Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...

a) the rating of the circuit breaker

b) the size of the cable

c) some other means.

By looking at the cable I cant determine its size (mm2?) - is there a
measurement that I can take of it to determine its maximum rating. Also a
quick breakdown of cable size against shower rating would be most useful if
anyone can help.

Thanks in advance for any help,

CM.

Also a quick breakdown of cable size against shower rating would be
most useful if anyone can help.

The length of the cable also comes into play. If a cable has to be long,
then it may need to be thicker for the same rating shower.

Christian.

"Christian McArdle" wrote in message
. net...
Also a quick breakdown of cable size against shower rating would be
most useful if anyone can help.

The length of the cable also comes into play. If a cable has to be long,
then it may need to be thicker for the same rating shower.

Christian.


Thanks for the information. I tempted to phone Triton and ask them the KW
rating of the current unit. No doubt there will be a range of ratings per
model!

CM.

"Charles Middleton" wrote in message
...

"Christian McArdle" wrote in message
. net...
Also a quick breakdown of cable size against shower rating would be
most useful if anyone can help.

The length of the cable also comes into play. If a cable has to be long,
then it may need to be thicker for the same rating shower.

Christian.


Thanks for the information. I tempted to phone Triton and ask them the KW
rating of the current unit. No doubt there will be a range of ratings per
model!

Bear in mind that there is no guarantee that the installed cable & circuit
breaker are suitably rated for the installed shower.

"Ric" wrote in message
...

"Charles Middleton" wrote in message
...

"Christian McArdle" wrote in message
. net...
Also a quick breakdown of cable size against shower rating would be
most useful if anyone can help.

The length of the cable also comes into play. If a cable has to be
long,
then it may need to be thicker for the same rating shower.

Christian.


Thanks for the information. I tempted to phone Triton and ask them the
KW
rating of the current unit. No doubt there will be a range of ratings
per
model!

Bear in mind that there is no guarantee that the installed cable & circuit
breaker are suitably rated for the installed shower.


Is there a way by looking at the cable breaker etc I can determine the
maximum rating possible?

CM.

In article ,
Charles Middleton wrote:

Is there a way by looking at the cable breaker etc I can determine the
maximum rating possible?

P = I * V

So if it's a 30A breaker, max. power would be 30 * 230 or 6.9KW.

But thats assuming 100% efficiency - you'll lose some to the cable at
those amps which I think was mentioned earlier in the thread..

If it were me, I'd uprate the wiring and breaker to handle the biggest
wattage shower I could get my hands on, having been fed-up in the past
with dribbly little 8KW showers in the middle of winter )-:

Gordon

"Charles Middleton" wrote in message
...
Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...

a) the rating of the circuit breaker

b) the size of the cable

c) some other means.

Take the old one off, open it up. Look at the rating on the heater inside

In article , Charles Middleton
writes
Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...

a) the rating of the circuit breaker

b) the size of the cable

c) some other means.

By looking at the cable I cant determine its size (mm2?) - is there a
measurement that I can take of it to determine its maximum rating. Also a
quick breakdown of cable size against shower rating would be most useful if
anyone can help.

Thanks in advance for any help,

CM.

Easy way is to turn off all major appliances (washing m/c, cooker etc but
lights/video don't really matter) then measure the power usage on the
electricity meter over a timed period. These things use so much juice that
the rating should be pretty clear from say just 5/6mins of use. Meter will
resolve 0.1kWhr at worst so 6mins on a 7kW will give 0.7kWhr, 8kW -
0.8kWhr etc.

Howzat?
-
fred

Charles Middleton wrote:

measurement that I can take of it to determine its maximum rating. Also a

Got a good thermometer and a bucket?

Measure the temperature of the cold water from a tap on the same mains
supply as the shower (kitchen will do) - let it run for a few mins to
get a stable reading of the actual incoming water temp.

Now calibrate your bucket with a marker so you know where 5L is.

Turn on your shower at maximum temperature and let it run for a bit to
get a stable temperature. Measure this temperature.

Now time how long it takes to fill your bucket to the 5L mark.

Now do some sums:

Find out how much energy the shower has added to the water. To do that
multiply the temperature rise, by the mass of water (assume 1L = 1kg),
and then by the specific heat capacity of water (4200).

Say the temperature difference between incoming and heated water was 40
degrees C you will get:-

40 * 5 * 4200 = 840,000 J

Now divide this by the time it took to fill in seconds. Say it took 80
seconds, you get:-

840000 / 80 = 10500 J/second (or Watts)

Thus you would have a 10.5kW shower.

(The above procedure will tell you the heat put into the water by the
shower - it will not tell you the energy lost in the supply cable to it.
So for example if you had a 10kW shower, you may only find 9.8 kW
getting as far as the water).


--
Cheers,

John.

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

John Rumm wrote in message ...
Charles Middleton wrote:

measurement that I can take of it to determine its maximum rating. Also a

Got a good thermometer and a bucket?

Measure the temperature of the cold water from a tap on the same mains
supply as the shower (kitchen will do) - let it run for a few mins to
get a stable reading of the actual incoming water temp.

Now calibrate your bucket with a marker so you know where 5L is.

Turn on your shower at maximum temperature and let it run for a bit to
get a stable temperature. Measure this temperature.

Now time how long it takes to fill your bucket to the 5L mark.

Now do some sums:

Find out how much energy the shower has added to the water. To do that
multiply the temperature rise, by the mass of water (assume 1L = 1kg),
and then by the specific heat capacity of water (4200).

Say the temperature difference between incoming and heated water was 40
degrees C you will get:-

40 * 5 * 4200 = 840,000 J

Now divide this by the time it took to fill in seconds. Say it took 80
seconds, you get:-

840000 / 80 = 10500 J/second (or Watts)

Thus you would have a 10.5kW shower.

(The above procedure will tell you the heat put into the water by the
shower - it will not tell you the energy lost in the supply cable to it.
So for example if you had a 10kW shower, you may only find 9.8 kW
getting as far as the water).


--
Cheers,

John.

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

Perhaps a measurement of the DC resistance across the electrical input
terminal to the shower with a meter might solve the mystery. You would
need to isolate the shower from the mains cable in order to do this.
So the power is calculated by multiplying the 230v mains by itself and
then dividing it by the resistance of the shower heating element.

Jason








shower

Jason wrote:

Perhaps a measurement of the DC resistance across the electrical input
terminal to the shower with a meter might solve the mystery. You would
need to isolate the shower from the mains cable in order to do this.
So the power is calculated by multiplying the 230v mains by itself and
then dividing it by the resistance of the shower heating element.

Perhaps... I expect you will find a heating element is a bit like a
light bulb in that respect, since its resistance when hot will be
different from cold. Hence you may tend to "over read" the actual power
based on the resistance looking lower than it really is.

If you are going to measure it, one way would be to pop the cover of the
cu and locate the feed from the MCB to the shower. Stick a clamp meter
round it and then go fire up the shower. The clamp meter will take a
direct reading of the current without needing to make physical contact
with the circuit.

--
Cheers,

John.

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

In message ,
"Charles Middleton" wrote:

Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...


There have been some very interesting and accurate posts on this thread,
but I suspect that the "real world" answer to your problem is much
simpler.

If the shower has been there some time, chances are that it will be
wired in 6mm2 T&E (this stuff is about half an inch wide altogether) and
fed from a 30A fuse or 32A MCB. If the shower has been rated at 240V
then it *should* be at most 7.6kW (32A*240V) though it is common to see
showers up to 8.5kW run in this way: a 32A MCB isn't going to trip for
that amount of overload, and it is highly likely that the cable will
handle it fine, depending on route and length. (Note that I would *not*
recommend installing an 8.5kW shower on a 32A MCB, or worse still a 30A
rewireable).

I am told that 7.5kW really doesn't do the job for much of the year.

When you buy your new shower you really need to get the most powerful
one you can afford so you should also be factoring in the cost of
running a new length of 10mm2 cable (it's about an inch wide: while you
are in B&Q (or wherever) looking for your shower, check out the cable in
the electrical aisle) and upgrading the MCB (and possibly your supply)
to accommodate the new shower.

While you're at it, you need to think about the shower disconnection
times and whether or not an RCD is required for it. This will largely
depend on the type of earthing your system has and the length of cable
from CU to shower. Don't forget to make sure your supplementary bonding
is up to scratch too.

One thing I'm surprised people often don't think about though is the
possibility of hanging a shower from the existing hot water system. It
seems that if there's an electric shower already installed many people
think that more of the same is their only option. Not so; most
combi boilers (should you have one) will give showers at least as good,
and in most cases better than most electric showers because a combi
might be putting 24kW into the water whereas the biggest practical
electric shower is only 10kW or so. Do invest in a thermostatic mixer
though.

Even if you have a hot water cylinder system it is possible to run a
very good shower from that. If it is one of the rare (at the moment)
mains pressure systems just bung on a thermostatic mixer. If it is
gravity fed then a shower pump will cost about the same as a new
electric shower and potentially give a better result. The difficulty is
re-arranging the plumbing.

For both the above though, the electrics are simplified. None at all are
needed for a thermostatic on combi or mains, and for a pumped system,
the pump takes a very small amount of power and can easily be run from
an existing sockets circuit.

Erm... sorry. I wrote a lot more there than I was intending.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... (((((((HYPNOTIC)))))))(((((((TAGLINE)))))))

Martin Angove wrote in message ...
In message ,
"Charles Middleton" wrote:

Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...


There have been some very interesting and accurate posts on this thread,
but I suspect that the "real world" answer to your problem is much
simpler.

If the shower has been there some time, chances are that it will be
wired in 6mm2 T&E (this stuff is about half an inch wide altogether) and
fed from a 30A fuse or 32A MCB. If the shower has been rated at 240V
then it *should* be at most 7.6kW (32A*240V) though it is common to see
showers up to 8.5kW run in this way: a 32A MCB isn't going to trip for
that amount of overload, and it is highly likely that the cable will
handle it fine, depending on route and length. (Note that I would *not*
recommend installing an 8.5kW shower on a 32A MCB, or worse still a 30A
rewireable).

I am told that 7.5kW really doesn't do the job for much of the year.

When you buy your new shower you really need to get the most powerful
one you can afford so you should also be factoring in the cost of
running a new length of 10mm2 cable (it's about an inch wide: while you
are in B&Q (or wherever) looking for your shower, check out the cable in
the electrical aisle) and upgrading the MCB (and possibly your supply)
to accommodate the new shower.

While you're at it, you need to think about the shower disconnection
times and whether or not an RCD is required for it. This will largely
depend on the type of earthing your system has and the length of cable
from CU to shower. Don't forget to make sure your supplementary bonding
is up to scratch too.

One thing I'm surprised people often don't think about though is the
possibility of hanging a shower from the existing hot water system. It
seems that if there's an electric shower already installed many people
think that more of the same is their only option. Not so; most
combi boilers (should you have one) will give showers at least as good,
and in most cases better than most electric showers because a combi
might be putting 24kW into the water whereas the biggest practical
electric shower is only 10kW or so. Do invest in a thermostatic mixer
though.

Even if you have a hot water cylinder system it is possible to run a
very good shower from that. If it is one of the rare (at the moment)
mains pressure systems just bung on a thermostatic mixer. If it is
gravity fed then a shower pump will cost about the same as a new
electric shower and potentially give a better result. The difficulty is
re-arranging the plumbing.

For both the above though, the electrics are simplified. None at all are
needed for a thermostatic on combi or mains, and for a pumped system,
the pump takes a very small amount of power and can easily be run from
an existing sockets circuit.

Erm... sorry. I wrote a lot more there than I was intending.

Hwyl!

M.

Sounds like you are a shower enthusiast then Hwyl! I'd wager you prefer a
pumped shower to the other options :-)


Jason

Martin Angove wrote:

If the shower has been there some time, chances are that it will be
wired in 6mm2 T&E (this stuff is about half an inch wide altogether)
[...]

[...] one you can afford so you should also be factoring in the cost of
running a new length of 10mm2 cable (it's about an inch wide:

Your suggestion that 10 mm^2 cable is about twice the width of 6 mm^2
didn't quite ring true. According to the Pirelli data sheet 6 mm^2 T&E
is approx. 13.1mm wide and 10 mm^2 is approx. 16.8 mm wide - so "just
over half an inch" and "getting on for eleven-sixteenths of an inch" is
nearer the mark.

While you're at it, you need to think about the shower disconnection
times and whether or not an RCD is required for it. This will largely
depend on the type of earthing your system has and the length of cable
from CU to shower.

And on the type of overcurrent protective device. For a 45A shower
circuit the maximum voltage-drop limited circuit length is 49 m. With a
PME supply there is no need for an RCD with any device type (other than
Type C or old Type 3 MCBs on circuits longer than 23 m - but these
device types aren't appropriate for a shower in any case).

For a TN-S earthed supply:

- with a BS 1361 cartridge fuse an RCD would be required for a circuit
longer then 10 m;

- with a re-wireable fuse (or old Type 1 MCB) the full 49 m is OK
without an RCD;

- for a Type B MCB the length limit without RCD is 35 m;

- other MCB types will require the RCD, regardless of length.

In all cases running a separate parallel 10mm^2 circuit protective
conductor to the shower (taking the same route as the 10 mm^2 T&E) could
also be considered.

Don't forget to make sure your supplementary bonding
is up to scratch too.

Absolootly :-)

--
Andy

In message ,
Andy Wade wrote:

Martin Angove wrote:

If the shower has been there some time, chances are that it will be
wired in 6mm2 T&E (this stuff is about half an inch wide altogether)
[...]

[...] one you can afford so you should also be factoring in the cost of
running a new length of 10mm2 cable (it's about an inch wide:

Your suggestion that 10 mm^2 cable is about twice the width of 6 mm^2
didn't quite ring true. According to the Pirelli data sheet 6 mm^2 T&E
is approx. 13.1mm wide and 10 mm^2 is approx. 16.8 mm wide - so "just
over half an inch" and "getting on for eleven-sixteenths of an inch" is
nearer the mark.

Ok, you win. I have actually been using the Pirelli stuff this weekend,
though I haven't gone so far as to measure it :-) Having said that, if
it were one of those nothing-to-compare-against, instant-guesstimate
things, I would probably look and say "half inch" or "inch". In the OP's
case all he needs to do is to say "is it a half inch, or significantly
bigger?"

Just thought... 4mm2 cable isn't *that* much smaller than 6, but then
you wouldn't find a... erm... would you? ;-)


While you're at it, you need to think about the shower disconnection
times and whether or not an RCD is required for it. This will largely
depend on the type of earthing your system has and the length of cable
from CU to shower.

And on the type of overcurrent protective device. For a 45A shower
circuit the maximum voltage-drop limited circuit length is 49 m. With a
PME supply there is no need for an RCD with any device type (other than
Type C or old Type 3 MCBs on circuits longer than 23 m - but these
device types aren't appropriate for a shower in any case).


Yes, and we're probably getting way out of the OP's depth by now. I
assumed he had MCBs when he was asking about sizing the shower by "the
rating of the circuit breaker"... but I do tend to assume things which
aren't necessarily the case.

49m is a heck of a long way (come to that, 35m is a fair old distance
too), especially since 10mm2 cable gets extremely unweildy if you have
to manhandle anything more than a 25m drum!

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Doing my part to preserve order in the universe

In message ,
(Jason) wrote:


Sounds like you are a shower enthusiast then Hwyl! I'd wager you prefer a
pumped shower to the other options :-)


The name's Martin. "Hwyl" is a greeting :-)

Not a particular enthuser over showers (difficult to take a book into
the shower to read), but I am confused that the electric shower seems to
be so common when there is often (granted not always) hot water freely
available from other, cheaper, more plentiful sources.

The pump is a compromise solution for the bog standard gravity-fed HW
system (yes, we have one). Most pumps (again, there are notable
exceptions) are noisy and give little impression of solidity, but the
cheapest pump on a gravity system can give even the most powerful
electric shower a good run for its money, and at a fraction of the
running cost - assuming the HW cylinder is in use and doesn't have to be
heated solely for the shower.

If you want lengthy and wide-ranging discussion on this and similar
topics, all you have to do is Google back into this group's past and
look for (particularly) anything written by IMM and Andy Hall on the
subject of hot water (try keywords such as "combi" or "two combis" or
"heat bank" or "plate heat exchanger"). Just don't go looking unless
you've a few hours to spare :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Get 'em by the balls and their hearts and minds will follow.