Replacing Mira Sport 9KW Electric Shower

[Fishwalker]

Hi all,

Our shower's on/off button has stopped working all together. No shower at all.

My OH likes to fix things himself and removed the casing for the existing Mira Sport shower, after turning off water and isolating electrics to shower and it says it is a 9kw 240v Mira Sport model.

He removed the shower after speaking with his father (a retired engineer and self professed DIY'er) and thought it was a straight case of nipping to a local shed and buying a new shower and installing.

I've checked this out though as I'm the researcher and I think we may have to have a sparky, even though we are totally skint and buying the shower was bad enough.

So Facts:

The Mira Sport shower was already installed when we moved in 6 years ago and is 9KW at 240V.

We had a modern RCD Consumer Unit installed in 2007 when we moved in.

On the RCD, the Shower has it's own switch stating B32 for 230 volts, the Cooker meanwhile says B40 (I assume this is the ampage). The Downstairs/upstairs sockets are on a B32 as well, while the lights say B6.

The Shower has it's own isolation switch inside the boiler cupboard (red flippy switch), as well as its switch on the RCD fuse box.

The cable running from the RCD to shower can't be more than 10 metres, as the bathroom sits 1 room from under the stairs in a small terrace.

The electric cable feeding the shower is routed under plaster with roughly 4 inch's neatly sticking out and looks in good condition BUT it is Red, Black and Earth, with the first two having 7 wires but the earth just being the 1 wire.

I have been struggling to decide as to whether this cable is 6mm or 10mm but I suspect 6mm, as just went to Bonus Electrical and looked at 10mm cable and that has 7 wires in the earth as well + looks very slightly bigger overall + obviously is blue and brown newer cabling inside.

So... questions...

If we only have red, black, earth - 6mm cabling, and that has been feeding a 9KW shower for 6 years quite happily, which our electrician must have checked somehow, as he installed a 32 amp fuse in the new RCD for it, and considering the old fuse box was the old, single copper wire system, which was wired previously to the same shower (surely bodgy!?), then can't we just install a new 8.5kw shower ourselves?

Only thing is, I checked the online manual for the Mira 8.5kw showers such as the Go and Vie, and they say they need a 40amp fuse in place and state you can use a max of 10mm wire for it, but not that you must use 10 mm.

Now my OH says he can just replace the fuse in the RCD with a 40amp and that is not hard, but I thought, does the cable have to be 10mm for a 40amp fuse or it will melt?

Also if we retain the current cabling and do a straight swap to a new 8.5kw shower and either leave fuse as 32amp or change to 40 amp, do we need to notify building regs?

Lastly, what sort of quote do you think we'd be looking at for replacing 10metres of 6mm cable for 10mm and checking fuse + labour for a sparky in Yorkshire area and would it involve ripping out tiles and pulling up floorboards etc?

Sorry for length of this but like to be thorough!

Untitled

• Fishwalker
• 11 May 2013
• 1

 

[EFLImpudence]

Firstly -

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

 

[Fishwalker]

Hi,

I have already checked out that link sorry before I wrote but still don't really get it. I am a visual person and don't really get the maths bit. Thank though.

 

[EFLImpudence]

Our shower's on/off button has stopped working all together. No shower at all.

Get a new switch.

My OH likes to fix things himself

But not in this case.

So Facts:

The Mira Sport shower was already installed when we moved in 6 years ago and is 9KW at 240V.

= 37.5 Amps

On the RCD, the Shower has it's own switch stating B32 for 230 volts, the Cooker meanwhile says B40 (I assume this is the ampage).

They should be the other way round (unless you have an industrial kiln)

BUT it is Red, Black and Earth,

That doesn't matter. They don't know what colour they are nor are they racist..

I have been struggling to decide as to whether this cable is 6mm or 10mm but I suspect 6mm,

6mm² is fine as long as it runs through NO thermal insulation.
Nor conduit with the correct 40A MCB

then can't we just install a new 8.5kw shower ourselves?

Yes but you still need 40A MCB.

Now my OH says he can just replace the fuse in the RCD with a 40amp and that is not hard, but I thought,

You mean MCB - as above.

does the cable have to be 10mm for a 40amp fuse or it will melt?

See above.

Also if we retain the current cabling and do a straight swap to a new 8.5kw shower and either leave fuse as 32amp or change to 40 amp, do we need to notify building regs?

As above - No notification but I would advise proper testing of cable and RCD.
As the MCB must have been overheating for all these years a new one should be fitted anyway.

Lastly, what sort of quote do you think we'd be looking at for replacing 10metres of 6mm cable for 10mm and checking fuse + labour for a sparky in Yorkshire area and would it involve ripping out tiles and pulling up floorboards etc?

If you can verify that the cable is run through NO thermal insulation NOR conduit then it is not necessary.

 

[ban-all-sheds]

Hi,

I have already checked out that link sorry before I wrote but still don't really get it. I am a visual person and don't really get the maths bit. Thank though.

One of you has to be able to do these:

• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  

 

[Fishwalker]

Hmmm. Checked those links e.g. the http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html but I don't know what the wiring will be touching on it's way up from under the stairs to the bathroom.

It's a 110yr old terrace with single brick walls and I have seen under the landing, roughly above the under stair cupboard and I think it's a hollow void with wires running along joists mostly. I doubt there will be any plaster board there or insulation. I saw under the floorboards when we had the boiler changed last year and it was just joists and laths and dust. What with the red and black wires being potentially from 1976 (when they were updated to blue and brown) and behind the shower being literally just fresh plaster (over brick probably), I'm not sure what that would mean for calculating whether I need 6mm or 10mm cable.

If I wanted a 9.5kw shower though, I imagine I would then need 10mm? We bought one today, but took it back as the water inlet was on the wrong side. That was what set all this off.

I have emailed a sparky anyway who my parents have used and will see what he advises too, but appreciate you guys input.

Meanwhile Bought a bath tap shower head.

Untitled

• Fishwalker
• 11 May 2013
• 1

 

[seco services]

Would of been easier to change the latching switch for £12.

 

[ban-all-sheds]

What with the red and black wires being potentially from 1976 (when they were updated to blue and brown)

No - that was in 2004: http://electrical.theiet.org/wiring-regulations/cable-colours/index.cfm

and behind the shower being literally just fresh plaster (over brick probably), I'm not sure what that would mean for calculating whether I need 6mm or 10mm cable.

The colours are irrelevant, but you do need to know how the cables are installed.

If I wanted a 9.5kw shower though, I imagine I would then need 10mm?

Not necessarily - 9.5kW is 40A (they always quote the performance at 240V), and 6mm² can carry between 23.5A and 47A.

Depending on how it's installed....

http://www.shepleyelectricalservices.com/Installation Method Codes.pdf

http://electrical.theiet.org/wiring-matters/28/appendix4.cfm

http://www.batt.co.uk/upload/files/4d5.pdf

We bought one today, but took it back as the water inlet was on the wrong side.

They always are.

 

[Luckyphil]

We bought one today, but took it back as the water inlet was on the wrong side.

They always are.[/quote]

NOT always I fitted a Mira Sport Multfit , yesterday , Water inlet left or right , top or bottom as is the Cable inlet , Plus its a large unit which hides any areas where tiles are cut out .

An excellent piece of kit for a retro fit - aint cheap though £200 +

Lucky

 

[ban-all-sheds]

Fairy nuff.

 

[Fishwalker]

Thanks guys.

Thought about it some more and remember the sparky when he fitted our RCD unit in 2007 checking the cut out switch inside the boiler cupboard in the bathroom for the shower and he would have been able to see the shower wiring by taking that cover off, so probably saw it was 6mm and put the 32amp fuse in based on an assumption of the shower wattage.

I can't see any condult near where the wire comes out of the wall behind the shower, would have to take a floor board up I think near the skirting board to see there but think its in free air mainly.

Spoke to OH Dad and think we may just go for a 7.5kw shower as then 32amp fuse and 6mm will be ok. Seen some on web but trying to find one that have a left mounted water inlet. Saw a Galaxy 1000 but water inlet is on right. Also it's a Sunday now so all the places that sell 7.5kw are trade centres and are closed.

Do you guys think a 7.5kw will be rubbish compared to what we wanted (a 9.5kw)? Will we notice much difference compared to our Mira Sport 9kw?

OH's dad also said we were thinking about this too much and that 32amp fuse with an 8.5kw would be find as the worst that will happen is the fuse will blow, even though the manual says you need a 40amp. Would having a 32amp in, void the warranty on the shower though?

 

[Luckyphil]

You can buy a variety of 7.5/8.5kw Showers from S-Fix on a Sunday , plus they stock a 9.0kw Mira Sport Multifit from there , excellent piece of Kit with a good Large Shower head and Hose.

Lucky

 

[ban-all-sheds]

Do you guys think a 7.5kw will be rubbish compared to what we wanted (a 9.5kw)?

Yes.

Will we notice much difference compared to our Mira Sport 9kw?

Colder water at the same flow rate, or a 20-25% reduction in flow for the same temperature.

OH's dad also said we were thinking about this too much and that 32amp fuse with an 8.5kw would be find as the worst that will happen is the fuse will blow, even though the manual says you need a 40amp.

You should stop listening to OH's Dad.

The worst that will happen is that the 32A breaker will overheat and eventually fail, or do some damage via overheating.