10.8 kw shower connection

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Sorry, this is yet another one of those electrical shower connection questions! Please could somebody advise me if my current set up is suitable for an upgrade to 10.8kw? My current shower is a Redring but without taking it off the wall I have no idea about its rating. It is connected via a 45amp pole switch to what I believe to be a 100A fuse board with 30a trip switches. The cabling is definitely 6mm. I would like to upgrade to a Mira Sport 10.8kw shower. The manual (I have also spoken to Mira who have confirmed this) states that as long as the cable run does not exceed 15mtrs, 6mm cable is fine. Please could someone advise a novice if it is therefore simply a case of swapping the showers over? Many thanks, your expertise is very much appreciated.
 
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6mm cable will be OK if, and only if, the cable is not insulated or buried in a wall (it will get warm, but this is OK if it can cool itself).
Look at the kevin boorn cable selector in 'for reference' for how to deduce what does and doesn't meet the rules. In nay case the 30A trip for the shower circuit will need to be upped to 45A.
Otherwise it might be a straight swap.
(is it 10.8KW at 240V or 230v - this affects the true current drawn - you are rather marginal..)
 
I wouldn't fancy it.

Cable size also depends on where/how the cable is run etc, plus various other factors, voltage drop etc.
Take a look at TLC's cable calculator - this can give you guidance as to what you need:
http://cirrus.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

Is the shower 10.8kW at 240v or 10.8kW at 230v ? Check the manual. You'll need to use the correct figure in the cable calc.

10.8kW at 230v is virtually 47amps meaning 6mm is out the question, as is your 45A dp switch. Even 10.8kW at 240v, 6mm would only suffice if its clipped direct, according to the cable calculator.
 
Many thanks to everyone for their prompt reply! Very impressed and thank you so much. It would appear I failed to include relevant info for example, I only require 8 mtrs of cable and the cable would be contained within a studwork wall (my house is timber frame!). Having checked the voltage is quoted at 240v and using the calculator (cheers Gazzza) the calculator advises that 6mm would suffice but is it better to err on the side of caution? As regards the 45A mcb, are they a straight swap for the 30a already installed? Once again, thanks lads your advice and comments are much valued!!
 
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If the cable is free in the wall, you may be able to pull a new one in using the old as draw wire. Or of course it may be clipped to the studs at 3" intervals...
In general using the next size up of cable is never a problem (unless the terminals are too small !), but using the next size down, might well be.

In general breakers only fit the fuseboard for which they were designed, (so much for 'standards') so a search by maker is what you need... Note the name and number on the old one, and if google can't find it then we can probably tell you if a straight swap 45A part exists.
 

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