Unusually low R1+R2 readings

[robbo777]

Hi All

So I've just extended two circuits and I've got home to type my results up for the certificate and I'm doubting my results, For the R1+R2 for the cooker circuit I got 0.02 ohms and for the ring I got 0.25 ohms, something seems a little off here.

Now by my calculations a 6mm cable should be giving me approx 0.03 per meter and the run to the board is approx 10m so i'm tinking my tester needs to go to be looked at, what do ya rekon?

 

[telectrix]

or you misread 0.20 as 0.02

 

[Des 56]

Or you didn't null your leads
Or your machine is not quite as accurate as you like to think
Or there are parallel paths
Or your eyesight is getting like the rest of us and its those eyes that need calibration

 

[ImpededLoop]

Tester set to the wrong range?

 

[robbo777]

Could be all of the above, I've just called the customer to tell them and that I'm sending my machine in to be recalibrated and then I'll be going round to retest, can't leave it with any doubt in my mind it'll drive me mad lol.

 

[Octopus]

Time to buy new leads! Is it a metrel?

 

[Silly Sausage]

Is this 0.02 reading from your MFT's memory (if it's got one) or is it a transcription error?

 

[robbo777]

Its a Kewtech KT65, leads are a few years old so maybe time to replace them

 

[robbo777]

Is this 0.02 reading from your MFT's memory (if it's got one) or is it a transcription error?

No it wasn't from the MFT's memory, I wrote it down with the intention of typing it up when I got home, the chances are I could have read it wrong or something daft like that but I can't be sure so I'll have to go back and retest.

 

[Andy78]

Hi All

So I've just extended two circuits and I've got home to type my results up for the certificate and I'm doubting my results, For the R1+R2 for the cooker circuit I got 0.02 ohms and for the ring I got 0.25 ohms, something seems a little off here.

Now by my calculations a 6mm cable should be giving me approx 0.03 per meter and the run to the board is approx 10m so i'm tinking my tester needs to go to be looked at, what do ya rekon?

Most probable that your MFT is not very accurate at low readings such as this. The R1+R2 of 6mm/2.5mm twin and earth cable should be 10.49mOhms/metre though according to OSG values.
0.25 Ohms for the R1+R2 of a ring final seems a perfectly reasonable result for an average sized house.

 

[Daveash123]

Why didn't you investigate when you got the low reading. Surely would be easier to check on site than ask in forum

 

[ImpededLoop]

Why didn't you investigate when you got the low reading. Surely would be easier to check on site than ask in forum

I would imagine that the OP has already thought that! Perhaps it had been a long day and it didn't occur until he came to write the certificate. We all have the occasional off-day...

 

[Deleted member 9648]

It's worth making or buying a simple calibration box. All you need is a couple of low value resistors (say 0.5 ohms or less and 1 ohm)and a 10 meg resistor,it's a simple matter then to verify your meters consistency on site.
I made ours for less than a tenner out of the above resistors,some brass M4 bolts and a 4x4 plastic box.