Low R2 and where to start

[telectrix]

and it is not necessary to fit cpc fly leads to knock-out boxes any more, but IMO it is good practice

 

[chiplard]

I'd bet on supplementary bonding.

 

[IQ Electrical]

Is someone paying you to find why the r2 reading is so good?

Part of the skill of periodic inspection is to know when a problem exists and also to anticipate where results on a real-world installation will differ from electrically perfect text book calculations.

Without this experience, we'd never finish an inspection, parallel paths are prolific, even on an 'all insulated' domestic installation.

Unless the installation is using conduit/trunking as the CPC then there is no requirement for fly leads on back boxes although it is good practice.

 

[tonys]

If your that concerned and want to get to the bottom of it, then break the ring down and test between each leg.

 

[nickblake]

and it is not necessary to fit cpc fly leads to knock-out boxes any more, but IMO it is good practice

Agree but only as long as the back box has one fixed lug , and also light switch back boxes need earthing

 

[malcolmsanford]

Agree but only as long as the back box has one fixed lug , and also light switch back boxes need earthing

Is that something new that's come out that as slipped by me without me noticing Nick?

 

[IQ Electrical]

Is that something new that's come out that as slipped by me without me noticing Nick?

Me too, Nick is quite correct on the '1 fixed lug' part but there is no distinction made between socket and lighting back boxes in BS7671:2008 or Guidance Note 8 (earthing and bonding).

 

[nickblake]

Knowing me im reading to deep into the regs but page 27 of the on site guide, the purpose of protective earthing is to ensure that in the event of a fault,line conductor to exposed conductive part sufficiant current flows to operate the protective device in the time required .as we all know. so correct me if im wrong , but there is no earth connection on light switches so when the face plate is screwed back with a solid lug on the back box then if the live wire of the switch breaks off or pops out as the do and touches an unearthed back box it wont blow the protective device but the face plate screws will be exposed and live ,so you can see my point .. unless its an earthed metal face plate then the same should apply as socket outlets because at the end of the day they are back boxes single or double

 

[Amp David]

Have they had a conservatory or extension built and the ring extended into it?

 

[topquark]

The boiler (downstairs in utility) was on the upstairs ring . Even after taking the bonding out of the equation there is still an extraneous connection (via the pipework itself I guess) giving a better than (I) expected R2.

All in all, was a useful exercise though. Was doing a check prior to changing the CU.

Is someone paying you to find why the r2 reading is so good?

I wish , no, this was for my elecsa inspection tomorrow, just me being a bit too picky

Last minute change of CU as the job I was going to use is going too slow (not due to me though ). Had to pay the LABC £141 for the privilege as well