Discuss CPC missing on ring final in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Reaction score
2
Morning All,

Currently carrying out an EICR and going through ring final steps with the following readings:
r1: 0.31ohm
rn: 0.32ohm
r2: 0.03ohm

Started taking sockets faces off to find that there is no cpc, only fly lead to metal patress box and steel conduit trunking. (See photo)

When i carry out R1+R2 i get a reading of 0.48ohm.

I suspect I'm picking up parallel paths for R1&R2 reading.
Question is what do i code this on report and any recommendations on remedial?

Thanks in advance
 

Attachments

  • CPC missing on ring final 15964478666846547067299451122068 - EletriciansForums.net
    15964478666846547067299451122068.jpg
    91 KB · Views: 57
  • CPC missing on ring final 15964479888626205509772439295598 - EletriciansForums.net
    15964479888626205509772439295598.jpg
    104.8 KB · Views: 57
  • CPC missing on ring final 15964480391569063757473801856757 - EletriciansForums.net
    15964480391569063757473801856757.jpg
    87.2 KB · Views: 53
Erm, what do you mean no CPC? Surely the low R2 readings are your confirmation that the CPC is actually rather good, as steel conduit usually is. Do you have concerns about the integrity of the conduit installation?
 
I expect the metal conduit is the CPC. You need to test the continuity of the conduit to the MET and get a satisfactory reading (although I'm guessing this is your R1+R2 that you already have, what did you actually test between to get this result?). Metal conduit used as the CPC is fine as long as it has continuity. Personally I have never come across it, others with more experience may offer extended advice to what I have written.
[automerge]1596449686[/automerge]
Erm, what do you mean no CPC? Surely the low R2 readings are your confirmation that the CPC is actually rather good, as steel conduit usually is. Do you have concerns about the integrity of the conduit installation?
Does the (r1+r2) / 4 = (approx) R1 + R2 still apply to a ring which partly has metal conduit used as the CPC Lucien? I can't see the above formula working out though as the CPC will not be a ring.
In the OP's post (r1+r2) / 4 < R1 + R2 by a large amount. In fact the r2 is incredibly low, this implies the earth of the twin and earth has continuity shortly after leaving the CU??

Ps.. You reminded me of @Murdoch when you started your post, he always started 'Hmmm' :D
 
Last edited:
The CPC of a ring final is required to be in the form of a ring except where provided by metallic containment, in which case no particular configuration is specified and the crossed ends test is applied to L & N only. If the conduit is sound, it will invariably provide a much lower R2 than a CPC within a cable and the testing merely needs to confirm that it is within limits. The inspection should include a visual and tightness check of an appropriate sample of conduit joints.
 
When i carry out R1+R2 i get a reading of 0.48ohm.

I suspect I'm picking up parallel paths for R1&R2 reading.
Question is what do i code this on report and any recommendations on remedial?

How are you carrying out an R1+R2 test with steel conduit used as the CPC of a ring?

You aren't picking up parallel paths, you are picking up the CPC.

So far there is nothing to be coded on the report as you've not told us anything that suggests non-compliance.
Steel conduit is a suitable CPC so as long as it is correctly connected and passes testing it is fine.
 
The CPC of a ring final is required to be in the form of a ring except where provided by metallic containment, in which case no particular configuration is specified and the crossed ends test is applied to L & N only. If the conduit is sound, it will invariably provide a much lower R2 than a CPC within a cable and the testing merely needs to confirm that it is within limits. The inspection should include a visual and tightness check of an appropriate sample of conduit joints.
Hi Lucien, The current installation of the ring final is a mixture of steel conduit (from the original installation), and 2.5mm T&E from an addition. I suspect they linked in to the original ring and then terminated at the DB in T&E, as all cables in the new DB are harmonised colours.
Hence when I carried out the ring final steps End to End and got the 0.03ohm's on CPC when r1 & rn were 0.31 & 0.32 respectively, I went on the hunt for the dodgy CPC and came across the original Ring final using the steel conduit as CPC!
I'm a little unsure of compliance in combining the methods in this manner?

I also came across a borrowed neutral to the Oven circuit (to who knows where, needs FI) which is tripping both RCCB's on the split board when trying to carry out Zs or even pushing the Test button! any advice on this one would also be appreciated!
[automerge]1596489781[/automerge]
How are you carrying out an R1+R2 test with steel conduit used as the CPC of a ring?

You aren't picking up parallel paths, you are picking up the CPC.

So far there is nothing to be coded on the report as you've not told us anything that suggests non-compliance.
Steel conduit is a suitable CPC so as long as it is correctly connected and passes testing it is fine.
Hi davesparks, please see my response to Lucien which answers your question on how I carried out the R1+R2 crossed, to get the avg 0.48ohm reading.
[automerge]1596489925[/automerge]
I expect the metal conduit is the CPC. You need to test the continuity of the conduit to the MET and get a satisfactory reading (although I'm guessing this is your R1+R2 that you already have, what did you actually test between to get this result?). Metal conduit used as the CPC is fine as long as it has continuity. Personally I have never come across it, others with more experience may offer extended advice to what I have written.
[automerge]1596449686[/automerge]

Does the (r1+r2) / 4 = (approx) R1 + R2 still apply to a ring which partly has metal conduit used as the CPC Lucien? I can't see the above formula working out though as the CPC will not be a ring.
In the OP's post (r1+r2) / 4 < R1 + R2 by a large amount. In fact the r2 is incredibly low, this implies the earth of the twin and earth has continuity shortly after leaving the CU??

Ps.. You reminded me of @Murdoch when you started your post, he always started 'Hmmm' :D
Hi Happyhippydad, many thanks for your comments, please see my response to Lucien which should clarify the situation.
 
Last edited:

Reply to CPC missing on ring final in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock