Am currently doing a rewire and have a few questions please...

1. (the main question!). I'm proposing the following circuits - does
this plan sound sensible? BTW total floor area is 70m2; CU is a Volex
split-load item: http://tinyurl.com/7fe6m (Screwfix 82204). So:

Non-RCD protected:
a) upstairs lights, 6A MCB, 1.5mm T&E cable
b) downstairs lights, 6A MCB, 1.5mm T&E
c) linked smoke alarms, 6A MCB, 1.5mm T&E
d) downstairs ringmain feeding specifically the oven, fridge-freezer and
gas combi boiler, 32A MCD, 2.5mm T&E cable

RCD protected:
e) upstairs ringmain, 32A MCB, 2.5mm T&E
f) downstairs ringmain - all sockets other than those in circuit (d) 32A
MCB, 2.5mm T&E
g) electric shower, 40A MCB, 10mm T&E

I expect circuit (d) to cause most comment?! I don't see the need for a
dedicated cooker circuit because I'll be fitting a built-in single oven
with 13A plug (plus gas hob), which could be plugged into an ordinary
ringmain. OK?

2. I've got some spare 1.0mm red/black cable which I'd like to use up -
would there be any issue with me mixing-and-matching 1.0mm and 1.5mm
cable within one installation (I don't have enough 1.0mm do do the
whole house)?

3. CU is under the stairs, which means that the route for all cables
will be running under the stairs, in a straight line, at ~45deg, in the
space created behind plasterboard attached to battens on the bottom of
the stairs (clear?!.) Now, if the plasterboard were 'ceiling', that
arrangement would unequivocably be perfectly OK; however if it were
'wall', it would definitely be unacceptable because the cables would be
well within 50mm of the surface. What I'm unclear about is what does a
45-deg-mounted surface count as - ceiling or wall? I think it's
ceiling, but I'd like reassurance that some future inspector isn't going
to throw a wobbler at it! Not sure what to do if it's unacceptable as
it is.

Thanks a lot
David

In article ,
Lobster writes:
Am currently doing a rewire and have a few questions please...

You haven't said what type of earthing your system is.

1. (the main question!). I'm proposing the following circuits - does
this plan sound sensible? BTW total floor area is 70m2; CU is a Volex
split-load item: http://tinyurl.com/7fe6m (Screwfix 82204). So:

Non-RCD protected:
a) upstairs lights, 6A MCB, 1.5mm T&E cable
b) downstairs lights, 6A MCB, 1.5mm T&E
c) linked smoke alarms, 6A MCB, 1.5mm T&E
d) downstairs ringmain feeding specifically the oven, fridge-freezer and
gas combi boiler, 32A MCD, 2.5mm T&E cable

RCD protected:
e) upstairs ringmain, 32A MCB, 2.5mm T&E
f) downstairs ringmain - all sockets other than those in circuit (d) 32A
MCB, 2.5mm T&E
g) electric shower, 40A MCB, 10mm T&E

I expect circuit (d) to cause most comment?! I don't see the need for a
dedicated cooker circuit because I'll be fitting a built-in single oven
with 13A plug (plus gas hob), which could be plugged into an ordinary
ringmain. OK?

It's fine.
Shower probably doesn't need to be RCD protected.
Smoke alarm circuits are often 3A MCBs if they're available for
your CU.

2. I've got some spare 1.0mm red/black cable which I'd like to use up -
would there be any issue with me mixing-and-matching 1.0mm and 1.5mm
cable within one installation (I don't have enough 1.0mm do do the
whole house)?

No problem mixing them providing all your cable is red and black.
(Whilst an installation can be mixed, you can't mix old and new
colours in the same job.)

3. CU is under the stairs, which means that the route for all cables
will be running under the stairs, in a straight line, at ~45deg, in the
space created behind plasterboard attached to battens on the bottom of
the stairs (clear?!.) Now, if the plasterboard were 'ceiling', that
arrangement would unequivocably be perfectly OK; however if it were
'wall', it would definitely be unacceptable because the cables would be
well within 50mm of the surface. What I'm unclear about is what does a
45-deg-mounted surface count as - ceiling or wall? I think it's
ceiling, but I'd like reassurance that some future inspector isn't going
to throw a wobbler at it! Not sure what to do if it's unacceptable as
it is.

I don't have the regs on me to confirm, but I don't think it
makes any difference from the point of view of depth of burying.

--
Andrew Gabriel

Andrew Gabriel wrote:
In article ,
Lobster writes:

Am currently doing a rewire and have a few questions please...

Thanks for the replies.

You haven't said what type of earthing your system is.

At the risk of provoking a
"what-the-hell-are-doing-rewiring-for-if-you-don't-know-this-for-chrissakes-get-a-pro-in"-type
response, what significance does the earthing system have on the circuit
design? In mine, it's provided by the armoured sheath of the main
supply cable; have to say I don't know any more than that. Do I need to
find out?

Thanks
David

In article ,
Lobster writes:
Andrew Gabriel wrote:
You haven't said what type of earthing your system is.

At the risk of provoking a
"what-the-hell-are-doing-rewiring-for-if-you-don't-know-this-for-chrissakes-get-a-pro-in"-type
response, what significance does the earthing system have on the circuit
design? In mine, it's provided by the armoured sheath of the main
supply cable; have to say I don't know any more than that. Do I need to
find out?

If the system was a TT system with your own earth rod, the
use of RCD's would have to be different.

--
Andrew Gabriel

Lobster wrote:
You haven't said what type of earthing your system is.

what significance does the earthing system have on the circuit
design?

Lots.

If you don't understand the difference between TT, TN-C, TN-C-S, etc
then you really should not be doing the job.

In mine, it's provided by the armoured sheath of the main
supply cable; have to say I don't know any more than that. Do I need to
find out?

If you intend to do the re-cabling yourself then your follow-up
certificate which will be required may prove to be very expensive. If
you've hot-wired the earthing within the installation wrong then it will
need to be ripped out and started over. It will be cheaper and easier to
do the wiring correctly the first time.

Andrew

--
Please note that the email address used for posting
usenet messages is configured such that my antispam
filter will automatically update itself so that the
senders email address is flagged as spam. If you do
need to contact me please visit my web site and
submit an enquiry - http://www.kazmax.co.uk

Andrew McKay wrote:
Lobster wrote:

what significance does the earthing system have on the circuit design?

Lots.

If you intend to do the re-cabling yourself then your follow-up
certificate which will be required may prove to be very expensive. If
you've hot-wired the earthing within the installation wrong then it will
need to be ripped out and started over. It will be cheaper and easier to
do the wiring correctly the first time.

OK, I'm listening...

What do you mean, hot-wiring the earthing? Of course I'll be doing it
properly, and getting it certified afterwards, which is why I posted my
circuit design here first for feedback, which I'm pleased to have
received. [It's my third full rewire, and my previous checks by a pro
came up (1) with very small easily remedied errors and (2)100% OK.
Previously I had run my wiring diagram past my pro first, who OK'ed it;
I assume that because my earthing plans were OK there was no need for
him to go into all the ins and outs of different earthing systems?]

Anyway - given the presence of an earthing block next to the CU,
connected to the CU, a clamp on the armoured cable, and (now) the
incoming gas/water pipes, what influence does this have on the wiring of
the ring mains and lighting circuits? They will all be T&E cable, with
CPCs wired in to the CU - how would this be affected by different earth
systems? Under what circumstances would all the wiring need to be
'ripped out and started over'?

Thanks
David

Lobster wrote:
OK, I'm listening...

I regret that I can't give you details - this is a DIY group after all.
I just know from having got my C&G2381 that earthing (and bonding) is a
complex subject. Making assumptions is not a good idea.

Andrew

--
Please note that the email address used for posting
usenet messages is configured such that my antispam
filter will automatically update itself so that the
senders email address is flagged as spam. If you do
need to contact me please visit my web site and
submit an enquiry - http://www.kazmax.co.uk

Lobster wrote:

Anyway - given the presence of an earthing block next to the CU,
connected to the CU, a clamp on the armoured cable, and (now) the
incoming gas/water pipes, what influence does this have on the wiring of
the ring mains and lighting circuits? They will all be T&E cable, with
CPCs wired in to the CU - how would this be affected by different earth

From the point of view of wiring individual "standard" circuits then
there (usually) won't be any difference - the basic construction and
testing will be the same.

Earth loop impedance testing is good practice for any new circuit since
it will establish that you can get the required fault currents to
provide the required disconnection times.

The sizing of equipotential bonding and other earthing conductors can
vary with different earthing schemes. Follow the tables in the On Site
Guide and you should be OK.

(you get most differences with TT systems)

systems? Under what circumstances would all the wiring need to be
'ripped out and started over'?

Slightly alarmist wording IMHO. "When wired by a complete muppet with
all the wrong cable sizes or following improper cable routes" might be
an appropriate answer ;-)

--
Cheers,

John.

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

In article ,
Lobster wrote:
I expect circuit (d) to cause most comment?! I don't see the need for a
dedicated cooker circuit because I'll be fitting a built-in single oven
with 13A plug (plus gas hob), which could be plugged into an ordinary
ringmain. OK?

I'd certainly have a separate ring for the kitchen - and also look
carefully at the load on that before running the oven from that. Because
it's all too easy to exceed the loading. A washing machine can take 13
amps when heating. Also a dishwasher. Drier? A kettle perhaps 10 amps.
Already, you're over the nominal 30 amps. Add in a toaster and say grill -
let alone your oven, and it's easy to see a possible problem.

2. I've got some spare 1.0mm red/black cable which I'd like to use up -
would there be any issue with me mixing-and-matching 1.0mm and 1.5mm
cable within one installation (I don't have enough 1.0mm do do the
whole house)?

None. I'd use 1.5mm for the feeds and the spare 1.0mm for the switch
drops. But for 6 amp circuits, 1.0mm is fine anyway.

--
*And don't start a sentence with a conjunction *

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

Dave Plowman (News) wrote:
In article ,
Lobster wrote:

I expect circuit (d) to cause most comment?! I don't see the need for a
dedicated cooker circuit because I'll be fitting a built-in single oven
with 13A plug (plus gas hob), which could be plugged into an ordinary
ringmain. OK?


I'd certainly have a separate ring for the kitchen - and also look
carefully at the load on that before running the oven from that. Because
it's all too easy to exceed the loading. A washing machine can take 13
amps when heating. Also a dishwasher. Drier? A kettle perhaps 10 amps.
Already, you're over the nominal 30 amps. Add in a toaster and say grill -
let alone your oven, and it's easy to see a possible problem.

Thanks to you (and Christian) for this advice. I take your point, but do
you not think that by pulling the oven out of the downstairs circuit,
I've pretty well done the same thing? I mean, all the high-load items
you describe above will be on the kitchen circuit, just that I'm calling
it a 'downstairs' circuit(!) - in addition to the (dining) kitchen, it
will only cover the living room and hall, and I can't see any high-load
appliances being used there. Just TV/table lights/hifi/vacuum cleaner,
that sort of thing (there will be a gas fire plus gas CH, so really see
no likelihood of any electric heaters.) When I looked at having another
kitchen circuit, it seemed like overkill having 3 downstairs ringmains
for such a small house.

Or maybe I should incorporate the living-room and hall circuits into the
upstairs ringmain, releasing the 'downstairs' ring just for the kitchen.
What do you think?

Thanks
David

Lobster wrote:
Dave Plowman (News) wrote:
I'd certainly have a separate ring for the kitchen - and also look
carefully at the load on that before running the oven from that.
... I mean, all the high-load items
you describe above will be on the kitchen circuit, just that I'm calling
it a 'downstairs' circuit(!) - in addition to the (dining) kitchen, it
will only cover the living room and hall, and I can't see any high-load
appliances being used there. ...
Or maybe I should incorporate the living-room and hall circuits into the
upstairs ringmain, releasing the 'downstairs' ring just for the kitchen.
What do you think?

You could consider splitting the rings front and back rather than
upstairs/downstairs. That way the kitchen shares with the back bedrooms,
the lounge with the front bedrooms. As well as giving you two circuits
on every floor (so you still have power on every floor without having to
run an extension lead up the stairs) it means that the kitchen is shared
with rooms which are probably lightly used during the day.

If people are in the lounge (and you have eg temporary electric heaters
plugged in) they're less likely to be in the bedrooms, but lounge and
kitchen/oven use is likely to coincide.

Owain

(there will be a gas fire plus gas CH, so really see no likelihood of
any electric heaters.)

Sorry to come in so slow on this. I've been away for a week.

One of the main reasons for the area limits on socket circuits is the fact
that they should be designed to provide emergency electric heating
requirements. Fixed electric heating should have its own circuits, whilst
socket circuits should be capable of running enough thermostatically
controlled fan heaters to heat the area, in case the main heating system
fails.

Christian.

a) upstairs lights, 6A MCB, 1.5mm T&E cable

OK (although 1mm would be fine and easier to squeeze cables into the
terminals).

b) downstairs lights, 6A MCB, 1.5mm T&E

OK.

c) linked smoke alarms, 6A MCB, 1.5mm T&E

OK.

d) downstairs ringmain feeding specifically the oven, fridge-freezer and
gas combi boiler, 32A MCD, 2.5mm T&E cable

* See below.

RCD protected:
e) upstairs ringmain, 32A MCB, 2.5mm T&E

OK.

f) downstairs ringmain - all sockets other than those in circuit (d) 32A
MCB, 2.5mm T&E

* See below.

g) electric shower, 40A MCB, 10mm T&E

OK.

The mains issue here is the dispostion and type of the socket circuits.
Firstly, I would ensure that the kitchen has at least one general purpose
socket circuit entirely to itself in addition to any fixed appliance
circuits. Secondly, fixed appliance circuits might be better implemented as
radial circuits, due to the unusual loading patterns.

For example, when designing my own setup, I had:

1. 32A 2.5mm RCBO (RCD protected) socket ring circuit (includes small oven,
but no other fixed appliances)
2. 32A 6.0mm MCB (not RCD protected) radial circuit for washing machine,
tumble dryer and dishwasher.
3. 16A 2.5mm MCB (not RCD protected) radial circuit for fridge/freezer.
4. 16A 2.5mm MCB (not RCD protected) radial circuit for central heating
(including immersion heater).
5. 32A 2.5mm RCBO (RCD protected) socket ring circuit for all non-kitchen
sockets in house (intend to split into 2 when can be bothered). This
preexisting circuit used to cover all sockets (including kitchen) in entire
house.

Christian.

"Christian McArdle" wrote in message
t...
a) upstairs lights, 6A MCB, 1.5mm T&E cable

snip

c) linked smoke alarms, 6A MCB, 1.5mm T&E

OK.


Thought these had to be triple & earth? (though it would be T&E from the CU
to the first one).


snip



--
Richard Sampson

mail me at
richard at olifant d-ot co do-t uk

Thought these had to be triple & earth? (though it would be T&E from the
CU
to the first one).

Correct. The linking cable is usually 3&E, although some systems using T&E
and either a radio link or inject a high frequency comms channel onto the
main mains signal.

Christian.

"Lobster" wrote in message
...
Am currently doing a rewire and have a few questions please...

1. (the main question!). I'm proposing the following circuits - does
this plan sound sensible? BTW total floor area is 70m2; CU is a Volex
split-load item: http://tinyurl.com/7fe6m (Screwfix 82204). So:

Non-RCD protected:
a) upstairs lights, 6A MCB, 1.5mm T&E cable
b) downstairs lights, 6A MCB, 1.5mm T&E
c) linked smoke alarms, 6A MCB, 1.5mm T&E
d) downstairs ringmain feeding specifically the oven, fridge-freezer and
gas combi boiler, 32A MCD, 2.5mm T&E cable

RCD protected:
e) upstairs ringmain, 32A MCB, 2.5mm T&E
f) downstairs ringmain - all sockets other than those in circuit (d) 32A
MCB, 2.5mm T&E
g) electric shower, 40A MCB, 10mm T&E

I expect circuit (d) to cause most comment?!

I know some people don't like to do it but I'd put the smoke alarms on one
of the lighting circuits to give a check on there being power there. This
is fine by the regs if you use battery backed up alarms, which I would
recommend anyway as they are only a quid or so more expensive. This gives
you a spare circuit for future use.

I assume the 13A sockets in the kitchen are non RCD protected. Personally I
don't like that, especially those above the worktop.

Mike wrote:
"Lobster" wrote in message
...

Am currently doing a rewire and have a few questions please...

1. (the main question!). I'm proposing the following circuits - does
this plan sound sensible? BTW total floor area is 70m2; CU is a Volex
split-load item: http://tinyurl.com/7fe6m (Screwfix 82204). So:

Non-RCD protected:
a) upstairs lights, 6A MCB, 1.5mm T&E cable
b) downstairs lights, 6A MCB, 1.5mm T&E
c) linked smoke alarms, 6A MCB, 1.5mm T&E
d) downstairs ringmain feeding specifically the oven, fridge-freezer and
gas combi boiler, 32A MCD, 2.5mm T&E cable

RCD protected:
e) upstairs ringmain, 32A MCB, 2.5mm T&E
f) downstairs ringmain - all sockets other than those in circuit (d) 32A
MCB, 2.5mm T&E
g) electric shower, 40A MCB, 10mm T&E

I expect circuit (d) to cause most comment?!


I know some people don't like to do it but I'd put the smoke alarms on one
of the lighting circuits to give a check on there being power there. This
is fine by the regs if you use battery backed up alarms, which I would
recommend anyway as they are only a quid or so more expensive. This gives
you a spare circuit for future use.

Yes, I hummed and ha'd a bit over that one. And I will be using
battery-backup alarms. Maybe I'll change my mind!

I assume the 13A sockets in the kitchen are non RCD protected. Personally I
don't like that, especially those above the worktop.

No, under the above scheme, the kitchen sockets come under circuit (f),
ie RCD-protected: it's just the kitchen items specified in circuit (e)
which are not RCD'ed.

David

On Mon, 25 Apr 2005 19:17:28 UTC, "Mike" wrote:

I know some people don't like to do it but I'd put the smoke alarms on one
of the lighting circuits to give a check on there being power there.

Or on a separate circuit, linked to a visible non-maintained emergency
light (say, on the stairs). If the power fails, you have light where
needed. If the circuit fails, the light comes on and you get a visual
indication.
--
Bob Eager
begin a new life...dump Windows!

Bob Eager wrote:

Or on a separate circuit, linked to a visible non-maintained emergency
light (say, on the stairs). If the power fails, you have light where
needed. If the circuit fails, the light comes on and you get a visual
indication.

Having one of those on the lighting circuit that illuminates the CU is a
good plan as well I think. That way you are not groping in the dark to
reset a MCB or RCD.


--
Cheers,

John.

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

John Rumm wrote:
Bob Eager wrote:
Or on a separate circuit, linked to a visible non-maintained emergency
light (say, on the stairs). If the power fails, you have light where
needed. If the circuit fails, the light comes on and you get a visual
indication.
Having one of those on the lighting circuit that illuminates the CU is a
good plan as well I think. That way you are not groping in the dark to
reset a MCB or RCD.

Specially when you've left the cover off the CU because you're in the
middle of something, and somebody trod on it and cracked it so you're
waiting on a new cover down the wholesalers as well as a three for the
price of two pack of tuits

Not that any of us would ever do that, no no no.

Owain