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In a pure Ring circuit, assuming Line and CPC conductors are of equal CSA, would R1 + R2 at each outlet be equal and thus ZS at each outlet also be equal?
Many thanks!
Many thanks!
Sorry to be pedantic but that should actually be (r1 + r2) / 4 = R1 + R2.(R1 + R2) / 4
So it should. I knew what I meant :red cardSorry to be pedantic but that should actually be (r1 + r2) / 4 = R1 + R2.Zs should be tested at mid-point of ring.
Yes. And as Jud stated, the CSAs don't have to be the same.In a pure Ring circuit, assuming Line and CPC conductors are of equal CSA, would R1 + R2 at each outlet be equal and thus ZS at each outlet also be equal?Many thanks!
Agreed.Zs should be tested at every socket (incl. spurs) and highest reading recorded.
Despite what the others say....In a pure Ring circuit, assuming Line and CPC conductors are of equal CSA, would R1 + R2 at each outlet be equal and thus ZS at each outlet also be equal?Many thanks!
I think about it a lot.......Me too :Applaud have you thought of getting out more specsGuinness
but respect due
Despite what the others say.... NO if you do a Zs reading at each outlet on a ring it will get progressively higher until you reach the mid point of the ring furthest from the CU.
I think they are confusing the three step test method to verify the integrity of a ring circuit described in section 10.3.2 On Site Guide.. Pages 80 - 82..
With the above cross-over test method you will get substantially equal continuity results around a correctly wired ring, (i.e. No fig '8' bridges across the ring)
BUT
this is NOT a Zs reading....
With the ring correctly connected at the CU the ZS will increase as you go around the ring proportional to the effects of the parallel resistances down the two lives and two CPC back to the CU..
Consider a hypothetical example of the parallel resistances of a pure equally spaced ring with identical conductor size using "easy numbers"..
A CU and Five socket outlets 'A', 'B', 'C', 'D', 'E' ('C' would be the mid point of the ring)
lets say each conductor is 5ohms between each outlet.
so Live and CPC from CU to midpoint 'C' would be
5ohm 'CU' to 'A'
5ohm 'A' to 'B'
5ohm 'B' to 'C'
e.g. 15ohms up each leg to mid point...
and total loop round ring CU to CU would be
5ohm 'CU' to 'A'
5ohm 'A' to 'B'
5ohm 'B' to 'C'
5ohm 'C' to 'D'
5ohm 'D' to 'E'
5ohm 'E' to 'CU'
e.g. 30ohms round each leg.
so mid point R1 is 2 x 15ohms in parallel = 7.5ohms
and R2 is 2 x 15ohms in parallel = 7.5ohms
So R1+R2 = 7.5+7.5 =15ohms
which IS as expected equal to r1+r2/4
30+30/4 = 15ohms.
BUT consider the values you would get at outlets 'A' and 'B' (same as 'D' & 'E')
So 'A' has an R1 with 5ohms in parallel with 25ohms = 4.17ohms
as our conductors are the same R2 will also be 4.17ohms back to the CU
So R1+R2 = 4.17+4.17 = 8.34ohms.... which don't = our mid point 15ohms!
the same calcs at outlet 'B' are 10ohms in parallel with 20ohms = 6.67ohms
thus R1 + R2 becomes 6.67+6.67 = 13.34ohms... again NOT equal to our mid point 15ohms!
So NO Zs is NOT the same at all outlets on a pure ring!
If you wanted to put in some 'realish' numbers do the same exercises but assume 20m of 2.5mm (Singles then T&E) between each of the five outlets
SINGLES
20m of 2.5mm = approx 0.15ohms total r1=0.90
20m of 2.5mm = approx 0.15ohms total r2=0.90
r1+r2/4 = 0.45ohm
But at outlet 'A' this would calc out to 0.25ohms
and outlet 'B' would calc to 0.40ohm
T&E
20m of 2.5mm = approx 0.15ohms total r1=0.90
20m of 1.5mm = approx 0.24ohms total r2=1.44
r1+r2/4 = 0.59ohm
But at outlet 'A' this would calc out to 0.33ohms
and outlet 'B' would calc to 0.52ohms
Obviously each of these figures would add onto you Ze for the Zs
but again in ALL cases Zs increases as you proceed around the ring to its furthest midpoint...
(No spurs involved)!
:coffee
Are you getting mixed up with Ring Main CONTINUITY tests?hmmm debate ROTFWL why does the onsite guide say substantially the same?
there is a note for singles saying it will increase towards the midpoint if an error in connection is made.
Its doing the cross-over connections that makes the difference...ah ha yes.double barrel question isn't it.
r1 + r2 will
but live testing zs won't
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