Hi,
I don't have the proper test equipment but tested my socket circuits
earth trip by connecting a 15w bulb to live and earth (15w is the
lowest I could find that draws 30ma). This test worked and I found a
few sockets that did not have an earth and I corrected this.

Next I tested my lighting circuits which don't have any earth wires
connected. I am replacing some existing lighting circuit wiring as I
have the ceiling pulled down during renovations. I have linked the
lighting earth to one of the existing socket earths. I found that
connecting the bulb from live to earth did not cause a trip. I also
tried with a 60w and 100w bulb. Just to ensure earth continuity I
connected the lamp from live on a socket junction to earth on the
lighting junction, this did not trip.
Is there some wiring that may need to be changed at the consumer panel
to get this to work? I wouldn't touch the consumer panel myself but I'd
appreciate any advice so I can get someone in if required.

Note that I ensured nobody else in the house would touch any metal
objects that might be earth bonded.

Thanks,
Declan.

Is there some wiring that may need to be changed at the consumer panel
to get this to work? I wouldn't touch the consumer panel myself but I'd
appreciate any advice so I can get someone in if required.

It is normal to not run lighting circuits through an RCD, as the risk of
injury from failing lighting during a "situation" (i.e. fire or chopping
through a cable with a power tool) is actually much greater than that posed
by a circuit without supplementary earth fault protection.

Indeed, it is close to not permissible these days to wire a consumer unit so
that the lighting shares an RCD with the socket circuits. There are
exceptions.

Christian.

"Christian McArdle" wrote
Indeed, it is close to not permissible these days to wire a consumer unit
so
that the lighting shares an RCD with the socket circuits. There are
exceptions.


Really? I've just had a consumer unit fitted and the sparky has put
everything
on the RCD side of the unit, including downstairs and upstairs lights
is this wrong then ?
--
Vass

Really? I've just had a consumer unit fitted and the sparky has put
everything
on the RCD side of the unit, including downstairs and upstairs lights
is this wrong then ?

Yes it is wrong, unless it is a TT system and it is all off a 100mA RCD.

The regs aren't particularly clear on the point though, so you could argue
the toss on it.

Christian.

"Christian McArdle" wrote in message
...
Really? I've just had a consumer unit fitted and the sparky has put
everything
on the RCD side of the unit, including downstairs and upstairs lights
is this wrong then ?

Yes it is wrong, unless it is a TT system and it is all off a 100mA RCD.

The regs aren't particularly clear on the point though, so you could argue
the toss on it.


Come to think of it, he did say I might want to move the lights over to the
non RCD side
if they keep tripping the RCD ???? no mention of regs though
--
Vass

** Just repeating this post as I accidentally replied to my own post
the last time.**

Thanks for the reply Christian,
In that case how should I provide earth protection on my metal light
switches and fittings (other than replacing them with plastic ones) ?
Is simply linking the lighting earth to the socket earth sufficient? I
want to make the lighting fittings and switches safe but prefer the
look of metal switches for the kitchen. If this is the case I suppose I
should just test for continuity between the lighting earths and a known
good socket earth.

Declan.

On 5 Jan 2006 06:30:52 -0800 someone who may be
wrote this:-

In that case how should I provide earth protection on my metal light
switches and fittings (other than replacing them with plastic ones) ?

What you need to do is run the new T&E cable back to the consumer
unit, where you can connect the protective conductor in the T&E to
the earth bar.

Using the protective conductor of another circuit is a no-no. For
testing it must be possible to disconnect the whole circuit at the
consumer unit.

As you are renovating things, now is a good time to replace all the
lighting circuit wiring. You may well be able to use the existing
wiring to pull through the new wiring.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Thanks David,
I was thinking it wasn't safe to leave it as it is anyway because I
suppose an earth fault in the lighting circuit could potentially make
other bonded metal live without tripping anything.
Perhaps time to call in the professionals as I don't really understand
why it doesn't cause the socket circuit to trip when I have power going
to earth from the lighting circuit.

Many thanks,
Declan.

Using the protective conductor of another circuit is a no-no. For
testing it must be possible to disconnect the whole circuit at the
consumer unit.

Well this is not entirely true. Whilst the earth should indeed be taken back
to the consumer unit, there is no requirement to be able to reliably
disconnect the earth at the consumer unit. This would be very difficult in
some cases, such as a bathroom supplementary bond between lighting circuits
and socket circuit for example.

New T&E back to the consumer unit is the way to go (or singles if the
original is in conduit).

Christian.

I'm curious, if you do have an earth fault on the lighting circuit
(lets say the earth goes back to the consumer unit earth bar). If
nothing trips how will anyone know that the fault has occurred. Surely
it can't run like that indefinitely?

If I can't run a new cable back to the CU is it better to have no earth
at all on the lighting circuit or to take it from the socket circuit? I
suppose I could take an earth off the lighting circuit now and connect
it to the CU whenever I renovate that area of the house (may be years
from now). I suppose plastic switches would be required until I get it
properly earthed.

I'm curious, if you do have an earth fault on the lighting circuit
(lets say the earth goes back to the consumer unit earth bar). If
nothing trips how will anyone know that the fault has occurred. Surely
it can't run like that indefinitely?

In the real world, an earth fault will be a dead short, not via a light
bulb. Therefore, there will be a dead short between the lighting circuit
live and the earth. When designing the installation, the earth loop
impedence is calculated, which gives the expected earth fault current. This
must be more than 5 times the MCB rating for the circuit. An MCB will
disconnect instantaneously at this multiple.

All circuits should be designed like this, even socket circuits. The RCD
then provides supplementary earth leakage protection to the socket circuits,
as it is more likely to have a non-short circuit earth fault, such as a
child sticking a screwdriver into the live whilst touching a radiator.
However, in the event of a dead earth short, both the MCB AND the RCD should
have a chance of cutting the power.

I suppose plastic switches would be required until I get it
properly earthed.

Yes, you may have to wait. Alternatively, I heard a rumour that some ranges
of metal light switches are available double insulated and do not require
earthing.

Christian.

That makes it much clearer for me, I was forgetting the difference
between my bulb test and a real world short !

Just to satisfy my remaining curiosity, I take it an RCD only trips
when power from it's own circuit goes to earth (as opposed to my test
which was live from the lighting circuit to socket earth).

Thanks a lot for the advice. I'll sleep much better at night with a
clear picture of how it all works :-)

Declan.

On Thu, 5 Jan 2006 15:26:22 -0000 someone who may be "Christian
McArdle" wrote this:-

Well this is not entirely true.

It was simplified. However, we both said to take the T&E back to the
consumer unit, which is the correct answer.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article . com,
wrote:
Just to satisfy my remaining curiosity, I take it an RCD only trips
when power from it's own circuit goes to earth (as opposed to my test
which was live from the lighting circuit to socket earth).

An RCD looks for an unbalanced current between neutral and line - which of
course may mean a 'short' to earth. But it will also protect on a two wire
circuit with no earth.

However, if you have a split load CU and the lighting circuit is on the
non RCD side running a lighting load to an RCD protected circuit earth
won't cause it to trip.

--
*Did you ever notice when you blow in a dog's face he gets mad at you? *

Dave Plowman London SW
To e-mail, change noise into sound.

Thanks again Christian/Dave/David. I now fully understand what's going
on and what I need to do (or get done).

Cheers,
Declan.