One of the jobs in need of doing shortly is the replacement of my Wylex
rewireable fuse consumer unit. Nothing actually wrong with it, but it
only has six ways and I am going to be needing eight in the near future,
so it seems like a good time to bring it up to date.

This brought about an investigation of the earthing setup. Never having
had need to look that closely at it in the past, I had not done a
detailed study of what was there, and had probably made a few
assumptions! A quick check over tonight raises some interesting points...

First assumption - Being a TT System (overhead power delivery) it will
have RCD protection. Having looked close up at said "RCD" I am now not
so sure. Have a look at the following (out of focus) pictu-

http://www.internode.co.uk/images/cb.jpg

Is that likely to be an RCD? Or is it more likely, as I now suspect, an
old style ELCB?

The words at the top read "Test this protective switch often by pressing
the yellow button", the words above the switch simply show "500V 50~", &
"60 AMP". It's made by Crabtree. Nothing else that I can see written on
it - no mention of a trip current. That feed through earth wire from the
CU looks a bit suspect as well!

The Henley block you see in the photo splits the tails from the meter,
one set go to the item in the photo - the second set go to a much newer
MK 30mA RCD that ultimately feeds the out buildings.

The second point of interest is the actual earth itself - So far the
only earth connection I can find is to the incoming (steel/iron) gas
main. Nothing that I have yet found seems to connect to the water main,
and as for an earth spike - if there is one, it is well hidden. (don't
even bother asking about suplimentary or equipotential bonding!) Not
sure how common this was/is on 50's properties? While the gas main might
be a resonable earth (not tested it yet I do know that there is no
plastic in it for a good 20m minimum) not sure I like the idea of
relying on only that.

(the outbuildings do have their own earth spike adjacent to them - I
have not yet verified if this is connected back to the house earth as
well - although it is certainly not isolated from the SWA armour on the
feeder cable).

Hence an upgrade to all things earth seems like a good plan.

How many earth rods, and to what depth would be recommened for a heavy
clay soil?



--
Cheers,

John.

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This is without doubt an old voltage trip and needs scrapping.

Many properties of this age were earthed to a rod using steel wire and over
the years lost the connection to rust so it may well have disappeared by
now.
Asking how many earth rods is a bit like asking how long is a piece of
string. You need a meter to check (not a multimeter) the final earth
resistance. Don't make the common mistake of banging in rods close to each
other thinking more is better; getting them too close actually increases the
resistance. In clay you probably only need one but you buy a 'proper' earth
rod they will screw together to achieve a greater depth should you need to.


---
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Jb wrote:

This is without doubt an old voltage trip and needs scrapping.

Thought as much...

Many properties of this age were earthed to a rod using steel wire and over
the years lost the connection to rust so it may well have disappeared by
now.

I could not even find evidence of a wire inside - the only obvious one
running downward from the install was the one to the gas main. If there
was a rod is it also possible it got burried when the previous owners
laid the concrete drive which continues up the side of the house beside
where the meter cupboard is located.

Asking how many earth rods is a bit like asking how long is a piece of
string. You need a meter to check (not a multimeter) the final earth
resistance. Don't make the common mistake of banging in rods close to each
other thinking more is better; getting them too close actually increases the
resistance. In clay you probably only need one but you buy a 'proper' earth
rod they will screw together to achieve a greater depth should you need to.

My plan was to measure the fault loop impeadance of what is there first
to see what the starting point is, and then add at least one proper
earth rod and carry on unitl I get a decent low enough value. Finally
add the cross bonding to the water main.

--
Cheers,

John.

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My plan was to measure the fault loop impeadance of what is there first
to see what the starting point is, and then add at least one proper
earth rod and carry on unitl I get a decent low enough value.

Make sure the earth loop impedence is OK with just the earth rod connected.
This means that when the gas supplier changes all their pipes to plastic
without telling you, you won't get fried.

Christian.

In article ,
John Rumm writes:
Jb wrote:

This is without doubt an old voltage trip and needs scrapping.

Thought as much...

Many properties of this age were earthed to a rod using steel wire and over
the years lost the connection to rust so it may well have disappeared by
now.

I could not even find evidence of a wire inside - the only obvious one
running downward from the install was the one to the gas main. If there
was a rod is it also possible it got burried when the previous owners
laid the concrete drive which continues up the side of the house beside
where the meter cupboard is located.

The right hand earth wire coming out of the Voltage Operated ELCB
should go to an earth rod, and nothing else.

Asking how many earth rods is a bit like asking how long is a piece of
string. You need a meter to check (not a multimeter) the final earth
resistance. Don't make the common mistake of banging in rods close to each
other thinking more is better; getting them too close actually increases the
resistance. In clay you probably only need one but you buy a 'proper' earth
rod they will screw together to achieve a greater depth should you need to.

My plan was to measure the fault loop impeadance of what is there first
to see what the starting point is, and then add at least one proper
earth rod and carry on unitl I get a decent low enough value. Finally
add the cross bonding to the water main.

There's no point with the ELCB in the circuit -- its coil will be
of the order 100-300 ohms most likely.

If you add more earth rods to such a setup, they should be spaced
well away from the existing one, and all connected to the main
earthing terminal, not the existing earth rod. Same goes for cross
bonding. The right hand earth terminal must only go to an earth rod,
which should be outside the resistance area of any other earth rods
or equivalent resistance area around bonded services. (The resistance
area is the area around an earth rod where the ground changes potential
due to current flow in the earth rod.) The ELCB works by monitoring
the voltage between your earth conductors and its earth rod, and
tripping before it reaches 50V.

You should add an RCD nowadays, but you can leave the ELCB there
harmlessly if you lower the overall earth impedance as above, and it
provides you with a means to isolate the CU.

--
Andrew Gabriel

(Andrew Gabriel) wrote in message ...
In article ,
John Rumm writes:
Jb wrote:

This is without doubt an old voltage trip and needs scrapping.

The ELCB works by monitoring
the voltage between your earth conductors and its earth rod, and
tripping before it reaches 50V.

You should add an RCD nowadays, but you can leave the ELCB there
harmlessly if you lower the overall earth impedance as above, and it
provides you with a means to isolate the CU.


A little explanation is in order. V-ELCBs are widely misundertood, and
are potentially dangerous. They work by /disconnecting/ all the house
earth wiring from earth, and measuring the V difference between real
earth and house earth wiring. Once this reaches 50v it should trip.

This means that assuming it is a v-elcb, none of your house wiring
will be earthed. V-elcbs must never be used with an electric shower.

With a v-elcb there is no current path from earth wiring to earth,
other than via the high impedance coil, so the impedance of your real
earth is immaterial. Bonding to a gas pipe is more than sufficient for
such an install as long as it is wired through the v-elcb.

It is important to test v-elcbs frequently as a failure leaves the
householder in real danger. Realise all earthed items are connected
together, and none are connected to earth.

The old earth connection may be ineffective with no v-elcb in circuit,
as it may be of high impedance and rely only on the v-elcb for
protection.

v-elcbs also dont trip on /all/ types of earth fault, so in fact a
v-elcb install can occasionally allow dangerous Vs to be acessible
even when not faulty. And due to the earth disconnection inherent with
v-elcbs, an earth fault anywhere in the house can leave the house
earth wiring ready to bite.

Theyre best replaced with more modern methods of protection. Their
only advantage is I've very rarely seen one nuisance trip. But despite
their clear risks I've yet to see them fry anyone. A bit of a bite
yes, but thats all so far.


Regards, NT

Andrew Gabriel wrote:

The right hand earth wire coming out of the Voltage Operated ELCB
should go to an earth rod, and nothing else.

It currently runs to an earth terminal block, from there is a connection
to the gas main, plus one other (as yet undefined) connection that runs
up to somewhere else in the building.

My plan was to measure the fault loop impeadance of what is there first
to see what the starting point is, and then add at least one proper
earth rod and carry on unitl I get a decent low enough value. Finally
add the cross bonding to the water main.


There's no point with the ELCB in the circuit -- its coil will be
of the order 100-300 ohms most likely.

Good point - I am certainly planning to ditch the ELCB anyway (space is
a bit limited in the cupboard) so that is not to much of a problem to
replace it with an RCD first.

If you add more earth rods to such a setup, they should be spaced
well away from the existing one, and all connected to the main
earthing terminal, not the existing earth rod. Same goes for cross
bonding. The right hand earth terminal must only go to an earth rod,
which should be outside the resistance area of any other earth rods

Keeping away from the existing one should be easy ;-) (since it's not
there). Keeping away from the other services is not quite as simple
since they both run down the side of the property. I also want to avoid
banging an earth rod through any drains if I can help it.

or equivalent resistance area around bonded services. (The resistance
area is the area around an earth rod where the ground changes potential
due to current flow in the earth rod.) The ELCB works by monitoring

I was thinking of placing the earth rod toward the front of the property
just beyond the last drain gully. That way I can be reasonably sure of
being clear of the drains (and other services). It also means I can run
a 10mm^2 earth wire inside the building to level with the rod and exit
through the wall right by it (about a 6m cable run it total).

The distance from the rod to the gas main (where it enters the property)
would then be approx 4m, and about 6m to the water main. The underground
pipes would however still pass within a couple of meters of the earth
rod in this situation. The other alternative would be to try and find a
route out the back of the house to the back garden - this is a little
more awkward however since there is a substantial patio area to cross.

Where do they normally site earth rods on new builds these days?

You should add an RCD nowadays, but you can leave the ELCB there
harmlessly if you lower the overall earth impedance as above, and it
provides you with a means to isolate the CU.

Looking through the TLC catalogue shows MK RCDs at twice to three times
the price of the Contactum, Hager, Volex ones etc. Any one got any
preference for brand? Are the MK ones worth the extra?

--
Cheers,

John.

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N. Thornton wrote:

A little explanation is in order. V-ELCBs are widely misundertood, and
are potentially dangerous. They work by /disconnecting/ all the house
earth wiring from earth, and measuring the V difference between real
earth and house earth wiring. Once this reaches 50v it should trip.

This means that assuming it is a v-elcb, none of your house wiring
will be earthed. V-elcbs must never be used with an electric shower.

Not much chance of that - I just put in a 35kW combi ;-)

With a v-elcb there is no current path from earth wiring to earth,
other than via the high impedance coil, so the impedance of your real
earth is immaterial. Bonding to a gas pipe is more than sufficient for
such an install as long as it is wired through the v-elcb.

Although I have not measured the impedence yet, I expect the gas main in
this case is relatively decent earth since it is fully metalic, and
passes through lots of heavy clay soil (mostly under concrete so it is
unlikely to ever dry out).

It is important to test v-elcbs frequently as a failure leaves the
householder in real danger. Realise all earthed items are connected
together, and none are connected to earth.

Probably less of an issue with no supplimentary equipotential bonding as
was common at the time the ELCB would have been instaled. Also for that
matter, the number of earthed appliances in use at the time would have
been far fewer as well.

The old earth connection may be ineffective with no v-elcb in circuit,
as it may be of high impedance and rely only on the v-elcb for
protection.

I shall demote the old connection to cross bonding only (might upgrade
the wire size while I am at it).

Theyre best replaced with more modern methods of protection. Their
only advantage is I've very rarely seen one nuisance trip. But despite
their clear risks I've yet to see them fry anyone. A bit of a bite
yes, but thats all so far.

Must admit in the ten+ years we have been here I have never had a trip
from either the ELCB or the RCD feeding the outbuildings (and yes they
do self test ok). Other than a mains halogen taking out a lighting
circuit fuse, I have never had any other fuses blow either (although
that could be related to the crummy earthing!)


--
Cheers,

John.

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\================================================= ================/

Good point - I am certainly planning to ditch the ELCB anyway (space is
a bit limited in the cupboard) so that is not to much of a problem to
replace it with an RCD first.

Make sure you replace it with a 100mA time delayed RCD. Your socket
circuits/outside electrics etc. should have additional 30mA instant acting
types. I would definitely continue to use a separate 30mA RCD for the
workshop compared to the house electrics.

Christian.

Christian McArdle wrote:

Make sure you replace it with a 100mA time delayed RCD. Your socket
circuits/outside electrics etc. should have additional 30mA instant acting

I could do that with RCBOs in place of the MCBs in the new consumer unit
for the relevant final rings. I chose a consumer unit that would accept
"tall" single width RCBOs in addition to the more common double width
ones - so the only downside would be the extra cost.

(There is not enough width available in the cupboard to use a split load CU)

I assume the main advantage of going for the discriminated RCD chain
like that is reducing the likelihood of nuisance trips? Compared with
the alternative (i.e. having a standard 30mA type AC RCD feeding the
whole CU), do you think the discriminated system is worth the extra expense?

types. I would definitely continue to use a separate 30mA RCD for the
workshop compared to the house electrics.

Yup was not planning on changing that (it is a far more recent addition
to the house electrics anyway and seems to be well implemented).

--
Cheers,

John.

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\================================================= ================/

I assume the main advantage of going for the discriminated RCD chain
like that is reducing the likelihood of nuisance trips? Compared with
the alternative (i.e. having a standard 30mA type AC RCD feeding the
whole CU), do you think the discriminated system is worth the extra
expense?

There are 3 basic methods (with variations, of course)

1. Whole system 30mA RCD
2. Split load 100mA time delay+30mA RCD
3. 100mA time delay + RCBOs

The problem with system 1 is that it kills the lights in the event of an
earth fault, which could be very dangerous, either due to rotating machinery
or fire escape. Some would say that system type 1 is no longer allowed by
the regulations, although it isn't very explicit about it, if I recall.

The advantages of system 3 over system 2 are twofold.

Firstly, it reduces the chance of a nuisance trip as there are fewer
appliances protected by one device, leading to a lower quiescent residual
current that isn't so close to the trip point.

Secondly, it reduces the effect of a nuisance trip, limiting it to the
circuit the trip occured on.

Obviously, system 3 can be very expensive if many circuits must be 30mA
protected. You would probably err on the side of protecting more circuits on
a TT system, as the consequences of a nuisance trip on the non-RCD protected
circuits are greater, as they would trip the time delay RCD and kill the
lights.

Personally, on a TT system, I'd be tempted to abandon the whole installation
RCD and use RCBOs for every circuit without exception and an insulated
consumer unit. This provides maximum discrimination, a single box solution
and the required RCD protection for every circuit. However, it is very much
more expensive than the cheapest permitted solution. I can't remember if the
consumer unit internals require RCD protection. If they do, you'd still need
the 100mA time delay incomer.

Christian.

In article ,
(N. Thornton) writes:
(Andrew Gabriel) wrote in message ...
In article ,
John Rumm writes:
Jb wrote:

This is without doubt an old voltage trip and needs scrapping.

The ELCB works by monitoring
the voltage between your earth conductors and its earth rod, and
tripping before it reaches 50V.

You should add an RCD nowadays, but you can leave the ELCB there
harmlessly if you lower the overall earth impedance as above, and it
provides you with a means to isolate the CU.


A little explanation is in order. V-ELCBs are widely misundertood, and

That's true, but unfortunately much of what you say afterwards is less
so.

are potentially dangerous. They work by /disconnecting/ all the house
earth wiring from earth, and measuring the V difference between real
earth and house earth wiring. Once this reaches 50v it should trip.

The house earth is connected through the ELCB, and it is allowed to
have any number of other parallel connections to earth too such as
additional earth rods (see ELCB wiring diagram towards back of 14th
edition wiring regs, in the testing section IIRC). Providing there's
no fault in the system, all the wiring remains earthed. In any event,
the system remains bonded.

This means that assuming it is a v-elcb, none of your house wiring
will be earthed.

You misunderstand voltage operated earth leakage circuit breakers.

V-elcbs must never be used with an electric shower.

Why?

With a v-elcb there is no current path from earth wiring to earth,
other than via the high impedance coil, so the impedance of your real
earth is immaterial. Bonding to a gas pipe is more than sufficient for
such an install as long as it is wired through the v-elcb.

No!

All bonding is done to the main earthing terminal (earthing strip in
your consumer unit or nearby where all the house earthing conductors
are brought together), just as with any type of earthing. You can have
zero or more earth rods connected to the main earthing terminal too.
You have to have one earth rod connected to the other side of the
voltage operated ELCB which must be outside of the resistance area of
any other earth rods so it is measuring true earth potential as far
as possible, and not affected by earth leakage from other earth rods,
yours or someone else's.

It is important to test v-elcbs frequently as a failure leaves the
householder in real danger. Realise all earthed items are connected
together, and none are connected to earth.

The danger is exactly the same as with a failed RCD on a TT system,
and an RCD is a far more complex device (I've seen failed RCDs, but
not failed VO-ELCB's).

The old earth connection may be ineffective with no v-elcb in circuit,
as it may be of high impedance and rely only on the v-elcb for
protection.

Certainly you shouldn't use an earth rod installed for a VO-ELCB
as your earth electrode if you remove the VO-ELCB without testing
the earth electrode impedance.

v-elcbs also dont trip on /all/ types of earth fault, so in fact a
v-elcb install can occasionally allow dangerous Vs to be acessible
even when not faulty. And due to the earth disconnection inherent with
v-elcbs, an earth fault anywhere in the house can leave the house
earth wiring ready to bite.

Only if your bonding is also broken.

Theyre best replaced with more modern methods of protection. Their
only advantage is I've very rarely seen one nuisance trip. But despite

Actually, their main problem is with nuisance tripping, due to stray
current leaking into your earthing system from their ground rod.
This could happen if someone too close starts leaking current into
the ground nearby, and during lightning storms.

their clear risks I've yet to see them fry anyone. A bit of a bite
yes, but thats all so far.

I would not advocate the use of VO-ELCB's nowadays as there are better
devices around. Also, you would be hard pressed to find anyone with a
test transformer for testing them. However, they performed an important
safety role for very many years, and they weren't and didn't suddenly
become dangerous just because the RCD was developed and is better.
They are now badly misunderstood.

--
Andrew Gabriel

"Christian McArdle" wrote
| 1. Whole system 30mA RCD
| 2. Split load 100mA time delay+30mA RCD
| 3. 100mA time delay + RCBOs
| The problem with system 1 is that it kills the lights in the event
| of an earth fault, which could be very dangerous, either due to
| rotating machinery or fire escape. Some would say that system
| type 1 is no longer allowed by the regulations, although it isn't
| very explicit about it, if I recall.


| Obviously, system 3 can be very expensive if many circuits must be
| 30mA protected. You would probably err on the side of protecting
| more circuits on a TT system, as the consequences of a nuisance
| trip on the non-RCD protected circuits are greater, as they would
| trip the time delay RCD and kill the lights.

An alternative could be to use a split load CU, with *all* the circuits off
the non-RCD main switch being RCBOs (say socket rings and lights), with the
RCD side being used for items where discrimination is less essential, eg
cooker, shower, immersion heater, radials to wall heaters, etc. (There would
be no whole-house RCD at all.)

That would provide the advantages of system 3 on power and lighting
circuits, which are more likely to suffer high quiescent residual current
and also form the greatest danger/inconvenience in the event of a trip,
whilst reducing the number of RCBOs required. If the washing machine and
dishwasher are wired to radials on the RCD side, a separate kitchen ring
might not be required, so most houses would be sufficed by 2 socket rings
and 2 lighting radials only requiring 4 RCBOs.

The downside is that most split-loads only have about 60A available through
the RCD.

Owain

Christian McArdle wrote:

There are 3 basic methods (with variations, of course)

1. Whole system 30mA RCD
2. Split load 100mA time delay+30mA RCD
3. 100mA time delay + RCBOs

Only 1 or 3 would be viable for me...

The problem with system 1 is that it kills the lights in the event of an
earth fault, which could be very dangerous, either due to rotating machinery
or fire escape. Some would say that system type 1 is no longer allowed by
the regulations, although it isn't very explicit about it, if I recall.

In my case, most rotating machinery is in my workshop which is on the
end of an external feed that is already connected via the 30mA RCD - so
I have lost that one before starting. While not an ideal situation, I
can't think of any situation where it would be a major problem should
all power get cut - just a case of stand still, stop pushing whatever
you are pushing and wait for the noise to stop ;-)

(all non hand tools have NVR switches)

The advantages of system 3 over system 2 are twofold.

Firstly, it reduces the chance of a nuisance trip as there are fewer
appliances protected by one device, leading to a lower quiescent residual
current that isn't so close to the trip point.

Secondly, it reduces the effect of a nuisance trip, limiting it to the
circuit the trip occured on.

The main nuisance would be loss of lights - I expect that in many case
some emergency lighting could be provided for less than the cost of
option 3...

Obviously, system 3 can be very expensive if many circuits must be 30mA
protected. You would probably err on the side of protecting more circuits on
a TT system, as the consequences of a nuisance trip on the non-RCD protected
circuits are greater, as they would trip the time delay RCD and kill the
lights.

I would as a minimum need to protect the downstairs, and kitchen ring
circuits. I also plan to install a heated towel rail in my new second
story that will have a 100W backup heater in it for summer use. Hence
that would really require another 30mA RCBO for that ring.

Personally, on a TT system, I'd be tempted to abandon the whole installation
RCD and use RCBOs for every circuit without exception and an insulated
consumer unit. This provides maximum discrimination, a single box solution
and the required RCD protection for every circuit. However, it is very much
more expensive than the cheapest permitted solution. I can't remember if the
consumer unit internals require RCD protection. If they do, you'd still need
the 100mA time delay incomer.

That or option 3 would certainly be the "nicest" solution... to be
honest I am leaning toward option 1 at the moment based on a suck it and
see approach. If it runs like the current setup (i.e. no unwanted trips
at all) then it can stay that way, if it causes problems, then I can
"upgrade" to option 3 at a later date without too much wasted expense
(i.e. just the cost of the unused incomer RCD that would get replaced by
the time delayed one).

As an aside, anyone know of a good source of time delayed 100mA RCDs
(60A rating would probably be enough). The only ones I can find are in
RS with their usual prices!

--
Cheers,

John.

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\================================================= ================/

As an aside, anyone know of a good source of time delayed 100mA RCDs
(60A rating would probably be enough). The only ones I can find are in
RS with their usual prices!

You could use an MK 6400S. Your main incomer should really be 100A rated.

Christian.

Owain wrote:

An alternative could be to use a split load CU, with *all* the circuits off
the non-RCD main switch being RCBOs (say socket rings and lights), with the
RCD side being used for items where discrimination is less essential, eg
cooker, shower, immersion heater, radials to wall heaters, etc. (There would
be no whole-house RCD at all.)

Nice idea, but I don't think it will work for me in this case. I
currently have 5 circuits, 3 final rings, and two lighting circuits. No
radials, no electric heating, showers, immersion etc. I will be adding
one extra final ring, and one extra lighting circuit, and a dedicated
smoke alarm circuit. So the above suggestion would require 7 RCBOs. The
secondary problem would be that a split load CU with enough ways will
not fit in the available space. That then turns the job of "swapping"
CUs into a much bigger job of relocating and replacing the CU.

That would provide the advantages of system 3 on power and lighting
circuits, which are more likely to suffer high quiescent residual current
and also form the greatest danger/inconvenience in the event of a trip,
whilst reducing the number of RCBOs required. If the washing machine and
dishwasher are wired to radials on the RCD side, a separate kitchen ring
might not be required, so most houses would be sufficed by 2 socket rings
and 2 lighting radials only requiring 4 RCBOs.

I could add the new second floor sockets and lighting to the existing
circuits since I would still be within the permitted maximum area and
loadings. However I much prefer having the ability to isolate each floor
discretely.

The downside is that most split-loads only have about 60A available through
the RCD.

Which is all my supply is good for anyway. Having said that I will
probably install a 100A RCD to allow for the possibility of future
upgrades.


--
Cheers,

John.

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\================================================= ================/

That then turns the job of "swapping" CUs into a much bigger job of
relocating and replacing the CU.

So basically you've got the choice of spending close around 300 quid on an
RCBO solution, or 60 quid on an MCB/whole installation RCD system that
doesn't really comply with regs...

Christian.

Nice idea, but I don't think it will work for me in this case.

Just a thought, does it help if you orientate the consumer unit 90 degrees
out?

Christian.

"Owain" wrote
| "Christian McArdle" wrote
| | 1. Whole system 30mA RCD
| | Some would say that system type 1 is no longer allowed by
| | the regulations, although it isn't very explicit about it,
| | if I recall.

I meant to add in the gap:

130-01-01 Good workmanship and materials shall be used.

130-02-01 All equipment shall be ...installed .. so as to prevent danger as
far as is reasonably practicable.

314-01-01 Every installation shall be divided into circuits as necessary to:
(i) avoid danger in the event of a fault, and (ii) facilitate safe
operation, testing and maintenance.

314-01-02 A separate circuit shall be provided for each part of the
installation which needs to be separately controlled for compliance with the
Regulations *or otherwise* to prevent danger, so that such circuits remain
energised in the event of failure of any other circuit of the installation,
and *due account shall be taken of the consequences of the operation of any
single protective device*.

from and copyright IEE Wiring Regulations Sixteenth Edition 1991. [* my
emphasis *]

Owain

Christian McArdle wrote:

Nice idea, but I don't think it will work for me in this case.


Just a thought, does it help if you orientate the consumer unit 90 degrees
out?

You mean install it so that the DIN rail is running verticaly?

Hmmm never seen on done that way round before but, I suppose it could
work. The things limiting the available height in the cupboard are at
least moveable (unlike the walls which limit the width!) It would still
result in having to crimp extensions onto a number of the circuit wire
ends though I would expect.



--
Cheers,

John.

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(Andrew Gabriel) wrote in message ... much about voltage operated ELCBs.


Ah! I had misunderstood the earthing arrangement. Couple of points
though...

You say their main problem is nuisance tripping, yet I have observed
that happen very rarely. Compared to RCDs they look like angels in
this respect. The RCD is vastly inferior when it comes to nuisance
trips.

As far as safety goes, v-ELCBs may not add a danger but they are so
inferior to RCDs that they do represent a risk relative to an RCD
protected TT system. TT systems are somewhat different to well earthed
ones, and do need some extra protection because of this. And a v-elcb
only goes so far in this respect.


Regards, NT

and *due account shall be taken of the consequences of the operation of
any
single protective device*.

Yes, I thought it said something like that. It doesn't actually explicitly
ban the use of a single device, just asks you to consider the consequences.
However, I got the impression that this had been recently reinterpreted to
effectively ban an overall non-time delayed RCD.

Christian.