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Old December 6th 17, 09:31 PM posted to uk.d-i-y
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Default Continuity between neutral and earth

Hi All

I have broken into a ring main to extend it to another room. Essentially cutting the return from one socket and then connecting each side of the extended ring to one of the cut ends.

I test the extended ring and it was sound (ie only continuity between the corresponding pairs of wire). I have just connected it to the main ring and did a quick continuity check. Live is ok but it seems that neutral (blue) and earth now have continuity. Given I tested the extended ring it would appear that the original ring suffered this problem. However if this was the case wouldn't the RCd at the MCU have tripped before.

Any ideas?

Thanks

Lee

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Old December 6th 17, 09:53 PM posted to uk.d-i-y
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Default Continuity between neutral and earth

leenowell wrote:

Live is ok but it seems that neutral (blue) and earth now have continuity.


Depending on your earthing arrangement, this is probably normal, do you
know type of supply you have?

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

The type determines whether or where your neutral meets earth ...


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Old December 6th 17, 10:04 PM posted to uk.d-i-y
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Default Continuity between neutral and earth

Thanks both. Looking at the wiki it looks like it is tn C's.

The incoming wire goes to a fused black box and outbof that comes over neutral and earth. Earth goes to cu and the live and neutral go to the meter and then to the cu via a new isolation switch.
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Old December 6th 17, 10:12 PM posted to uk.d-i-y
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Default Continuity between neutral and earth

leenowell wrote:

Looking at the wiki it looks like it is tn C's.
The incoming wire goes to a fused black box and outbof that comes over neutral and earth.


You're *probably* correct, though depending what connections are made
inside the black box (cutout) it could be TNC-S or TN-S, as some of the
photos show (those with/without links from N to E inside the box).

Earth goes to cu and the live and neutral go to the meter and then
to the cu via a new isolation switch.





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Old December 6th 17, 10:16 PM posted to uk.d-i-y
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Default Continuity between neutral and earth

The black box has the electric company fuse in it so don't want to take the cover off to check . The incoming cable comes in from the bottom earth comes out to the right and live and neutral out to the too where the fuse is.. In coming is a single black cable.

Does that help in any way. Would both give the symptoms I describe?
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Old December 7th 17, 09:24 AM posted to uk.d-i-y
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Default Continuity between neutral and earth

Hi

Yes I think it is TN CS. This picture looks very much like my installation

http://wiki.diyfaq.org.uk/index.php/File:PME1.jpg

So sounds like neutral and earth continuity is correct for my installation.

Thanks for your help

Lee
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Old December 7th 17, 10:23 AM posted to uk.d-i-y
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Default Continuity between neutral and earth

I was always told that Neutral was supposed to be earth, or almost so.
Otherwise we would have two lives.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"T i m" wrote in message
...
On Wed, 6 Dec 2017 12:31:30 -0800 (PST),
wrote:

Hi All

I have broken into a ring main to extend it to another room. Essentially
cutting the return from one socket and then connecting each side of the
extended ring to one of the cut ends.

I test the extended ring and it was sound (ie only continuity between the
corresponding pairs of wire). I have just connected it to the main ring
and did a quick continuity check. Live is ok but it seems that neutral
(blue) and earth now have continuity. Given I tested the extended ring it
would appear that the original ring suffered this problem. However if this
was the case wouldn't the RCd at the MCU have tripped before.

Any ideas?


I'm not sure this is the case in every installation but I think the
neutral and earth are connected together somewhere (CU?) and further,
the earth is actually supplied via the neutral on the incoming supply
sometimes?

So, as long as you don't have any N to E [1] or L to E leakage current
on your side of the RCD you should be ok?

Or something like that .. I'm sure someone will be along shortly to
give it to you more accurately. ;-)

Cheers, T i m

[1] Often seen when cutting though a cable even with that cct MCB
switched off.



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Old December 7th 17, 10:44 AM posted to uk.d-i-y
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Default Continuity between neutral and earth

On Wednesday, 6 December 2017 20:31:35 UTC, wrote:
Hi All

I have broken into a ring main to extend it to another room. Essentially cutting the return from one socket and then connecting each side of the extended ring to one of the cut ends.

I test the extended ring and it was sound (ie only continuity between the corresponding pairs of wire). I have just connected it to the main ring and did a quick continuity check. Live is ok but it seems that neutral (blue) and earth now have continuity. Given I tested the extended ring it would appear that the original ring suffered this problem. However if this was the case wouldn't the RCd at the MCU have tripped before.

Any ideas?

Thanks

Lee


Neutral and earth are bonded together back at the substation.
It's important that this is the only place they are bonded.
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Old December 7th 17, 10:51 AM posted to uk.d-i-y
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Default Continuity between neutral and earth

On 07/12/2017 08:24, wrote:
Hi

Yes I think it is TN CS. This picture looks very much like my installation

http://wiki.diyfaq.org.uk/index.php/File:PME1.jpg

So sounds like neutral and earth continuity is correct for my installation.


N&E continuity (of some sort) is correct for the vast majority of
installations (assuming you are doing the test with the circuit
connected to the CU[1]). With TN-C-S the link is in your property. With
TN-S its back at a substation. With TT its via the general mass of the
earth, and may have a higher resistance, but is still good enough to
make a continuity test "pass" in many cases.


[1] If you want to test your "new" combined circuit in isolation, then
you need to disconnect it at the CU end and test there. That way you
will be free of the influences of the supply itself and any EQ bonding
connections.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/


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