R1+r2

[Cj24]

Hi I am just looking through certain tests and was getting slightly confused, when finding out your r1+r2 you link out your phase and CPC at board and test on continuity across phase and CPC at furthest point of circuit, this is called continuity of CPC test??? But is this just on radial circuits?? Because don't you find your r1+r2 on your rings when you ring final continuity by linking out your opposite phase and CPC sides of the ring and test r1+r2 at the sockets?? Sorry if gone on abit n don't quite make sense

 

[needasparks]

Have you looked at the onsite guide, it will give you advice you need with priddy pictures.

 

[Cj24]

Ze and zs

Hi, I am just trying to get my head round ze and zs, am I right in thinking both are for testing earth fault loop impedance but ze is testing across phase, neutral and CPC at then end of each circuit and zs is tested across same conductors but supply side of the main switch?? Am I right or no where near???

 

[NMc]

You are right to think r1, rn and r2 and to to with a ring. They are find in the first step of the ring continuity test

 

[needasparks]

Ze is your earth loop at origin of supply. R1+R2 is resistance of circuit, Zs (resultant earth loop) is resistance of both combined.

Ze+R1+R2 = Zs

 

[ringer]

Re: Ze and zs

Hi, I am just trying to get my head round ze and zs, am I right in thinking both are for testing earth fault loop impedance but ze is testing across phase, neutral and CPC at then end of each circuit and zs is tested across same conductors but supply side of the main switch?? Am I right or no where near???

Other way round mate. Ze is the external earth fault loop impedance which is measured at the supply side of the main incomer on your CU (with incomer isolated and main earth disconnected from the earthing bar to avoid parallel earth paths). Zs is the earth fault loop impedance of a particular circuit, measured at the extremity of that circuit, and makes use of parallel earth paths through bonding etc. If you forget which way round they are, then look at some certs - you will see Ze is requested as part of the supply characteristics, and Zs is requested for each circuit tested.

 

[Deleted member 26818]

r1+r2 is the end to end resistance of your Line and CPC.
R1+R2 is the resistance of your RFC conductors, when they are connected together in a figure of eight, and then measured at any point on the RFC.
This value should be 1/4 of the r1+r2 value.

 

[Cj24]

I thought your end to end result was higher then your r1+r2 reading because you had your phase to phase result to your neutral to neutral result and divide that by 4 which gives you your r1+r2 result

 

[Deleted member 26818]

The end to end r1+r2 measurement is higher because you are measuring the full length of each conductor.
When measuring R1+R2, you are measuring at a point which is effectivly in the middle of the conductors, which would halve the resistance, and because you then have two sets of conductors in parallel, the resistance would be halved again.
Phase to phase added to neutral to neutral would be r1+rn.
r1+r2 is line to line added to CPC to CPC.

 

[needasparks]

I thought your end to end result was higher then your r1+r2 reading because you had your phase to phase result to your neutral to neutral result and divide that by 4 which gives you your r1+r2 result

reading between the lines of your question I think your confusion is the neutral which plays no part in the r1+r2 calculations, yes it is important to check its continuaty,polarity and insulation and is sometimes refered to as a phase conductor within testing but is omitted when working out unless you are recording values to a ring circuit (RFC) as spin above has explained.
Phase or line conductor is R1 and Earth (cpc) is your R2.
It is measured and recorded to find out the resistance path under fault conditions of live to earth to asses your overcurrent device and conductor size is correct (within described values) for your circuit. There are other factors that need to be worked out also in those calculations but that is the main part that i could not get my head round when i started out.
hope that helps.

 

[Cj24]

So I do end to end testing and add my phase to phase reading to my CPC to CPC reading to get my r1+r2??? I will get the same reading as if I cross linked the phase and cpc's then went round the sockets??

 

[Cj24]

And divide my phases and CPC added together by 4 I ment to say

 

[telectrix]

first. please learn to differentiate between R1 and r1 etc. the use of the lower case r applies only to end/end resistance of a ring final. R1 +R2 is your result when you either a. link line/cpc at CU and measure at extremity of a radial, or, b. cross connect in CU for a RFC. and measure at the furthest ( 1/2 way ) point. because you have cross connected, all points should read the same, except if you have a spur.

 

[needasparks]

yes, remember RFC is one circuit even though you have two lives and cpc's at the board (cu).


a picture is the best way to explain but i don't have any to hand, i'm sure someone will post one up now.

perhaps an easier way to think of it is r1+r2 of a radial circuit is measured at furthest point in series,
and the r1+r2 of a RFC is measured in parallel, it can be calculated if you have the end to end R values and add together and divide by 4 .

 

[telectrix]

is r1+r2 of a radial circuit is measured at furthest point in series,

​NO! it's R1+R2. please!!!!!