confused with results

[One_of_them]

guys,

ring wired in 2.5mm singles, contained in tray (roof) then conduit buried in wall down to dado trunking. end to end L 0.69 N 0.69 CPC 0.41
R1+R2 0.41
Zs 0.38
RCD trips within times

using megger 1730

as far as I can tell the CPC is 1 run to outlets no connections onto tray/conduit etc so wouldnt have thought parallel paths would be considered however I have been wrong many times before


unable to gain Zdb of board as not allowed to turn off

 

[jumpin jax]

May i ask how singles are used on tray and how you came about your R1+R2 result and if the conduit is metal

 

[Brightspark2]

Did you use plug or probes on socket back?

 

[One_of_them]

May i ask how singles are used on tray and how you came about your R1+R2 result and if the conduit is metal

well its the tray with lid dont know how much more you want me to tell you?
cross connected at board. conduit is not used as the CPC if this is where you are going?
conduit is metal

 

[One_of_them]

Did you use plug or probes on socket back?

socket back

 

[jumpin jax]

If the conduit is connected to metal clad sockets then the first socket is going to be joined to all the other metal clad sockets through the CPC and the conduit hence having a lower R2

 

[One_of_them]

sockets are in dado (sorry that should be in the beginning bit)
tray runs in roof, conduit buried in wall to behind the dado and then to sockets

 

[somersetsparks]

Somehow, somewhere you must be picking up a paralell path, count it as a bonus!

 

[jumpin jax]

CPC is 4mm?

 

[One_of_them]

Has anybody ever seen it so you would run a CPC from board to tray, rely on this and conduit for cpc, then run a new CPC cable at the end of conduit onto the sockets?? Effectively saving on a bit of cable length?

 

[somersetsparks]

Has anybody ever seen it so you would run a CPC from board to tray, rely on this and conduit for cpc, then run a new CPC cable at the end of conduit onto the sockets?? Effectively saving on a bit of cable length?

I have seen it done like this, and IMO it is acceptable, however personally I would usually use conduit/trunking for CPC only if it it was continuous to each socket, If it was in the situation you described, I would begrudingly run a cpc in with the other singles.

Has the job you are on been done like this? hence your low R2

 

[somersetsparks]

thinking about it, is it not likely that the dado was added later over the original conduit drops (which were utilising the tube as a CPC), hence they have just extened the CPC from the original socket positions using G/Y singles?

 

[One_of_them]

I have seen it done like this, and IMO it is acceptable, however personally I would usually use conduit/trunking for CPC only if it it was continuous to each socket, If it was in the situation you described, I would begrudingly run a cpc in with the other singles.

Has the job you are on been done like this? hence your low R2

to be honest I aint pulled it apart that much to confirm. It was just supposed to be a simple addition of a couple of sockets. Fairly new build office block to.
As I started this thread it just dawned that maybe this is something that might have been done. I have never seen it but I can understand it been acceptable but not how I would ever do it. With the readings I got I believe circuit to be safe so I'm not too worried, just confused.

 

[Brightspark2]

socket back

Could of been a bad connection with the probes, you can get screws that will give you high readings on the R1+R2 but fine on Zs. Light fittings are common for this in my experiance.

Just an idea...to go with the other possibilities...

 

[One_of_them]

thinking about it, is it not likely that the dado was added later over the original conduit drops (which were utilising the tube as a CPC), hence they have just extened the CPC from the original socket positions using G/Y singles?

yeah could well be possible. Worth asking the question