6mm cable rating??

[shugrover]

Hi, having a hob installed in my ex's kitchen, the hob is 6.8kw, the dual oven is 3.8, so I guess the 6mm is way too small for both, the problem is there is a socket next to oven, thinking that could have been used, obviously it cannot now. Do I need to put a new run of 2.5 in, with a 32amp trip just for the oven? Or is it too much for put onto the existing ring circuit? The oven will be around 10-12m from the consumer unit.

 

[TopTrumper]

your 6mm will be fine

 

[shugrover]

That makes it 10.6kw, sounds a lot, what trip should be fitted for both?

 

[securespark]

10600W comes out at 46.09A at 230V.

You can apply diversity, but if you wish to allow for flc, then you should split up the appliances and use the 6milli for the hob (32A) and put in another for the oven (20A).

You don't need 6 for the oven, but it will allow for a larger oven in the future.

 

[miajanjua]

The diversity for a cooker is 10A + (1/3 x Total Cooker Amps)

6.8Kw+3.8Kw = 10.6Kw Giving a current of 46 Amps @ 230V

After Diversity the Design Load for the cooker is 10+1/3x46 = 25.3Amps

6mm2 Cable is rated @ 32Amps

So well in access to what is required to supply the Hob and the oven together!!!

 

[shugrover]

Hi, thanks for that, so what size trip do I use to put them both on the same radial circuit with 6mm? I assume I can use 2 seperate control switches, so I can isolate each seperate appliance?

 

[miajanjua]

Hi, thanks for that, so what size trip do I use to put them both on the same radial circuit with 6mm? I assume I can use 2 seperate control switches, so I can isolate each seperate appliance?

If these a two separate individual appliances, then it is best to run two
2.5mm2 cables as radials to the CU with a 20A and 16A breaker for each
appliance and then install seperate isolators locally.

 

[JohnD]

The hob takes about 30Amps so miajanjua is mistaken.
use your 6A cable and a 32A MCB.
2.5mm cable is too small. So is a 20A MCB too small.


The oven is 16A and 2.5mm is OK if you are running a separate circuit.
However to give capacity for a double oven in future another 6mm would be preferable.


If you are putting them both on a single circuit you should use 10mm.

edited: I see Mr. Secure very wisely said all this already.

It is better not to apply much diversity to domestic cookers, because at times (e.g. cooking Christmas dinner) you will have all the rings and oven full on. When you first turn them on they use full current until they reach temperature and the thermostats start to cycle.

 

[shugrover]

Hi, thanks, there is currently a 6mm which I wil use for the hob, I will run in a 2.5 for the oven, that is a dual oven though. What trip do I need? 20A?

 

[JohnD]

Best to have a look at the spec of the oven. If it is 20A or less you can get by on 2.5mm unless it is a long cable or it passes through insulation or a hot space (cable capacity can be calculated for this but it is a bit tedious). If it is more than 20A you need a bigger cable.

 

[miajanjua]

The hob takes about 30Amps so miajanjua is mistaken.
use your 6A cable and a 32A MCB.
2.5mm cable is too small. So is a 20A MCB too small.


The oven is 16A and 2.5mm is OK if you are running a separate circuit.
However to give capacity for a double oven in future another 6mm would be preferable.


If you are putting them both on a single circuit you should use 10mm.

Where rrrrrr u getting your figures from JOHNd?

Diversity for a cooker is 10A+1/3x(Cooker Full load Current)

For the hob 6.8Kw @ 230V the full load current is 29.56A, 1/3 of this is 9.85Amps.

So after diversity, the load for the Hob is 10+9.85Amps =19.85Amps

Since you can run a radial of 20A on a 2.5mm2 cable, a 2.5mm2 cable
for this hob is as per the regs and perfectly safe.

However if you want to make the circuit future proof then run a 6mm2 cable for the hob and fit a 20A breaker to it.

 

[JohnD]

I am familiar with the diversity rule-of-thumb for cookers. However, it is better not to apply much diversity to domestic cookers, because at times (e.g. cooking Christmas dinner) you will have all the rings and oven full on. When you first turn them on they use full current until they reach temperature and the thermostats start to cycle.

Hence my recommendation to rate it at max load.

I agree that a 2.5mm cable is safe if the MCB is 20A, so that it trips on Christmas day but I recommend 32A for this hob to save the inconvenience.

 

[shugrover]

Thanks, so what do I use for the dual, oven? Its 3.8kw, I assume 2.5mm is fine now, even for 12 metres, it will be outside all but 10 inches either end. 16A trip??

 

[JohnD]

16A would be OK, or you could fit 20A, not much diff and either is safe but the next oven that goes in might have a rotisserie or something and be better with 20A - I would.

 

[nozspark]

Thanks, so what do I use for the dual, oven? Its 3.8kw, I assume 2.5mm is fine now, even for 12 metres, it will be outside all but 10 inches either end. 16A trip??

What do you mean outside?? Flat T&E is not designed for outdoor use!!