R1+R2 of zero zilch nothing?......

[Baddegg]

Testing R1/R2 on 10mm/4mm T&E cable and the reading is 0.00? Never had this before, can I record 0 on the cert?

 

[Pete999]

Really??

Yes really mine did when I last saw it

 

[Ian1981]

Yes really mine did when I last saw it

What year was that then?

 

[Wilko]

Hi - my KT leads and croc clips are 0.03 Ohms. Perhaps confirm you get in that ball park with the null off.

 

[telectrix]

could always test with your wander lead, the resistance of which you should know ( typically 0.3 - 0.5 ohms), then deduct similar to previous suggestions.

 

[Strima]

could always test with your wander lead, the resistance of which you should know ( typically 0.3 - 0.5 ohms), then deduct similar to previous suggestions.

My wander lead is around 1.5 ohms, shall I chop 30m off to get the reading down?

 

[Toneyz]

My wander lead is around 1.5 ohms, shall I chop 30m off to get the reading down?

Only the middle bit so you have the ends.

 

[Deleted member 26818]

My wander lead is wireless.
I wonder where it’s gone?

 

[telectrix]

My wander lead is around 1.5 ohms, shall I chop 30m off to get the reading down?

my lead is 30m, so if i chop off 30m there be nothing left. a bit like elsparko's brain.

 

[Lucien Nunes]

I was always taught not record a 'measurement' of zero, mark it up as 0.01.

It's more satisfying to see a plausible-looking number but may be technically less correct. It depends whether whoever is reading the results understands measurements properly. If you give the precision, or it's apparent from the number of digits, you are not claiming that the resistance is actually zero, but that it lies in a range that is numerically displayed as zero on the instrument.

R=0.0Ω means R lies between -0.05Ω and +0.049Ω, +/- any of the normal sources of error: Instrument offset, scaling error, display precision error and reading error.
R=0.00Ω means between -0.005Ω and +0.0049Ω likewise.
For passive circuits obviously the negative part of the range is not applicable.

In engineering and scientific work, one must always record what the instrument displays. That way, the results should be reproducible by someone else with the same instrument. If you make it up, you can't backtrack in the light of some later discovery (e.g. that the instrument always reads 0.02Ω low) or that some assumption you made was valid, because the original information (that the display said 0.0Ω) is lost.

With MFTs and low resistance cables, I agree that a common source of error is making better contact during the test than during cable nulling, in which case the computed reading will be low by the amount that the stored null offset is high.

 

[GBDamo]

You cannot record zero on the cert as this would be incorrect, the cable is 8m long there must be some measurement of resistance there.

If your testers calibrated and functioning as designed then you enter the result it gives you, anything else is a fabricated number.

 

[Pete999]

You could always use a Low Resistance Ohmmeter.

 

[markythesparky]

What was the Zs reading for this circuit?

 

[Baddegg]

0.18 same as Ze,(tncs) i hit test 3 times when doing Ze and it was always the 0.18 mark (slightly lower but the 0.18 was the highest reading) Zs was probs straight onto bare cable after terminating into back of cooker (I would normally be happy to calculate Zs on a single radial like that but did the test anyway due to the low R1+R2) i installed new 2 way Cu after splitting the tails through a new henly block,new tails (25mm) new 16mm earth and new 10mm (IR >2000) as before no more than 8 mtrs from cooker to new cu (in trunking whole route) 100a main switch and 40a rcbo (rcbo tested fine 32.6 ms x 1 and 29 ms x 5) as per previous post I wasn’t willing to install new circuit in existing Cu due to state it was in,newish board (not to 17th Editon) but clearly not fitted by anyone with any experience of electrical works in any capacity ever,

 

[Baddegg]

Giving it some thought, if I’d gone with the lowest Ze of 0.16 and then did Zs and got 0.18 I’d have been happy but that still wouldn’t explain the 0 R1+R2 result? Or am I missing something?

 

[Pete999]

Giving it some thought, if I’d gone with the lowest Ze of 0.16 and then did Zs and got 0.18 I’d have been happy but that still wouldn’t explain the 0 R1+R2 result? Or am I missing something?

See post 56