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Borrowed Neutral
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Kevin Holohan
Sep 20, 2021, 2:54:10 AM9/20/21
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I was investigating a crackling light switch in the garage yesterday. The switch also provides power to an outside PIR security light which the previous owner of the house had provisioned.
Removing the switch showed there was just live/switched live and earth for the garage light, so the individual (not me!) who connected the outside light used the earth as the neutral. I guess the logic was that neutral and earth are connected back together at some point (either in the meter cupboard or at the local substation) but I don't think this arrangement is entirely acceptable.
I have disconnected the outside security light and I will run a cable from the garage ceiling light to allow a more suitable connection to the lighting circuit for the security light.
A couple of years ago I did replace my old CU with one using RCBOs. One lighting circuit (this one!) would not allow the RCBO to latch so I replaced it with a regular MCB. I wonder if borrowing the neutral was the reason for the RCBO not wanting to latch on?
Removing the switch showed there was just live/switched live and earth for the garage light, so the individual (not me!) who connected the outside light used the earth as the neutral. I guess the logic was that neutral and earth are connected back together at some point (either in the meter cupboard or at the local substation) but I don't think this arrangement is entirely acceptable.
I have disconnected the outside security light and I will run a cable from the garage ceiling light to allow a more suitable connection to the lighting circuit for the security light.
A couple of years ago I did replace my old CU with one using RCBOs. One lighting circuit (this one!) would not allow the RCBO to latch so I replaced it with a regular MCB. I wonder if borrowing the neutral was the reason for the RCBO not wanting to latch on?
Andy Burns
Sep 20, 2021, 3:18:59 AM9/20/21
to
Kevin Holohan wrote:
> I wonder if borrowing the neutral was the reason for the RCBO not wanting to latch on?
That's not the usual definition of borrowing a neutral (which is using a
> I wonder if borrowing the neutral was the reason for the RCBO not wanting to latch on?
neutral from one circuit as part of another circuit)
But using earth as though it was neutral will absolutely trip an
RCD/RCBO unless it's really tiny current such as a neon indicator.
Kevin Holohan
Sep 20, 2021, 3:37:40 AM9/20/21
to
Unknown
Sep 20, 2021, 4:50:06 AM9/20/21
to
Kevin Holohan submitted this idea :
then many metal cased appliances would then become live, with the
obvious risks.
> I have disconnected the outside security light and I will run a cable from
> the garage ceiling light to allow a more suitable connection to the lighting
> circuit for the security light.
> A couple of years ago I did replace my old CU with one using RCBOs. One
> lighting circuit (this one!) would not allow the RCBO to latch so I replaced
> it with a regular MCB. I wonder if borrowing the neutral was the reason for
> the RCBO not wanting to latch on?
The above would be an obvious cause of the RCD tripping, though
possibly not the only cause.
A 'borrowed nuetral' is not one where the earth is used as the nuetral.
It describes the case where the nuetral from another entirely separate
circuit is used. That would also cause an RCD to trip.
> Removing the switch showed there was just live/switched live and earth for
> the garage light, so the individual (not me!) who connected the outside light
> used the earth as the neutral. I guess the logic was that neutral and earth
> are connected back together at some point (either in the meter cupboard or at
> the local substation) but I don't think this arrangement is entirely
> acceptable.
It is not acceptable. If you were to loose your main earth connection,
> the garage light, so the individual (not me!) who connected the outside light
> used the earth as the neutral. I guess the logic was that neutral and earth
> are connected back together at some point (either in the meter cupboard or at
> the local substation) but I don't think this arrangement is entirely
> acceptable.
then many metal cased appliances would then become live, with the
obvious risks.
> I have disconnected the outside security light and I will run a cable from
> the garage ceiling light to allow a more suitable connection to the lighting
> circuit for the security light.
> A couple of years ago I did replace my old CU with one using RCBOs. One
> lighting circuit (this one!) would not allow the RCBO to latch so I replaced
> it with a regular MCB. I wonder if borrowing the neutral was the reason for
> the RCBO not wanting to latch on?
possibly not the only cause.
A 'borrowed nuetral' is not one where the earth is used as the nuetral.
It describes the case where the nuetral from another entirely separate
circuit is used. That would also cause an RCD to trip.
John Rumm
Sep 20, 2021, 5:01:20 AM9/20/21
to
On 20/09/2021 07:54, Kevin Holohan wrote:
> I was investigating a crackling light switch in the garage yesterday.
> The switch also provides power to an outside PIR security light which
> the previous owner of the house had provisioned. Removing the switch
> showed there was just live/switched live and earth for the garage
> light, so the individual (not me!) who connected the outside light
> used the earth as the neutral.
Have you checked at the other end of that cable to see what the earth
> I was investigating a crackling light switch in the garage yesterday.
> The switch also provides power to an outside PIR security light which
> the previous owner of the house had provisioned. Removing the switch
> showed there was just live/switched live and earth for the garage
> light, so the individual (not me!) who connected the outside light
> used the earth as the neutral.
wire is connected to there?
Obviously using an actual earth as a neutral is unacceptable for many
reasons, however it might be that the earth wire was repurposed as an
actual neutral by connecting it as such at *both* ends.
(if you do that then it must be over marked at both ends - and you can
only do it on a wire that is part of a cable - not a single).
I am guessing from the RCD comment that was probably not what happened!
> I guess the logic was that neutral and
> earth are connected back together at some point (either in the meter
> cupboard or at the local substation) but I don't think this
> arrangement is entirely acceptable. I have disconnected the outside
> security light and I will run a cable from the garage ceiling light
> to allow a more suitable connection to the lighting circuit for the
> security light. A couple of years ago I did replace my old CU with
> one using RCBOs. One lighting circuit (this one!) would not allow the
> RCBO to latch so I replaced it with a regular MCB. I wonder if
> borrowing the neutral was the reason for the RCBO not wanting to
> latch on?
earth circumventing the RCD.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
charles
Sep 20, 2021, 3:31:08 PM9/20/21
to
In article <bb3deda7-9f35-4ebb...@googlegroups.com>, Kevin
very likely Different currents in L&N.
--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
ARW
Sep 20, 2021, 4:00:24 PM9/20/21
to
two RCBOs to trip.
But it looks like the OP has found his problem
--
Adam
Kevin Holohan
Sep 21, 2021, 2:28:16 AM9/21/21
to
On Monday, 20 September 2021 at 10:01:20 UTC+1, John Rumm wrote:
> On 20/09/2021 07:54, Kevin Holohan wrote:
> Have you checked at the other end of that cable to see what the earth
> wire is connected to there?
>
Not looked yet but it will be clear when I access the wiring for the garage light to see what is connected to where.
> On 20/09/2021 07:54, Kevin Holohan wrote:
> Have you checked at the other end of that cable to see what the earth
> wire is connected to there?
>
Thanks for the feedback from you and others - it's much appreciated.
Brian Gaff (Sofa)
Sep 21, 2021, 3:05:00 AM9/21/21
to
The design of the original installation does sound very peculiar to me.
There can be loads of reasons why your so called earth and neutral are not
the same potential or lack of potential when the live follows a completely
different path that its asking for somebody to get a nasty shock.
Brian
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This newsgroup posting comes to you directly from...
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Blind user, so no pictures please
Note this Signature is meaningless.!
"Andy Burns" <use...@andyburns.uk> wrote in message
news:iqqquu...@mid.individual.net...
There can be loads of reasons why your so called earth and neutral are not
the same potential or lack of potential when the live follows a completely
different path that its asking for somebody to get a nasty shock.
Brian
--
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
bri...@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"Andy Burns" <use...@andyburns.uk> wrote in message
news:iqqquu...@mid.individual.net...
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