Total mystery with 10.5kW shower

[randomdave]

Maybe someone can explain this to me ...

I have a 10.5 kW Triton Ivory II shower that has been in the bathroom since before we moved in 3 years ago. Its developed an internal leak - when I take the front panel off and start it up, water squirts out from the temperature control dial. I'm therefore looking to change it and I want to get an equivilent 10.5kW shower unit so as to not loose any performance. I enjoy my morning shower and I don't wish to "down-grade"!

Having explored a little, it turns out that my shower is connected to a 40A fuse via a 6mm cable but (having spoken to an electrician in the family) this is surely impossible! Shouldn't a 10.5kW shower blow that fuse every time I turn it on?! My uncle (who unfortunately lives too far away to come and look) says that the highest power shower that my wiring and fuse should cope with is 8.5kW and I would be wise to replace my unit with an 8.5, but the one I have on that wall blatantly has a sticker on the bottom saying 10.5kW! I don't want to have to go and down-grade for the sake of it, but I equally don't want to buy and fit a shower that wont work! Nothing in my existing setup appears to make sense!

The other option is to try and fix the one I already have. As I said, the temperature dial appears to be dead and I can get a replacement from http://www.onlineplumbingsupplies.co.uk/products/spare_parts/triton_ivory_ii but I don't know how easy that would be to fit or what the chances are of it solving the problem.

Any thoughts? All advice is gratefully appreciated!

 

[randomdave]

Update ... the stabiliser valve (which appears to be the bit I'd need) seems to be discontinued for 10.5kW models anyway. This is looking like being one of THOSE jobs!

 

[stem]

Basically your uncle is probably correct. Most 10.5 kW showers are installed using 10mm cable with 45A or 50A overload protection.

First the fuse, which you say is rated at 40A. This is a rating that it can handle continuously without deterioration. It would take considerably more current over a long period of time before it blows. Your shower will be taking something like 45A, so you are overloading it slightly and for relatively short periods of time, so no, I wouldn't expect it to blow.

Then there's the cable. The current this can carry safely varies depending upon where the cable is installed, the ambient temperature, and if any of it runs in thermal insulation. Enter the details of your installation in the link below and it will calculate the required cable size for you. (the fuse protection is there to prevent the cable becoming overloaded)

Cable calculator

The instructions for your existing shower also say 45A overload, and 10mm cable is recommended. See link below.

Installation Instructions

Repairing the 10.5 kW or fitting a new 10.5 Kw still leaves you with the same scenario.

 

[First-time-buyer]

Not exactly knowing the operation of the shower, i could guess that water flow on expensive showers remains the same, and its the heater that is switched in/out.

Therefore, on a High Setting, with the temperature turned to the Max you could feel 10.5Kw, however on Medium and 1/2 way you might be at 8Kw for example.

Older cheaper showers, when you turned the temperature dial, the flow was reduced and it was noticed when turning it right down to cold, as the shower head would usually move..

 

[ericmark]

Because a shower in not used for long the over load does not have enough time to heat up to the point where it trips and neither will the cable have enough time to over heat.

However with being over loaded on a regular basis the MCB over time will degrade and will in time reach a point where it starts to trip and the time you can shower for will get shorter and shorter.

My instant heat shower is 27kW gas of course you can't get that with electric my father-in-law does not use instant heat but has a storage tank both systems give really good showers but with electric 10.5kW = 45.7 amp so to reduce to 40A = 9.2kW so although slightly over a 9.5kW would likely work with out any problem.

Although you may be able to use 10mm² cable many consumer units just don't have the option of fitting larger MCB's so in real terms yes a 10.5kW may work but getting a 9.5kW would make more sense.

 

[winston1]

10,500/240 gives 43.75 amps. Less than 10% overload for a short time is not going to trip the MCB (as you have discovered). Personally I would not worry about it and replace like for like.

 

[ban-all-sheds]

Personally I would not worry about it and replace like for like.

Yes, but personally you DGAS about doing things properly, do you.

 

[EFLImpudence]

If 230V nominal voltage is used for calculation (can't have it both ways) your present shower is 42A.

My uncle (who unfortunately lives too far away to come and look) says that the highest power shower that my wiring and fuse should cope with is 8.5kW .

He is not right - 9.6kW @ 240V is 40A.

 

[RF Lighting]

Personally I would not worry about it and replace like for like.

You just can't help but post bad advice on here can you?

 

[Taylortwocities]

I have warned WINSTON about THOUGHTCRIME in the past.

Big Brother is watching him…...

 

[JohnW2]

10,500/240 gives 43.75 amps. Less than 10% overload for a short time is not going to trip the MCB (as you have discovered).

In fact, "less than 10% overload" should never cause a Type B MCB to trip, since they are required to carry 13% overload 'indefinitely' without tripping.

Having said that, it is not, strictly, either 'right' or compliant with regs to have any degree of 'designed overload' (in this case Ib > In) - unless it is possible to apply diversity considerations (which is not possible with showers).

Kind Regards, John

 

[westie101]

So the OP says

it turns out that my shower is connected to a 40A fuse

Yet by the 4th answer it has become an MCB, continued in the 10th!

 

[JohnW2]

So the OP says

it turns out that my shower is connected to a 40A fuse

Yet by the 4th answer it has become an MCB, continued in the 10th!

You forgot to mention the 5th one

Yes, I confess that I hadn't noticed that - but what I've just written ("10th") is at least as true of a fuse as of an MCB. A fuse would never operate with "less than 10% overload", and it's as true of a fuse as of an MCB that, strictly speaking, it's neither 'right' nor reg-complaint to have a 'designed' Ib>In.

Kind Regards, John

 

[westie101]

 

[ban-all-sheds]

So the OP says

it turns out that my shower is connected to a 40A fuse

Yet by the 4th answer it has become an MCB, continued in the 10th!

It's not unknown for people to say "fuse" when they've got MCBs.