how to carry out r1+r2 reading on swa

[deano the spark]

hi all,
looking for some advice please on how to carry out an r1+r2 reading on a 35.mm,(3p+n)4 core,swa cable. it is a sub main cable with a parallel 35.mm cpc. however both ends are terminated into a steel main panel,and a steel distribution board respectively, with a number of other parallel earth paths. the installation is also galv conduit and steel trunking continuous and all linked back to main panel/distribution boards.
i believe that i would have to disconnect both glands of the 35.mm swa and parallel 35.mm cpc from both ends,and link across each phase (individually) to parallel 35.mm cpc to get my true r1+r2 reading.
(not practicable i know) but was just double checking .

hope you can help
many thanks
deano

 

[Sintra]

Easiest thing to do is forget about R1+R2 and just do an R2 with a wander lead.

 

[deano the spark]

quite a distance but i think i agree.
thanks for reply.
cheers.
deano

 

[Guest55]

just link the seperate 35mm cpc to any of the 3 lives at the DB and measure the reading at the panel board.
its not practical to physically disconnect the cable at both ends , for a periodic anyway.

 

[deano the spark]

thanks biff 55.
if the parallel cpc was only 10.mm could i still carry out the test in the same way you advised or would i need to take into account the steel wire armour. again i do appreciate in an ideal world.
cheers
deano

 

[Guest55]

the seperate earth is performing the task of cpc not the swa , otherwise theres no point it being there.
although the glands and steel enclosures will help bring down the Zs by providing additional earth paths , the pvc 35mm is still the R2.

 

[deano the spark]

thanks biff 55
i thought maybe the 10mm parallel cpc was too small, and i would have to take into account the swa as part of a true r1+r2 reading, or is it fair to say that this would be ok for reading/cert as we obviously have additional cpc csa with regard to swa also being used.
thanks again
cheers
deano

 

[ackbarthestar]

If its a particularly long run then I might make the connections in the DB. Since the armour is bonded with a fly lead with the cpc conductor to the earthing bar, then I would have thought that a jump lead across from L1/L2/L3 of the mcb to the earthing bar and just measure at the load end .

However, an interpretation of a 'true' R1+R2 is more likely to be the reading with everything connected up as this under fault conditions will be the true fault path.