R1 + r2 ?!

[AcB85]

Hey peeps...

I'm sure this must be a regular from learners to be posted on here so I'm sure you've seen it before! But i can't find a thread explaining so here goes..

When doing a continuity test on a ring final circuit, after taking readings for your R1/Rn, its then you do the line/CPC, correct? so is the value of R1+R2 the maximum reading you get from a socket outlet upon this test? or is it the minimum as this shows weak resistance and therefore the route a fault current would take?



Thanks in advance

**Just noticed the small R2 in the title.. typo!

 

[zupos40]

Hey peeps...

I'm sure this must be a regular from learners to be posted on here so I'm sure you've seen it before! But i can't find a thread explaining so here goes..

When doing a continuity test on a ring final circuit, after taking readings for your R1/Rn, its then you do the line/CPC, correct? so is the value of R1+R2 the maximum reading you get from a socket outlet upon this test? or is it the minimum as this shows weak resistance and therefore the route a fault current would take?



Thanks in advance

**Just noticed the small R2 in the title.. typo!

If you have connected the conductors correctly and all terminations are both electrically and mechanically secure, then r1+ r2 measured at each outlet should be roughly the same, but for twin + earth the reading will increase slightly toward the mid-point and reduce as you return to the CCU, in that case record the highest value.

If Line and CPC are the same size then like the L-N the r1+r2 should be quarter of the end to end values for Line and neutral.

 

[fog]

hi there
I would use the G3 Guidance notes 3 book its excellent for testing procedures, but anyway it would be the maximum R1+R2 value in theory and i state in theory if its a ring the R1+R2 values should be the same anywhere on the ring but would be higher if there is a spur of the ring i wwould test all points on the ring and put down the maximum reading hope this is of some help

 

[ezzzekiel]

r1 r2 is not the same as R1 R2

 

[AcB85]

Thanks zupos40 / fog, thats of some help.

ill be getting hold of guidance note 3 book, sounds like i could do with it!

cheers again guys

 

[Des 56]

Perhaps the best way would be to use the theory that is taught to you

If you have a conductor that is forming a ring main, it will have a value depending on the length of cable and the cross sectional area of that cable (It can also be affected by temperature and bad connections but ignore for now)
A smaller conductor of the same length will therefore have a higher resistance


The end to end continuity test reading would be the same wherever on the ring that test is taken
The figures you read (L+E) should be added together then divided by 4 to give a figure that you can compare with the figure of 8 cross connections test

For the figure of 8 test
If you begin at the consumer unit (because the interconnections for the figure of 8 values should be made there) Sockets near the consumer unit will have a short lenghth of reduced size cpc ( the more length of reduced cpc the higher the reading will be )
The further away from the consumer unit the longer the length of reduced cpc,so the value you read will increase the further towards the centre of the ring
The highest value is the recorded figure
The reason for that is so that,when it is added to ZE It can be compared to the maximum permitted Zs for the MCB to see if the circuit complies