7kw electric shower - 4mm2 too risky?

[Yonny24]

Hi all,

Been a while since I've posted - got a new project to install a small 7kw electric shower.

The shower will be about 7 metres from the main fusebox on the upper floor.
There seems to be a lot of debate about 4mm2 or 6mm2 wiring.

Due to the diameter of the wall conduits, I doubt very much I'll be able to fit 2 x 6mm2 cables in there so I was thinking of 4mm2.

Obviously, I want to keep it all safe. Would I get away with 4mm2?

If I used 4mm2 would I need to keep it outside of the wall in the air?

The house has electric underfloor heating and all is cabled with 4mm2 also between the lower and upper fuseboxes (short distance about 1.5 metres).

We rarely use the underfloor heating on the upper floor - only the small bathrooms rated at 300w.

Both floors have the usual master circuit breakers, RCD's etc.

The house is installed with a 'three phase 2 wire corner grounded delta' btw

Thanks!

 

[James]

If you want us to double check your cable calculations, just post them here.
it would be unusual for a diy person to install a shower because of the building control notification and certification can be troublesome.

do you have an electrician that you have used before and can trust or are you looking for one?

 

[Yonny24]

If you want us to double check your cable calculations, just post them here.
it would be unusual for a diy person to install a shower because of the building control notification and certification can be troublesome.

do you have an electrician that you have used before and can trust or are you looking for one?

Nobody has electric showers here in Uruguay. I brought it from UK.
I have zero trust in electricians here (especially with an electric shower that they most probably have never seen before), many times I've had to fix and improve electrical installations done by previous owners using so-called qualified electricians!
I research well and make sure everything is installed correctly first.

The model is a Triton Seville

 

[Avo Mk8]

I understand the mains voltage in Uruguay is 220V.

The Triton Seville spec shows the 7.5kW is at 240V

By my calculations, and assuming it is a resistive (7.67 ohm equiv.) load, the current it will take on 220V is 28.7A

I think two 4mm singles in conduit would be OK, perhaps others here can comment. Don't know what your regulations require in Uruguay

 

[Dustydazzler]

I wouldn't have any issues wiring such shower in 4mm at such a short cable run on a 32amp device

Shower will only being pulling load for 4-5 minutes for a normal persons shower

In a perfect world we would all use 6mm but if space is tight in an existing conduit system I myself would just use 4mm

 

[Yonny24]

I wouldn't have any issues wiring such shower in 4mm at such a short cable run on a 32amp device

Shower will only being pulling load for 4-5 minutes for a normal persons shower

In a perfect world we would all use 6mm but if space is tight in an existing conduit system I myself would just use 4mm

That's good to know thanks.
Makes the installation 100 times easier.
First few runs I'll keep an eye on the temp of the cables though

 

[marconi]

Would someone cover equipotential bonding please and nearby double pole pull cord isolating switch with neon or on/off indicator .

Make sure the 30mA RCD and the 32A typeB mcb are double pole. If you can it would be neater to use a combined RCD and MCB called an RCBO.

 

[Dustydazzler]

That's good to know thanks.
Makes the installation 100 times easier.
First few runs I'll keep an eye on the temp of the cables though

I would be very surprised if the cables get warm to the touch after a normal length shower (3-4 minutes)

Cables only tend to get very hot to touch after a good while of constant overload

 

[marconi]

Connect across lines with lowest loading.

What is the size of the main fuses/circuit breakers?

Can you see thick earth conductors connecting your main earth terminal to incoming gas and water pipes? Is pipework within home plastic or metal or a mixture of both.

Check there is a thick earth conductor between main earth terminal and to an earth electrode.

Photos are helpful.

 

[Yonny24]

Connect across lines with lowest loading.

What is the size of the main fuses/circuit breakers?

Can you see thick earth conductors connecting your main earth terminal to incoming gas and water pipes? Is pipework within home plastic or metal or a mixture of both.

Check there is a thick earth conductor between main earth terminal and to an earth electrode.

Photos are helpful.

Hi Marconi,

No there aren't any connections to pipes. Al the water pipes are modern green thermofusion plastic-type and we do not have gas pipes.
I will need to install an earth wire through the conduit from the bathroom to the fusebox though. 4mm2 also?

MCB and RCD:


Thanks

 

[Yonny24]

Would someone cover equipotential bonding please and nearby double pole pull cord isolating switch with neon or on/off indicator .

Make sure the 30mA RCD and the 32A typeB mcb are double pole. If you can it would be neater to use a combined RCD and MCB called an RCBO.

Is this an RCBO? It says in Spanish translated - 'circuit breaker - RCD'.
Thanks

 

[marconi]

Is this an RCBO? It says in Spanish translated - 'circuit breaker - RCD'.
Thanks

View attachment 99255

No. That is an rcd and a double pole one rated at 16A. I will send info on an rcbo once we decide on what is practical to fit.

yes you will need to run a 4mm2 circuit protection conductor from consumer unit to the shower.

The sassin is rated at 40A. Please take a picture of the front of it when turned off so I can confirm what poles it switches.

the Schneider rcd to the right of the power meter is only rated for 25A so you cannot feed the shower via it.

please carefully take the cover off the consumer unit, keep you fingers and any tools out if it and then take a picture of inside it so I can confirm how many lines are present.

I seem to remember without going back to our previous posts that you have another ‘fuse box’ at the point where the electricity company provides your supply. If my memory is correct please take a photo of it so I can see the fuse/mcb ratings.

Also take a picture showing all the outgoing ways of the cream consumer unit and label what they are for.

And I note that all water pipes into and in your house are plastic ones.

enough for now.

 

[Yonny24]

No. That is an rcd and a double pole one rated at 16A. I will send info on an rcbo once we decide on what is practical to fit.

yes you will need to run a 4mm2 circuit protection conductor from consumer unit to the shower.

The sassin is rated at 40A. Please take a picture of the front of it when turned off so I can confirm what poles it switches.

the Schneider rcd to the right of the power meter is only rated for 25A so you cannot feed the shower via it.

please carefully take the cover off the consumer unit, keep you fingers and any tools out if it and then take a picture of inside it so I can confirm how many lines are present.

I seem to remember without going back to our previous posts that you have another ‘fuse box’ at the point where the electricity company provides your supply. If my memory is correct please take a photo of it so I can see the fuse/mcb ratings.

Also take a picture showing all the outgoing ways of the cream consumer unit and label what they are for.

And I note that all water pipes into and in your house are plastic ones.

enough for now.

Thanks will get some new photos taken later. I looked at my old post with all the photos but they are not accessible anymore. Possibly been erased?
Our house does have a fairly heavy-duty power supply coming in- rated to supply 15,000w (3 -phase) at least for the underfloor heating in 10 rooms, plus all the appliances etc (we only use 2 of these 10 floor heating zones for 2 hours a day)

 

[marconi]

Thanks will get some new photos taken later. I looked at my old post with all the photos but they are not accessible anymore. Possibly been erased?
Our house does have a fairly heavy-duty power supply coming in- rated to supply 15,000w (3 -phase) at least for the underfloor heating in 10 rooms, plus all the appliances etc (we only use 2 of these 10 floor heating zones for 2 hours a day)

Assuming 15kW is the figure then over ‘3 phases’ (actually two lines and a neutral) that is 5KW a ‘phase’ which is not enough to run a 7.2KW shower which is single phase and must be connected across L1-N or L2-N or L1-L2. This why we need to check carefully your supply is adequate.

 

[Yonny24]

Assuming 15kW is the figure then over ‘3 phases’ (actually two lines and a neutral) that is 5KW a ‘phase’ which is not enough to run a 7.2KW shower which is single phase and must be connected across L1-N or L2-N or L1-L2. This why we need to check carefully your supply is adequate.

The 1st photo shows the main consumer box with the exterior cable coming in with the thick red, white and brown cables.
Then the 3 white cables shown with the arrow are the ones that go upstairs to the upper floor consumer box.

The 2nd photo shows the main MCB with the 3 white cables coming in from the lower floor main consumer box. 3 of these split off into a separate circuit for the floor heating.

I guess the shower RCBO(or RCB and MCB) 32A would be fed from the thick white cables that come directly from downstairs
BUT I see the main circuit breaker downstairs is a C63 isn't it (which would support the 15000W)?
The shower manual states if the house does not have an 80A or more main switch then a consumer unit serving just the shower would be required.

Not sure why the manual states 80A. Is this a UK requirement perhaps?