continuity on ring main

[rosscohans]

Hi. be nice for some feed back on this. I'm testing a ring main for an eicr. I know that the cpc reading should be around the 1.6 times higher than the live conductors but I'm getting 0.66 on live, 0.67 on neutral and 0.61 on cpc. I'm wondering, if the cpc are connected through the metal k.o box on some points would this bring the reading down? As I've checked every socket and all seems fine.

 

[dagrat]

Is it in twin and earth or singles? If singles then the cpc is more than likely the same CSA as the live conductors and consequently the same resistance, within a range of about 0.05 ohms.
Additionally the cpc of an existing installation can have parallel earth paths and so can produce much lower readings.
carry on with the other crossover tests to confirm its a ring etc

 

[loop3]

On te 2.5mm the earth is 1.732 greater resistance . As mentioned above, parallels?

 

[dagrat]

On te 2.5mm the earth is 1.732 greater resistance . As mentioned above, parallels?

Actually on a 2.5mm twin cable the cpc is 1.5mm which is 1.67 x smaller which produces a resistance which is 1.67 x higher than the line conductor. This is the norm.
A parallel path is a secondary route to earth other than the primary cpc path. Examples are main bonding conductors, supplementary bonding etc etc
These paths will reduce the resistance and consequently your resistance readings may be less than you would expect

 

[bartkusal]

On te 2.5mm the earth is 1.732 greater resistance . As mentioned above, parallels?

You most probably mixed uo with that. It is 1.67 greater cpc the line on 2.2x1.5 T&E. 1.732 is square root of 3 in 3phase calculations...

 

[loop3]

You're right! 1.732 is the square root of three. Lol

 

[loop3]

Thanks for the refresher lads!

 

[bartkusal]

we all have black outs :moon:

 

[rosscohans]

Thanks for the reply. Did find it to be the parallel paths of cross bonding. Cheers

 

[Spazz]

As has been said above the CPC in this circuit is the same size as the Line and neutral weather its 1.5mm, 2.5mm, etc
Even if the CPC did go though back boxes it would not make any difference - however if you had metal trunking/conduit and that was used as the CPC that would bring the r2 down.