A quickie for you 16th Edition Guru's:

I'm installing some wiring in our (covered) outside
passage/outbuildings viz:- an extension to the downstairs ring, (not a
spur), and additionally a spur from the downstairs lighting circuit.
The wiring from the house passes through the wall of the house, and I
then intend to connect Hi-Tuf cable for the wiring in the passage
within an adaptable box or something similar. Obviously the phase and
neutral conductors for the three t&e's must remain separate in order
to be a conventional ring and a separate lighting circuit. My
question is though, is it acceptable to join together all 3 CPC's
within the adaptable box?

"Mike Hall" wrote in message
om...

A quickie for you 16th Edition Guru's:

Guru's what? (See Truss L., /ibid./)

My question is though, is it acceptable to join together all 3
CPC's within the adaptable box?

Yes, provided that the circuits in question originate from the same consumer
unit or dis-board, and that the CPC for the ring remains in the form of a
ring.

--
Andy

"Andy Wade" wrote in message ...

Yes, provided that the circuits in question originate from the same consumer
unit or dis-board, and that the CPC for the ring remains in the form of a
ring.

Andy, but therin lies the crux of my question! - If I've joined all 3
cpc's, (2 halves of the ring and the lighting circuit) then the cpc
for the ring is now not a simple ring in itself.

In article ,
(Mike Hall) writes:
"Andy Wade" wrote in message ...

Yes, provided that the circuits in question originate from the same consumer
unit or dis-board, and that the CPC for the ring remains in the form of a
ring.

Andy, but therin lies the crux of my question! - If I've joined all 3
cpc's, (2 halves of the ring and the lighting circuit) then the cpc
for the ring is now not a simple ring in itself.

I think that's fine. I can't quite remember exactly what the regs say,
but there are cases of ring circuits where the CPC clearly isn't a
ring, such as when it's provided by conduit or the outer of mineral
insulated cable. I think the important point is the CPC impedance at
any point must be no worse than if it was a ring, or you are going to
have to do calculations to ensure you are still withing allowable
earth fault loop impedance for whatever your protective devices are.
No amount of extra connections between CPC's can make it worse, actually
quite the opposite.

--
Andrew Gabriel

"Mike Hall" wrote in message
om...
A quickie for you 16th Edition Guru's:

I'm installing some wiring in our (covered) outside
passage/outbuildings viz:- an extension to the downstairs ring, (not a
spur), and additionally a spur from the downstairs lighting circuit.
The wiring from the house passes through the wall of the house, and I
then intend to connect Hi-Tuf cable for the wiring in the passage
within an adaptable box or something similar. Obviously the phase and
neutral conductors for the three t&e's must remain separate in order
to be a conventional ring and a separate lighting circuit. My
question is though, is it acceptable to join together all 3 CPC's
within the adaptable box?

you should try and keep the cpcs separate if you intend to extend the ring
main so that at no point do you end up with a figure of 8 arrangement
otherwise when it is tested at the consumer unit it would appear to be
continuous even if you had lost the cpc continuity in the passage way
leading to the possibility that one leg could have to take the full current
in the event of a fault. not really sure what the benefit of joining them
together would be. I can see the hazards.

reddi-sparks

On 16 Jul 2004 12:21:16 GMT, (Andrew
Gabriel) strung together this:

In article ,
(Mike Hall) writes:
"Andy Wade" wrote in message ...

Yes, provided that the circuits in question originate from the same consumer
unit or dis-board, and that the CPC for the ring remains in the form of a
ring.

Andy, but therin lies the crux of my question! - If I've joined all 3
cpc's, (2 halves of the ring and the lighting circuit) then the cpc
for the ring is now not a simple ring in itself.

I think that's fine. I can't quite remember exactly what the regs say,
but there are cases of ring circuits where the CPC clearly isn't a
ring, such as when it's provided by conduit or the outer of mineral
insulated cable. I think the important point is the CPC impedance at
any point must be no worse than if it was a ring, or you are going to
have to do calculations to ensure you are still withing allowable
earth fault loop impedance for whatever your protective devices are.
No amount of extra connections between CPC's can make it worse, actually
quite the opposite.

Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince people
that it's correct than it would've taken me to do it the common method
in the first place.
--

SJW
A.C.S. Ltd

not really sure what the benefit of joining them together
would be. I can see the hazards.

Presumably saving on several ways in the terminal block.

Christian.

Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince people
that it's correct than it would've taken me to do it the common method
in the first place.

I'd agree. What's the point in complicating matters by using non-standard
methods that can only confuse those who come after you?

Christian.

On Fri, 16 Jul 2004 17:01:40 +0100, "Christian McArdle"
strung together this:

not really sure what the benefit of joining them together
would be. I can see the hazards.

Presumably saving on several ways in the terminal block.

Well, 2 actually.
--

SJW
A.C.S. Ltd

"Lurch" wrote in message ...

[Mike Hall]
Andy, but therin lies the crux of my question! - If I've joined all
3 cpc's, (2 halves of the ring and the lighting circuit) then the
cpc for the ring is now not a simple ring in itself.

It has to be in the form of a ring with both ends connected to the earth bar
in the CU. This does not forbid cross-connection with the CPC of another
circuit - see reg. 543-02-09 (and see below re. supplementary bonding in
bathrooms).

[Andrew Gabriel]
I think that's fine. I can't quite remember exactly what the regs
say, but there are cases of ring circuits where the CPC clearly
isn't a ring, such as when it's provided by conduit or the outer of
mineral insulated cable. I think the important point is the CPC
impedance at any point must be no worse than if it was a ring, or
you are going to have to do calculations to ensure you are still
withing allowable earth fault loop impedance for whatever your
protective devices are.
No amount of extra connections between CPC's can make it worse,
actually quite the opposite.

Agreed.

[Lurch]
Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince
people that it's correct than it would've taken me to do it the
common method in the first place.

Although I agree with the general drift of that (don't adopt unusual circuit
arrangements in domestic installations) I don't agree that it applies here.

Cross-connection between the CPCs of different circuits can be expected to
occur in some situations - e.g. between 'upstairs' and 'downstairs' lighting
circuits where they meet at one or more 2-gang 2-way switches (one switch on
each circuit) for hall and landing. Another case where cross-connection is
actually _required_ by the regs is in a bathroom (within the zones) where
you have some combination of shower, fused conn. unit on ring (for heater or
towel rail etc.), and luminaire and/or shaver outlet. Here the CPCs of the
relevant circuits must be cross connected by supplementary bonding. Since
the 2001 edition of BS 7671 came into force this bonding is required whether
or not the equipment connected to the said circuits has any
exposed-conductive-parts - in fact the bonding is still required if all the
items are Class 2.

--
Andy

On Sat, 17 Jul 2004 11:03:26 +0100, "Andy Wade"
strung together this:

[Lurch]
Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince
people that it's correct than it would've taken me to do it the
common method in the first place.

Although I agree with the general drift of that (don't adopt unusual circuit
arrangements in domestic installations) I don't agree that it applies here.

Cross-connection between the CPCs of different circuits can be expected to
occur in some situations - e.g. between 'upstairs' and 'downstairs' lighting
circuits where they meet at one or more 2-gang 2-way switches (one switch on
each circuit) for hall and landing. Another case where cross-connection is
actually _required_ by the regs is in a bathroom (within the zones) where
you have some combination of shower, fused conn. unit on ring (for heater or
towel rail etc.), and luminaire and/or shaver outlet. Here the CPCs of the
relevant circuits must be cross connected by supplementary bonding. Since
the 2001 edition of BS 7671 came into force this bonding is required whether
or not the equipment connected to the said circuits has any
exposed-conductive-parts - in fact the bonding is still required if all the
items are Class 2.

That's exactly what I mean, it would have taken 2 minutes to complete
the job in the conventional method.
A day and a half after the OP everyone's still trying to convince each
other why the uncommon method is accepetable.
I wasn't disagreeing with you, but you've proved my point, ta.
--

SJW
A.C.S. Ltd

Lurch wrote in message . ..
On 16 Jul 2004 12:21:16 GMT, (Andrew
Gabriel) strung together this:

In article ,
(Mike Hall) writes:
"Andy Wade" wrote in message ...

Yes, provided that the circuits in question originate from the same consumer
unit or dis-board, and that the CPC for the ring remains in the form of a
ring.

Andy, but therin lies the crux of my question! - If I've joined all 3
cpc's, (2 halves of the ring and the lighting circuit) then the cpc
for the ring is now not a simple ring in itself.

I think that's fine. I can't quite remember exactly what the regs say,
but there are cases of ring circuits where the CPC clearly isn't a
ring, such as when it's provided by conduit or the outer of mineral
insulated cable. I think the important point is the CPC impedance at
any point must be no worse than if it was a ring, or you are going to
have to do calculations to ensure you are still withing allowable
earth fault loop impedance for whatever your protective devices are.
No amount of extra connections between CPC's can make it worse, actually
quite the opposite.

Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince people
that it's correct than it would've taken me to do it the common method
in the first place.


I agree.

Also linking them probably increases the chance of confusing whoever
next works on the installation - at least if they are doing it as DIY.
Presumably a professional would take the time to figure out what was
going on, not just make assumptions.

Depending on how obvious the layout is I can see some poor DIYer in a
few years adding a spur socket that uses the ring live and lighting
neutral.

Actually I am not keen on the whole idea of bringing two separate
circuits into one box - this means two circuits need to be isolated
before working in the box and what are the chances of every future
DIY-novice understanding this! (Yes I know it happens in ever hall
light switch...)

In article ,
Matt Beard wrote:
Actually I am not keen on the whole idea of bringing two separate
circuits into one box - this means two circuits need to be isolated
before working in the box and what are the chances of every future
DIY-novice understanding this! (Yes I know it happens in ever hall
light switch...)

Rule 1 is to test *anything* before working on it. What seems logical to
you, circuit wise, will not be the same to others.

--
*If God dropped acid, would he see people?

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

Matt Beard wrote:

Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince people
that it's correct than it would've taken me to do it the common method
in the first place.


I agree.

Also linking them probably increases the chance of confusing whoever
next works on the installation - at least if they are doing it as DIY.
Presumably a professional would take the time to figure out what was
going on, not just make assumptions.

Quite the opposite I would have thought. A 'professional' simply
doesn't have the time to waste figuring it out, if he's making his
living time is, very literally, money. A D-I-Y'er on the other hand
may well set about working out how something is wired almost for the
sake of the intellectual exercise.

--
Chris Green

Thinking a little further through this I think I might be agreeing
with Andy Wade as cross connects of CPC's in a domestic situation are
fairly common as he describes.
What I was intending to do was use a steel adaptable box for the task
in my original post. Obviously this would need earthing, and if I just
used one of the CPC's to earth the box, then at some point in the
future someone could disconnect the lighting circuit, (for example),
at the CU and hence leave the steel adaptable box unearthed. - Any
more thoughts on THIS situation anyone ?

In article ,
Mike Hall wrote:
What I was intending to do was use a steel adaptable box for the task
in my original post. Obviously this would need earthing, and if I just
used one of the CPC's to earth the box, then at some point in the
future someone could disconnect the lighting circuit, (for example),
at the CU and hence leave the steel adaptable box unearthed. - Any
more thoughts on THIS situation anyone ?

Use a choccy block for the earths and run a tail out to the box.

--
*Don't worry; it only seems kinky the first time.*

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

wrote in message ...
Matt Beard wrote:

Although, I personally would seperate them as I have had occasions
where I have done something that is within the regs but extremely
uncommon and then spent more time and effort trying to convince people
that it's correct than it would've taken me to do it the common method
in the first place.


I agree.

Also linking them probably increases the chance of confusing whoever
next works on the installation - at least if they are doing it as DIY.
Presumably a professional would take the time to figure out what was
going on, not just make assumptions.

Quite the opposite I would have thought. A 'professional' simply
doesn't have the time to waste figuring it out, if he's making his
living time is, very literally, money. A D-I-Y'er on the other hand
may well set about working out how something is wired almost for the
sake of the intellectual exercise.

Some DIYers sure - but there are loads out there with "a little
knowledge" and we all know what that makes...

"Dave Plowman (News)" wrote in message ...
In article ,
Matt Beard wrote:
Actually I am not keen on the whole idea of bringing two separate
circuits into one box - this means two circuits need to be isolated
before working in the box and what are the chances of every future
DIY-novice understanding this! (Yes I know it happens in ever hall
light switch...)

Rule 1 is to test *anything* before working on it. What seems logical to
you, circuit wise, will not be the same to others.

Sure, but do you think there may be anyone out there that ignores this
rule? Just because you disapprove of their sloppyness doesn't mean
you should disregard their safety!

In article ,
Matt Beard wrote:
Sure, but do you think there may be anyone out there that ignores this
rule? Just because you disapprove of their sloppyness doesn't mean
you should disregard their safety!

Having an odd junction box - like an adaptable box - would ring my alarm
bells anyway. As would seeing different sizes of cable.

--
*I don't know what your problem is, but I'll bet it's hard to pronounce

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