Old problem with circuit length calcs

[sivoodoo]

Sorry to bring up an old post but im confused.

I have carried out tests on a kitchen ring final wired in 2.5mm/1.5mm T&E, results as follows:

r1=0.36 rn=0.34 r2=0.59

I then joined leg 1 of line conductor to leg 2 of cpc and leg 2 of line conductor to leg 1 of cpc and measured the R1+R2 at each socket outlet, the highest reading for R1+R2 = 0.26.

We know that:
1.5mm = 12.10 mOhms/m
2.5mm = 7.41 mOhms/m

12.10 + 7.41 = 19.51

19.51 mOhms/1000 = 0.01951Ohms/metre

therfore R1+R2 / 0.01951 = length in meters

0.26 / 0.01951 = 13.326m

But the cable I have used is about 35 meters?

Could someone please explain my results and offer any advice

Thank you all

 

[Lou7]

the readings seem ok to me, don't forget r1r2 will be double the length taking you up to 26m,I doubt if your meter is 100% accurate, I wouldn't worry about it if I was you

 

[Sparky Ninja]

The numbers look fine considering your readings.

If I was reviewing those figures I would be very satisfied.

(r1 x 1.67) should equal r2 - (0.36x1.67=0.60) You measured 0.59 which is spot on.

(r1+r2)/4 should equal R1+R2 - ((0.36+0.59)/4=0.24) You measured 0.26 which is expected.



As for the length, those numbers will never be 100%, for a kitchen ring final these numbers make perfect sense.

 

[ChristianG]

Thanks for that, at college I had a maths maniac who went very very deep into this and it confused me slightly. This has helped me get a better grasp of testing Thanks

 

[Sintra]

Sorry to bring up an old post but im confused.

I have carried out tests on a kitchen ring final wired in 2.5mm/1.5mm T&E, results as follows:

r1=0.36 rn=0.34 r2=0.59

I then joined leg 1 of line conductor to leg 2 of cpc and leg 2 of line conductor to leg 1 of cpc and measured the R1+R2 at each socket outlet, the highest reading for R1+R2 = 0.26.

We know that:
1.5mm = 12.10 mOhms/m
2.5mm = 7.41 mOhms/m

12.10 + 7.41 = 19.51

19.51 mOhms/1000 = 0.01951Ohms/metre

therfore R1+R2 / 0.01951 = length in meters

0.26 / 0.01951 = 13.326m

But the cable I have used is about 35 meters?

Could someone please explain my results and offer any advice

Thank you all

To calculate the length of your cable you need to add your R1 and R2 readings.
ie 0.36 + 0.59 = 0.95

0.95 / 0.01951 = 48.7M

or add your R1 and Rn readings
ie 0.36 + 0.34 = 0.70

0.70 / 0.01482 = 47.25M

Using these figures i would calculate your cable run to be between 47 & 49 M