Trainee Question for Inspection and testing

[Pete999]

Yes definatly. Even with the leads nulled, there is still a 0.05 margin.

Never heard that one, where do I find this info? or is it an unwritten rule?

 

[dave440]

I wonder i the 0.05 allowance is the point of the question (to test my knowledge and catch me out).

The best answer I can think of, is that, the Measured Ze is 0.17, and the calculated Zs would usually be slightly higher.

So in this case, the Measured Zs is slightly lower due to possible parralel paths relating to maybe the water connection.

I remebered that the Ze is meaured without the parallel paths connected, but after energising, the parallel paths would be connected, and that might account for a slightly lower Zs reading.

Theres is no other information given to me, but (if eveyone else agrees), then I'm pretty sure I have found my answer.

(if anyone would like to scrutinise my opinion, I would be grateful.)

(Getting it wrong only means I learn more, so I have no problems with my answers being scruitinised).

 

[davesparks]

Yes definatly. Even with the leads nulled, there is still a 0.05 margin.

I've never heard of that one before! Where has that idea come from?

 

[TJ Anderson]

I am thinking back myself as it was back at college. I will have to look back for written evidence but it IIRC it is due to the fact that 0.05 ohms is a negligible impedance and allows for contact resistance. It is the same reason for Socket R1+R2 0.05 ohm allowance in GN3.

 

[Paul.M]

Have a look in the big book (whatever colour) for resistance of terminations and bends. This will explain the R1 and Rn difference as well.

 

[dave440]

I remember rading in the GN£ book about the slight diffferences and tollerances.
Unfortunately I d;t have this bok to hand right now. But would peopel be kind enough to confirm my ideas and opinions?

 

[TJ Anderson]

I remember rading in the GN£ book about the slight diffferences and tollerances.
Unfortunately I d;t have this bok to hand right now. But would peopel be kind enough to confirm my ideas and opinions?

GN3 4.3 says about contact resistance and how it cannot be eliminated with two terminal testers. It however does not give the 0.05 value. It was when I did 2391 Course I was taught this, I have also spoke with NAPIT assessor on inspections who was aware of it.

 

[Andy78]

I wonder i the 0.05 allowance is the point of the question (to test my knowledge and catch me out).
The best answer I can think of, is that, the Measured Ze is 0.17, and the calculated Zs would usually be slightly higher.

So in this case, the Measured Zs is slightly lower due to possible parralel paths relating to maybe the water connection.

I remebered that the Ze is meaured without the parallel paths connected, but after energising, the parallel paths would be connected, and that might account for a slightly lower Zs reading.

Theres is no other information given to me, but (if eveyone else agrees), then I'm pretty sure I have found my answer.

(if anyone would like to scrutinise my opinion, I would be grateful.)

(Getting it wrong only means I learn more, so I have no problems with my answers being scruitinised).

The question is asking you to display your knowledge of:

• the relationship between end to end results and R1+R2 results on a ring final
• the relationship between Zs values and R1+R2 and Ze values
• the relationship between line and cpc resistance values in t+e flat cable
• the differences between calculated and measured results and the reason for them
• the formulas and workings for all of the above

I think you have pretty much got it

 

[dave440]

Thank you so much!
I'm impressed that I'm finding the right answers!

 

[Leesparkykent]

Thank you so much!
I'm impressed that I'm finding the right answers!

Let us know how you get on.

 

[dave440]

I will.. My lecture is tomorrow, so I'll let you knw what my lecturer says

Thanks for the help everyone!