Replacing an electric shower

[TheZapster1111]

Hi

I'm replacing the shower - old one is a Mira 7.2KW - what KW can I replace it with?

I've done a search and am now really confused - the wire that leads to the shower is 10mm, it runs under the bath and into the plasterboard wall, presumably up into the loft. The house is very small and 20 years old, the RCB is a 30A trip (for the shower part). There's only me in the house, so the shower will be used 3/4 times a week only.

Given that info, is it ok to stick a 9.5kw shower in?

Cheers

 

[Carloss]

you can replace it with 7.3Kw shower as you have a 32A mcb.
however, you can replace the 32a mcb with a 40A and will be able to run 9.2Kw. Thats assuming it is 10mm cable feeding it.
Depending on the cable run length you could put a 45A mcb in and run 10.3Kw.

This circuit should also be protected by a 30mA rcd.

hope this helps.

carlos

 

[rebuke]

Note that while replacing the shower isn't, replacing the protective device (i.e. uprating the MCB from 30/32A to 40A or whatever) is notifiable to your LABC before doing the work under Part P of the bulding regulations.

Also, although 10mm can nominally take 40/45A, it depends entirely on how it's been installed, in particular if it runs under a certain amount of thermal insulation, then it must be derated. Your best bet if you do want a more powerful shower, is probably to get a qualified electrician in who can take a look, and tell you exactly what you can go for...

Also, something to check is you say the RCB is a 30A trip, you should have one of two things, either an MCB (with e.g. 30 or 32A written on it) that is protected by a separate RCD/RCCB (which will have a test button, and probably say 30mA on it somewhere), or a single RCBO device which will have something such as a B32 30mA written somewhere (and have a test button). If you just have an MCB (so no test button), then you need to get RCD protection added to the circuit (otherwise a faulty shower might give you a potentially fatal shock)...

 

[ban-all-sheds]

Changing the MCB and/or adding an RCD makes it notifiable, if that is of interest to you.

//www.diynot.com/wiki/electrics:part-p

 

[TheZapster1111]

Thanks. It is the former (I think) - it is a series of switches, each labeled lights, shower, cooker etc. The left hand side, covering, sockets, cooker and shower (30A each) have a marking saying these are covered by the RCCB - the switches to the right - lights, heater etc - have a marking saying they are not covered by the RCCB. There is also a test switch on the left.

What difference does thermal insulation make? Do you mean loft-type insulation?

I'm actually quite prepared to replace the shower with the same 7.5kw, but they don't seem to sell them anywhere. It would be a lot less hassle. What I want to know is, if I put a 8.5kw shower into my existing set, will I die?

 

[TheZapster1111]

How easy is it to replace a 32A MCB (I think mine's actually 30?) with a 40A?

 

[Spark123]

Couple of 7.2kw units here:
http://www.tlc-direct.co.uk/Main_Index/Showers_Index/Showers_Sadia/index.html

 

[Spark123]

How easy is it to replace a 32A MCB (I think mine's actually 30?) with a 40A?

You'd firstly need to check that the cable is suitable, isolator etc are suitable, that you can still buy them for your CU. As has been said, replacing an MCB with one of a greater size also needs to be nofitied to your LABC under part p.

 

[ban-all-sheds]

What difference does thermal insulation make?

Cables can only carry a certain amount of current before they get too hot. If they cannot dissipate all of the heat that the current generates, e.g. because they are covered in insulation, or in a hot environment, or bunched together with other cables, then they can't safely carry as much current.

http://www.kevinboone.com/cableselection_web.html

Do you mean loft-type insulation?

That's one example. Insulation in stud partition walls is another.

I'm actually quite prepared to replace the shower with the same 7.5kw, but they don't seem to sell them anywhere.

'cos they is carp.

It would be a lot less hassle. What I want to know is, if I put a 8.5kw shower into my existing set, will I die?

Almost certainly be fine, if it's 10mm² cable all the way.

I have a slight worry though that it isn't - it would have been unusual back when it was installed to have used 10mm² cable for a 7.2kW load on a 30A circuit - are you sure of the size? How did you measure it?

//www.diynot.com/wiki/electrics:cable_types:flatpvccables

 

[Carloss]

To me and other competent electricians its no worries to change the mbc and acess the cable routing, locating double pole switched isolation as well as ensure the circuit is safe to use before energized. i.e. test and inspection carried out to ensure it is safe to use and all functional devices are in full working order! In my opinion you should get a fully qualified electrician in who is able to replace the shower, issue a suitable certificate and part p. alternatively:

http://www.plumbworld.co.uk/aqualisa-showers-1265-0000?s_kwcid=aqualisa shower|697135080

carl

 

[TheZapster1111]

I measured it's width with a tape measure - 10mm exactly.

I guess now you're going to tell me there's more to it than that? There generally is!

 

[Steve]

YES! 10mm refers to the conductor's cross sectional area!!!!

A cable which is 10mm across its outer sheath is 2.5mm² CSA.

A cable with 10mm² CSA is 17.1mm across its outer sheath.



//www.diynot.com/wiki/electrics:cable_types:flatpvccables

 

[DCC]

To expand further, no way can you have a higher power shower, in fact isn't 30A too much for a 2.5mm cable anyway? At this point you probably need to get someone qualified in to take a look at things.

 

[ColJack]

Basically it's time for a new shower and a registered sparky to fit it for you.... it'll be cheaper than trying to DIY it..

 

[ban-all-sheds]

//www.diynot.com/wiki/electrics:cable_types:flatpvccables

I measured it's width with a tape measure - 10mm exactly. I guess now you're going to tell me there's more to it than that? There generally is!

I'd already told you how to measure the size of cables when you wrote that.

What is the FP of coming here to ask advice if you aren't going to read it?