Distibution radial protection

[KEVINDOE]

Hi all,

I have a job in progress where a loft conversion has been completed a while ago, since then the property has changed hands and the new owner wants the cu changed and brought up to date.
my problem is with the 16mm t+e supplying the loft conversion c.u.,,I have changed this to a standard 17th edition 5x5 box with the 30m/a protection.
The final circuits are a 8.5kw shower, one ring final, one 100w towel rail, and one lighting circuit.
could any one give some advice on protection for the 16mm t+e, ??
The cable leaves a fcu and is set "loose in a stud wall and then clipped direct in the side of said loft into c.u.
My first thoughts were a 50amp m.c.b. and time delayed 30m/a rcd.
?
Any advice wuold be a great help ,, many thanks

 

[Sintra]

Unfortunately there is no such thing as a 30mA time delayed rcd as it would be useless for the requirements of additional protection.

 

[Amp David]

Which CU have you changed here, the one in the loft or the one feeding the loft?

 

[IQ Electrical]

Which CU have you changed here, the one in the loft or the one feeding the loft?

I was wondering that, if it's the one feeding the loft then surely the distribution circuit will now be 30mA rcd protected from the main consumer unit?

 

[Amp David]

I was wondering that, if it's the one feeding the loft then surely the distribution circuit will now be 30mA rcd protected from the main consumer unit?

Thats what I was thinking

 

[KEVINDOE]

Thanks for replies,,
Loft box has been changed, main box will be done this week, i think im right in saying that the distribution circuit needs r.c.d protection as its in a stud wall, ? it will not be supplied from the main box, this is my reason for help on protecting it , im not coming across very clearly , sorry for that.

 

[Amp David]

The distribution circuit will need protection yes, due to type of cable and the installation methods.

The circuits in the loft then will already have 30ma RCD protection then. Not the best design really, but what else can you do without replacing the cable/installation methods?

 

[KEVINDOE]

Thanks amp david,

Yes, this is my piont, if i r.c.d the distribution circuit, and its tripped, the whole lot goes out, i also have a feeling that they intend to use it as a granny annex at some stage , hence the seperate supply,also, do you think a 50amp breaker would be ok?, is there any issues with using a bigger one in a domestic instalation ?

 

[Deleted member 19807]

The mcb is there to protect the cable so work out any de-rating factors and size mcb on the result.