Hi all,

Will be helping my Dad fit a new electric shower in a few weeks. My Mum
has made him go for the most powerful one she could find which is
10.5Kw. For this we will need to add a 45A breaker to the CU which is
an oldish Wylex unit with MCBs marked as NB05, NB15, etc. My question
is, is it possible to get 45 amp rated MCBs to fit this board and if so,
where? I've seen a few NB40 and NB50 ones on eBay, but no luck on the
45A front.


And help muchly appreciated.

Thanks,
Richard.

On Mon, 28 Apr 2008 13:16:56 +0100 someone who may be Richard Conway
wrote this:-

Will be helping my Dad fit a new electric shower in a few weeks. My Mum
has made him go for the most powerful one she could find which is
10.5Kw. For this we will need to add a 45A breaker

I make that 45.7A @ 230V. I would fit a 50A one if that is
available, but see below.

to the CU which is
an oldish Wylex unit with MCBs marked as NB05, NB15, etc. My question
is, is it possible to get 45 amp rated MCBs to fit this board and if so,
where? I've seen a few NB40 and NB50 ones on eBay, but no luck on the
45A front.

According to places like
http://www.thefusecompany.com/fuse.php?cPath=58&products_id=398
and http://www.connectstores.com/P.E.D/sp_11801-10.html it appears
they are only available new up to 40A. The latter mention that
Proteus models can be fitted, so you might just get a higher rated
one.

Amongst the things to consider before installing either is
diversity. Will this be the only high power circuit, or is there a
cooker or something else rated at more than 32A? Are they likely to
be in use at the same time, if so for how long? Is the consumer unit
(and the cables feeding it) going to be able to cope with the new
load?

The next thing to consider is the cable size. If fitting a 50A MCB
it may be necessary to go up a cable size. There is also the
question of cable size with regard to the installation methods. For
instance, will the cable run through insulation or be in a conduit?

Lastly, if you can't find a suitable MCB you may find a suitable
fuse. However, the carrier will be two modules wide.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

"David Hansen" wrote in message
...
On Mon, 28 Apr 2008 13:16:56 +0100 someone who may be Richard Conway
wrote this:-

Will be helping my Dad fit a new electric shower in a few weeks. My Mum
has made him go for the most powerful one she could find which is
10.5Kw. For this we will need to add a 45A breaker

I make that 45.7A @ 230V. I would fit a 50A one if that is
available, but see below.

Except its probably 10.5kW at 240V. The manual will make clear. These
numbers are not accidental but by design.

This is all too marginal for easy advice to a non-expert. Don't forget the
installation instructions may *recommend* an RCD.

If the OP cares about his mum he should chose a shower rating which works
with 32A 6sqmm. Or get it done properly.

And hey isnt't it Part P territory for a reason?

Jim A

Hi Richard,

I've just gone through this exercise for a friend. There is no 45A MCB
for the Wylex only 40A or 50A in the MCB. Wylex do make a 45A fuse but
there is no holder to put it into the existing fuse box. Not wanting to
risk a 50A MCB I brought an MK IP65 Shower Unit. This comes with a 30mA
RCD switch and and 50A MCB but you can buy 45A MCB for it. I got it from
Screwfix, cost £42.99 for the unit and £4.57 for the 45A MCB.

Luckily there was a secondary fuse box connected to nothing so I was
able to replace this for yourself it could mean a complete fuse box
replacement which isn't nice!!

I hope it helps a bit but sorry its not what you want.

Take care,
Ryan

On Mon, 28 Apr 2008 14:42:51 +0100 someone who may be "Jim
Alexander" wrote this:-

If the OP cares about his mum he should chose a shower rating which works
with 32A 6sqmm.

32A in thermal insulation. 38A in conduit and 46A clipped direct.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Richard Conway wrote:

Will be helping my Dad fit a new electric shower in a few weeks. My Mum
has made him go for the most powerful one she could find which is
10.5Kw. For this we will need to add a 45A breaker to the CU which is
an oldish Wylex unit with MCBs marked as NB05, NB15, etc. My question
is, is it possible to get 45 amp rated MCBs to fit this board and if so,
where? I've seen a few NB40 and NB50 ones on eBay, but no luck on the
45A front.

I think you may be out of luck with this board. You could use a 50A
breaker if you run 10mm^2 cable and a reasonably simple cable run
without any need to de-rate the cable. Check the earth loop impedance
carefully if you are not using a RCD.

--
Cheers,

John.

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\================================================= ================/

On Mon, 28 Apr 2008 14:49:18 +0100 someone who may be Ryan
wrote this:-

Wylex do make a 45A fuse but
there is no holder to put it into the existing fuse box.

The 45A fuse is the same size as the 35A (and the 40A if they make
one), though I wouldn't be rash enough to assume that a 35A carrier
has as much metal inside it as a 45A one. 45A carriers are certainly
available for some "modern" consumer units, there is one a few
metres away from me as I type.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

John Rumm wrote:
Richard Conway wrote:

Will be helping my Dad fit a new electric shower in a few weeks. My
Mum has made him go for the most powerful one she could find which is
10.5Kw. For this we will need to add a 45A breaker to the CU which is
an oldish Wylex unit with MCBs marked as NB05, NB15, etc. My question
is, is it possible to get 45 amp rated MCBs to fit this board and if
so, where? I've seen a few NB40 and NB50 ones on eBay, but no luck on
the 45A front.

I think you may be out of luck with this board. You could use a 50A
breaker if you run 10mm^2 cable and a reasonably simple cable run
without any need to de-rate the cable. Check the earth loop impedance
carefully if you are not using a RCD.


Thanks for the replies everyone.

Just to clarify, the instructions do call for a 45A protective device
along with recommending an RCD (the current CU is split load so would
obviously out on RCD side). The cable run is fairly straightforward as
the bathroom is pretty much directly above the CU. The cable will run
in trunking from the CU to the downstairs ceiling then under the floor a
bit followed by a short run through the uninsulated stud wall that the
shower will be fitted to. Probably not much more than five meters in
total. I was planning on using 10mm^2 anyway to be on the safe side.

It does look as though I'm pretty buggered here which is a shame. Looks
like I'll be replacing the CU then!

One option not mentioned which I assume would be okay would be to have
45A breaker in a seperate enclosure wired back to a 50A breaker in the
existing CU. Although this would seem a bit overkill considering a new
kit box with more than enough MCBs probably wouldn't cost much more.
Only benefit to this that I can see is it wouldn't require me to break
the seal on the main supply fuse - but I don't have too many quarms over
that having done my own not too long ago.

Thanks again,
Richard

Richard Conway wrote:

One option not mentioned which I assume would be okay would be to have
45A breaker in a seperate enclosure wired back to a 50A breaker in the
existing CU. Although this would seem a bit overkill considering a new
kit box with more than enough MCBs probably wouldn't cost much more.
Only benefit to this that I can see is it wouldn't require me to break
the seal on the main supply fuse - but I don't have too many quarms over
that having done my own not too long ago.

It would probably be simpler to leave the CU as is, and split the tails
feeding it via a Henley. Then you can have the new mini CU with RCD
completely independent of the existing one. Saves adding more circuits
to the main RCD as well.

--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
news:d9ednRx5iIDCy4rVRVnyiwA@plusnet...
Richard Conway wrote:

One option not mentioned which I assume would be okay would be to have
45A breaker in a seperate enclosure wired back to a 50A breaker in the
existing CU. Although this would seem a bit overkill considering a new
kit box with more than enough MCBs probably wouldn't cost much more. Only
benefit to this that I can see is it wouldn't require me to break the
seal on the main supply fuse - but I don't have too many quarms over that
having done my own not too long ago.

It would probably be simpler to leave the CU as is, and split the tails
feeding it via a Henley. Then you can have the new mini CU with RCD
completely independent of the existing one. Saves adding more circuits to
the main RCD as well.

--
Cheers,

John.

It might be worth noting that my 10.5kW@ 240V shower has worked fine from a
40A MCB for the last 6 years. Changing the MCB is on the things to do list.

AdAM

ARWadworth wrote:

"John Rumm" wrote in message
news:d9ednRx5iIDCy4rVRVnyiwA@plusnet...
Richard Conway wrote:

One option not mentioned which I assume would be okay would be to
have 45A breaker in a seperate enclosure wired back to a 50A breaker
in the existing CU. Although this would seem a bit overkill
considering a new kit box with more than enough MCBs probably
wouldn't cost much more. Only benefit to this that I can see is it
wouldn't require me to break the seal on the main supply fuse - but I
don't have too many quarms over that having done my own not too long
ago.

It would probably be simpler to leave the CU as is, and split the
tails feeding it via a Henley. Then you can have the new mini CU with
RCD completely independent of the existing one. Saves adding more
circuits to the main RCD as well.

--
Cheers,

John.

It might be worth noting that my 10.5kW@ 240V shower has worked fine
from a 40A MCB for the last 6 years. Changing the MCB is on the things
to do list.

AdAM

Interesting. There is a spare 40A MCB in this unit already, so if that
did work it could save me a job. Can anyone think of any reason NOT to
do this?

"Richard Conway" wrote in message
...

ARWadworth wrote:

"John Rumm" wrote in message
news:d9ednRx5iIDCy4rVRVnyiwA@plusnet...
Richard Conway wrote:

One option not mentioned which I assume would be okay would be to have
45A breaker in a seperate enclosure wired back to a 50A breaker in the
existing CU. Although this would seem a bit overkill considering a new
kit box with more than enough MCBs probably wouldn't cost much more.
Only benefit to this that I can see is it wouldn't require me to break
the seal on the main supply fuse - but I don't have too many quarms
over that having done my own not too long ago.

It would probably be simpler to leave the CU as is, and split the tails
feeding it via a Henley. Then you can have the new mini CU with RCD
completely independent of the existing one. Saves adding more circuits
to the main RCD as well.

--
Cheers,

John.

It might be worth noting that my 10.5kW@ 240V shower has worked fine from
a 40A MCB for the last 6 years. Changing the MCB is on the things to do
list.

AdAM

Interesting. There is a spare 40A MCB in this unit already, so if that
did work it could save me a job. Can anyone think of any reason NOT to do
this?

Yes, it's a 10.5kW shower.

It's a pity you didn't reign in the choice to 9.5kW

Jim A


Jim A

Richard Conway wrote:

It might be worth noting that my 10.5kW@ 240V shower has worked fine
from a 40A MCB for the last 6 years. Changing the MCB is on the things
to do list.

AdAM

Interesting. There is a spare 40A MCB in this unit already, so if that
did work it could save me a job. Can anyone think of any reason NOT to
do this?

Chances are it will work just fine, but you would be designing the
system a little out of spec. A 40A MCB will probably supply a sustained
overload at 45A indefinitely. According to the trip curves in BS7671,
even a 50A load would probably take 30 mins to cause a trip. As long as
the cable is of adequate rating there is unlikely to be any harm caused.

(might be worth checking what your nominal voltage is, If it is below
240V then that is in your favour. If however you routinely get 250V then
I would be less inclined to do as above.


--
Cheers,

John.

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

In message b_-dneEJ1N_k44XVnZ2dneKdnZydnZ2d@plusnet, John Rumm
writes
Richard Conway wrote:

It might be worth noting that my 10.5kW@ 240V shower has worked fine
from a 40A MCB for the last 6 years. Changing the MCB is on the
things to do list.

Is the Wylex NB range thermally compensated? if not, and the 40A rating
is at 40Deg.C ambient then at typical UK temperatures the thermal trip
would be at a higher current.
As a shower is a resistive load the current it draws is proportional to
the voltage at its terminals.If your cable run is long enough to drop
the supply by 4% the current will also drop by 4%.
But then of course the mains is 230V +10/-6%
Aaaaaah.............
--
Neil J. Harris