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?

 

[marconi]

Thank you. I will study tomorrow morning. It is 1830 here now.

 

[marconi]

Forgive the 'questions, questions, questions' but I want to be sure about things.

What size are the conductors in the incoming supply cable with the red, white and brown conductors going to the input to the C63A below?

What size are the three white conductors leaving the C63A and heading to the C40A upstairs?

Is there any space inside the upper consumer unit for either an rcd and mcb or an rcbo? If not is there space 'somewhere' very adjacent for a separate enclosure containing these?

Which of the pairings L1-N, L2-N, L1-L2 has the most spare capacity ie has the lowest kW of connected loads.

What does the C16 to the left of the C63A supply? Is it connected across L1 and L2 ie red and brown/blue

If I remember correctly L1 and L2 are red and blue and N is white (except for the three whites between the C63A and C40A.

Have you found your home's earth electrode?

And should to get the picture straight in my mind, apart from C16 below, the C63 only feeds the C40 above? I ask because it looks like may be some reds go into the bottom left of the C63 - see blue arrow in my attachment.

 

[marconi]

Special locations.

In the UK we have strict regulations for electrical equipment and its wiring in special locations such as wet rooms, bathrooms and showers. I have attached a short video which should help you understand what can and cannot go where. I do not know what is expected in Uruguay. I assume you can find out. You should plan your shower installation carefully which includes positioning and IP rating of lighting, extractor fans, switches and even the running and protection of cables. All cables passing through a bathroom, wet room or shower must be rcd protected.

Will you have underfloor electric heating near the shower?

For any detailed questions on this topic I ask you to rely on the practicing electricians of the EF. I am only introducing you to the requirements.

 

[Yonny24]

Many thanks all.
Will take me a bit of time to make notes to the questions, winter school holidays now so weekends are busy with the kids/family. Also got a big repair to do on our flat roof which takes priority.

First job though is to upgrade the home's earth electrode point outside. These ones here seem to be widely used with an inspection hole. 1.5 metre copper.

Thanks

 

[telectrix]

leave existing rod in, clean connection/s if requred. add another rod 2m away, parallel. up and get a reading.

 

[Yonny24]

leave existing rod in, clean connection/s if requred. add another rod 2m away, parallel. up and get a reading.

Also the current grounding rod is very far from the main consumer box in the front garden 6 metres also from the house. Probably better to place a new one in the backyard which is just 2 meters from the main box in the kitchen.

 

[LastManOnline]

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

View attachment 99255

That's almost certainly an rcbo.It says C16.If it was an rcd it would say "16 amps".

My electric shower is wired in 4mm (its a rented house).Its a T90 si, approx 1 kw larger than yours.The 4mm made me a little nervous at first and I checked the cable regularly for the first year or 2.The supply cable is in mint condition.I dont check it any more.
Before installing another electrode I would check first what kind of supply system you have (TNCS or TT)

 

[123]

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

I take it you have no girlfriend/wife or any daughters then?

To be fair in my own home or on holiday I'm in shower a damn sight longer than 3 minutes too.

 

[Yonny24]

I take it you have no girlfriend/wife or any daughters then?

To be fair in my own home or on holiday I'm in shower a damn sight longer than 3 minutes too.

My misses will spend 15-20 mins and 12 Yr old so the same or more if he has his music playing
Currently we have those Spanish style water heaters (calefon). 1500w element in a 60 ltr tank that hangs on the wall. So inefficient as when you are using the hot water cold water enters the tank at the same time.
As an expat I miss the power showers, no limits and instant hot water.
Wife is always asking is there hot water? When we moved I brought the Triton shower with us in the container but never installed it.

 

[marconi]

Top guy Telectrix who knows his onions - ask him about zones etcetera in bathrooms.

It is a good idea to have some small holes in the cover over the earth rod so that rain water can pass through and keep the ground underneath moist. This is what I have seen in rural southern Italy where my aunt lives which is hot and dry for long period with occasional rain.

To re-iterate - you require an additional electrode close to the consumer unit as Telectrix advised. Use 6 or 10mm2 insulated green yellow cable between it and CU. Don't disconnect the present one further away. You will connect the new electrode to the earth bar in the CU. Two metres away or thereabouts is fine.

 

[Yonny24]

Forgive the 'questions, questions, questions' but I want to be sure about things.

What size are the conductors in the incoming supply cable with the red, white and brown conductors going to the input to the C63A below?

What size are the three white conductors leaving the C63A and heading to the C40A upstairs?

Is there any space inside the upper consumer unit for either an rcd and mcb or an rcbo? If not is there space 'somewhere' very adjacent for a separate enclosure containing these?

Which of the pairings L1-N, L2-N, L1-L2 has the most spare capacity ie has the lowest kW of connected loads.

What does the C16 to the left of the C63A supply? Is it connected across L1 and L2 ie red and brown/blue

If I remember correctly L1 and L2 are red and blue and N is white (except for the three whites between the C63A and C40A.

Have you found your home's earth electrode?

And should to get the picture straight in my mind, apart from C16 below, the C63 only feeds the C40 above? I ask because it looks like may be some reds go into the bottom left of the C63 - see blue arrow in my attachment.

What size are the conductors in the incoming supply cable with the red, white and brown conductors going to the input to the C63A below?
hard to tell tbh but looks like 6mm2 but appears a little thicker than the ones leaving to upstairs. May just have thicker insulation?
I understand that because it has 2 x 6mm2 cables for L it can handle that substantial current for the underfloor heating etc.

What size are the three white conductors leaving the C63A and heading to the C40A upstairs?
6mm2

Is there any space inside the upper consumer unit for either an rcd and mcb or an rcbo? If not is there space 'somewhere' very adjacent for a separate enclosure containing these?
I can install a separate enclosure adjacent.

Which of the pairings L1-N, L2-N, L1-L2 has the most spare capacity ie has the lowest kW of connected loads.
Note sure tbh - but I assume the pair that supplies the rest of the lower floor C16 rail has the highest kW usage.

What does the C16 to the left of the C63A supply? Is it connected across L1 and L2 ie red and brown/blue

Just a small C16 and RCD for a few exterior appliances at the end of the garden for some led lights/small pool pump and router.
I wanted the exterior appliances on their own circuit and RCD so if they tripped it would not trip the whole house.


If I remember correctly L1 and L2 are red and blue and N is white (except for the three whites between the C63A and C40A.

Have you found your home's earth electrode?
Yes, but as discussed I will install a new one closer to the CU on the other side of the house with a new 6mm earth cable.

And should to get the picture straight in my mind, apart from C16 below, the C63 only feeds the C40 above? I ask because it looks like may be some reds go into the bottom left of the C63 - see blue arrow in my attachment.
This C63 in the main CU also supplies a rail of C16 breakers below that feed the lower floor lighting, and sockets for the living room, dining room, and kitchen.

 

[marconi]

Thank you . I will study tomorrow morning.

 

[marconi]

I have been re-reading the discussion we had on your uf. I found this post by you:

Here we have the ground floor contactors. 4 thermostats (cheap copies of Honeywell and do not work well at all). Installing a central digital thermostat that will send a signal to the sonoff switch in the fuse box.

Living room
Dining room
Breakfast room and kitchen (2 zones).

Living room about 11-12m2 consumes about 2000 kwh.
Dining room a little less and kitchen/breakfast about 1800 combined.

No more than 6000 kwh. (230v)

Could you confirm that you are reporting the power in kW of the ufh in these rooms and not their power consumption in kWh.

If you are reporting power in kW can you tell me how the power in spread over the three lines? I cannot open up any earlier diagrams you produced. Is each room’s ufh fed by it’s own breaker, a 20A I seem to remember? I vaguely remember we installed two power meters and after these the ufh was equally split over the lines.
Are these rooms ufh all supplied from the same board (via the C40breaker)?

Do you have an electric oven and an electric hob? If yes what lines do they connect to And via what size breakers. To which board does the oven and hob connect to? Can you see the power of these appliances on their spec plates?

Let me tell you that what I want to confirm is the shower can safely be supplied after the C40 breaker between L1 and N or L2 and N, the pair selected having the capacity to provide 28A for the shower and with 12A remaining for everything else which may by drawing significant current While the shower is on. So shower, oven, hob and a third of the ufh on one L-N pair would be a problem Since 28 + 10 + 20 + 10 = 68A Which would trip the C40. whereas shower plus 1/3 of ufh would be 28 + 10 = 38A which would not trip C40.

 

[Yonny24]

I have been re-reading the discussion we had on your uf. I found this post by you:

Here we have the ground floor contactors. 4 thermostats (cheap copies of Honeywell and do not work well at all). Installing a central digital thermostat that will send a signal to the sonoff switch in the fuse box.

Living room
Dining room
Breakfast room and kitchen (2 zones).

Living room about 11-12m2 consumes about 2000 kwh.
Dining room a little less and kitchen/breakfast about 1800 combined.

No more than 6000 kwh. (230v)

Could you confirm that you are reporting the power in kW of the ufh in these rooms and not their power consumption in kWh.

If you are reporting power in kW can you tell me how the power in spread over the three lines? I cannot open up any earlier diagrams you produced. Is each room’s ufh fed by it’s own breaker, a 20A I seem to remember? I vaguely remember we installed two power meters and after these the ufh was equally split over the lines.
Are these rooms ufh all supplied from the same board (via the C40breaker)?

Do you have an electric oven and an electric hob? If yes what lines do they connect to And via what size breakers. To which board does the oven and hob connect to? Can you see the power of these appliances on their spec plates?

Let me tell you that what I want to confirm is the shower can safely be supplied after the C40 breaker between L1 and N or L2 and N, the pair selected having the capacity to provide 28A for the shower and with 12A remaining for everything else which may by drawing significant current While the shower is on. So shower, oven, hob and a third of the ufh on one L-N pair would be a problem Since 28 + 10 + 20 + 10 = 68A Which would trip the C40. whereas shower plus 1/3 of ufh would be 28 + 10 = 38A which would not trip C40.

Many thanks Marconi.

Before I go into details later it does look like it will not provide enough power if we were to have the shower on plus the electric hob/oven we have (which goes to the C16 breakers - induction hob is a low current type with a 13amp fuse plug attached.) and UFH.
The UFH on the lower floor is 6000W approx. (Living room 2000w) which I believe is split between L1/N,L2/N. Yes all go through the C40 but the UFH does have its own CU adjacent with another breaker and RCD.
We only use 2 zones of the UFH now during the winter for about 2 hours a day - about 3800W per hour.

The utility company provides a fixed kwh service that can be upgraded but at an extra monthly cost (fixed fee).

If we were to install the shower on the current contract with C40, it appears that we would need to ensure the UFH is off while in use which isn't ideal. Fine in summer but now we'd need to switch the UFH off if anyone is switching on the shower I'm sure.
An automation could be created in my smart home as the contactors for the UFH are turned on by wifi switches - could be one or the other, never both on at the same time.

Ours is the 15* contract shown below. I assume if it was upgraded to 20 or 25* then they would also upgrade the C40 to a higher rating. I will anyway ask how much more to upgrade if even possible. The cabling to the house may be a limitation.

​

Suministro Trifásico (potencia en kW)
6, 8, 10, 12 *
15 *
20 *
25 *
30 *
35 *
40 *
41 a 50 *

 

[marconi]

There is a way of detecting when the shower is switched on and then switching off large loads until the shower is turned off - a shower priority unit. This would work well if the shower and some of the ufh were supplied by the same LN pair. It would not matter that the ufh was off for a little while. Something like this:

Garo Priority Shower Board 6 Amp IP40 1 Row - https://www.meteorelectrical.com/distribution-control/consumer-units-accessories-1/garo-priority-shower-board-choose-priority.html