Fresh 9.5KW Shower Install

Hey all.

I'm just about to install a Triton Martinique 9.5kw shower, a few queries....

CU is an older Qwikline - 100A mains switch. No RCD present at the moment.
After reading through various posts, i gathered that I would need a 45A MCB. However, I've been told buy my local wholeseller that Qwikline don't make a 45A MCB, only a 40A + 50A. So, i'm assuming 50A is the way to go?
I've also been generiously donated a seperate Wylex Shower RCD, 63A + 30mA, to run along side the CU.

So, my questions are, is this installation acceptable? i.e. Purcasing a 50A MCB, connecting from the MCB on to the RCD, then onto Pull Switch, Shower etc etc.

And, what size cable should I be using? Cable run is about 6 Metres, 4 of which will be clipped.
Personally, i'd rather lean on the side of caution, and go for 16mm, but i'd like a educated opinion.


I know some will say, replace the board. But, if I've only got to pay for an MCB, i'd rather go that way.


Many thanks in advance.

breaker size is a tricky one, if you go by the headline fiqures you'd be lead to believe it (the shower) takes 9500/230 = 41.3A however if you read the specs more closely you'll most likely find that its actually 9500@240v and about 8700w@230v, so you actually need to design for a current of 9500/240=39.6A

I think that as long as you meet disconnect times and as long as the cable rating is higher than the breaker rating, which in turn is higher than what the appliance takes ( //www.diynot.com/forums/viewtopic.php?t=7553&postdays=0&postorder=asc&start=21 ), then whether you use a 40A or 50A breaker is somewhat accedemic

And yes, perfectly acceptable to run the shower circuit from an MCB through an RCD then onto the isolator, etc, remember to bit RCD in suitable enclosure first.

As long as you arn't running in a bundle, or through insulation then 10mm² will be the right size to use, 16mm² would be a bastard to terminate (although possible)

Make sure your main and supplimentary bonding is up top scratch, and remember that if you are in england or wales then this work should be notified to your local building control office

The RCD comes in its own dedicated enclosure, so no problem there.
One more question, as ridiculous as it sounds ....
There seems to be nowhere to bond the earths in the RCD! What's the best way to connect them?

As for the cable, the run itself is; 2m clipped, up the wall from the CU, 2m through the loft space, 2m clipped down from the loft to the back of airing cupboard wall, then about 10cm through the wall (Insulated, I assume) into the back of the shower.

Many thanks for the info Adam, it's much appreciated.

10mm T&E if installed single layer spaced has a max current of 57amps so a 50amp breaker is fine. You will need a 50amp pull switch as well if you use a 50amp breaker. Based on your load, the 40amp should be fine type B or C

fazed said:

The RCD comes in its own dedicated enclosure, so no problem there.
One more question, as ridiculous as it sounds ....
There seems to be nowhere to bond the earths in the RCD! What's the best way to connect them?

Click to expand...

Crimps, the earth will be 4mm², so you want a yellow insulated crimp, and put it on using a proper rachet action crimping tool, or I suppose you could use one piece of cable, cut the phase and neutral and leave the earth continous (you wouldn't be able to sleeve it tho )

As for the cable, the run itself is; 2m clipped, up the wall from the CU, 2m through the loft space, 2m clipped down from the loft to the back of airing cupboard wall, then about 10cm through the wall (Insulated, assume) into the back of the shower.

Click to expand...

10mm² cable will be sufficent

type B or C

Click to expand...

Would stick to B for a shower, no reason to use a C, and at the current showers use, the Zs for a C might be difficult to meet.

I'd lean towards a 40A, as the design current at 240v would be 39.6A but I'd be a tad wary of going that close, not sure whether the breaker would weaken over time (anyone about to confirm/deny?)

http://www.tlc-direct.co.uk/Main_In...hite_Contactum_Index/Pull_Cord_B_2/index.html

and a 50 I think

39.6A....I'm assuming that's with the shower running at it's maxiumum heat setting, right?

If so, a 40A breaker should be fine? I doubt that the shower will ever be set at maximum, and even if it did, the load will still be .4A under the breaker value.

Correct me if i'm wrong?!?!

As Adam has pointed out, there is no point running a breaker so near its max when a 50amp breaker will be fine. When I wrote my first post I was not sure if they did a 50amp DP pull switch off the shelve but as they do, a 50amp breaker is better than a 40

Yep Pensdown, I'd agree. But if I'm using a 50A breaker, I'd have to use 16mm cable, as it will run through loft insulation etc etc at some point. I've read 10mm is only good for about 43A when going thru insulation.

I was just trying to see if it was possible to go the 40A route....obviously...there's no easy way around it, and, I'm not going to compromise on safety. 50A it is!

Thanks for all the advice guys.

fazed said:

Yep Pensdown, I'd agree. But if I'm using a 50A breaker, I'd have to use 16mm cable, as it will run through loft insulation etc etc at some point. I've read 10mm is only good for about 43A when going thru insulation.

Click to expand...

there is a school of thought that you don't have to provide overload protection for the shower, because it can't overload the cable (at least unless a DIYer, or painter swaps it blindly for a bigger one)

I was just trying to see if it was possible to go the 40A route....obviously...there's no easy way around it, and, I'm not going to compromise on safety.

Click to expand...

40A satisfies the requirement for breaker rating being over design current and both being below the cable rating. and I don't think you'll have any problems in practice with running the breaker that close to its tabulated rating, my concern was that it might be bad practice to do so.

FWIW, we have a 8.5kw shower on 6mm² cable on a 32A breaker, a cumulation of different peoples DIY bodges, its been like that that for 5 years, the shower has been used every day, the breaker has never tripped, so in practice it hasn't weakened with taking a sustained overload repeatedly

Oh, and a side note, the main temperature control on a shower doesn't actually change the power it takes, just the flow rate (same power + less water = hotter water), if your shower has a separatre On/Off/Cold/Eco (summer) dial (as have most tritton showers), then that one controls the power

Off = Element one = Off / Element two = Off / Water flow valve = Off
Cold = Element one = Off / Element two = Off / Water flow valve = On
Eco = Element one = On / Element two = Off / Water flow valve = On
On = Element one = On / Element two = On / Water flow valve = On

Can you get hold of an RCBO??

I'll bet you have your shower on full all the time we NEVER turn ours down from full power. I would also place a bet that your shower only has 2 heat settings. ours does!

Cant you buy a new enclosure for the RCD and fit a 45A MCB next to it?