Concerning R1 + R2 and r1,rn,r2 ring final results ?

[Soulsurfer]

Hi all,
Can anyone shed any light on some strange really low readings on a ring final circuit I've just 2nd fixed including replacing some legs as the IR was bad in places on old cabling before.

Thought it could be my MFT batteries going and therefore giving possibility of silly results but upon getting home I tested a part used drum of 1.5mm T & E and got good results ! I'm new to doing my own testing so am a bit baffled. Drum I tested I estimate at 60-70 metres or so left on maybe a touch more but can't find my OSG to look up the resistance per metre of 1.5 Twin, readings were L-E 1.43 ohms, N-E 1.49 ohms, and L-N 1.15 ohms which looked reasonable whereas on the ring r1 was 0.00 ohms, rn also 0.00 ohms and r2 0.16 ohms !! Thinking something silly has been overlooked here ? R1 + R2 tested at almost certainly furthest point too and had 0.00 ohms there too ?? Have two sockets wired as spurs too and no difference there either ! I expected higher resistance readings on them.

Half hoping that due to being up best part of week these nights with poorly 5 yr old my brain has overlooked a fundamental mess up !

 

[davesparks]

It sounds like incorrect nulling of the leads to me

 

[Soulsurfer]

Hey Dave, I actually forgot to post that I read exactly that and also batteries on the decline on the Fluke giving spurious readings and the batteries are low'ish showing on self test at 7.2V and should be 9V when new batteries in it. But by testing the drum of 1.5mm I thought if batteries I'd still get 0.00 or near, but I actually got a reading as above that looked o.k.

I did null leads using the zero function and via deducting the read resistance myself to make sure, Croc clips together and by using the little fluke zero adapter that was in the case ! ( piece of pricey metal !! lol )

and usually once zeroed / nulled it's retained as zero but this time / a few times it read 0.07 ohms say, then after showed random 0.3 ohms on display etc.. or such like but when continuity tested was reading leads at zero ! so seemed o.k. so tried zero / null button again and get a different reading each time on leads and then instead of 0.0 on screen would show random still results ! weird that. It's a 1653B in case that makes any odds and has been brilliant and calibrated 2 months ago.

 

[ruston]

Have you tried it with another set of leads.
I am not familiar with fluke , but leads can be worky tickets.

 

[Soulsurfer]

Not as yet Ruston, just thinking if leads were shot surely all other tests like IR, Zs etc.. would've gone the way of the pear too ?

 

[ruston]

I'm sorry I must not of read post properly , I did not see were you had done IR testing .
If leads were faulty it would show through the ranges.

 

[Soulsurfer]

I'm sorry I must not of read post properly , I did not see were you had done IR testing .
If leads were faulty it would show through the ranges.

No apology required buddy, I never mentioned that I had done IR tests or similar, only listed the r1 rn etc.. at first, just thought even though basic stuff that I may have made a huge fowl up somehow.

 

[ruston]

As I said , I am not familiar with MFT's. I use Megger separates. I had a similar problem with a faulty lead; and a bad contact on the batteries.

 

[David M]

As it has already been mentioned, it sounds like faulty leads. I had a similar problem last year with mine and a new set sorted the problem.

My leads were intermittently faulty, which I discovered when I compared them to my mate's leads (same make leads) on my tester

 

[Soulsurfer]

OK great, I have spare leads of different makes and I'll get some new batteries too and try that next day or so. Cheers all.

 

[Pete999]

Hi all,
Can anyone shed any light on some strange really low readings on a ring final circuit I've just 2nd fixed including replacing some legs as the IR was bad in places on old cabling before.

Thought it could be my MFT batteries going and therefore giving possibility of silly results but upon getting home I tested a part used drum of 1.5mm T & E and got good results ! I'm new to doing my own testing so am a bit baffled. Drum I tested I estimate at 60-70 metres or so left on maybe a touch more but can't find my OSG to look up the resistance per metre of 1.5 Twin, readings were L-E 1.43 ohms, N-E 1.49 ohms, and L-N 1.15 ohms which looked reasonable whereas on the ring r1 was 0.00 ohms, rn also 0.00 ohms and r2 0.16 ohms !! Thinking something silly has been overlooked here ? R1 + R2 tested at almost certainly furthest point too and had 0.00 ohms there too ?? Have two sockets wired as spurs too and no difference there either ! I expected higher resistance readings on them.

Half hoping that due to being up best part of week these nights with poorly 5 yr old my brain has overlooked a fundamental mess up !

Appendix I Page 190

 

[Soulsurfer]

Hey all, not been back to the install yet but did a different place today and got new batteries, tried different leads and another tester too and both gave same results on a number of tests as my MFT did on old batteries and leads old & new read the same !

Thats made it seem even stranger now, prob back to site on Sunday and will go over test again !

 

[i=p/u]

Reading your first post I was thinking open circuit ... What you upto sur

 

[Soulsurfer]

What you up to sur ??
You've lost me mate.

 

[i=p/u]

Forget my jokes,

just when u said in original post you got r1 0.00 rn 0.00 but r2 0.16

suggests open circuit, no loop

isit possible cables mixed up somehow

 

[davesparks]

Forget my jokes,

just when u said in original post you got r1 0.00 rn 0.00 but r2 0.16

suggests open circuit, no loop

isit possible cables mixed up somehow

Quite the opposite, 0.00 is no resistance or a perfect conductor

 

[Soulsurfer]

That's exactly what blew me away first time as the readings were as if there was no resistance on the entire circuit, definitely ring as quite a few legs were removed along with old JB's as the IR as installing new cabling was 0.77 Megohms on the lounge, hall & bedrooms x 2 ring final cct. Replaced legs as client did not want a rewire in entirety and IR was all at >500Mohms after replacing old legs, also tested each leg before and after to identify if perfect IR before testing from CU ( also replaced ) at the end. This is when I had very low / perfect ( although not feasible ) r1, etc.. But yet Zs was ok !

 

[Soulsurfer]

Rough estimate entire ring circuit approx 35 metres including 2 x sockets ( one each bedroom ) wired as spurs although still not got some resistance. Will need to check OSG tomorrow and total up resistance value as wont be much on 35 metres or so of 2.5/1.5 twin.

 

[Soulsurfer]

Surely on the MFT open cct reads usually >2000 ohms.

 

[Soulsurfer]

Update: today while finishing the whole job I got great results ! r1 0.41, rn 0.43, r2 0.78 & R1+R2 0.35 with Zs at 0.79 slightly above calculated Zs but well within 1.1 ohms Zs allowable so really happy
and just completed the certs now !

time to get paid and same guy just bought another house to fix up from ground up 3 storey and put in planning for another property new build too ! No rest for me then... You're all legends for your help guys and if ever you're in Jersey I'll get the beers in.