Greetings all - returning to uk.d-i-y after a couple of years absence
(mostly due to work. grrr.) Glad to see many familiar contributors
still around.

Current project - kitchen extension and complete refit. Have a builder
doing this (I'd love to do it but just no time) & electrician to do the
electrics/certification (construction being done under Building Notice
application, so no chance of any Pee avoidance. I'd want a regs
compliant installation in any event).

One part of the work is to run SWA down the garden (about 15m) and
connect up the shed. Shed has small garage CU in it, with 30mA RCD, 6A
lighting ciruit MCB and 20A socket circuit MCB. 5 double sockets on the
latter and about 8 metres of 2.5mm^2 t&e in total.

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

Does anyone have chapter & verse on such an arrangement?

Of course I could quickly adapt it to a ring, or even slot an adaptable
box or similar so that the 2 x radials go into that, and single t&e to
the shed CU, making it a single radial. But if I don't need to, I
really would rather not do. A single ring would normally be on 32A MCB,
of course, but is there anything fundamentally incorrect about putting
the circuit on a 20A MCB? (the cable would if anything be over-
protected in this arrangement, surely).

Also, I have an externally mounted socket, RCD protected. I'd rather
not have to run two separate circuits to the kitchen (one RCD'd, the
other not - for the fridge, etc), arguing that the external protected
socket makes the use of internal sockets for external portable equipment
very UNlikely. Are there other regs that come into play here?

On a final, OT, note - anyone working in The City know of any useful
bookshops or other retailers where I might be able to get my hands on a
16th edition OSG? Decent bookshops in The City seem to be a bit of a
rarity these days if my wanderings are anything to go by.

TIA

--
Richard Sampson

"RichardS" OREPLY wrote
in message ...

Greetings all - returning to uk.d-i-y after a couple of years absence
(mostly due to work. grrr.) Glad to see many familiar contributors
still around.

Current project - kitchen extension and complete refit. Have a builder
doing this (I'd love to do it but just no time) & electrician to do the
electrics/certification (construction being done under Building Notice
application, so no chance of any Pee avoidance. I'd want a regs
compliant installation in any event).

One part of the work is to run SWA down the garden (about 15m) and
connect up the shed. Shed has small garage CU in it, with 30mA RCD, 6A
lighting ciruit MCB and 20A socket circuit MCB. 5 double sockets on the
latter and about 8 metres of 2.5mm^2 t&e in total.

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

Ask him how it would be different to running 20 cm of cable to a junction
box and splitting it into two?

On 2007-10-07 19:50:35 +0100, RichardS
OREPLY said:


Greetings all - returning to uk.d-i-y after a couple of years absence
(mostly due to work. grrr.) Glad to see many familiar contributors
still around.

Hello Richard, welcome back.




Current project - kitchen extension and complete refit. Have a builder
doing this (I'd love to do it but just no time) & electrician to do the
electrics/certification (construction being done under Building Notice
application, so no chance of any Pee avoidance. I'd want a regs
compliant installation in any event).

One part of the work is to run SWA down the garden (about 15m) and
connect up the shed. Shed has small garage CU in it, with 30mA RCD, 6A
lighting ciruit MCB and 20A socket circuit MCB. 5 double sockets on the
latter and about 8 metres of 2.5mm^2 t&e in total.

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

Does anyone have chapter & verse on such an arrangement?

There's a commentary here on cable sizes and protection MCB ratings

http://www.tlc-direct.co.uk/Book/6.3.3.htm





Of course I could quickly adapt it to a ring, or even slot an adaptable
box or similar so that the 2 x radials go into that, and single t&e to
the shed CU, making it a single radial. But if I don't need to, I
really would rather not do. A single ring would normally be on 32A MCB,
of course, but is there anything fundamentally incorrect about putting
the circuit on a 20A MCB? (the cable would if anything be over-
protected in this arrangement, surely).

Also, I have an externally mounted socket, RCD protected. I'd rather
not have to run two separate circuits to the kitchen (one RCD'd, the
other not - for the fridge, etc), arguing that the external protected
socket makes the use of internal sockets for external portable equipment
very UNlikely. Are there other regs that come into play here?

On a final, OT, note - anyone working in The City know of any useful
bookshops or other retailers where I might be able to get my hands on a
16th edition OSG? Decent bookshops in The City seem to be a bit of a
rarity these days if my wanderings are anything to go by.

Foyles would probably have it, otherwise go to any bookstore and ask
them to order it in.

In article , am says...
On 2007-10-07 19:50:35 +0100, RichardS
OREPLY said:

snip

Hello Richard, welcome back.

:-) thankyou!

snip

One part of the work is to run SWA down the garden (about 15m) and
connect up the shed. Shed has small garage CU in it, with 30mA RCD, 6A
lighting ciruit MCB and 20A socket circuit MCB. 5 double sockets on the
latter and about 8 metres of 2.5mm^2 t&e in total.

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

Does anyone have chapter & verse on such an arrangement?

There's a commentary here on cable sizes and protection MCB ratings

http://www.tlc-direct.co.uk/Book/6.3.3.htm


thanks Andy, I'd satisfied myself that 2.5mm^2 radials on a 20A MCB was
fine for this (I haven't made a howler here, have I??)

It's more the point about that 2 radials terminating into the same 20A
MCB that is the question - electician was exceptionally uneasy about
this & until I get my mits on that OSG I couldn't ascertain whether it
was within the letter of the regs other than a vague recollection of a
post by a trusted regular that it was OK.

(Foyles is a little out of my lunchtime range unfortunately, even with
the Brompton. Just wondered whether anyone knew of a square mile place,
but I'll probably ring & order a copy from my home-local bookshop for
collection on Saturday otherwise).

--
Richard Sampson

"RichardS" OREPLY
wrote in message ...

snip

On a final, OT, note - anyone working in The City know of any useful
bookshops or other retailers where I might be able to get my hands on
a
16th edition OSG?

If you mean to buy your own copy, as against memorising odd pages that
you browse, www.bookkoob.co.uk shows several places selling it for
around 16 quid with free delivery, though heaven knows when, with our
present postal anarchy.


--
Kevin Poole
**Use current month and year to reply (e.g. )***

RichardS wrote:

Greetings all - returning to uk.d-i-y after a couple of years absence
(mostly due to work. grrr.) Glad to see many familiar contributors
still around.

Long time no hear, welcome back!

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Not even that unusual really. I think people get confused with radials
thinking they need to be a linear chain of sockets connected from one to
the next. The reality is with a radial any topology is acceptable. You
can branch anywhere you like. So two legs connected to the CU is fine,
as would be the second leg connected to the first socket. The design is
such that the cable can take the maximum circuit design load, and the
fault protection at the head end will protect the cable in any location.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

It is compliant. You could even have a ring with a spur originating at
the CU if you wanted. (this is explicitly mentioned in the OSG)

Does anyone have chapter & verse on such an arrangement?

Ask your sparks to show where it is forbidden ;-)

Of course I could quickly adapt it to a ring, or even slot an adaptable
box or similar so that the 2 x radials go into that, and single t&e to
the shed CU, making it a single radial. But if I don't need to, I
really would rather not do. A single ring would normally be on 32A MCB,
of course, but is there anything fundamentally incorrect about putting
the circuit on a 20A MCB? (the cable would if anything be over-
protected in this arrangement, surely).

No, that would also be fine...

There is even an obscure case where you could have two 2.5mm^2 radials
each feeding a FCU or a socket outlet, and legitimately connect them
both to a single 32A MCB, even though its trip current exceeds the
rating of the cable. This would rely on splitting the responsibility for
fault current protection and overcurrent protection. The MCB would
provide adequate fault current protection for the single 2.5mm^2 cable
(in much the same was as it protects a spur from a ring), while the
local fusing in the FCU or plug is responsible from preventing overload
of the single cable.

Also, I have an externally mounted socket, RCD protected. I'd rather
not have to run two separate circuits to the kitchen (one RCD'd, the
other not - for the fridge, etc), arguing that the external protected
socket makes the use of internal sockets for external portable equipment
very UNlikely. Are there other regs that come into play here?

Not really (yet - 17th edition will change this).


--
Cheers,

John.

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

On a final, OT, note - anyone working in The City know of any useful
bookshops or other retailers where I might be able to get my hands on a
16th edition OSG? Decent bookshops in The City seem to be a bit of a
rarity these days if my wanderings are anything to go by.

TIA

--
Richard Sampson

IET bookshop, though not quite the City:

http://www.theiet.org/about/libarc/v...isit/index.cfm

On Sun, 7 Oct 2007 19:50:35 +0100 someone who may be RichardS
OREPLY wrote
this:-

Now, I'm pretty sure that I have read here before from the 'lectrical
cognoscenti that 2 radials into one MCB was unusual, but permissable.
Of course I can't find the post now... Due to the layout of the shed
workspaces & with thoughts of economy of installation, I'd prefer to
install 2 radial circuits rather than one ring, so this is how I wired
it.

Quick discussion with electrician today revealed he had a different take
on it, and that he didn't think that such an arrangement could be
compliant.

To add to what the others have said, it would be good practice for
this radial circuit should be labelled as a radial to avoid any
future confusion.



--
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 ,
MOVETHISTOREPLY says...


Just want to say thanks folks.

I think that Owain and John you put your finger on it in that even
though it "looks" like two radials it is in fact one - I suspect the
single daisy-chained idealised example of the radial is the one that
sticks in peoples minds whereas it can be much more tree-like.

I did find the example of the spur off a ring connected directly to the
circuit origin within the OSG - it's odd that the OSG doesn't also
include definitions or examples for radial circuits. Perhaps it does
and I just haven't found it yet.

I've also come to a decision on the kitchen circuits - am going to
protect the general socket circuits with an RCD/RCBO and have a
completely separate circuit for fixed appliances, including the
fridge/freezer. The outside sockets will be protected by their own
RCD/RCBO.

Incidentally - do external luminaires require RCD protection? Or can
they be run directly off the lighting circuit? (they'll be low energy
units so a small current draw)

thanks again

--
Richard Sampson

RichardS wrote:

Incidentally - do external luminaires require RCD protection? Or can
they be run directly off the lighting circuit? (they'll be low energy
units so a small current draw)

They don't require RCD protection (unless on a TT install). If they have
it, then it ought to be a different RCD from that protecting the
internal circuits.

--
Cheers,

John.

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

On Thu, 11 Oct 2007 00:59:50 +0100 someone who may be RichardS
OREPLY wrote
this:-

Incidentally - do external luminaires require RCD protection? Or can
they be run directly off the lighting circuit? (they'll be low energy
units so a small current draw)

In addition to what John has said there are two situations to
consider. One is lights on the outside of a house and one is lights
in the garden/path/drive. The former can be fed from the "inside"
circuit but it is better for the latter to be on their own circuits
if only to avoid a fault on them preventing inside lights from being
used.



--
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

David Hansen wrote:
On Thu, 11 Oct 2007 00:59:50 +0100 someone who may be RichardS
OREPLY wrote
this:-

Incidentally - do external luminaires require RCD protection? Or can
they be run directly off the lighting circuit? (they'll be low energy
units so a small current draw)

In addition to what John has said there are two situations to
consider. One is lights on the outside of a house and one is lights
in the garden/path/drive. The former can be fed from the "inside"
circuit but it is better for the latter to be on their own circuits
if only to avoid a fault on them preventing inside lights from being
used.

Outdoor electrics is generally of much lower reliability than indoor,
so its not generally a great idea to put any outdoor stuff on indoor
circuits.


NT

On Thu, 11 Oct 2007 05:24:38 -0700 someone who may be
wrote this:-

Outdoor electrics is generally of much lower reliability than indoor,
so its not generally a great idea to put any outdoor stuff on indoor
circuits.

Whether outdoor electrics is more reliable depends on how well it is
done and how much weather it is exposed to. That is why I suggested
a division between lights mounted on an outside wall of the house
and ones further away. Millions of houses have the former on
"indoor" circuits without great tales of woe. Indeed such lamps may
experience less damp than lamps in a room containing a shower.



--
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