Hi,

My mother would like her electric shower replaced. The hot water
header tank is in the airing cupboard, not the loft, so I think the
shower is higher than the tank meaning negative head, which may make a
pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather
than shower as and when she likes, so for both reasons we may stick
with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped
on the side. I had a feeling it was quite meaty but the MCB is only
32A, which limits us to a 7.5kW shower. Is there a reason an
electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very,
very old. Perhaps it is 7.5kW and since 32A was all it needed,
that's all that was fitted? I have seen one 7.7kW shower in the Wickes
catalogue but if the MCB could be upgraded that would allow more
options.

On my to do list is to see where the cable goes. If it runs under
insulation I guess the cable will have to be derated and a bigger MCB
may not be allowed.

My next problem is the plumbing. I could run the pipe up or down. I
would prefer down. If it goes up, it would go into the loft which is
pretty inaccessible and liable to freeze.

If the pipe goes down, do I chase it into the wall or surface mount
chrome pipe? The advantage of chasing is it hides the pipe, which
appeals to me but perhaps there is an argument for the pipe being
accessible?

If I run chrome down the wall, it saves the mess of chasing and making
good. I'd prefer not to create more jobs to do! Can chrome pipe be
bent or will I have to use chrome plated elbows to get round corners?

The shower is in a cubicle with walls around three sides. The next
problem is getting the pipe through the wall. That's another thing on
the to-do list: find out whether they are brick walls.

It is the quickest way, perhaps not the most elegant, to take the pipe
through the wall. On the other side of the wall is the wash basin fed
from the rising main and I could tee into that.

Would there be a problem taking the pipe through a sleeve in the wall
and using sanitary sealant to make it watertight?

Thanks in advance.

On 18/12/2010 17:29, Fred wrote:
Hi,

My mother would like her electric shower replaced. The hot water
header tank is in the airing cupboard, not the loft, so I think the
shower is higher than the tank meaning negative head, which may make a
pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather
than shower as and when she likes, so for both reasons we may stick
with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped
on the side. I had a feeling it was quite meaty but the MCB is only
32A, which limits us to a 7.5kW shower. Is there a reason an
electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very,
very old. Perhaps it is7.5kW and since 32A was all it needed,
that's all that was fitted? I have seen one 7.7kW shower in the Wickes
catalogue but if the MCB could be upgraded that would allow more
options.

On my to do list is to see where the cable goes. If it runs under
insulation I guess the cable will have to be derated and a bigger MCB
may not be allowed.

My next problem is the plumbing. I could run the pipe up or down. I
would prefer down. If it goes up, it would go into the loft which is
pretty inaccessible and liable to freeze.

If the pipe goes down, do I chase it into the wall or surface mount
chrome pipe? The advantage of chasing is it hides the pipe, which
appeals to me but perhaps there is an argument for the pipe being
accessible?

If I run chrome down the wall, it saves the mess of chasing and making
good. I'd prefer not to create more jobs to do! Can chrome pipe be
bent or will I have to use chrome plated elbows to get round corners?

The shower is in a cubicle with walls around three sides. The next
problem is getting the pipe through the wall. That's another thing on
the to-do list: find out whether they are brick walls.

It is the quickest way, perhaps not the most elegant, to take the pipe
through the wall. On the other side of the wall is the wash basin fed
from the rising main and I could tee into that.

Would there be a problem taking the pipe through a sleeve in the wall
and using sanitary sealant to make it watertight?

Thanks in advance.


If you're doing a like for like replacement, why is there any plumbing
to do? Can't you use the existing pipework?
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On Sat, 18 Dec 2010 20:23:56 +0000, Roger Mills
wrote:

If you're doing a like for like replacement, why is there any plumbing
to do? Can't you use the existing pipework?

The existing pipe goes up into the loft into the most inaccessible
corner (behind a chimney) and it has recently frozen, which is what
had prompted the decision to upgrade everything. Since the basin is
next to the shower cubicle, I could run a new pipe from that and there
would be no danger of anything freezing and not having to crawl
through the loft. Really it was the pipe that needs changing but I
thought I may as well change the medieval shower it is fitted to at
the same time.

On Dec 18, 5:29*pm, Fred wrote:
Hi,

My mother would like her electric shower replaced. The hot water
header tank is in the airing cupboard, not the loft, so I think the
shower is higher than the tank meaning negative head, which may make a
pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather
than shower as and when she likes, so for both reasons we may stick
with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped
on the side. I had a feeling it was quite meaty but the MCB is only
32A, which limits us to a 7.5kW shower. Is there a reason an
electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very,
very old. Perhaps it is *7.5kW and since 32A was all it needed,
that's all that was fitted? I have seen one 7.7kW shower in the Wickes
catalogue but if the MCB could be upgraded that would allow more
options.

On my to do list is to see where the cable goes. If it runs under
insulation I guess the cable will have to be derated and a bigger MCB
may not be allowed.

My next problem is the plumbing. I could run the pipe up or down. I
would prefer down. If it goes up, it would go into the loft which is
pretty inaccessible and liable to freeze.

If the pipe goes down, do I chase it into the wall or surface mount
chrome pipe? The advantage of chasing is it hides the pipe, which
appeals to me but perhaps there is an argument for the pipe being
accessible?

If I run chrome down the wall, it saves the mess of chasing and making
good. I'd prefer not to create more jobs to do! Can chrome pipe be
bent or will I have to use chrome plated elbows to get round corners?

The shower is in a cubicle with walls around three sides. The next
problem is getting the pipe through the wall. That's another thing on
the to-do list: find out whether they are brick walls.

It is the quickest way, perhaps not the most elegant, to take the pipe
through the wall. On the other side of the wall is the wash basin fed
from the rising main and I could tee into that.

Would there be a problem taking the pipe through a sleeve in the wall
and using sanitary sealant to make it watertight?

Thanks in advance.

Electric showers are connected to the cold water mains, nothing to do
with any tanks in the roof space.
Pumped showers use water from a separate hot water system, the two are
quite separate beasts. I think you're better leaving alone if you
don't know these very elementary thingds.

On Dec 18, 5:29*pm, Fred wrote:
Hi,

My mother would like her electric shower replaced. The hot water
header tank is in the airing cupboard, not the loft, so I think the
shower is higher than the tank meaning negative head, which may make a
pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather
than shower as and when she likes, so for both reasons we may stick
with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped
on the side. I had a feeling it was quite meaty but the MCB is only
32A, which limits us to a 7.5kW shower. Is there a reason an
electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very,
very old. Perhaps it is *7.5kW and since 32A was all it needed,
that's all that was fitted? I have seen one 7.7kW shower in the Wickes
catalogue but if the MCB could be upgraded that would allow more
options.

On my to do list is to see where the cable goes. If it runs under
insulation I guess the cable will have to be derated and a bigger MCB
may not be allowed.

My next problem is the plumbing. I could run the pipe up or down. I
would prefer down. If it goes up, it would go into the loft which is
pretty inaccessible and liable to freeze.

If the pipe goes down, do I chase it into the wall or surface mount
chrome pipe? The advantage of chasing is it hides the pipe, which
appeals to me but perhaps there is an argument for the pipe being
accessible?

If I run chrome down the wall, it saves the mess of chasing and making
good. I'd prefer not to create more jobs to do! Can chrome pipe be
bent or will I have to use chrome plated elbows to get round corners?

The shower is in a cubicle with walls around three sides. The next
problem is getting the pipe through the wall. That's another thing on
the to-do list: find out whether they are brick walls.

It is the quickest way, perhaps not the most elegant, to take the pipe
through the wall. On the other side of the wall is the wash basin fed
from the rising main and I could tee into that.

Would there be a problem taking the pipe through a sleeve in the wall
and using sanitary sealant to make it watertight?

Thanks in advance.

You will be lucky to have the CSA stamped on the cable. You will
probably have to measure the cable.

With 4mm cable you are stuck with the 7.5kW shower.

As for the plumbing, then anyway you want it. Through the wall or
buried are both fine.

--

Adam

harry writes:

Electric showers are connected to the cold water mains, nothing to do
with any tanks in the roof space.
Pumped showers use water from a separate hot water system, the two are
quite separate beasts. I think you're better leaving alone if you
don't know these very elementary thingds.

He was discussing the idea of either keeping an electric shower of some
kind, or of fitting an ordinary shower instead.
Though maybe his post wasn't quite as clear as he could have made it.

--
Windmill, Use t m i l l
@ m i l l r t
. p l u s
. c o m

On Dec 18, 5:29*pm, Fred wrote:
Hi,

My mother would like her electric shower replaced. The hot water
header tank is in the airing cupboard, not the loft, so I think the
shower is higher than the tank meaning negative head, which may make a
pumped shower expensive. Unless anyone knows better?

It may also confuse her having to wait for a tank of hot water rather
than shower as and when she likes, so for both reasons we may stick
with what she knows and do a like for like swap.

I haven't looked at the cable yet. Hopefully the CSA will be stamped
on the side. I had a feeling it was quite meaty but the MCB is only
32A, which limits us to a 7.5kW shower. Is there a reason an
electrician would fit 40A capable cable but fit a 32A MCB?

I haven't looked at the old shower to see its rating but it is very,
very old. Perhaps it is *7.5kW and since 32A was all it needed,
that's all that was fitted? I have seen one 7.7kW shower in the Wickes
catalogue but if the MCB could be upgraded that would allow more
options.

On my to do list is to see where the cable goes. If it runs under
insulation I guess the cable will have to be derated and a bigger MCB
may not be allowed.

My next problem is the plumbing. I could run the pipe up or down. I
would prefer down. If it goes up, it would go into the loft which is
pretty inaccessible and liable to freeze.

If the pipe goes down, do I chase it into the wall or surface mount
chrome pipe? The advantage of chasing is it hides the pipe, which
appeals to me but perhaps there is an argument for the pipe being
accessible?

If I run chrome down the wall, it saves the mess of chasing and making
good. I'd prefer not to create more jobs to do! Can chrome pipe be
bent or will I have to use chrome plated elbows to get round corners?

The shower is in a cubicle with walls around three sides. The next
problem is getting the pipe through the wall. That's another thing on
the to-do list: find out whether they are brick walls.

It is the quickest way, perhaps not the most elegant, to take the pipe
through the wall. On the other side of the wall is the wash basin fed
from the rising main and I could tee into that.

Would there be a problem taking the pipe through a sleeve in the wall
and using sanitary sealant to make it watertight?

Thanks in advance.

There are a couple of other shower options than electric or pumped.
Venturi showers can successfully use the cold water pressure to draw
hot water up out of the tank - http://www.heatweb.com/products/venturi/h2o.htm
I don't know if that model is still available, but others are.

Alternatively, http://www.heatweb.com/products/show...owermaster.htm

Whether either of those are sensible solutions depends on the layout
of the existing setup.

A

On Sun, 19 Dec 2010 00:53:00 -0800 (PST), harry
wrote:

I think you're better leaving alone if you
don't know these very elementary thingds.

I suggest you re-read the original post.

I said that the existing electric shower was fed from a pipe in the
loft. A pipe. I never said that this was fed from a header tank. FYI
whoever fitted the shower decided it was easier to take the rising
main into the loft and across the ceiling and down into the bathroom,
hence there is a pipe in the loft and it is fed from the mains.

I knew someone would suggest that the electric shower be replaced with
a power shower, and I quite agree that the latter is much better, but
the header tank is lower than the shower (i.e. negative head) and this
is why I talked about header tanks elsewhere in the post.

On Sun, 19 Dec 2010 03:15:05 -0800 (PST), Adam Wadsworth
wrote:

You will be lucky to have the CSA stamped on the cable. You will
probably have to measure the cable.

With 4mm cable you are stuck with the 7.5kW shower.

As for the plumbing, then anyway you want it. Through the wall or
buried are both fine.

Thanks. I thought I had seen T&E with 1.5 or 2.5 printed on the sides
but perhaps I have imagined that or perhaps I have just been lucky
with the brands I have seen. Before Harry chips in, of course I would
not dream of using such small cables for an electric shower!

I've been and had a look at the cable to the shower and as you
expected, the grey insulation (where it enters the isolation pull
switch) has nothing printed on it. Is there a foolproof way to tell
4mm^2 and 6mm^2 apart? Stick a vernier caliper across the conductor
with the power OFF?

The CU is in the room beneath the bathroom so the cable run is quite
short (so possibly could be changed without too much hassle) but all
the cables run up the wall in some sort of trunking and then under the
floorboards together so I guess I need to check about grouping
derating too.

Thanks.

On Dec 19, 3:12*pm, Fred wrote:
On Sun, 19 Dec 2010 03:15:05 -0800 (PST), Adam Wadsworth

wrote:
You will be lucky to have the CSA stamped on the cable. You will
probably have to measure the cable.

With 4mm cable you are stuck with the 7.5kW shower.

As for the plumbing, then anyway you want it. Through the wall or
buried are both fine.

Thanks. I thought I had seen T&E with 1.5 or 2.5 printed on the sides
but perhaps I have imagined that or perhaps I have just been lucky
with the brands I have seen. Before Harry chips in, of course I would
not dream of using such small cables for an electric shower!

I've been and had a look at the cable to the shower and as you
expected, the grey insulation (where it enters the isolation pull
switch) has nothing printed on it. Is there a foolproof way to tell
4mm^2 and 6mm^2 apart? Stick a vernier caliper across the conductor
with the power OFF?

The CU is in the room beneath the bathroom so the cable run is quite
short (so possibly could be changed without too much hassle) but all
the cables run up the wall in some sort of trunking and then under the
floorboards together so I guess I need to check about grouping
derating too.

Thanks.

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes


gives a good guide for the external diameter of the outer PVC sheath.

Adam

On Sun, 19 Dec 2010 14:19:59 GMT, lid
(Windmill) wrote:

Though maybe his post wasn't quite as clear as he could have made it.

Sorry.

On Sun, 19 Dec 2010 07:24:31 -0800 (PST), Adam Wadsworth
wrote:

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes


gives a good guide for the external diameter of the outer PVC sheath.


Thanks. I'm reading using agent and whenever anyone posts a link to
the faq, I always see a "3D" after the equals sign. Have I got a
setting wrong somewhere?

I think in my earlier posts I was worrying whether it was 6mm^2 or
10mm^2. It seems more likely that the choice is now between 4mm^2 or
6mm^2. If it is 4mm^2 then that would explain the 32A MCB because
isn't that the limit for 4mm^2?

I've never seen 4mm^2 T&E. From what I have read here, people don't
like it because the cpc is too small. Perhaps that will be another
clue to help identify it?

Are 7.5kW showers worth bothering with? Most seem to start at 8.5kW,
with 9.5kW being a common option. I worry that putting in another
7.5kW model might be disappointing. I think it might be best to change
the cable. The CU is "squared D". I see their mcbs are available from
toolstation. Who are square D; are they a good make?

I would think if you are fitting an electric shower it is best to go
for the most power-hungry one you can find? A 10kW model could be ruin
at 8kW but an 8kW model could never be turned up to 10kW. That's my
reasoning; is it flawed?

TIA

Fred wrote:

Thanks. I'm reading using agent and whenever anyone posts a link to
the faq, I always see a "3D" after the equals sign. Have I got a
setting wrong somewhere?

The post you replied to is using Quoted Printable encoding:

Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

This allows special characters to be posted by encoding them as a
sequence beginning with "=". This then requires an actual "=" to be
encoded (so it's not mistaken for the start of an encoded character),
and an encoded "=" is "=3D". Possibly Agent doesn't understand
quoted-printable encoding and shows you the encoded version.


Mike

Fred wrote:
On Sun, 19 Dec 2010 07:24:31 -0800 (PST), Adam Wadsworth
wrote:

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes


gives a good guide for the external diameter of the outer PVC sheath.


Thanks. I'm reading using agent and whenever anyone posts a link to
the faq, I always see a "3D" after the equals sign. Have I got a
setting wrong somewhere?

I think in my earlier posts I was worrying whether it was 6mm^2 or
10mm^2. It seems more likely that the choice is now between 4mm^2 or
6mm^2. If it is 4mm^2 then that would explain the 32A MCB because
isn't that the limit for 4mm^2?

I've never seen 4mm^2 T&E. From what I have read here, people don't
like it because the cpc is too small. Perhaps that will be another
clue to help identify it?

Are 7.5kW showers worth bothering with? Most seem to start at 8.5kW,
with 9.5kW being a common option. I worry that putting in another
7.5kW model might be disappointing. I think it might be best to change
the cable. The CU is "squared D". I see their mcbs are available from
toolstation. Who are square D; are they a good make?

If the CU is a new one and match Toolstations MCBs (an slightly older CU may
have different MCBs) then that is fine.


I would think if you are fitting an electric shower it is best to go
for the most power-hungry one you can find? A 10kW model could be ruin
at 8kW but an 8kW model could never be turned up to 10kW. That's my
reasoning; is it flawed?

Yes, get the highest powered one that you can that is suitable for your
cable.

The difference between 4mm and 6mm cable is easy to check if you have a bit
of 2.5 T&E knocking about. The cpc(earth) of 4mm T&E is 1.5^2 the same as
the cpc of the 2.5 T&E. The cpc of 6mm T&E is 2.5^2 - the same size as the
2.5 oddly enough:-)

Cheers
--
Adam

On 19/12/2010 15:12, Fred wrote:

Is there a foolproof way to tell 4mm^2 and 6mm^2 apart?

Assuming you're familiar with 2.5 T&E, or have got a bit to hand, look
at the earth conductor in the 4 or 6 mm^2 cable. Then:

- if it's 6 mm^2 the earth will be the same size as the L & N conductors
in the 2.5 sample;

- if it's 4 mm^2 the earth will be the same size as the earth
conductor in the 2.5 sample.

--
Andy

On Sun, 19 Dec 2010 18:03:03 -0000, "ARWadsworth"
wrote:

If the CU is a new one and match Toolstations MCBs (an slightly older CU may
have different MCBs) then that is fine.

That was my worry, that they may have changed the design. I can't
remember when the house was rewired but it is definitely in red and
black, so how long ago is that? 2006? I think it must have been
rewired in the early 2000s but that's 10 years ago. Will they have
changed in that time?

If so, can you buy "old" mcbs or do you have to look on ebay?

The difference between 4mm and 6mm cable is easy to check if you have a bit
of 2.5 T&E knocking about. The cpc(earth) of 4mm T&E is 1.5^2 the same as
the cpc of the 2.5 T&E. The cpc of 6mm T&E is 2.5^2 - the same size as the
2.5 oddly enough:-)

Thanks. That's clever.

I have a horrible feeling it will be 4mm^2, otherwise why use a 32A
mcb?

I know fat T&E is expensive but I'd only need what, 5 metres ?, at
most so if I had to put 6mm^2 in, it wouldn't be the end of the world.
I suppose you'll say that if I am changing the wire to go to 10mm^2?

Re. the other reply about venturis. They are a good idea, thanks, but
the URL you gave said they need a 30cm head. I think the header tank
is more or less at shower height; in fact the shower is probably
higher than the bottom of the tank, so this rules out venturis. I
think it rules out power showers because all the neg. head pumps I
have seen are in the region of £400

The wall is hollow, so that's some good news but with my luck, I'll
want to drill through a stud. Assuming it's got some studs. I have a
zircon detector but IME it is useless.

Thanks again.

"Fred" wrote in message
...

I have a horrible feeling it will be 4mm^2, otherwise why use a 32A
mcb?

If its along length of cable they could use 6 mm^2 to avoid voltage drop.
You would still fuse it at 32A if that's what the fitting instructions said.


I know fat T&E is expensive but I'd only need what, 5 metres ?, at
most so if I had to put 6mm^2 in, it wouldn't be the end of the world.
I suppose you'll say that if I am changing the wire to go to 10mm^2?

Probably, its hard to make cable too big, it just gets harder to fit in the
terminals and to bend. ;-)

..

On Sun, 19 Dec 2010 20:33:55 -0000, "dennis@home"
wrote:

If its along length of cable they could use 6 mm^2 to avoid voltage drop.
You would still fuse it at 32A if that's what the fitting instructions said.

Thanks. I'll have to measure the conductors to see. Let's hope I am
lucky and they rewired in 6mm^2 but used a 32A MCB because that was
all that was needed by the (presumably) 7kW shower.

Since the wall is hollow, could I thread plastic pipe inside it or
would it need supporting at regular intervals? I don't want it falling
off and flooding the place!

Thanks

"Fred" wrote in message
...

Since the wall is hollow, could I thread plastic pipe inside it or
would it need supporting at regular intervals? I don't want it falling
off and flooding the place!

You can get coils of plastic pipe so there wouldn't be anything to fall off
inside the wall.
I have had plastic pipe in my system for 30 years and nothing bad has
happened yet.
I do know of copper pipe that has failed in less time (but there is a lot of
copper pipe that old and not much plastic that old).

On Mon, 20 Dec 2010 08:37:05 +0000, Fred wrote:

On Sun, 19 Dec 2010 20:33:55 -0000, "dennis@home"
wrote:

If its along length of cable they could use 6 mm^2 to avoid voltage drop.
You would still fuse it at 32A if that's what the fitting instructions said.

Thanks. I'll have to measure the conductors to see. Let's hope I am
lucky and they rewired in 6mm^2 but used a 32A MCB because that was
all that was needed by the (presumably) 7kW shower.

That's what I did, 30 years ago when 7kW was the norm., then fitted a 40A
MCB for the 8.5kW unit - both on 6mm² cable.


--
Peter.
The gods will stay away
whilst religions hold sway

Fred wrote:
On Sun, 19 Dec 2010 18:03:03 -0000, "ARWadsworth"
wrote:

If the CU is a new one and match Toolstations MCBs (an slightly
older CU may have different MCBs) then that is fine.

That was my worry, that they may have changed the design. I can't
remember when the house was rewired but it is definitely in red and
black, so how long ago is that? 2006? I think it must have been
rewired in the early 2000s but that's 10 years ago. Will they have
changed in that time?

If so, can you buy "old" mcbs or do you have to look on ebay?

The difference between 4mm and 6mm cable is easy to check if you
have a bit of 2.5 T&E knocking about. The cpc(earth) of 4mm T&E is
1.5^2 the same as the cpc of the 2.5 T&E. The cpc of 6mm T&E is
2.5^2 - the same size as the
2.5 oddly enough:-)

Thanks. That's clever.

I have a horrible feeling it will be 4mm^2, otherwise why use a 32A
mcb?

I know fat T&E is expensive but I'd only need what, 5 metres ?, at
most so if I had to put 6mm^2 in, it wouldn't be the end of the world.
I suppose you'll say that if I am changing the wire to go to 10mm^2?

I am:-) And for only a few pennies more.


Re. the other reply about venturis. They are a good idea, thanks, but
the URL you gave said they need a 30cm head. I think the header tank
is more or less at shower height; in fact the shower is probably
higher than the bottom of the tank, so this rules out venturis. I
think it rules out power showers because all the neg. head pumps I
have seen are in the region of £400

Not my link mate.

The wall is hollow, so that's some good news but with my luck, I'll
want to drill through a stud. Assuming it's got some studs. I have a
zircon detector but IME it is useless.

Of course there will be studs in just the wrnong place! Measure the existing
cable first and satart from there

--
Adam

On Mon, 20 Dec 2010 13:03:43 -0000, "dennis@home"
wrote:

You can get coils of plastic pipe so there wouldn't be anything to fall off
inside the wall.

Yes, that's what I was thinking of. I just wondered whether it needed
clipping to a stud at certain intervals. That would be easy to do if
you were building the wall from scratch but since the wall is already
there, I will not be able to do this. I wasn't sure whether the pipe
might "kick" when switched on and off and whether over time this might
make it loosen any compression joints. Hopefully I am being far too
pessimistic. Thanks.

On Mon, 20 Dec 2010 16:16:57 +0000, PeterC
wrote:

That's what I did, 30 years ago when 7kW was the norm., then fitted a 40A
MCB for the 8.5kW unit - both on 6mm² cable.

Thanks to the table in the UK.DIY FAQ, and thanks to ARW for posting
the link, I think it is 6mm^2 cable that is in place.

It is red and black cable. Was that fatter than the blue and brown? I
had a small off cut of blue and brown 6mm^2 with me and it did look
smaller overall. Perhaps the insulation is thinner on the new coloured
stuff?

I measured the overall size as being 13.4mm x 7.5mm. The FAQ says
6mm^2 cable is 13.1mm x 6.8 mm. So this one is slightly thicker than
expected. Do the cables vary by manufacturer? If so, this might
explain the difference.

The table says that a 2.5mm^2 CPC would have a diameter of 1.78mm, so
let's call that 1.8mm to one decimal place. I measured 1.9mm on a
vernier calliper, so that's pretty close to the expected result. So
far so good.

I measured the diameter of the neutral (once the circuit had been
disconnected). I measured an overall diameter of 3.0mm but I am not
sure how accurate this was as I guess it depends how the individual
cores lie. I measured a single core and it was 1.0mm. The table says
it should be 1.04 but I would not have been able to see the 0.04, so I
guess my result matches the table.

I am pretty confident this is 6mm^2 T&E. Is there any reason to doubt
this now?

The table gives much bigger values for the various dimensions of
10mm^2 T&E so I am sure it is not that.

The only thing that concerns me now is the path of the cable. All the
cables leave the CU and go up the wall in sort of trunking. Does this
count as clipped direct to the wall? I was worrying that the trunking
makes it count as being in conduit. I'll have to take a closer look at
what it actually is and how the cables are grouped inside it. I
suspect they are just all thrown in together.

The cables then appear under the bathroom floorboards. They then run
3' or so all next to each other and where there are joists in the way,
the cables go through one big hole in the middle of the joist. I
thought you were supposed to have a separate hole for each cable and
space the holes by three times their diameter?

But since this is "red and black" wiring, perhaps the regs. were more
relaxed then? Were they? It was rewired by a pro, so I hope it was
done properly at the time.

It's crazy really because the cable is not far from the corner with
the shower cubicle and all that needed to be done was for the cable to
go up the wall to a pull switch on the bathroom ceiling. For reasons I
cannot understand (perhaps he didn't want to chaser the wall nor have
cable clipped or trunked or otherwise visible), the cable does not do
this; instead it turns and runs away from the cubicle!

The cable runs to the airing cupboard in the opposite corner of the
room and then runs up the inside of the cupboard and into the loft. I
don't know whether the cable is buried under any insulation because
that part of the loft is inaccessible. Because it is inaccessible,
there shouldn't be any insulation there but who knows?!

It is a little old lady living on her own, so I don't expect the
wiring ever gets near full load but all the same, should I derate the
shower cable on the basis that it runs close to everything else and
may or may not be under insulation in the loft?

If so, what should I derate it to?

I think, but will check, that there is another 6mm^2 cable for the
electric cooker and there is an immersion heater (2.5mm^2 ?). Quite
often she has an electric fire plugged in to a socket downstairs.
These are the only big loads I can think of that exist in the house.

That said, the cooker is only on for short periods of time at meal
times and the boiler rather than the immersion is used for HW, and a
ring main can cope comfortably with an electric heater, so I don't
think any of these would be on at the same time as the shower and I
doubt any of the loads would be on long enough to cause any heating of
the cables. That only leave the insulation to worry about.

What do you all think? I could lay the cable in a more sensible route
but I'd prefer to avoid the hassle if necessary.

TIA

On Dec 19, 7:42*pm, Fred wrote:
On Sun, 19 Dec 2010 18:03:03 -0000, "ARWadsworth"

wrote:
If the CU is a new one and match Toolstations MCBs (an slightly older CU may
have different MCBs) then that is fine.

That was my worry, that they may have changed the design. I can't
remember when the house was rewired but it is definitely in red and
black, so how long ago is that? 2006? I think it must have been
rewired in the early 2000s but that's 10 years ago. Will they have
changed in that time?

If so, can you buy "old" mcbs or do you have to look on ebay?

The difference between 4mm and 6mm cable is easy to check if you have a bit
of 2.5 T&E knocking about. The cpc(earth) of *4mm T&E is 1.5^2 the same as
the cpc of the 2.5 T&E. The cpc of 6mm T&E is 2.5^2 - the same size as the
2.5 oddly enough:-)

Thanks. That's clever.

I have a horrible feeling it will be 4mm^2, otherwise why use a 32A
mcb?

I know fat T&E is expensive but I'd only need what, 5 metres ?, at
most so if I had to put 6mm^2 in, it wouldn't be the end of the world.
I suppose you'll say that if I am changing the wire to go to 10mm^2?

Re. the other reply about venturis. They are a good idea, thanks, but
the URL you gave said they need a 30cm head. I think the header tank
is more or less at shower height; in fact the shower is probably
higher than the bottom of the tank, so this rules out venturis.

I hadn't noticed that. I posted it because it explains the principle
well. The other 2 brands I've seen (Trevi Boost and Newteam) both
handle small negative heads. Replacing the electric does sound like
the simplest option though.

A