Earth continuity

[nicsin02]

Hi there this is been happening in a few houses now I've been testing and im
a little confused, when testing my ring continuity my earth hasn't been the standard 1.67x bigger than live and neutral when using twin and earth 2.5 cable, what causes this? There is no chrome fittings or that so that wouldn't effect any earth readings just standard white plastic, today my neural and lives were 0.8ohms but my earth was only 0.6ohms which is well short, any ideas guys and can someone point me in the direction for the forum app as I can't find it anymore, thanks

 

[Pete999]

Hi there this is been happening in a few houses now I've been testing and im
a little confused, when testing my ring continuity my earth hasn't been the standard 1.67x bigger than live and neutral when using twin and earth 2.5 cable, what causes this? There is no chrome fittings or that so that wouldn't effect any earth readings just standard white plastic, today my neural and lives were 0.8ohms but my earth was only 0.6ohms which is well short, any ideas guys and can someone point me in the direction for the forum app as I can't find it anymore, thanks

Any parallel earth paths that are still connected?

 

[Farmelectrics]

still good readings don't worry the tester never lies lol

 

[Deleted member 26818]

Do any of these houses have metal conduit?

 

[nicsin02]

No metal conduit, just standard twin and earth clipped, it's happened a few times now and was wondering if anyone had any ideas? Could it be down to if the earths are twisted quite a lot at each socket ?

 

[davesparks]

Do N and L match?

 

[nicsin02]

Do N and L match?

Yeah live and neutral were both 0.8

 

[Deleted member 26818]

The fact that the earth conductor has a lower resistance than the line and neutral in T&E, suggests that there are high resistance joints on the line and neutral conductors.

 

[davesparks]

The fact that the earth conductor has a lower resistance than the line and neutral in T&E, suggests that there are high resistance joints on the line and neutral conductors.

Or parallel paths affecting the earth

 

[nicsin02]

The fact that the earth conductor has a lower resistance than the line and neutral in T&E, suggests that there are high resistance joints on the line and neutral conductors.

Thats what I was thinking but for both live and neutral to be slack the exact same amount to give the same reading I thought was unlikely ?

 

[Hellmooth]

Parallel paths seems the most likely.

 

[Guest77]

Agree with Spinlondon actually, that was my first initial thought

 

[TJ Anderson]

Agree with Spinlondon actually, that was my first initial thought

Really. 2 conductors of the same size having matching poor terminations to give identical readings...... so say both incorrect, based purely on the fact that cpc end to end is lower than expected value. Lottery odds that one. Obviously parallel earth paths.

 

[davesparks]

Agree with Spinlondon actually, that was my first initial thought

Thats why is asked about L and N being simillar, which as they are suggests that it is unlikely for that to be the issue

 

[davesparks]

Really. 2 conductors of the same size having matching poor terminations to give identical readings...... so say both incorrect, based purely on the fact that cpc end to end is lower than expected value. Lottery odds that one. Obviously parallel earth paths.

Not quite as clear cut as that, I think 'more likely to be' would be a better description.

 

[happysteve]

Any supplementary bonding in place? That would do it. (Parallel paths, as other have said.)

 

[polo1]

Is there a central heating supply fed from the RFC? If so, try disconnecting the cpc at the fused connection unit and retest.

 

[rattlehead85]

Firstly you'll be lucky to ever reach the exact line-c.p.c. ratio on rings especially in big houses with lots of sockets. Usually these sort if readings would be caused by parallel earth paths such as bonding or conduit wiring containment earthed back at source or throughout the circuit.
As you say you have no conduit i would definitely put it done more to an earth bond or sups through heating system or bathroom.
The fact you have equal line and neutral readings suggests that this is more likely the case. Your main concerns really should be to ensure your circuit Zs readings comply, you have adequate fault and additional protection in place and your IR readings are of an acceptable value. Most sparks who do testing these days fudge ring continuity readings coz they can't be assed to go fault finding when a problem does show itself especially when it happens in occupied properties full of gear and inaccessible outlets behind furniture etc etc. Poor really!

 

[nicsin02]

If the circuits are disconnected from db and there's nothing plugged in what could the parallel paths be?

 

[rattlehead85]

Well think about it for a minute....do you have anything on the ring running through the bathroom i.e spur for heater, towel rail, fan without over run, shower pump..... all which may have sup bonding connected especially if an installation to previous 16th norm.
Or you could have the good ol' "useless cross bonding" under a boiler run back into a spur next to it. These would all cause unexpected low cpc end-end continuity results below the value of your L & N readings.

 

[nicsin02]

Well think about it for a minute....do you have anything on the ring running through the bathroom i.e spur for heater, towel rail, fan without over run, shower pump..... all which may have sup bonding connected especially if an installation to previous 16th norm.
Or you could have the good ol' "useless cross bonding" under a boiler run back into a spur next to it. These would all cause unexpected low cpc end-end continuity results below the value of your L & N readings.

there is none of the above, this is a brand new house and the circuit is just a ring circuit with nothing added, no cross bonds,

 

[richy3333]

Then it must be non BASEC. approved cable?

 

[Guest77]

Really. 2 conductors of the same size having matching poor terminations to give identical readings...... so say both incorrect, based purely on the fact that cpc end to end is lower than expected value. Lottery odds that one. Obviously parallel earth paths.

Yes really, if the readings were done at the board with all conductors disconnected at the time of testing which is perfectly possible then how would parallel paths come into it? if he tested around the ring with conductors still connected in the board then yes I agree very very likely parallel paths, there is more ways to kill a pig than just stabbing it.

 

[polo1]

Yes really, if the readings were done at the board with all conductors disconnected at the time of testing which is perfectly possible then how would parallel paths come into it? if he tested around the ring with conductors still connected in the board then yes I agree very very likely parallel paths, there is more ways to kill a pig than just stabbing it.

See my earlier post. If the heating is a gas boiler and fed from the RFC, and the gas supply is bonded, this may be the parallel path?

 

[telectrix]

See my earlier post. If the heating is a gas boiler and fed from the RFC, and the gas supply is bonded, this may be the parallel path?

even so, it c an't provide a parallel path if the RFC conductors are all dissed from the CU.

 

[nicsin02]

even so, it c an't provide a parallel path if the RFC conductors are all dissed from the CU.

It's definitely not connected to heating or that just a simple ring circuit, could it be cheap cable? Or I noticed the earths were twisted fully at each socket??

 

[Midwest]

Hi there this is been happening in a few houses now I've been testing and im
a little confused, when testing my ring continuity my earth hasn't been the standard 1.67x bigger than live and neutral when using twin and earth 2.5 cable, what causes this? ...........today my neural and lives were 0.8ohms but my earth was only 0.6ohms which is well short ....

Are you sure that the L-L & N-N are correct. A figure of 0.8ohms (2.5mm) suggest a cable length of over 100m? Whereas 0.6ohms (1.5mm) suggest a cable length of 50m. Just a thought.

 

[telectrix]

possibvly not nulled meter and leads for the L-L and N-N??????

 

[nicsin02]

The leads get zero' before every test I do, it's possible the L and N could be wrong but I thought it would be unlikely for both to have the exact same slack resistance?? Out of curiousity what is the formula for calculating length of run? Cheers

 

[Midwest]

Out of curiousity what is the formula for calculating length of run? Cheers

Errr.....cough, got mine out of a book. 100m of cable, is quite a large RFC? Can you assess you RFC length and then compare to your test results?

 

[HandySparks]

even so, it c an't provide a parallel path if the RFC conductors are all dissed from the CU.

A couple of water heaters spaced apart on the ring could easily provide a parallel path to the cpc and produce a lower r2 reading.

 

[Midwest]

A couple of water heaters spaced apart on the ring could easily provide a parallel path to the cpc and produce a lower r2 reading.

OP is saying he's testing at CU with ends disconnected, no appliances or loads connected.

 

[Risteard]

OP is saying he's testing at CU with ends disconnected, no appliances or loads connected.

But HandySparks is saying that if he had two water heaters spaced apart then there would be two cpc connections along with copper pipework connecting between, so these would reduce the resistance of the cpc (by effectively making a parallel cpc path) even with both ends disconnected at the distribution board.

 

[Midwest]

But HandySparks is saying that if he had two water heaters spaced apart then there would be two cpc connections along with copper pipework connecting between, so these would reduce the resistance of the cpc (by effectively making a parallel cpc path) even with both ends disconnected at the distribution board.

Dunno, think the OP is saying no such heaters present?

 

[Risteard]

Dunno, think the OP is saying no such heaters present?

Perhaps. But depending on what is connected and how (e.g. with dual boxes creating connections to other circuits' cpcs) it is possible for there to be parallel cpc paths, although not near as likely as on a job with steel containment obviously!

 

[Midwest]

Perhaps. But depending on what is connected and how (e.g. with dual boxes creating connections to other circuits' cpcs) it is possible for there to be parallel cpc paths, although not near as likely as on a job with steel containment obviously!

Yep you could be right, perhaps the OP can confirm.Still think the RFC quite large, unless the whole property has only one RFC, or it's just big?

 

[HandySparks]

OP is saying he's testing at CU with ends disconnected, no appliances or loads connected.

Maybe not applicable to this case, but I was just replying to tel's implication that disconnecting the CPCs from the board would be enough to eliminate parallel paths when measuring r2 on a ring.

 

[Guest77]

See my earlier post. If the heating is a gas boiler and fed from the RFC, and the gas supply is bonded, this may be the parallel path?

Yeah I did see your post my friend, and of course agree, but don't think it is in relation in this case, good shout though, I accept your view if there would be a boiler in the circuit as you have suggested.

 

[Deleted member 26818]

Another possibility, is that there is an RCD socket or perhaps an item of equipment connected which is skewing the results.

 

[Guest77]

Maybe not applicable to this case, but I was just replying to tel's implication that disconnecting the CPCs from the board would be enough to eliminate parallel paths when measuring r2 on a ring.

Well in general tel is correct, I agree it isn't always the case but he has a point.