We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

In message
,
Richard Russell writes
We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one trace
a fault like this? Dig up the entire garden?

I think the answer is "Yes!".

My son's house has an RCD in the garage that feeds the cooker, an
outside plantroom (that feeds some garden lights, pumps and other
things), a summerhouse with leaking roof, some street lights up his
drive and the filter and pump in the fish pond.

Every few days, in the middle of cooking a meal, the RCD would trip. I
took my old wind up megger down there, but was met with contempt.

Disconnecting the feed on from the plant room cured the problem so he
re-wired the summerhouse - no change. Replaced and rewired the outside
box feeding the pond. No change. Bought and installed a new submersible
pump. No change. He bought and installed some awful cylindrical in-line
connectors between the new box and the pond pump and separately the
filter. It was the filter. Dismantled it and discovered water had leaked
past a seal. Dried out and re-gunged and so far it has been OK.

This took us weeks to find, and at least he now has more knowledge of
the distribution (we still don't know how the street lights are wired)
and some of the installation is good. He did the wiring. I went along to
be a second pair of hands and to do the semaphore during testing.

I must find out what the in-line connectors were so that I am never
tempted to use them.
--
Bill

On Jun 18, 4:48*pm, Bill wrote:
I think the answer is "Yes!".

What would be the acceptability, under the regs, of fitting an
isolating transformer? No chance of tripping the RCD then, leakage or
no leakage!

Richard.
http://www.rtrussell.co.uk/

Richard Russell wrote:
On Jun 18, 4:48 pm, Bill wrote:
I think the answer is "Yes!".

What would be the acceptability, under the regs, of fitting an
isolating transformer? No chance of tripping the RCD then, leakage or
no leakage!


Apart from the lack of the required RCD protection?

--
Adam

Well if you know the route it takes one could start at the furthest one and
disconnect, then reconnect if it still trips and move closer etc. the snag
occurs if its branched ie several circuits or you do not know what goes
where first!

Brian

--
From the Sofa of Brian Gaff Reply address is active
"Richard Russell" wrote in message
...
We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Ah and then just watch for the smoke when the leak gets worse, brill.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Richard Russell" wrote in message
...
On Jun 18, 4:48 pm, Bill wrote:
I think the answer is "Yes!".

What would be the acceptability, under the regs, of fitting an
isolating transformer? No chance of tripping the RCD then, leakage or
no leakage!

Richard.
http://www.rtrussell.co.uk/

On Tuesday, June 18, 2013 3:19:47 PM UTC+1, Richard Russell wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?
Richard.
http://www.rtrussell.co.uk/

Divide & conquer. Simple as that. Its going to mean undoing many connections as you megger it all bit by bit.

If its a practical option to feed it off more than one rcd, that would ensure half of it stays on in a fault.


NT

On Jun 18, 7:22*pm, "Brian Gaff" wrote:
Well if you know the route it takes one could start at the furthest one and
disconnect, then reconnect if it still trips and move closer etc. the snag
occurs if its branched ie several circuits or you do not know what goes
where first!

Every single connection is in a buried waterproof box - there are a
lot of them - so such an approach would involve lots of digging (in a
mature garden with pretty much the entire ground surface covered with
plants and/or weed membrane and gravel). It's not very practical!

Richard.
http://www.rtrussell.co.uk/

On Jun 18, 6:33*pm, "ARW" wrote:
Apart from the lack of the required RCD protection?

I don't know what the letter of the regs says, but if an isolation
transformer (with a 115-0-115 secondary) is considered safe for on-
site power tools I dont really see what the objection would be to
using one for garden lighting.

Richard.
http://www.rtrussell.co.uk/

On Tuesday 18 June 2013 23:03 Richard Russell wrote in uk.d-i-y:

On Jun 18, 6:33 pm, "ARW" wrote:
Apart from the lack of the required RCD protection?

I don't know what the letter of the regs says, but if an isolation
transformer (with a 115-0-115 secondary) is considered safe for on-
site power tools I dont really see what the objection would be to
using one for garden lighting.

Richard.
http://www.rtrussell.co.uk/

That's 55-0-55 aka 110V you're thinking of and the 55V (relative to earth)
counts as ELV.


--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

On Jun 18, 11:46*pm, Tim Watts wrote:
That's 55-0-55 aka 110V you're thinking of and the 55V (relative to earth)
counts as ELV.

Fair point, but isolation transformers with a 230v secondary are sold
as 'safety site transformers', which is what I was meaning. For
example these from RS:

http://uk.rs-online.com/web/p/safety...rmers/0405565/
http://uk.rs-online.com/web/p/safety...rmers/2604238/

Our house is of a vintage (built six years ago) when no RCD protection
was required on the lighting circuits, so in that context I can't get
myself too worked up about garden lighting with no RCD protection,
especially if it's only running at 115 volts wrt ground.

Richard.
http://www.rtrussell.co.uk/

On Wednesday 19 June 2013 00:03 Richard Russell wrote in uk.d-i-y:

On Jun 18, 11:46 pm, Tim Watts wrote:
That's 55-0-55 aka 110V you're thinking of and the 55V (relative to
earth) counts as ELV.

Fair point, but isolation transformers with a 230v secondary are sold
as 'safety site transformers', which is what I was meaning. For
example these from RS:

http://uk.rs-online.com/web/p/safety...rmers/0405565/
http://uk.rs-online.com/web/p/safety...rmers/2604238/

I will have to check chapter and verse - but even if fully floating, relying
on it is a bad idea IMO.

Our house is of a vintage (built six years ago) when no RCD protection
was required on the lighting circuits, so in that context I can't get
myself too worked up about garden lighting with no RCD protection,
especially if it's only running at 115 volts wrt ground.

"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk (wet
ground/rain/etc) *and* you are more likely to expose a member of the public
to risk (eg visitors).

Richard.
http://www.rtrussell.co.uk/
--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

On Tuesday, June 18, 2013 10:59:32 PM UTC+1, Richard Russell wrote:

Every single connection is in a buried waterproof box - there are a
lot of them - so such an approach would involve lots of digging (in a
mature garden with pretty much the entire ground surface covered with
plants and/or weed membrane and gravel). It's not very practical!

If its really not doable, I'm struggling to see a better option than going 55-0-55.


NT

On Wednesday, June 19, 2013 8:26:43 AM UTC+1, Tim Watts wrote:
"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk (wet
ground/rain/etc) *and* you are more likely to expose a member of
the public to risk (eg visitors).

I can't say I agree. AIUI, the requirement to have RCD protection at all on garden lighting circuits is a fairly recent one. In addition, garden luminaires are far better protected from accidental contact than a domestic (bayonet or screw) light fitting, because of the weatherproofing requirement.

To gain access to the bulb, let alone remove it to expose a live terminal, typically requires unscrewing a watertight cover - something which I know from experience is not easy even when you want to do it! The idea that a visitor might unscrew one of these covers, remove the bulb (presumably lit) and poke their finger into the exposed socket - mostly GU10 so that's not easy - seems wildly implausible to me.

As it happens the point is moot anyway. As an experiment I bypassed the RCD so I could power up the circuit for a few hours. The result is that (maybe through some local heating drying out the moisture) the leak is now reduced below the trip threshold and it's running fine again with the RCD re-instated. The problem may recur, of course, but I'll worry about that if and when it happens.

Richard.
http://www.rtrussell.co.uk/

On Wed, 19 Jun 2013 01:38:12 -0700 (PDT), Richard Russell wrote:

"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk
(wet
ground/rain/etc) *and* you are more likely to expose a member of
the public to risk (eg visitors).

I can't say I agree. AIUI, the requirement to have RCD protection at
all on garden lighting circuits is a fairly recent one.

Think it's any circuit "exported" not just lighting. B-)

But given the choice between a traditional L 230 V wrt ground and N
bonded to ground circuit and a fully floating nominal 115V L and N
wrt to ground but 230 V l to N I'd prefer the latter. If you touch
either it drops to essentially ground you'll still get a belt but
nothing like the one you'd get from touching the L in the first case.
Problems come when there is a fault to earth on one side of the
fullly floating circuit and you touch the other...

--
Cheers
Dave.

On Tue, 18 Jun 2013 14:59:32 -0700 (PDT), Richard Russell wrote:

Every single connection is in a buried waterproof box -

Design failure, there is no such thing as a "waterproof box" unless
you fill it with something to stop water getting in, be that a
potting compound or hard setting tar.

If there is a void water will get in, either by capillary action
through any seals or as water vapour and then condensation through
the seals or even the box material itself.

They should have been left accessable in some way or marked, At the
very least an accurate map of cable routes and joins made.

--
Cheers
Dave.

On Wednesday, June 19, 2013 9:38:12 AM UTC+1, Richard Russell wrote:

As it happens the point is moot anyway. As an experiment I bypassed the RCD so I could power up the circuit for a few hours. The result is that (maybe through some local heating drying out the moisture) the leak is now reduced below the trip threshold and it's running fine again with the RCD re-instated. The problem may recur, of course, but I'll worry about that if and when it happens.

it inevitably will.

Converting to 12-0-12v is another option


NT

On 19/06/2013 09:38, Richard Russell wrote:
On Wednesday, June 19, 2013 8:26:43 AM UTC+1, Tim Watts wrote:
"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk
(wet ground/rain/etc) *and* you are more likely to expose a member
of the public to risk (eg visitors).

I can't say I agree. AIUI, the requirement to have RCD protection at
all on garden lighting circuits is a fairly recent one.

Not especially no. Outside circuits in general require RCD protection.

In addition,
garden luminaires are far better protected from accidental contact
than a domestic (bayonet or screw) light fitting, because of the
weatherproofing requirement.

So lets say the cause of the fault is that you have a live to case
short on a lamp and the case is not earthed, and only under certain
circumstances is there enough leakage to earth to cause your trip. Still
fancy leaning against that lamp post with the RCD disabled?

To gain access to the bulb, let alone remove it to expose a live
terminal, typically requires unscrewing a watertight cover -
something which I know from experience is not easy even when you want
to do it! The idea that a visitor might unscrew one of these covers,
remove the bulb (presumably lit) and poke their finger into the
exposed socket - mostly GU10 so that's not easy - seems wildly
implausible to me.

Implausible yes, but not relevant either.

As it happens the point is moot anyway. As an experiment I bypassed
the RCD so I could power up the circuit for a few hours. The result
is that (maybe through some local heating drying out the moisture)
the leak is now reduced below the trip threshold and it's running
fine again with the RCD re-instated. The problem may recur, of
course, but I'll worry about that if and when it happens.

Ah, the ostrich algorithm ;-)


--
Cheers,

John.

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

In message , John
Rumm writes
As it happens the point is moot anyway. As an experiment I bypassed
the RCD so I could power up the circuit for a few hours. The result
is that (maybe through some local heating drying out the moisture)
the leak is now reduced below the trip threshold and it's running
fine again with the RCD re-instated. The problem may recur, of
course, but I'll worry about that if and when it happens.

Ah, the ostrich algorithm ;-)


I've got the answer. Bypass the RCD, insert a series diode, let it run
until a period of rain, then walk round the garden with a candle.
--
Bill

On 18/06/2013 20:38, wrote:
On Tuesday, June 18, 2013 3:19:47 PM UTC+1, Richard Russell wrote:

We have an extensive, professionally installed, garden lighting
system which has recently started tripping its dedicated RCD. I
have eliminated all the bulbs, luminaires and accessible cables
which, sadly, means the problem is almost certainly in one of the
many 'waterproof' underground connection boxes. How on earth does
one trace a fault like this? Dig up the entire garden? Richard.
http://www.rtrussell.co.uk/

Divide & conquer. Simple as that. Its going to mean undoing many
connections as you megger it all bit by bit.

If you go the binary chop route, you can eliminate 3/4s of the circuit
by digging up just two of the junctions...


--
Cheers,

John.

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

Richard Russell writes:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Donkey's moons ago there used to be things called TDRs, Time Domain
Reflectometers, which would show the location of discontinuities in a
transmission line by the squiggles on a built-in oscilloscope screen.

Hard to interpret and I imagine it would be even more difficult if all
you were looking for was a fairly high leakage resistance rather than a
short, and even more difficult if the circuit branched.

But treating live and earth as a transmission line and using a TDR to
examine its characteristics might just possibly reveal something.

OTOH one might have more luck with a couple of bent hazel sticks !

--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
All that is gold does not glister / Not all who wander are lost

On Jun 19, 4:06*pm, John Rumm wrote:
So lets say the cause of the fault is that *you have a live to case
short on a lamp and the case is not earthed

That's a double-fault scenario (live-to-case short *and* case not
earthed). One doesn't normally attempt to protect against such
unlikely occurrences. In any case an entirely disconnected earth
isn't very plausible when the stainless steel lamp column physically
enters the ground!

Ah, the ostrich algorithm ;-)

Seems entirely reasonable to me. If the solution to a problem will
inevitably be difficult, expensive and time-consuming, putting it off
as long as possible (without compromising safety) makes perfect sense!

Richard.
http://www.rtrussell.co.uk/

Tim Watts writes:

On Wednesday 19 June 2013 00:03 Richard Russell wrote in uk.d-i-y:

On Jun 18, 11:46 pm, Tim Watts wrote:
That's 55-0-55 aka 110V you're thinking of and the 55V (relative to
earth) counts as ELV.

Fair point, but isolation transformers with a 230v secondary are sold
as 'safety site transformers', which is what I was meaning. For
example these from RS:

http://uk.rs-online.com/web/p/safety...rmers/0405565/
http://uk.rs-online.com/web/p/safety...rmers/2604238/

I will have to check chapter and verse - but even if fully floating, relying
on it is a bad idea IMO.

Our house is of a vintage (built six years ago) when no RCD protection
was required on the lighting circuits, so in that context I can't get
myself too worked up about garden lighting with no RCD protection,
especially if it's only running at 115 volts wrt ground.

"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk (wet
ground/rain/etc) *and* you are more likely to expose a member of the public
to risk (eg visitors).

In N. America they use 115v but they also use RCDs (they call them
GFIs) with a sensitivity of only 5 mA. not 30 mA.
So they're still worried even though the voltage is lower.

--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
All that is gold does not glister / Not all who wander are lost

Richard Russell writes:

On Jun 19, 4:06=A0pm, John Rumm wrote:
So lets say the cause of the fault is that =A0you have a live to case
short on a lamp and the case is not earthed

That's a double-fault scenario (live-to-case short *and* case not
earthed). One doesn't normally attempt to protect against such
unlikely occurrences. In any case an entirely disconnected earth
isn't very plausible when the stainless steel lamp column physically
enters the ground!

If you measure the resistance between two of those columns (which will
be about twice the resistance of one column to earth) you may be
surprised - it'll likely be of the order of K ohms.

--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ O n e t e l . c o m
All that is gold does not glister / Not all who wander are lost

In article , Windmill spam-no-
lid scribeth thus
Richard Russell writes:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Donkey's moons ago there used to be things called TDRs, Time Domain
Reflectometers, which would show the location of discontinuities in a
transmission line by the squiggles on a built-in oscilloscope screen.

Hard to interpret and I imagine it would be even more difficult if all
you were looking for was a fairly high leakage resistance rather than a
short, and even more difficult if the circuit branched.


There're still around used on the other week to find a fault on a buried
co-ax cable it showed it up very accurately. Two discontinues one major
one not so. There used to be a design around for a brew you own but
needed a scope to go with it not that practical. Theres a BT test unit
comes up on ebay from time to time thats very good...

But treating live and earth as a transmission line and using a TDR to
examine its characteristics might just possibly reveal something.

OTOH one might have more luck with a couple of bent hazel sticks !

Well that might tell you the line is there but not much else. Seen it
done on buried water pipes, seems to work very well with some people but
not all..
--
Tony Sayer

On Wednesday, June 19, 2013 11:21:21 PM UTC+1, John Rumm wrote:
On 18/06/2013 20:38, wrote:
On Tuesday, June 18, 2013 3:19:47 PM UTC+1, Richard Russell wrote:

We have an extensive, professionally installed, garden lighting
system which has recently started tripping its dedicated RCD. I
have eliminated all the bulbs, luminaires and accessible cables
which, sadly, means the problem is almost certainly in one of the
many 'waterproof' underground connection boxes. How on earth does
one trace a fault like this? Dig up the entire garden? Richard.
http://www.rtrussell.co.uk/

Divide & conquer. Simple as that. Its going to mean undoing many
connections as you megger it all bit by bit.

If you go the binary chop route, you can eliminate 3/4s of the circuit
by digging up just two of the junctions...

Yup. You've got a fair chance of getting a lot of the circuit operational quite quickly. But it is also possible the OP has more than one leaky cable or jbox, or that the leak is in the one and only feed line for the lot.

There's really no other way to fix it than divide & conquer. The only other options are workarounds that keep going with wet cable or jboxes, which have a high risk of later total failure.

With luck you may be able to trace much of it with a basic metal detector.


NT

On 2013-06-20, Windmill wrote:

Tim Watts writes:

On Wednesday 19 June 2013 00:03 Richard Russell wrote in uk.d-i-y:

Our house is of a vintage (built six years ago) when no RCD protection
was required on the lighting circuits, so in that context I can't get
myself too worked up about garden lighting with no RCD protection,
especially if it's only running at 115 volts wrt ground.

"Only 115V"? I think you *should* worry about that - outside is a
particularly special case as you both have enhanced shock risk (wet
ground/rain/etc) *and* you are more likely to expose a member of the public
to risk (eg visitors).

In N. America they use 115v but they also use RCDs (they call them
GFIs) with a sensitivity of only 5 mA. not 30 mA.
So they're still worried even though the voltage is lower.

They don't use GFCIs everywhere in the house, just (typically) for
sockets in kitchens & bathrooms & outdoors.

On 19/06/2013 23:36, Windmill wrote:

But treating live and earth as a transmission line and using a TDR to
examine its characteristics might just possibly reveal something.

Or not... With the 'fault' being a fairly high resistance leak to earth
the reflection coefficient probably won't be high enough to show up.

OTOH one might have more luck with a couple of bent hazel sticks !

Sort of. My suggestion is as follows:

Disconnect the feed-point from the RCD. Strap the L & N outgoing
conductors together and energise them at mains voltage via a
precautionary low value fuse (1 or 2 A, say). The point(s) of leakage
will now be injecting some current into the soil. If you're worried
about safety then reduce the applied voltage using a suitable
transformer or auto-transformer. 50 V might be enough.

Now use a highish impedance AC voltmeter (an ordinary DMM will do) and
probe for ground potential gradients - i.e. earth one side of the meter
to a reference, the mains earth should do, via a long flying lead. On
the other side, rig up a probe a few inches long to stick in the ground
- this ought to a have an insulated handle for obvious reasons. Probe
around, following the cable routes, if known. Look for the highest
voltage and dig there.

If water has got into a joint box it will only be a matter of time
before the situation develops into a low impedance L-N fault. I fear
that feeding via an isolating transformer would only give a short-term fix.

--
Andy

On 21/06/2013 23:57, Andy Wade wrote:
On 19/06/2013 23:36, Windmill wrote:

But treating live and earth as a transmission line and using a TDR to
examine its characteristics might just possibly reveal something.

Or not... With the 'fault' being a fairly high resistance leak to earth
the reflection coefficient probably won't be high enough to show up.

OTOH one might have more luck with a couple of bent hazel sticks !

Sort of. My suggestion is as follows:

Disconnect the feed-point from the RCD. Strap the L & N outgoing
conductors together and energise them at mains voltage via a
precautionary low value fuse (1 or 2 A, say). The point(s) of leakage
will now be injecting some current into the soil. If you're worried
about safety then reduce the applied voltage using a suitable
transformer or auto-transformer. 50 V might be enough.

Now use a highish impedance AC voltmeter (an ordinary DMM will do) and
probe for ground potential gradients - i.e. earth one side of the meter
to a reference, the mains earth should do, via a long flying lead. On
the other side, rig up a probe a few inches long to stick in the ground
- this ought to a have an insulated handle for obvious reasons. Probe
around, following the cable routes, if known. Look for the highest
voltage and dig there.

Nice plan...

Might be worth adding a step of doing an additional probing before
energising the circuit, just to establish that you are not going to be
lead up the garden path (so to speak) by stray ground currents from
other sources not connected with the actual circuit in question.

If water has got into a joint box it will only be a matter of time
before the situation develops into a low impedance L-N fault. I fear
that feeding via an isolating transformer would only give a short-term fix.

and could ultimately end up costing in electricity keeping the ground
warm if you are unlucky.


--
Cheers,

John.

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

On 22/06/2013 03:06, John Rumm wrote:

Nice plan...

Might be worth adding a step of doing an additional probing before
energising the circuit, just to establish that you are not going to be
lead up the garden path (so to speak) by stray ground currents from
other sources not connected with the actual circuit in question.

Good idea - and in retrospect my suggestion to use mains earth as the
voltmeter's reference point wasn't too clever, especially it's PME. A
'clean' reference spike somewhere in the garden, but known to be well
away from the lighting cables, should be a much better bet.

--
Andy

On Saturday, June 22, 2013 3:06:01 AM UTC+1, John Rumm wrote:
On 21/06/2013 23:57, Andy Wade wrote:
On 19/06/2013 23:36, Windmill wrote:

Sort of. My suggestion is as follows:

Disconnect the feed-point from the RCD. Strap the L & N outgoing
conductors together and energise them at mains voltage via a
precautionary low value fuse (1 or 2 A, say). The point(s) of leakage
will now be injecting some current into the soil. If you're worried
about safety then reduce the applied voltage using a suitable
transformer or auto-transformer. 50 V might be enough.

Now use a highish impedance AC voltmeter (an ordinary DMM will do) and
probe for ground potential gradients - i.e. earth one side of the meter
to a reference, the mains earth should do, via a long flying lead. On
the other side, rig up a probe a few inches long to stick in the ground
- this ought to a have an insulated handle for obvious reasons. Probe
around, following the cable routes, if known. Look for the highest
voltage and dig there.

Nice plan...
Might be worth adding a step of doing an additional probing before
energising the circuit, just to establish that you are not going to be
lead up the garden path (so to speak) by stray ground currents from
other sources not connected with the actual circuit in question.

or use a flasher in the feed


NT

On 23/06/2013 08:16, wrote:
On Saturday, June 22, 2013 3:06:01 AM UTC+1, John Rumm wrote:
On 21/06/2013 23:57, Andy Wade wrote:
On 19/06/2013 23:36, Windmill wrote:

Sort of. My suggestion is as follows:

Disconnect the feed-point from the RCD. Strap the L & N outgoing
conductors together and energise them at mains voltage via a
precautionary low value fuse (1 or 2 A, say). The point(s) of leakage
will now be injecting some current into the soil. If you're worried
about safety then reduce the applied voltage using a suitable
transformer or auto-transformer. 50 V might be enough.

Now use a highish impedance AC voltmeter (an ordinary DMM will do) and
probe for ground potential gradients - i.e. earth one side of the meter
to a reference, the mains earth should do, via a long flying lead. On
the other side, rig up a probe a few inches long to stick in the ground
- this ought to a have an insulated handle for obvious reasons. Probe
around, following the cable routes, if known. Look for the highest
voltage and dig there.

Nice plan...
Might be worth adding a step of doing an additional probing before
energising the circuit, just to establish that you are not going to be
lead up the garden path (so to speak) by stray ground currents from
other sources not connected with the actual circuit in question.

or use a flasher in the feed

I am sure you don't mean an old git in a rain coat, so could you elaborate?

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
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\================================================= ================/

On Sunday, June 23, 2013 12:03:49 PM UTC+1, John Rumm wrote:
On 23/06/2013 08:16, wrote:
On Saturday, June 22, 2013 3:06:01 AM UTC+1, John Rumm wrote:
On 21/06/2013 23:57, Andy Wade wrote:
On 19/06/2013 23:36, Windmill wrote:

Sort of. My suggestion is as follows:

Disconnect the feed-point from the RCD. Strap the L & N outgoing
conductors together and energise them at mains voltage via a
precautionary low value fuse (1 or 2 A, say). The point(s) of leakage
will now be injecting some current into the soil. If you're worried
about safety then reduce the applied voltage using a suitable
transformer or auto-transformer. 50 V might be enough.

Now use a highish impedance AC voltmeter (an ordinary DMM will do) and
probe for ground potential gradients - i.e. earth one side of the meter
to a reference, the mains earth should do, via a long flying lead. On
the other side, rig up a probe a few inches long to stick in the ground
- this ought to a have an insulated handle for obvious reasons. Probe
around, following the cable routes, if known. Look for the highest
voltage and dig there.

Nice plan...
Might be worth adding a step of doing an additional probing before
energising the circuit, just to establish that you are not going to be
lead up the garden path (so to speak) by stray ground currents from
other sources not connected with the actual circuit in question.

or use a flasher in the feed

I am sure you don't mean an old git in a rain coat, so could you elaborate?

If you pull the fuse or switch the mcb off, and clip a flashing light bulb across it, you then get a mains feed that goes on and off frequently. You can thus tell with your ground probe how much difference the mains feed is making, it just means you can do one sweep not 2. Its a classic old fashioned way to trace circuits.


NT

On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in the arse.

--
Money can't buy you true love.
It does however put you in a good bargaining position.

In article , Gefreiter Krueger
scribeth thus
On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in the
arse.

Theres speaks someone who has never been accidentally connected across
the mains..

I have an I can tall you its ****ing painful squared!..

If I should swear(
--
Tony Sayer

Gefreiter Krueger wrote:
On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:
We have an extensive, professionally installed, garden lighting
system which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy.


RCDs are a pain in the arse.

The double pole ones are.

--
Adam

On Sunday 23 June 2013 18:50 Gefreiter Krueger wrote in uk.d-i-y:

On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in
the arse.


Are you insane offering that as "advice" on a public group?

No of course you should not dispense with an RCD, *especially* on an outside
domestic circuit.
--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

On Sun, 23 Jun 2013 18:54:32 +0100, tony sayer wrote:

In article , Gefreiter Krueger
scribeth thus
On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in the
arse.

Theres speaks someone who has never been accidentally connected across
the mains..

I have an I can tall you its ****ing painful squared!..

If I should swear(

If you're connected across the mains, the RCD won't trip. You need an earth for that. Anyway it's only painful for a short period till you let go or fall off the ladder.

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On Sun, 23 Jun 2013 19:33:23 +0100, Tim Watts wrote:

On Sunday 23 June 2013 18:50 Gefreiter Krueger wrote in uk.d-i-y:

On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in
the arse.


Are you insane offering that as "advice" on a public group?

No of course you should not dispense with an RCD, *especially* on an outside
domestic circuit.

We managed just fine before RCDs were invented. Why has the world turned all girly?

--
Question: Are there too many immigrants in Britain?
17% said yes, 11% said no, 72% said "I am not understanding the question please."

In article , Gefreiter Krueger
scribeth thus
On Sun, 23 Jun 2013 18:54:32 +0100, tony sayer wrote:

In article , Gefreiter Krueger
scribeth thus
On Tue, 18 Jun 2013 15:19:47 +0100, Richard Russell
wrote:

We have an extensive, professionally installed, garden lighting system
which has recently started tripping its dedicated RCD. I have
eliminated all the bulbs, luminaires and accessible cables which,
sadly, means the problem is almost certainly in one of the many
'waterproof' underground connection boxes. How on earth does one
trace a fault like this? Dig up the entire garden?

Richard.
http://www.rtrussell.co.uk/

Change it to a good old fuse. They weren't so fussy. RCDs are a pain in the
arse.

Theres speaks someone who has never been accidentally connected across
the mains..

I have an I can tall you its ****ing painful squared!..

If I should swear(

If you're connected across the mains, the RCD won't trip. You need an earth for
that. Anyway it's only painful for a short period till you let go or fall off
the ladder.



In fact it was an electric drill, metal cased in the one hand, to an
earthed ladder and it was inside reaching out thru a window to move it a
bit sideways as it was in the way of where I was about to drill and I
can tell you if I could have fallen over I would have done anything to
"disconnect" but as your totally paralysed you cant move a bloody
thing!.

Duff house wiring that was due to and only leakage too not directly
connected but sufficient!...
--
Tony Sayer