50 amp mcb on 40 amp RCD for shower unit

[grahamdoc]

Hi I have a 40amp RCD shower unit and am replacing the current 40amp mcb on this to 50amp to fit a new more powerful 10.5kw shower. The wiring is 16mm. Is this OK?

Thanks in advance
Grahamdoc

 

[Taylortwocities]

That 16mm cable. How are you measuring the 16mm?

 

[Chri5]

Hi I have a 40amp RCD shower unit and am replacing the current 40amp mcb on this to 50amp to fit a new more powerful 10.5kw shower. The wiring is 16mm. Is this OK?

Thanks in advance
Grahamdoc

Whats a 40 amp RCD unit ?


Or do you mean "I have a 40amp mcb with RCD at the fuse board controlling the shower circuit"?

A 10,500 watt shower divided by 230v is just under 46 amps of load.

So the shower mcb should be update to 50 amp mcb. A 16mm should cope with the extra load BUT

1- What is the lenth of run between fuse board (CU) and the shower isolation pull switch ?
2- How does the cable run
3- What does the cable run in
4- How you going to test the circuit with the new MCB

Would you please consider the safety of you and yours, the unsafe nature of water and electrics and confirm that you have no intention of doing the work without testing the works safety after ?

 

[skenk]

You need to be able to confirm the installation method of the cable (is it in trunking, insulation, plaster etc.). Also how are you measuring (how do you know) the cable is 16mm?

 

[davelx]

impossible to say without more information. For a start:

1) How long is the cable run

2) How is the cable installed - what environments does it run through - trunking, conduit, insulation etc?

3) Is the cable grouped with others, if so how many and what loads do they each carry

4) What is the Ze of your installation?

(cue sound of multiple posts colliding )

 

[skenk]

A shower advertised at 10500w is normally at 240v so the actual load using the nominal voltage calc is 43.75A.

 

[Chri5]

5 posts in 5 minutes, all sort of saying the same thing.

re: manufactures figures based on 240v, and me (as I keep on doing) working to the 230v design rules per NICEIC inductions and courses.

 

[ajrobb]

One example where it would not be suitable is Reference method 103; in a stud wall with thermal insulation with cable not touching the inner wall surface (42.5 A).

The cable should not be more than 97 m long.

 

[Chri5]

The cable should not be more than 97 m long.

Big house

 

[grahamdoc]

Thanks all for the information folks. Ive uploaded 3 images to explain this better. Its the 40amp fuse in the mcb that im changing with a 50 amp. The RCD is 40amp but only replacing the fuse on this. Do i need to replace the whole RCD to a 50 amp one?

The wire from the shower into the RCD is 16mm. The length of this wire in 7metres

ps I will not be doing this myself

Images are taking a while to upload - will be here

//www.diynot.com/network/grahamdoc/albums/

large grey wire measured with ruler

 

[DetlefSchmitz]

You need to specify how you measured the 16mm.

 

[RossR]

large grey wire measured with ruler

Do you mean you measured the width of the cable and it was about 16mm? If so, it is most likely 10mm² conductor cross sectional area, which is confusingly often referred to as 10mm cable. This might be OK, or it might not. It depends on the route the cable takes. The RCD will need to be uprated in any case.

 

[1john]

16mm diameter cable is not the same as 16mm2 cable. the figures used for cables refer to the csa of the live conductors.

 

[ban-all-sheds]

ps I will not be doing this myself

Then leave it all alone, and let the person who you'll be wanting to sign to say he designed it and he installed it to select the right protective devices and the right cable.