There is currently a promotion in my area for free or subsidised Cavity
Wall Insulation. I can get it installed for 90 quid. It should be a no
brainer but one problem I have is that the electric shower cable runs up
the wall cavity and insulating the cavity would mean the cable needs to
be de-rated. The shower is 9.5kW and the cable is 6mm which is just
enough with an uninsulated cavity. I hope to get away with replacing the
6mm cable with 10mm. I used the cable calculator at tlc direct but it is
flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.
A shower will consume a higher current at 240v than at 230v.

When I installed the shower cable about 20 years ago I also replaced the
CU so the shower is fed from a 40A MCB on the RCD protected side of the
CU. The cable runs up the cavity into the loft, along the gable end then
over the loft insulation down a stud partition to the shower. Re-routing
the cable to not use the cavity is not something I relish. Any comments?

Archie

"Archie" wrote in message
...
There is currently a promotion in my area for free or subsidised Cavity
Wall Insulation. I can get it installed for 90 quid. It should be a no
brainer but one problem I have is that the electric shower cable runs up
the wall cavity and insulating the cavity would mean the cable needs to be
de-rated.

I wouldn't bother changing the cable, it will be OK. That is how mine was
done!
5 years later = no problem.

On Sat, 10 Oct 2009 15:03:53 +0100, Roger wrote:

"Archie" wrote in message
...
There is currently a promotion in my area for free or subsidised Cavity
Wall Insulation. I can get it installed for 90 quid. It should be a no
brainer but one problem I have is that the electric shower cable runs up
the wall cavity and insulating the cavity would mean the cable needs to be
de-rated.

I wouldn't bother changing the cable, it will be OK. That is how mine was
done!
5 years later = no problem.

With a shower the period of use is usually[1] a few minutes, so any rise in
temperature should be limited by that.

[1] Unusual/more fun useage might invalidate this point.
--
Peter.
The head of a pin will hold more angels if
it's been flattened with an angel-grinder.

Archie wrote:
I used the cable calculator at tlc direct but it is
flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.

Which is correct, because the TLC calculator is based on the rated
voltage of the appliance, not the voltage of your supply.


A shower will consume a higher current at 240v than at 230v.


Correct also providing you're talking about the supply voltage not the
rated voltage.


This is what TLC calculator does: -

Shower rated 9.5kW @ 240V gives current demand of 9500/240 = 39.58A

Shower rated 9.5kW @ 230V gives current demand of 9500/230 = 41.30A


But this is what you're thinking of: -

Shower rated 9.5kW @ 230V run on a 240V supply gives current demand of
41.03A x 240/230 = 42.81A

Shower rated 9.5kW @ 240V run on a 230V supply gives current demand of
39.58A x 230/240 = 37.93A

On Oct 10, 5:02*pm, Dave Osborne wrote:
Archie wrote:

* I used the cable calculator at tlc direct but it is

flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.

Which is correct, because the TLC calculator is based on the rated
voltage of the appliance, not the voltage of your supply.

A shower will consume a higher current at 240v than at 230v.

Correct also providing you're talking about the supply voltage not the
rated voltage.

This is what TLC calculator does: -

Shower rated 9.5kW @ 240V gives current demand of 9500/240 = 39.58A

Shower rated 9.5kW @ 230V gives current demand of 9500/230 = 41.30A

But this is what you're thinking of: -

Shower rated 9.5kW @ 230V run on a 240V supply gives current demand of
41.03A x 240/230 = 42.81A

Shower rated 9.5kW @ 240V run on a 230V supply gives current demand of
39.58A x 230/240 = *37.93A

But, but, but: Voltage in the UK is required to be 230V -5% +10% (or
something) - same as in the rest of the EU. However, UK /actual/
voltage is 240V (and continental voltages are /actually/ 230V).

For calculating overheating etc, I'd be more interested in the current
with an actual 240V.

Martin Bonner wrote:
On Oct 10, 5:02 pm, Dave Osborne wrote:
Archie wrote:

I used the cable calculator at tlc direct but it is

flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.
Which is correct, because the TLC calculator is based on the rated
voltage of the appliance, not the voltage of your supply.

A shower will consume a higher current at 240v than at 230v.
Correct also providing you're talking about the supply voltage not the
rated voltage.

This is what TLC calculator does: -

Shower rated 9.5kW @ 240V gives current demand of 9500/240 = 39.58A

Shower rated 9.5kW @ 230V gives current demand of 9500/230 = 41.30A

But this is what you're thinking of: -

Shower rated 9.5kW @ 230V run on a 240V supply gives current demand of
41.03A x 240/230 = 42.81A

Shower rated 9.5kW @ 240V run on a 230V supply gives current demand of
39.58A x 230/240 = 37.93A

But, but, but: Voltage in the UK is required to be 230V -5% +10% (or
something) - same as in the rest of the EU. However, UK /actual/
voltage is 240V (and continental voltages are /actually/ 230V).


Well, that's true, but only nominally so.

You will find in practice that most people in the UK get more than 240V.
Here, I am about 80m of cable away from the substation and (at 2.30 p.m.
in the afternoon on a sunny day) have a voltage of 248V (I just measured
it). I expect that later on (about 9.00 p.m.) when it's dark and much
colder, the voltage will drop to 245V or so. I expect that people at the
far-end of the cable 200-300m away from the substation with have figures
more like 240V falling to 237V.

Don't forget that 90% of the regulations exist to act as a protection
against the risk of fire and 10% against electric shock. A shower that
pulls 42.8A instead of 37.9A doesn't make for a significantly increased
fire risk and has no increased risk of causing electric shock (provided
that the cable isn't grossly under-rated of course).

For calculating overheating etc, I'd be more interested in the current
with an actual 240V.

Only if you've actually got 240V...

It's only Ohm's Law (V=I*R) and the Power Law (P=V*I) and a bit of
algebra. You don't need no stinkin' website calculator from TLC to work
it out ;-)

On Mon, 12 Oct 2009 14:47:36 +0100, Dave Osborne wrote:

You will find in practice that most people in the UK get more than 240V.
Here, I am about 80m of cable away from the substation and (at 2.30 p.m.
in the afternoon on a sunny day) have a voltage of 248V (I just measured
it). I expect that later on (about 9.00 p.m.) when it's dark and much
colder, the voltage will drop to 245V or so.

It might but here the volts drop during the working day when the load
is really on the grid. We have our own transformer and about 15m of
240v cable to the meters. From about midnight the volts are up and
pretty steady just under 240, then come 0600 they start to fall
reaching a minimum about 0800 of 230ish. The rest of the day then
generally bounces about with an upward trend back to 240v by
midnight. The weekends have less variation.

http://www.flickr.com/photos/allsorts-60/4004361303/ - Thu 1st Oct
2009
http://www.flickr.com/photos/allsorts-60/4004361301/ - Sun 4th Oct
2009

The stepping is due to the 2v or so resolution(*) of the APC Smart
UPS that is providing the data I'm logging.

(*) WTF it reports to one decimal place when it only ever reports
discreet 2v or so steps is beyond me. This gives a very false
impression of the voltage measurement accuracy.

--
Cheers
Dave.

Dave Liquorice wrote:
On Mon, 12 Oct 2009 14:47:36 +0100, Dave Osborne wrote:

You will find in practice that most people in the UK get more than 240V.
Here, I am about 80m of cable away from the substation and (at 2.30 p.m.
in the afternoon on a sunny day) have a voltage of 248V (I just measured
it). I expect that later on (about 9.00 p.m.) when it's dark and much
colder, the voltage will drop to 245V or so.

It might but here the volts drop during the working day when the load
is really on the grid. We have our own transformer and about 15m of
240v cable to the meters. From about midnight the volts are up and
pretty steady just under 240, then come 0600 they start to fall
reaching a minimum about 0800 of 230ish. The rest of the day then
generally bounces about with an upward trend back to 240v by
midnight. The weekends have less variation.

http://www.flickr.com/photos/allsorts-60/4004361303/ - Thu 1st Oct
2009
http://www.flickr.com/photos/allsorts-60/4004361301/ - Sun 4th Oct
2009

The stepping is due to the 2v or so resolution(*) of the APC Smart
UPS that is providing the data I'm logging.

(*) WTF it reports to one decimal place when it only ever reports
discreet 2v or so steps is beyond me. This gives a very false
impression of the voltage measurement accuracy.


OK, Thanks for that. Do you measure the voltage at the point of your
supply or somewhere along a final circuit? Does the load on the final
circuit cable have a significant effect on the measured voltage or does
the voltage vary this much at the point of supply?

I work from home and live in a moderate sized commuter town with a small
light-industrial estate. Max demand is winter TV prime-time when the
adverts come on and the kettle gets put on!

Anyway, if you have a shower at work, you would get a better shower if
you get in early...

On Oct 12, 3:43*pm, "Dave Liquorice"
wrote:
http://www.flickr.com/photos/allsorts-60/4004361303/- Thu 1st Oct
2009
http://www.flickr.com/photos/allsorts-60/4004361301/- Sun 4th Oct
2009

Don't you realize that is entirely contrary to the spirit of Usenet?
How are we supposed to get a good argument going, if you go and spoil
it with actual *data*? :-)

Seriously, thanks for that. Very interesting to get an idea of how
high the /real/ variation is.

On Oct 12, 10:34*am, Martin Bonner wrote:
On Oct 10, 5:02*pm, Dave Osborne wrote:





Archie wrote:

* I used the cable calculator at tlc direct but it is

flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.

stan wrote:

But a suggestion; if it is a wood stud wall; the studs are spaced at
say 16 inches (or closer?)?
Is there any way you can avoid putting foam into the one particular
stud space that has the cable.

The OP said it was a cavity wall, not a stud wall. The cavity will be
between an outer skin of brick and an inner skin of either brick or
block depending on age. There are no studs and no individual spaces
between them.

Pete

On Oct 10, 2:11*pm, "Archie" wrote:
There is currently a promotion in my area for free or subsidised Cavity
Wall Insulation. I can get it installed for 90 quid. It should be a no
brainer but one problem I have is that the electric shower cable runs up
the wall cavity and insulating the cavity would mean the cable needs to
be de-rated. The shower is 9.5kW and the cable is 6mm which is just
enough with an uninsulated cavity. I hope to get away with replacing the
6mm cable with 10mm. I used the cable calculator at tlc direct but it is
flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.
A shower will consume a higher current at 240v than at 230v.

When I installed the shower cable about 20 years ago I also replaced the
CU so the shower is fed from a 40A MCB on the RCD protected side of the
CU. The cable runs up the cavity into the loft, along the gable end then
over the loft insulation down a stud partition to the shower. Re-routing
the cable to not use the cavity is not something I relish. Any comments?

Archie

Its worth it. The cost of rerouting the cable is small compared to
typical savings.


NT

On Oct 10, 2:11*pm, "Archie" wrote:
There is currently a promotion in my area for free or subsidised Cavity
Wall Insulation. I can get it installed for 90 quid. It should be a no
brainer but one problem I have is that the electric shower cable runs up
the wall cavity and insulating the cavity would mean the cable needs to
be de-rated. The shower is 9.5kW and the cable is 6mm which is just
enough with an uninsulated cavity. I hope to get away with replacing the
6mm cable with 10mm. I used the cable calculator at tlc direct but it is
flawed. e.g. for a given set of parameters and using the default 230V it
gives a higher current answer than if 240V is used in their calculator.
A shower will consume a higher current at 240v than at 230v.

When I installed the shower cable about 20 years ago I also replaced the
CU so the shower is fed from a 40A MCB on the RCD protected side of the
CU. The cable runs up the cavity into the loft, along the gable end then
over the loft insulation down a stud partition to the shower. Re-routing
the cable to not use the cavity is not something I relish. Any comments?

Archie

I see you have had lots of replies regarding your current/heat
concern.

Have considered the impact the insulation may have on the cable
protection? I have read that the poly beads (if thats what you are
intending to get) can cause problems with the cable insulation. I
have no personal experience of this, its just something that I read.

Alan

On Oct 15, 4:33*pm, AlanC wrote:
Have considered the impact the insulation may have on the cable
protection? *I have read that the poly beads (if thats what you are
intending to get) can cause problems with the cable insulation. *I
have no personal experience of this, its just something that I read.

If he keeps a cable in the cavity, it must be larger CSA in conduit.
- He can argue the cable is 50mm from the surface
- However anyone drilling (CWI) does not expect a cable

I have a suspicion you need 10mm 6242BH (90oC XLPE BS7211) or 16mm
6242H (70oC PVC BS6004). Obviously wiring accessories will not
tolerate 90oC, but we are concerned with the length of cable in
insulation. The same argument is used re 6242BH 90oC lighting cable
run in domestic loft insulation.

Unfortunately Screwfix stop at 6mm in 6242BH, there isn't any 10mm or
16mm on Ebay either.

I know people do not like "conduit on outside walls".
However in this instance if possible I would thro-drill to the outside
and run 10mm 6491X & 4mm 6491X (or 10mm FTE) in 25mm black conduit
from besa-box to besa-box w/gasket & brass screws to enter a thro-
drilled hole in the bathroom. The larger 25mm size can actually work
better than small sizes. If your downpipes are brown you are a bit
stuffed of course, if they are white you may want to try white (BESA
boxes & conduit cost nothing, hence the wasted cost is immaterial).

It allows CWI to go in without delay - you get the energy saving
benefit this winter, which can offset the cost of a) doing it b)
improving safety re cable in cavity and c) giving a good incentive to
get the cable routed internally anyway.

I personally prefer polybead re waterproof-bonded over fibre.