Shower replacement

[Harry Bloomfield]

It happens that ARW formulated :

Or use oxygen free copper pipe :oÞ

[Joe Bloggs]

Thanks again for that. What about running the shower through a 50A 30mA RCBO fitted on the non-RCD side of my CU?

[ARW]

I agree.

[ARW]

Then get a pro in. A TT supply should not have a non RCD side.

[John Rumm]

Under the insulation you *must not* do in this circumstance - even with

10mm^2 cable. Assuming you have 100mm or more of insulation that would mean you are using installation method 101 which would drop the tabulated current carrying capacity of the cable to 36A (and that is if it remains in contact with the plasterboard below - its even lower if surrounded by insulation). See the table here:

also look at the insulation methods here:

(note there are many more scenarios described in BS7671, but the ones listed there are the most commonly applicable to domestic wiring).

So above the insulation is vastly preferable. (and leave a bit of space round it where it goes through the insulation on the way up and down)

Note also that if the airing cupboard is normally above 30 degrees, then you may also need to allow for some de-rating due to ambient temperature. See the table 4B1 here:

So long as you don't complicate it with running cables in insulation then the 10mm^2 cable is good for up to 64A, which will be more than adequate by a long way. (in reality, even the 6mm^2 cable would be ok on a 10.5kW shower)

Not going to make much difference in this particular case...

I take it your incoming main fuse is rated at 60A or better? (otherwise a more powerful shower may push you close to the limit with other household loads).

[Joe Bloggs]

There is nothing connected to the non-RCD side of the CU. But what would be wrong with taking the shower supply from it through a 30mA RCBO?

[Joe Bloggs]

Ok, thanks. I certainly won't run it under the insulation then.

The incoming fuse is 80A.

[rick]

Electric Showers taken a big leap in power since I last installed one. Think it was around 6 or 6.5kW

[Harry Bloomfield]

rick brought next idea :

They have changed in capability too. The original showers were only really usable in summer and you had to adjust the flow, to set the temperature.

Modern ones are usable in winter and the control system is much more clever. On mine you just set the temperature you desire and it modulates the water flow and current to achieve that.

[tabbypurr]

should support the full 100A if you run the pipes through the CU :) 24kW.

NT

[John Rumm]

As you are probably aware, all circuits must have RCD protection on a TT install. Typically this was done with a 100mA time delayed RCD on the incoming side of a traditional split load CU to protect "everything", and then other 30mA RCDs would protect circuits where "direct contact" protection (or "basic protection" as its now called) was required.

A traditional split load with shared RCDs on one side, and then all RCBOs on the other is also fine for TT. (all RCBOs being the "nicest" option).

[Joe Bloggs]

I am a 'pro', and I was a 'pro' when you were in short trousers, but I am not an electrician.

My world was machine control, telecommunications and electronics, and my qualifications in that area of the electrical world are a great deal higher than most electricians. But domestic electrics are not my thing, and therefore I am not completely au fait with all the regulations that apply. That's why I generally seek advice from those that are before I do anything, and I am very grateful to those here who have been generous with their help and advice. Advice which I shall be careful to take heed of.

I can assure you, that I am no fool, and if I come over that way it is largely because I don't believe in pretending to know things that I clearly don't. The electrical world is vast, and contains many specialities and disciplines, a world where it is possible to be an expert in some aspects and know very little about others. It is also one, like most others, that the more you know the more you realise how little you know. Clearly you haven't got there yet.

[ARW]

Nothing, I was looking at your 50A MCB post:-(