R1+R2 per metre - trying to test against book values.

[newtothis]

I find working as a labourer I never have to think about basic theory, so it's easy for me to forget.
Doing some experimenting tonight with 11meters of 2.5 T&E and a continuity tester.
End to end on the line 0.15ohm CPC 0.20 Ohm

It's not exactly what I expect. Is the difference something to worry about or not ?
0.35 Ohm measured and 0.21Ohm theoretical

OSG Page 190 table 11
2.5/ 1.5 mm2 cable R1+R2 resistance per metre m ohm 19.51

19.51 x 11mtrs = 0.21W (R1+R2)
1000

I realise I could be barking up the wrong tree somewhere, it's very frustrating. :smiley2:

 

[telectrix]

so have you nulled your leads for both measurements? and don't forget, if measured cold, the resistance will be lower. then nthere'salways the problem of a bit of contact resistance on your croc clips to the casble.

 

[newtothis]

so have you nulled your leads for both measurements? and don't forget, if measured cold, the resistance will be lower. then nthere'salways the problem of a bit of contact resistance on your croc clips to the casble.

Thanks for your time Telectrix
is there a correction factor for that, am I supposed to multiply the 0.35 by 0.8 ?
nulled the crocs and clamped them on nice and tight. They were reading 0.06 before nulling.

 

[telectrix]

the 0.8 is used to correct from 20deg. to 70deg. in normal usage, 70deg.is rarely seen.

 

[newtothis]

oops I'm getting that 0.8 from calculating the working Zs.

Hmmm...I'm learning essential skills on the practical side, at the same time the theory is going out the window.:sad_smile:

 

[Leesparkykent]

Might be wort getting a calcard so you can check the accuracy.

 

[newtothis]

Might be wort getting a calcard so you can check the accuracy.

thanks Leesparkykent, I've just got the tester back from megger today, with a cert saying it's within spec.
One of those calcards is on my list though.

 

[telectrix]

generally, for measurements below 1 ohm, i don't null leads, just subtract after. tends to give more accurate results.

 

[newtothis]

Just been and tried that L 0.15 CPC 0.20 ohm
when the line is 0.15 the ratio 1.67 it should be more like 0.25 ?
Do you fallas think I should speak to megger tech support, I didn't want to speak to them
with lack of knowledge and look like a mug LOL

 

[Leesparkykent]

Have you got another set of leads you can try?

 

[newtothis]

I haven't got a spare set, I'm using the leads they asked to be sent away with the tester.
I'd assume they tested with them, but you never know.

I just tried swapping the blue lead in each terminal for each in turn but the reading stayed the same.
Do you think I have enough to call them up and put my findings to them ?

 

[newtothis]

Borrowing some leads tommorow
Will test on an installed circuit if it don't work I'm not having it back - fed up.
Then again; it's not the end of the world. :grinningelf:

 

[newtothis]

Problem is sorted. User error, nuff said- I'm decling to give details.:rofl:

Been at my new CU and replicated most of the values on the EIC
for the CU change carried out by a mate with 1720
All except the values that were made up, that is.