MCB for cooker

[Shropshire]

Our old kitchen / hob have been removed (they were separate units). They were supplied by 6mm cable and 32a mcb.

The location of the new oven (requires only 13a) is being located further away from the existing cable (see above). We won't be having a hob.

Can I extend the existing cable with a lower size cable and downrate the mcb to 16a?

 

[Murdochcat]

Maybe consider extending the circuit in 6mm and fit a 13A socket for the oven?

That would allow for maximum flexibility in the future

 

[morqthana]

We won't be having a hob.

Not of any type?

 

[Shropshire]

Not of any type?

No, we have an AGA for normal use. The oven is for emergencies (like Christmas day!)

 

[pete01]

You could extend in 2.5mm and fit a 13 amp socket but I like the 6mm future proof answer better.

Now you'll have a socket it'll need rcd protection unless the cooker circuit already has it.

 

[Shropshire]

Maybe consider extending the circuit in 6mm and fit a 13A socket for the oven?

That would allow for maximum flexibility in the future

Thanks, yes that was my first thought, but I don't have any 6mm cable at present, hence looking at other options.

 

[ericmark]

My copy of BS 7671 is old, it says

433.2 Position of devices for protection against overload
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.
NOTE: A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.

So it would seem you will need to use a FCU, maybe someone can say if this has changed.

 

[Shropshire]

My copy of BS 7671 is old, it says So it would seem you will need to use a FCU, maybe someone can say if this has changed.

By reading the 433.2.2, it seems I can add a FCU at the after the reduction as my length of cable will be approx 1 metre.

 

[morqthana]

My copy of BS 7671 is old, it says So it would seem you will need to use a FCU, maybe someone can say if this has changed.

What do 433.2.2 & 433.3 say in your copy?

 

[ericmark]

What do 433.2.2 & 433.3 say in your copy?

433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor if the part of the run between the point where a change occurs (in cross-sectional area, method of installation, type of cable or conductor. or in environmental conditions) and the position of the protective device has neither branch circuits nor outlets for connection of current-using equipment and fulfils at least one of the following conditions:
(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) Its length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum, and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons (see also Regulation 434.2.1).
433.3 Omission of devices for protection against overload
This regulation shall not be applied to installations situated in locations presenting a fire risk or risk of explosion or
where the requirements for special installations and locations specify different conditions.

 

[SUNRAY]

It's perfectly OK to add a 2.5mm² spur on a 32A circuit as long as downstream OCD is fitted, is there a reason it should be unacceptable to extend a 32A circuit with 2.5mm² as long as downstream OCD is fitted.

 

[pete01]

It's perfectly OK to add a 2.5mm² spur on a 32A circuit as long as downstream OCD is fitted, is there a reason it should be unacceptable to extend a 32A circuit with 2.5mm² as long as downstream OCD is fitted.

Of course, its exactly the same as a ring final spur.

 

[ebee]

My preference would be to continue with 6.0 cable as being the simplest answer, I would normally already have such cable but a DIYer might not though.

Providing that three things are covered (if required) then all well and good:-
1/ Overload.
2/ Short Circuit.
3/ Earth Fault.

1/ Overload protection may be omitted if the nature of the load renders overload impossible.