Electric Shower Wiring

[ibby]

Hi Guys,

I have had an electrician come along and do my first fix.

I was going to replace my vented system via a big combi boiler, but the maintenance costs and if it breaks down - repair costs have put me off.

So I have decided to run a combi boiler, 33KW for downstairs with an electrical shower upstairs.

My electrician didnt run any first fix cables for the upstairs shower as he was under the assumption that it would be all running off the boiler.

I went out to screw fix and purchased 10mm 2 core rated cable. I rather than waste his time asking him back to run a length of cable, I just need to understand;

- Will the cable run directly to the shower?
or will it
- terminate into a fused box / on off box and then another length will run to the shower ?

I won't be wiring anything up, just running the cable and creating some slack so he is able to wire-up without any issues.
Thanks

 

[Risteard]

No Electrician will connect this up for you after the fact. You need to engage your Electrician to do this job now and not fire it in yourself.

 

[ibby]

No Electrician will connect this up for you after the fact. You need to engage your Electrician to do this job now and not fire it in yourself.

Really,

even If I take pictures of the run and run them along the same way hes bought the wires upstairs to the loft. ( Its all open loft conversion.)

 

[winston1]

I was going to replace my vented system via a big combi boiler, but the maintenance costs and if it breaks down - repair costs have put me off.

So I have decided to run a combi boiler, 33KW for downstairs with an electrical shower upstairs.

Time to re consider. Running off the combi boiler will give a better shower than electric. The biggest electric showers are around 8kW, far less than the 33kW output of your boiler. Electricity costs three time as much as gas. Modern combi boilers come with long guarantees (7 years) so breakdown repairs costs don't come into it.

 

[ban-all-sheds]

I rather than waste his time asking him back to run a length of cable...

But it won't be a waste of his time, and it will be more than just running a length of cable. There will be the calculations to ensure the right cable is used, and then there will be the testing and certification.

 

[charliegolf]

Time to re consider. Running off the combi boiler will give a better shower than electric. The biggest electric showers are around 8kW, far less than the 33kW output of your boiler. Electricity costs three time as much as gas. Modern combi boilers come with long guarantees (7 years) so breakdown repairs costs don't come into it.

We have both- the leccy one is handy when the boiler breaks down! (Not in the same space!)

 

[ban-all-sheds]

I feel the same - things do break down, even when maintained, and a guarantee, be it for 7 years or 70 doesn't prevent breakdowns. Loss of gas CH can be worked around, but cold showers are pretty damn miserable.

Rather than have an electric shower as a backup, if you get an electric heater which has proper thermostatic control, and can therefore be used with a thermostatic shower mixer, this becomes an option:

(The heater and valve can go in a cupboard).

 

[charliegolf]

I like that idea...

 

[ban-all-sheds]

Do note that this aspect:

... an electric heater which has proper thermostatic control ...

is absolutely vital. Heaters which adjust the temperature of the output by controlling the flow through the heater cannot be used.

 

[ibby]

But it won't be a waste of his time, and it will be more than just running a length of cable. There will be the calculations to ensure the right cable is used, and then there will be the testing and certification.

I had a chat with him, he's going to run some calculations and come back to me.

sounds like he may send out one of his underlings to put the wire in

 

[ibby]

Do note that this aspect:

​

is absolutely vital. Heaters which adjust the temperature of the output by controlling the flow through the heater cannot be used.

I though all electric showers controlled the heating aspect themselves ?

 

[ibby]

We have both- the leccy one is handy when the boiler breaks down! (Not in the same space!)

Thats one other reason why I went for an electric shower upstairs nothing like a crap cold shower

 

[ibby]

I feel the same - things do break down, even when maintained, and a guarantee, be it for 7 years or 70 doesn't prevent breakdowns. Loss of gas CH can be worked around, but cold showers are pretty damn miserable.

Rather than have an electric shower as a backup, if you get an electric heater which has proper thermostatic control, and can therefore be used with a thermostatic shower mixer, this becomes an option:

(The heater and valve can go in a cupboard).

I like this idea, what parts do I need to use ? and more interestingly does any have this working

 

[ban-all-sheds]

I though all electric showers controlled the heating aspect themselves ?

An electric shower is just an instant water heater packaged up into a wall mounted thing with the controls on it.

I'm talking about a heater like these: https://www.redring.co.uk/catalogue/water-heating/instantaneous-water-heaters/powerstream/

Although that make is no good for the application shown in my diagram. It works in the same way that many/most electric showers work, which you're probably familiar with - the heater runs at a constant power (maybe on one of two settings), and you control the temperature by adjusting the rate of flow of water through the heater. The temperature knob is a valve. More water through the shower = cooler temperature, less water = hotter.

But that's no good if you want to put a normal shower mixer valve on the output, as the way they work is at odds with the way the heater works. With a shower mixer, if it's too hot, you turn the knob and the mixer reduces the amount of hot water being used and increases the cold. If the hot water comes from one of those electric heaters then when the flow is reduced by the shower mixer it gets hotter. So you turn the mixer knob a bit more, and reduce the hot flow a bit more, and the hot water gets hotter. This cycle continues until the heater over-temperature cutout shuts it down. Similarly if your shower water is too cool, you call for more hot water using your mixer, and increased flow through the heater makes the water cooler. Redring do make a mixer designed to work with their instant heaters, and it doesn't look too bad,

but it won't necessarily match your other fittings, and if it's a backup it means having that as well as your normal shower mixer.

There are some showers with thermostatic controls which don't work that way - they modulate the heater, but instant heaters which do that are rarer, and you couldn't repurpose one as a heater supplying a mixer shower as you must not have taps on the output. There is this heater: https://www.electric-heatingcompany.co.uk/product/bonus-instant-water-heater/ and I have asked them, and they say that it is OK on a normal mixer, so if they make one, possibly other companies do.

 

[securespark]

The biggest electric showers are around 8kW

They are?