCB with the meter. this will give you a true Zs.

don't forget to remove the short before re-energising.

 

[ELECNEWT]

In addition to Tel's excellent description and drawing see this link to Chris Kitcher carrying out this method:

 

[Mikegh]

here is a method.you turn off the RCD and/or MCB. short L-E at point you want to measure. them MFT on hi current Zs setting (2 leads).bridge to RCD.MCB with the meter. this will give you a true Zs.
View attachment 90663
don't forget to remove the short before re-energising.

Good method, can't say I've ever had to carry this type of check in practice,don't even have a 2-wire tester

The theory is routine enough though

 

[EddieB]

here is a method.you turn off the RCD and/or MCB. short L-E at point you want to measure. them MFT on hi current Zs setting (2 leads).bridge to RCD.MCB with the meter. this will give you a true Zs.
View attachment 90663
don't forget to remove the short before re-energising.

Thank you my man, I'll be doing this early next week and I'll let you know how it goes.

 

[Mikegh]

Is the high current reading like 20a ?

Better for troubleshooting those issues

 

[telectrix]

Is the high current reading like 20a ?

Better for troubleshooting those issues

something like that. the higher current helps to get past tarnished contacts, that's why low current test often gives slightly different results. ( well that's my theory, anyway ).

 

[Mikegh]

something like that. the higher current helps to get past tarnished contacts, that's why low current test often gives slightly different results. ( well that's my theory, anyway ).

Yes that's my theory on the low current testing , should be more reliable at the higher current here

Similar to IR troubleshooting at 1000v where it can be more effective at locating a fault, when safe to test

 

[Mikegh]

I would put my bets on RCD uplift as @telectrix suggested, I had some BG ones a while ago that made some circuits wildly high Zs.
If you can do a bypassed Zs on the circuit that will prove it one way or another. To do this I isolate the supply then put a R1+R2 link cable in between live and earth at the furthest point on the circuit in question. Then put the tester on high loop and place between the outgoing circuit feed and the non isolated incoming live, this will give you a non uplifted reading to compare with your current one!
Be very careful when doing this test!

Dont think you'll find these particular tests in any reference books will you ?

 

[SparkySy]

No but very useful at times!