Query regarding old 2391 question - RE sequence of tests

[thebigcheese]

Hi,
I've been having a nose through some of the old past Chief Examiner reports and the December 2011 edition has on page 5 has the following quote:

Many candidates were unable to identify the first three tests to be carried out on a newly installed ring final circuit, with many beginning with continuity of cpc followed by ring final circuit continuity. The tests are ring final circuit continuity, insulation resistance, earth fault loop impedance.

Can anyone explain why Continuity of CPC is not the first test? Is it purely because if you get an end to end reading on the CPC then that is sufficient as I thought you had to take a reading at every point???

Cheers guys!

http://cdn.cityandguilds.com/Produc...01_Chief_examiner_report_December_2011_v1.pdf

 

[Richard Burns]

Because you are talking about a new ring final circuit the first test is the three step test to ensure ring final circuit continuity and determine R1+R2. Whilst it is possible that the first measurement you take is end to end of the cpc, this is only one section of the entire test: three end to ends, r1+rn, r1+r2 the latter two at every point of utilisation.

 

[Jay Sparks]

Because you are talking about a new ring final circuit the first test is the three step test to ensure ring final circuit continuity and determine R1+R2. Whilst it is possible that the first measurement you take is end to end of the cpc, this is only one section of the entire test: three end to ends, r1+rn, r1+r2 the latter two at every point of utilisation.

Im not saying your wrong but I cant work that out in my head.
The first test on a ring final circuit is:
Step 1:
r1 end to end i.e resistance of the line conductor from one leg to the other.
rn end to end i.e resistance of the neutral conductor from one leg to the other.
r2 end toend i.e resistance of the cpc from one leg to the other.
r1 and rn readings should be within 0.05ohms of each other.
Step 2:
R1 + Rn i.e connect neutral from one leg to the line of the other leg and vice versa (figure of 8) take the reading at each socket. The result should be (r1 + rn)/4.

Step 3:
R1 + R2 i.e connect line from one leg to cpc of the other leg and vice versa (figurs of 8) take the reading at each socket. The result should be (r1 + r2)/4.

If this is what you meant RB, then I apologise.


Jay

 

[Richard Burns]

Im not saying your wrong but I cant work that out in my head.
The first test on a ring final circuit is:
Step 1:
r1 end to end i.e resistance of the line conductor from one leg to the other.
rn end to end i.e resistance of the neutral conductor from one leg to the other.
r2 end toend i.e resistance of the cpc from one leg to the other.
r1 and rn readings should be within 0.05ohms of each other.
Step 2:
R1 + Rn i.e connect neutral from one leg to the line of the other leg and vice versa (figure of 8) take the reading at each socket. The result should be (r1 + rn)/4.

Step 3:
R1 + R2 i.e connect line from one leg to cpc of the other leg and vice versa (figurs of 8) take the reading at each socket. The result should be (r1 + r2)/4.

If this is what you meant RB, then I apologise.


Jay

I am possibly guilty of assuming too much knowledge.
Your post is exactly what I said.

I may have missed some details but I was only referencing and not describing.

 

[Jay Sparks]

I am possibly guilty of assuming too much knowledge.
Your post is exactly what I said.

I may have missed some details but I was only referencing and not describing.

Like I said, I may have misunderstood. Then again, I have had two bottles of red. I'm having trouble p1ssing in the pot, let alone understanding a technical post. The post I put up was one I had written ages ago...lol I just copied and pasted...lol

Jay

 

[thebigcheese]

Ahh ok I understand now. I guess the sequence of tests 'CRIPPLER' refers to the installation as a whole. By the same logic the sequence of tests for a radial wouldn't include the Polarity (Dead) test as this would have been confirmed already by the R1+R2 reading?

Cheers guys!