Hi,

Can anyone give me a clue ?

I am trying to work out how to specify the re-wiring of the kitchen
( 2 ring main circuits)
assuming consumer unit with 32A MCB can the total cabling length (out
from consumer unit, once around the kitchen and back to the consumer
unit) be 60metres?

I am told that the maximum cable length for a ring main with MCB as
protection is 50metre??

Cheers

G

On 2 Mar 2007 10:03:04 -0800, "blue"
mused:

Hi,

Can anyone give me a clue ?

I am trying to work out how to specify the re-wiring of the kitchen
( 2 ring main circuits)
assuming consumer unit with 32A MCB can the total cabling length (out
from consumer unit, once around the kitchen and back to the consumer
unit) be 60metres?

I am told that the maximum cable length for a ring main with MCB as
protection is 50metre??

The maximum area a 32A ring main wired in 2.5mm cable is 100m2, how
you'd do that with 50m I don't know.

As long as your kitchen isn't huuuuge, or your run from the CU to the
kitchen anythig ridiculous like 250m then you'll be fine.
--
Regards,
Stuart.

On Fri, 02 Mar 2007 10:03:04 -0800, blue wrote:

Hi,

Can anyone give me a clue ?

I am trying to work out how to specify the re-wiring of the kitchen
( 2 ring main circuits)
assuming consumer unit with 32A MCB can the total cabling length (out
from consumer unit, once around the kitchen and back to the consumer
unit) be 60metres?

I am told that the maximum cable length for a ring main with MCB as
protection is 50metre??

Cheers

G

No it's 84m. On both PME and TT-S systems.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On 2 Mar, 19:31, Ed Sirett wrote:
On Fri, 02 Mar 2007 10:03:04 -0800, blue wrote:
Hi,

Can anyone give me a clue ?

assuming consumer unit with 32A MCB can the total cabling length (out
from consumer unit, once around the kitchen and back to the consumer
unit) be 60metres?

I am told that the maximum cable length for a ring main with MCB as
protection is 50metre??

Cheers

G

No it's 84m. On both PME and TT-S systems.

--
Ed Sirett - Property maintainer and registered gas fitter.

Thanks, I could find lots of references to 100m2 (which would imply a
theoretical room 100m x 1 m = run of 202 metres) but nothing I could
understand about total run lengths.

In article . com,
"blue" writes:
Thanks, I could find lots of references to 100m2 (which would imply a
theoretical room 100m x 1 m = run of 202 metres) but nothing I could
understand about total run lengths.

The 100m2 is the floor area the ring serves, not the area enclosed
by the cable loop.

It is a recommendation only, and applies only where there is no
specific data about the power requirements in the area. If you
know what the power requirements in the area are going to be,
then use that to work out the maximum area a ring circuit can
cover.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Ed Sirett wrote:

No it's 84m.

Agreed, assuming a 32 A Type B MCB. For other situations Table 7.1 in
the On-Site Guide is your friend.

On both PME and TT-S systems.

TT-S? ITYM "TN-S" - only a typo I'm sure.

--
Andy

On 3 Mar, 09:58, Andy Wade wrote:
Ed Sirett wrote:
No it's 84m.

Agreed, assuming a 32 A Type B MCB. For other situations Table 7.1 in
the On-Site Guide is your friend.

On both PME and TT-S systems.

TT-S? ITYM "TN-S" - only a typo I'm sure.

--
Andy

Thanks Chaps,
briefly - house has solid ground floor, so means running all services
in either under the 1st floor floorboards OR taking everything up into
the loft space, along the loft & back down again. So chanelled into
walls. Since all the plaster is shot & has to be replaced, whilst the
floorboards are fine seems logical to spare the floorboards. But hence
my question about the maximum run, which would be (approx) 3m up the
wall to to the loft, 13m along the loft, 5.5m back down to the kitchen
= 43m then once around the kitchen 14m = 57m.

May I impose on your kindness with supplemental questions, please? :
I am assuming that I can specify standard twin-and-earth 2.5mm for
ringmain, 4mm for cooker and 1.5mm for lighting ?
Channeling into wall : enclosed in plastic conduit, covered by earthed
metal cap ?

the complicated run is up from consumer unit into loft, where a whole
bunch of cables will be close together. I have found some metal
conduit internal 225x22.5mm which would do to take the general
household circuits (4 x rings & 3 x lighting) but I am thinking to
specify the 'kitchen' circuits to be run in individual conduits (1 x
4mm and 2 x 2.5mm).

Is there anything there that rings alarm bells?

Finally, do you think I am allowing enough circuits?
3 lighting : 1 upstairs, 1 downstairs, 1 for hallways & stairs.
4 'general' rings : 2 for upstairs (3 bedrooms) and 2 for downstairs
('parlour' and sitting room)
2 'kitchen' rings' = 1 for heavy appliances (dishwasher, washing
machine, dryer) and 1 for 'above the worktop' appliances
1 cooker

comment gratefully received

Che

On 4 Mar, 08:26, "blue" wrote:
On 3 Mar, 09:58, Andy Wade wrote:

Ed Sirett wrote:
No it's 84m.

Agreed, assuming a 32 A Type B MCB. For other situations Table 7.1 in
the On-Site Guide is your friend.

On both PME and TT-S systems.

TT-S? ITYM "TN-S" - only a typo I'm sure.

--
Andy

Thanks Chaps,
briefly - house has solid ground floor, so means running all services
in either under the 1st floor floorboards OR taking everything up into
the loft space, along the loft & back down again. So chanelled into
walls. Since all the plaster is shot & has to be replaced, whilst the
floorboards are fine seems logical to spare the floorboards. But hence
my question about the maximum run, which would be (approx) 3m up the
wall to to the loft, 13m along the loft, 5.5m back down to the kitchen
= 43m then once around the kitchen 14m = 57m.

May I impose on your kindness with supplemental questions, please? :
I am assuming that I can specify standard twin-and-earth 2.5mm for
ringmain, 4mm for cooker and 1.5mm for lighting ?
Channeling into wall : enclosed in plastic conduit, covered by earthed
metal cap ?

the complicated run is up from consumer unit into loft, where a whole
bunch of cables will be close together. I have found some metal
conduit internal 225x22.5mm which would do to take the general
household circuits (4 x rings & 3 x lighting) but I am thinking to
specify the 'kitchen' circuits to be run in individual conduits (1 x
4mm and 2 x 2.5mm).

Is there anything there that rings alarm bells?

Finally, do you think I am allowing enough circuits?
3 lighting : 1 upstairs, 1 downstairs, 1 for hallways & stairs.
4 'general' rings : 2 for upstairs (3 bedrooms) and 2 for downstairs
('parlour' and sitting room)
2 'kitchen' rings' = 1 for heavy appliances (dishwasher, washing
machine, dryer) and 1 for 'above the worktop' appliances
1 cooker

comment gratefully received

Che

The lighting sounds fine. Watch conductor size for volt drop if the
route is tortuitous and long
I doubt the need for two rings for bedrooms. The loading from 3
bedrooms is unlikely to merit this.
Its also unlikely you need two rings for parlour and sitting room.
The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each. Again watch volt drop over the length. It
might be neccessary to use 6mm at least for the run from CSU to
kiltchen.
Also allow for volt drop on the cooker circuit and a if you use a
control with a socket it must meet 0.4 second disconnection times with
Earth Loop Impedance (5 seconds if no socket).

Don't forget to run in any supplementary bonding for the bath/ shower
rooms while routes are accessible. 4mm minimum or 2.5mm if protected
along entire runs.
Watch grouping factor where applicable and insulation where
applicable. Have you got the Regs and On Site Guide. Also worth look
at the "Green Book" An Electricians Guide to the Building Regulations
which is helpful in avoiding problems with holes or notches in joists
etc, penetration of walls, chase depths and so on.

HTH

Hi Cynic,
(I like your handle)

Thanks very much. Really helpful. Just to impose some more....I've
added some bits below

The lighting sounds fine. Watch conductor size for volt drop if the
route is tortuitous and long

-- I think the lighting circuits are ok as these will virtually follow
the same pathway as the old wiring (which seems to be a single circuit
for the whole house)

I doubt the need for two rings for bedrooms. The loading from 3
bedrooms is unlikely to merit this.
Its also unlikely you need two rings for parlour and sitting room.

-- I know, it does sound overkill doesn't it? but the layout of
stairs, bathroom, and the solid ground floor means that effectively
the house is in two parts 'front' and 'back' (with the kitchen as a
separate issue owing to likely loads)

The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each. Again watch volt drop over the length. It
might be neccessary to use 6mm at least for the run from CSU to
kiltchen.

-- 4 or 6mm from csu to kitchen junction box and then drop to 2.5mm
for the 'local' part of the circuit ?

Also allow for volt drop on the cooker circuit and a if you use a
control with a socket it must meet 0.4 second disconnection times with
Earth Loop Impedance (5 seconds if no socket).

-- actually being put in place 'against future requirement'

Don't forget to run in any supplementary bonding for the bath/ shower
rooms while routes are accessible. 4mm minimum or 2.5mm if protected
along entire runs.

-- I'm glad you mentioned that. Is it better to use plastic type pipes
for water? Was mentioned to me that was much safer than copper piping
with earthing?

Watch grouping factor where applicable and insulation where
applicable.

-- This is something I didn't understand I read up some bits but I'm
non-technical so, whoosh! straight over the head.
was an issue that was worrying me a bit, as maybe I would try to
specify something that isn;t possible to do.

Have you got the Regs and On Site Guide.

-- sadly not!

Also worth look
at the "Green Book" An Electricians Guide to the Building Regulations
which is helpful in avoiding problems with holes or notches in joists
etc, penetration of walls, chase depths and so on.

-- I found most of this in the bldg regs (after a lot of reading &
cross-referencing) but I am praying that I can avoid any tearing up
of (any more) floorboards & (any more) holes in joists!

Cheers

Che

On 4 Mar, 10:55, "blue" wrote:
Hi Cynic,
(I like your handle)

Thanks very much. Really helpful. Just to impose some more....I've
added some bits below



The lighting sounds fine. Watch conductor size for volt drop if the
route is tortuitous and long

-- I think the lighting circuits are ok as these will virtually follow
the same pathway as the old wiring (which seems to be a single circuit
for the whole house)

I doubt the need for two rings for bedrooms. The loading from 3
bedrooms is unlikely to merit this.
Its also unlikely you need two rings for parlour and sitting room.

-- I know, it does sound overkill doesn't it? but the layout of
stairs, bathroom, and the solid ground floor means that effectively
the house is in two parts 'front' and 'back' (with the kitchen as a
separate issue owing to likely loads)

You may care to think about radial circuits then. A domestic multi
outlet 2.5mm radial with 20A breaker can serve 50 square metres of
floor area. The loading is not normally a problem for bedrooms or
living areas

The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each. Again watch volt drop over the length. It
might be neccessary to use 6mm at least for the run from CSU to
kiltchen.

-- 4 or 6mm from csu to kitchen junction box and then drop to 2.5mm
for the 'local' part of the circuit ?

Also allow for volt drop on the cooker circuit and a if you use a
control with a socket it must meet 0.4 second disconnection times with
Earth Loop Impedance (5 seconds if no socket).

-- actually being put in place 'against future requirement'

Right


Don't forget to run in any supplementary bonding for the bath/ shower
rooms while routes are accessible. 4mm minimum or 2.5mm if protected
along entire runs.

-- I'm glad you mentioned that. Is it better to use plastic type pipes
for water? Was mentioned to me that was much safer than copper piping
with earthing?

Hepworth say so g As long as any bonding is in place and connected
it should be safe either way


Watch grouping factor where applicable and insulation where
applicable.

-- This is something I didn't understand I read up some bits but I'm
non-technical so, whoosh! straight over the head.
was an issue that was worrying me a bit, as maybe I would try to
specify something that isn;t possible to do.

Have you got the Regs and On Site Guide.

-- sadly not!

See what ebay have to offer


Also worth look

at the "Green Book" An Electricians Guide to the Building Regulations
which is helpful in avoiding problems with holes or notches in joists
etc, penetration of walls, chase depths and so on.

-- I found most of this in the bldg regs (after a lot of reading &
cross-referencing) but I am praying that I can avoid any tearing up
of (any more) floorboards & (any more) holes in joists!

The green book is a condensed version of the bits you need. Your local
library might be a good place to spend an afternoon.


Cheers

Che

Library it is then !

Very very many thanks for your help

Vheers

G

On 4 Mar 2007 00:26:00 -0800, "blue"
mused:

May I impose on your kindness with supplemental questions, please? :
I am assuming that I can specify standard twin-and-earth 2.5mm for
ringmain, 4mm for cooker and 1.5mm for lighting ?

Standard where? Standard, as in common in the UK, would be 2.5mm for
32A ring main, 6mm for 32A cooker circuit and 1.0mm for lighting.

Channeling into wall : enclosed in plastic conduit, covered by earthed
metal cap ?

Whatever you want, assuming it is run in the prescribed zones.

the complicated run is up from consumer unit into loft, where a whole
bunch of cables will be close together. I have found some metal
conduit internal 225x22.5mm which would do to take the general
household circuits (4 x rings & 3 x lighting) but I am thinking to
specify the 'kitchen' circuits to be run in individual conduits (1 x
4mm and 2 x 2.5mm).

Why all the conduits?

Is there anything there that rings alarm bells?

Yes, but you'd probably get shirty if I said that I thought it was
your competence so I won't say anything.

Finally, do you think I am allowing enough circuits?
3 lighting : 1 upstairs, 1 downstairs, 1 for hallways & stairs.
4 'general' rings : 2 for upstairs (3 bedrooms) and 2 for downstairs
('parlour' and sitting room)
2 'kitchen' rings' = 1 for heavy appliances (dishwasher, washing
machine, dryer) and 1 for 'above the worktop' appliances
1 cooker

I'd say that sounds reasonable for a 5 bedroom detached haouse of
reasonable size.

comment gratefully received

I can't imagine that.
--
Regards,
Stuart.

On 4 Mar 2007 02:03:37 -0800, "cynic" mused:

The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each.

Check the tables in the regs. You could probably get away with 32A
radial circuits run in 4mm if they are about 3m long.
--
Regards,
Stuart.

On 5 Mar, 02:06, Lurch wrote:
On 4 Mar 2007 02:03:37 -0800, "cynic" mused:

The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each.

Check the tables in the regs. You could probably get away with 32A
radial circuits run in 4mm if they are about 3m long.

4mm twin and cpc volt drop tabulated is 11mV per Ampere per metre run.
At 32A load and 4% of 230 volts( = 9.2 volts) permitted volt drop that
works out to approximately 26 metres. Where did your 3metres come from
Stuart? (Maybe you missed a zero off your post?)

--
Regards,
Stuart.

On Sat, 03 Mar 2007 09:58:23 +0000, Andy Wade wrote:

Ed Sirett wrote:

No it's 84m.

Agreed, assuming a 32 A Type B MCB. For other situations Table 7.1 in
the On-Site Guide is your friend.

On both PME and TT-S systems.

TT-S? ITYM "TN-S" - only a typo I'm sure.

Sorry, yes TN-S or TN-C-S (PME).

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On 4 Mar, 08:26, "blue" wrote:
//snip//
but I am thinking to
specify the 'kitchen' circuits to be run in individual conduits (1 x
4mm and 2 x 2.5mm).

Is there anything there that rings alarm bells?

err, yes if not the alarm bell, then a definite warning whistle

1. Avoid 4mm FTE cable the CPC (the 'earth' conductor) is too small
in cross-section area for most purposes. Effect is to severely
curtail the length of a 4mm^2 circuit. If you want to use it you need
to DIY the sums for circuit length as there is only limited
information for radial circuits in the On-Site Guide (table 7.1.1) and
none at all for ring circuits. You'd do better to use 6mm^2 for
cooker circuits, though technically you should check the cooker rating
first. [ie cabling should be specified to meet the load required by
installed equipment; not t'other way round]

2. Inserting cable in conduit generally reduces the maximum rated
current - see on-site guide table 6D1 - compare ratings for ref method
1 with ref method 3 for instance - reduction is around 20%
More normal is to clip cable directly to a wall and bury under
plaster. You can channel out blockwork or brick a little if plaster
depth is inadequate. Some think it good practice to cover the cable
with metal capping to protect against minor damage such as drawing
pins being stuck in the plaster.

You also do better to run cable horizontally or vertically from
fitting to fitting - see OSG for permitted routes. That keeps cable
runs shorter, and incidentally reduces volts drop in the circuit which
reduces the amount of elec energy - paid_for_by_you - wasted in the
cable.

3. beware of cable bunching which also may reduce cable rating. Again
see OSG

HTH

On 5 Mar 2007 11:11:10 -0800, "cynic" mused:

On 5 Mar, 02:06, Lurch wrote:
On 4 Mar 2007 02:03:37 -0800, "cynic" mused:

The kitchen is the likely place for heavy loading - washing machine,
dishwasher, dryer etc. A dedicated ring for these is likely going to
be fairly well loaded. You might be better running two 4mm radials
with 32A protection each.

Check the tables in the regs. You could probably get away with 32A
radial circuits run in 4mm if they are about 3m long.

4mm twin and cpc volt drop tabulated is 11mV per Ampere per metre run.
At 32A load and 4% of 230 volts( = 9.2 volts) permitted volt drop that
works out to approximately 26 metres. Where did your 3metres come from
Stuart? (Maybe you missed a zero off your post?)

Maybe I should read the tables in the regs then?
--
Regards,
Stuart.

On 5 Mar, 22:33, "jim" wrote:
On 4 Mar, 08:26, "blue" wrote:
//snip//
but I am thinking to

specify the 'kitchen' circuits to be run in individual conduits (1 x
4mm and 2 x 2.5mm).

Is there anything there that rings alarm bells?

err, yes if not the alarm bell, then a definite warning whistle

1. Avoid 4mm FTE cable the CPC (the 'earth' conductor) is too small
in cross-section area for most purposes. Effect is to severely
curtail the length of a 4mm^2 circuit. If you want to use it you need
to DIY the sums for circuit length as there is only limited
information for radial circuits in the On-Site Guide (table 7.1.1) and
none at all for ring circuits. You'd do better to use 6mm^2 for
cooker circuits, though technically you should check the cooker rating
first. [ie cabling should be specified to meet the load required by
installed equipment; not t'other way round]

2. Inserting cable in conduit generally reduces the maximum rated
current - see on-site guide table 6D1 - compare ratings for ref method
1 with ref method 3 for instance - reduction is around 20%
More normal is to clip cable directly to a wall and bury under
plaster. You can channel out blockwork or brick a little if plaster
depth is inadequate. Some think it good practice to cover the cable
with metal capping to protect against minor damage such as drawing
pins being stuck in the plaster.

You also do better to run cable horizontally or vertically from
fitting to fitting - see OSG for permitted routes. That keeps cable
runs shorter, and incidentally reduces volts drop in the circuit which
reduces the amount of elec energy - paid_for_by_you - wasted in the
cable.

3. beware of cable bunching which also may reduce cable rating. Again
see OSG

HTH

Thanks, It looks like I'm going to spend some time in the library.
I've got a lot to think about

Cheers

Che