Possibly replacing electric shower, what other works reqd?

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Hi all, looking at changing my bathroom, currently have an electric shower fitted over the bath but am going to put a replacement electric shower in and a new shower cubicle, looking at my electrics last night I have a seperate unit/switch on the board for the shower rated 30ma with a 30 amp fuse in, shower I am looking at putting in says "We recommend the inclusion of a 30mA residual current device (RCD). This may be part of the consumer unit or a separate unit" so it looks like I have that covered, however also says "The appliance requires a 40 Amp supply fuse" could someone explain this for me,

Many thanks in advance for you help ;)
 
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You've got a 30A fuse.

Your new shower needs a 40A one.

Why do you need that explained?

You will also (I can virtually guarantee) need to replace the cable for the shower circuit, and probably the switch.

The new circuit needs to be properly designed, and it should be properly tested and an EIC issued for it.

And it's all notifiable work, so you'd be strongly advised to use a registered electrician to do it.
 
so swapping the fuse out is sufficient, I have not measured the cable running up to the bathroom looks substantial and is easily accessible so if needed to be swapped out could be, I was more concerned with having to swap the switch on the board
 
unless its very old, the switch on the board will be the "fuse", its called a minature circuit breaker.

Can you post an image of the board? Or is there a model name/number on it?
 
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so swapping the fuse out is sufficient,
FFS.
You will also (I can virtually guarantee) need to replace the cable for the shower circuit


I have not measured the cable running up to the bathroom looks substantial
So how do you know that swapping the fuse is sufficient?

You don't know what the size of the cable is, so how can you know what it's current carrying capacity is?

Do you know how it's installed, and whether any insulation or grouping factors need to be applied to derate it's capacity?

Do you know how long it is, and whether the voltage drop will be within limits and whether its R1+R2 will be low enough to give you an acceptable Zs for a 40A device?


so swapping the fuse out is sufficient,
Almost certainly not, and absolutely definitely not without checking the suitability of the circuit first.


I was more concerned with having to swap the switch on the board
What switch?
 
so swapping the fuse out is sufficient,
FFS.
You will also (I can virtually guarantee) need to replace the cable for the shower circuit

FFS Helpful!


I have not measured the cable running up to the bathroom looks substantial
So how do you know that swapping the fuse is sufficient?

You don't know what the size of the cable is, so how can you know what it's current carrying capacity is?

Will measure it tonight but would say it looks more like 10mm

Do you know how it's installed, and whether any insulation or grouping factors need to be applied to derate it's capacity?

When you say how its installed, please explain, insulation no it runs along the inside wall of the garage, up through the floor into the bathroom which is on the back corner of the house, I would say total cable length is less than 10m, seeing as this cable along with a 30a fuse is currently running a 8.5kw shower I dont see how capacity will be an issue, but please let me have your thoughts

Do you know how long it is, and whether the voltage drop will be within limits and whether its R1+R2 will be low enough to give you an acceptable Zs for a 40A device?

As above circa 10m


so swapping the fuse out is sufficient,
Almost certainly not, and absolutely definitely not without checking the suitability of the circuit first.

What about swapping out the MCB for a higher ampage?


I was more concerned with having to swap the switch on the board
What switch?

The MCB refered above by Aragon
 
You cant just wedge a larger fuse/MCB in without ensuring the wiring is upto scratch.

The fuse is there to protect the WIRING, not the device on the end of it.

You say the wiring is easy to get to. In that case, i would replace it with 10mm stuff, then install your larger MCB and you should be ok.

6mm cable can work for loads upto around 45A but the length of the run, and how its mounted can affect how much it can safely carry.
 
Thanks I think thats probably going to be the way to go, I will get measurements and pics on here later, thanks again
 
Will measure it tonight but would say it looks more like 10mm
It might be, but it would have been unusual to install such a large cable for a 30A circuit.

You do realise that 10mm² refers to the cross-sectional area of the phase & neutral conductors, not any other dimension?

When you say how its installed, please explain,
This isn't up to date, but it will give you an idea: http://www.tlc-direct.co.uk/Book/4.3.3.htm


insulation no it runs along the inside wall of the garage, up through the floor into the bathroom which is on the back corner of the house,
Sounds like Method 20.


I would say total cable length is less than 10m, seeing as this cable along with a 30a fuse is currently running a 8.5kw shower I dont see how capacity will be an issue, but please let me have your thoughts
My thoughts are:
1) A 30A fuse is undersized for an 8.5kW shower.
2) A cable sized with the expectation of a 30A circuit could be undersized for an 8.5kW shower.
3) Your new shower requires a 40A circuit.


As above circa 10m
Not too long.


What about swapping out the MCB for a higher ampage?
The MCB refered above by Aragon
What MCB?:
I have a seperate unit/switch on the board for the shower rated 30ma with a 30 amp fuse
 
Hi all, pictures here

http://i461.photobucket.com/albums/qq331/punkyb_photos/IMGP2954.jpg
http://i461.photobucket.com/albums/qq331/punkyb_photos/IMGP2955.jpg
http://i461.photobucket.com/albums/qq331/punkyb_photos/IMGP2959.jpg
http://i461.photobucket.com/albums/qq331/punkyb_photos/IMGP2960.jpg[/QUOTE]
Right - having looked at those....

What about swapping out the MCB for a higher ampage?
The MCB refered above by Aragon
What MCB?


I have a seperate unit/switch on the board for the shower rated 30ma with a 30 amp fuse in
What RCD?


looks like I am certainly in need of a new one for the more powerful shower
Yes, but you already knew that - the instructions for the shower told you.

And cable size? Not sure that looks like 10mm² to me....
 
i suspect you'll want to replace the entire box

You MUST replace that old fuse box.

First of all it has no provision for RCD protection to your shower which is required by the regs.

Second of all, if you try and run a load larger than 30A from that fusebox well erm, it kind of goes on fire.

I was looking for Securespark's picture, but couldn't find it.
 

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