ELECTRIC SHOWER - 10.5KW

[BakerMaker]

We are refitting the main bathroom and want to install a 10.5kw electric shower - the Mira Dual Decor to be precise. A new 10mm cable is being installed from the consumer unit. The run is about 11m. It runs through wood / plasterboard and does not touch any other cables along its run. Once in the bathroom it runs through a stud wall - again no other cables present and no insulation along its length. It will obviously be on its own circuit and a currently unused MCB in the consumer unit will be upgraded to 50a - the recommended is 45 but wylex don't seem to make one. There will obviously be a separate pull cord switch in bathroom for the shower. This is all in the planning stage but is there anything else I should be thinking about/need to consider?
thanks in advance

 

[EFLImpudence]

You seem to have it all in hand.

6mm² cable would be adequate.


Crabtree 50A pull switches are best and much easier to wire.
https://www.toolstation.com/crabtree-50a-pull-switch/p34147?searchstr=crabtree 50A

 

[winston1]

There will obviously be a separate pull cord switch in bathroom for the shower.

Not obviously at all. There is no requirement for a separate isolator as isolation can be carried out at your 50a MCB.

Do you have a gas boiler for central heating/hot water? Running your shower off this would be one third of the cost.

 

[BakerMaker]

Yes we have a combi boiler and shower on the ground floor which is very efficient and the main one which will be used. However, we wanted the option of a shower in the first floor where there isn't quite enough pressure to run a conventional mixer and being a combi boiler, we can't install a shower pump - this is the reason we are going for an electric shower. The shower we are opting for requires the abilty to disable it locally hence the pull switch.

 

[bernardgreen]

Melting shower unit, dripping wet you hurry off to find the consumer unit to isolate the mal-functioning shower unit.

 

[winston1]

Yes we have a combi boiler and shower on the ground floor which is very efficient and the main one which will be used. However, we wanted the option of a shower in the first floor where there isn't quite enough pressure to run a conventional mixer and being a combi boiler, we can't install a shower pump - this is the reason we are going for an electric shower.

Seeing as the pressure comes from the mains in either case I can't see what the difference is.

The shower we are opting for requires the ability to disable it locally hence the pull switch.

Who says? If it is the manufacturer pretending it is the regs they are wrong. The only time you need to isolate it is for maintenance. The CU is local enough for that. Never isolate it after every use, you will knacker the pull switch.

 

[winston1]

Melting shower unit, dripping wet you hurry off to find the consumer unit to isolate the mal-functioning shower unit.

Ever heard of this happening? If it was a common or even rare occurrence the regs would require very local isolation.

 

[bernardgreen]

Ever heard of this happening?

Yes,

If it was a common or even rare occurrence the regs would require very local isolation

Common sense and personal safety overide regulations that fail to cover every eventuality.

 

[BakerMaker]

This is the relevant bits from the installation instructions. I seem to remember that most electric showers I've come across (in other people's houses) do usually have some kind of pull switch.

6. This shower must be provided with means for local disconnection that is incorporated into the fixed wiring in accordance with the relevant local wiring regulations. This must be a double pole switch, which has at least 3 mm contact separation in each pole. The switch can be a ceiling mounted pull-cord type within the shower room or a wall mounted switch fitted in the applicable zone area.
7. For new installations a 30mAResidual Current Device (RCD) must be incorporated into the electrical supply to the shower in accordance with the current wiring regulations. When replacing an existing electric shower we recommend that a 30mA RCD is incorporated in accordance with current wiring regulations if not already provided.

 

[EFLImpudence]

Well, 7 is correct. That's something.

 

[Risteard]

Not obviously at all. There is no requirement for a separate isolator as isolation can be carried out at your 50a MCB.

No it can't, as in a domestic premises isolation requires the breaking of all live conductors.

 

[chivers67]

Personally if I was installing a Shower it would have local isolation inside the room, the Crabtree pull cord that ELI posted a link to is what I had on our Instant power shower before we got a Combi boiler and could use that method instead and as above mentioned by Risteard an MCB will only diconnect the Live, the Neutral would still be connected.

It's been mention that the OP has a Wylex board - must be an older style if the Consumer unit doesn't accept anything larger than 40A? Maybe the board needs an upgrade or a Seperate shower isolator supply is required?

 

[BakerMaker]

I think it accepts more than 40A - its just that Mira recommend 45a but Wylex only seem to produce a 40 or a 50 as far as I can make out. I think the unit should be ok - it was fitted about 9 years ago?

 

[EFLImpudence]

The fact remains that the regulations do not require local isolation for any appliances.

They might be a good idea but that does not make them required.

 

[winston1]

This is the relevant bits from the installation instructions. I seem to remember that most electric showers I've come across (in other people's houses) do usually have some kind of pull switch.

Maybe so but it is not a requirement.

6. This shower must be provided with means for local disconnection that is incorporated into the fixed wiring in accordance with the relevant local wiring regulations.

The local wiring regs say nothing about that.