Cable Installation method

[Minkyman]

Hi All,

We are having part of our kitchen partitioned off with a stud wall and I took the opportunity to move our cooker cable(10mm2 on 45amp breaker) for what will be our new layout in the kitchen. The part of the cable in the partition has a vertical run of about 1.7m which is clipped to the centres of the frame and then about a 50cm horizontal run which passes through the centres and then into a block wall. The issue arises as our builder put rockwool or similar in the framework which I wasn't expecting, would this make the whole installation of cable classed as method 103 or just the horizontal part classed as 103 and the vertical classed as method 102?
Would it be easiest to just stick all of the cabling in a conduit to satisfy method A?

The partition framework is 75mm should that make any difference.

Thanks for your help.

 

[securespark]

You would downgrade the whole cable.

I have not got the book to hand at the mo, maybe someone could post the figures.

 

[Gutterball]

you use the worst factor over the whole cable run.

 

[EFLImpudence]

Change the MCB to 32A and limit your cooker (oven and hob) to 15kW then all will be well.

 

[JohnW2]

... our cooker cable(10mm2 on 45amp breaker) ...The issue arises as our builder put rockwool or similar in the framework which I wasn't expecting, would this make the whole installation of cable classed as method 103 or just the horizontal part classed as 103 and the vertical classed as method 102?

Unfortunately, as you have been told (and for fairly obvious reasons, given that the same current flows through all of the cable), you have to use the worst-case method which exsists anywhere in the cable run.

Would it be easiest to just stick all of the cabling in a conduit to satisfy method A?

Theoretically, that wouldn't quite do it - I think you'll find that the CCC of 10mm² with Method A is only 43A, fractionally lower than your MCB rating of 45A.

... but do you really need a 45A MCB? By application of 'diversity', you can run a cooker of up to around 19kW (a bit less if the circuit also supplies a socket) off a 32A breaker - which I think would be (just) OK with Method 103.

Kind Regards, John
Edit: slow typing again!!

 

[Risteard]

Or you could use the larger csa cable just through the insulation if you were prepared to joint it prior to this point.

But as said, 45A seems excessive for a domestic cooking appliance!

 

[JohnW2]

Or you could use the larger csa cable just through the insulation if you were prepared to joint it prior to this point.

In theory, yes, but who wants to be playing with 16mm² cable for a cooker circuit, and the joints at either end would have to be 'accessible' (you're not going to find an 'MF' JB for 10/16mm² cable!).

But as said, 45A seems excessive for a domestic cooking appliance!

Indeed - it is surely therein that lies the (very simple) solution.

Kind Regards, John

 

[Minkyman]

Thanks for the input. I guess there is no reason for preserving the 45amp circuit for the sake of it when a 32amp MCB will do. I do only need about 28amp(6.5kw hob, 4kw oven, and socket) with diversity applied.

 

[Risteard]

Thanks for the input. I guess there is no reason for preserving the 45amp circuit for the sake of it when a 32amp MCB will do. I do only need about 28amp(6.5kw hob, 4kw oven, and socket) with diversity applied.

I make it 25.7A using OSG calculation, but either way 32A circuit breaker should be fine!

 

[JohnW2]

I make it 25.7A using OSG calculation, but either way 32A circuit breaker should be fine!

I agree with your calculation (assuming the powers quoted are at 230V, which I doubt) - but, as you say, even if one went with the OP's figure, it would still be well under 32A.

In reality, the cooker powers are probably quoted at 240V, so the after-diversity total current (calculated at 230V) would probably be a bit under 25.7A.

Kind Regards, John