Cable sizes

[bernardgreen]

Is this wrong and if so why ?

MCB is 16 amp. Cable from CU is 10mm² for a run of 45 metres to a 60 amp junction box ( only size that would take the 10 mm² ). From the JB a metre of 2.5mm² goes to an FCU with 13 amp fuse. From the FCU less than a metre of 2.5mm² to feed a 13 amp unswitched socket under work top for 2.8 Kw cooker.

The JB is accessible, the FCU cannot take 10mm² The CU is labeled with 16 Amp Max over the MCB

Reason for 10 mm² is to reduced voltage drop and power wastage in the 45 metre run.

The jobsworth objector is saying that in the future some one will see 10mm² in the MCB and assume it is safe to up-grade to a 32 or 40 amp MCD leaving the 2.5mm² at the far end without safe protection.

Would he have been better to have come from the CU in 2.5mm² to a 60 amp JB and run the 20mm² from there.

 

[festa]

Cant see much wrong if the FCU is labeled up as to its purpose and like you have done already marked up on the C.U as to the purpose for the 16amp MCB.
Suppose you could draw out a diagram with measurements for the dedicated circuit and leave them inside the C.U cupboard.

I know you shouldn't drop down cable size at a junction box but your 16amp clears protection ratings for the lowest cable in the circuit @ 2.5mm.

personally i would have just run the entire circuit in either 4mm or 6 mm to the FCU and then 2.5mm from that down to the socket.

 

[securespark]

I can't see anything wrong if you label up how the circuit is constructed. The jobsworth talketh out of his anus.

If somebody wants to alter the circuit in the future, it's their responsibility to check it to make certain it will meet his/her needs.

The jobsworth needs to be gently (with a sledgehammer!) reminded of this fact.

You are NOT designing this circuit for future, you are designing it for NOW.

 

[plugwash]

what IMO would be dodgy is having a circuit where both exposed ends are 10mm but there is a section in between that isn't.

If you use a good brand and a deep backbox you should be able to terminate the 10mm directly in the FCU anyway.

 

[bernardgreen]

Have just been told the "Jobs-worth" has been "re-educated" and passed the installation.

But Jobs-worth still mumbled about it should have been 2.5mm² from the MCB to a JB outside the CU to ensure that the MCB was never up-rated to one suitable for 10mm²