Loft conversion sub main & diversity

[Gringoking88]

Hi all,

I am currently having a loft conversion completed and want to put in its own board in the loft. The main reason for this is if in the future, I want to let it out as a self contained unit, it will be much easier.

The conversion will initially have a ring main 32 amp and a lighting circuit 6 amp, however, I want to provide the wiring for a possible shower circuit and a cooker circuit, e.g. have the wires in the walls just not connected at either end.

My question is two fold:

A) would you guys use 10mm SWA from a henley block via an adapatable box from the main meter tails to feed the new board?

B) Caclulating diversity from the onsite guide I make the total load to be 69.3amp
Cooker 16amp (32amp mcb)
Shower 40amp (40amp mcb)
Lights 0.5amp (6amp mcb 20 led downlights)
Sockets 12.8amp (40% of 32amp)

Its this figure that seems exceptionally high given what it is, I guess I am miscalculating diversity????

Many thanks,

Martin

 

[Spoon]

What size is your main fuse?
I don't think you have thought this through properly mate.... or I have mis-read your post.
You intend to use 10mm cable from the meter to the new CU in the loft? This is too small. Also, anything over 3 meters has to have a fused isolator.
If you are having a shower and the loft shower is being used at the same time, then you will have about 80 amps there alone.
You may wish to scrap off the electric shower.

 

[Gringoking88]

What size is your main fuse?
I don't think you have thought this through properly mate.... or I have mis-read your post.
You intend to use 10mm cable from the meter to the new CU in the loft? This is too small. Also, anything over 3 meters has to have a fused isolator.
If you are having a shower and the loft shower is being used at the same time, then you will have about 80 amps there alone.
You may wish to scrap off the electric shower.

Hi,

Sorry, yes I was going to use a 10mm cable but only to supply the loft conversion and the circuits listed on my original post, I would also use a fused isolator. The main fuse is 60amp.

It would only be the loft that would have an electric shower an nowhere else as the rest of the house is on a combi. If the time comes to let it out I dont want it to affect the rest of the house.

Thanks for the reply and sorry if I was not clear.

Martin

 

[Spoon]

Oh, ok. I thought your main fuse was going to be bigger than 60A.

I would also use a fused isolator.

What sized fused isolator are you thinking of using?

 

[Gringoking88]

Oh, ok. I thought your main fuse was going to be bigger than 60A.



What sized fused isolator are you thinking of using?

I was going to use a 63amp dp fused isolator switch

 

[Spoon]

I was going to use a 63amp dp fused isolator switch

Sorry mate. What I meant was, what size fuses are you thinking of using?
Considering that you only have a 60A main fuse and you need discrimination.

 

[Leesparkykent]

Never going to achieve discrimination with a 60A main fuse but I don’t really see that being an issue in this case. If you use the general rule of thumb of 1.6:1 for discrimination between fuses then with your 60A cutout that gives you 37.5A. If your cutout could be upgraded to 100A then that gives you 62.5A if you deem discrimination or selectivity as it’s now defined in the BBB necessary. I would install a switch fuse to adhere to DNO terms of use etc.
If it was me then I’d probably use 16mm T&E and install it in such a manner that additional protection wasn’t required by means of a 30mA RCD.

 

[bill01803]

Get cutout upgraded, last one I had done was free, and run 25mm split con to loft then you can cover all bases

 

[mickfred]

You could come off the main board with a MCB (if the board is rcd protect ed)