Fire risk on ring main?

[bowgieman]

Hi,

I have just had a new 10 way consumer unit with 2RCD's installed. The supply to the Kitchen uses 2 MCB's. The 40amp MCB is directly connected to the built in single oven using 4mm T&E, and a 32amp MCB supplies the kitchen ring main for the following appliances:

Kettle, Toaster, Microwave, Combi Boiler, Cooker Hood, Gas Cooker Ignition, Washine Machine, Tall Fridge and worktop sockets.

My electrician says that it is fine for all these appliances to run on the 32amp ring, but i'm a little bit concerned. Wouldn't this be a huge load for the 32amp MCB?

Thanks,

 

[NewOrder]

I am no expert but I would have thought even if everything is running at the same time it would not exceed 32 amps. If you had a dish washer and tumble dryer etc then I would not run them all at the same time. Stuff like the cooker ignition uses nothing.

Most old houses don't even have a separate ring for the kitchen. Edit I would have though 4mm for the cooker is too small though Edit just re-read that it seems the hob is gas so is probably ok but a spark will know for sure. What load does the oven consume?

 

[PrenticeBoyofDerry]

I would be more concerned that you have 4.00m T&E on a 40A device, as the maximum current 4.00mm cable can carry is 37A, that is if clipped direct and no additional de-rating factors to consider. It would be better on a 32A device.
Will regards to the second circuit for the rest of the kitchen, if you overload it probably the worst thing that can happen is that the MCB trips!
Which can be inconvenient but the cooker circuit has not been designed right and could be a potential danger if a cooker/oven has installed demanding a load in excess of the current rating of the cable, but not large enough to operate the protective device.

 

[bowgieman]

The oven is this one
http://www.trade-point.co.uk/kitchens/appliances/cooke-lewis-single-fan-oven/152732_TP.prd

I'm not sure what the load is, but its says 13amp.

 

[roberta1000]

4mm will be fine unless the oven is some wondrous beast. Many just need 2.5.

<edit> just read the previous post - 4mm is overkill but good future-proofing (as noted earlier, better on 32A which is still overkill.</edit>

 

[xr4x4]

It makes no odds what the circuit is connected too and what rating it is.

A 40a mcb is too big for 4mm, are you sure it's 4mm and not 6mm?

 

[PrenticeBoyofDerry]

4mm will be fine unless the oven is some wondrous beast. Many just need 2.5.

The circuit has not been designed safely, it is as simple as that!

 

[EFLImpudence]

As Paul asked, it's probably 6mm².

 

[bowgieman]

You all got me worried!!

I have had a proper look and it turns out that its a 6mm afterall.

So how about the ring main? Is it safe?

 

[Aragorn84]

Yes, its fine.

 

[PrenticeBoyofDerry]

You all got me worried!!

I have had a proper look and it turns out that its a 6mm afterall.

So how about the ring main? Is it safe?

If cooker is 6.00mm T&E that should be okay (again providing there are no de-rating factors) The rule of thumb using diversity would allow up to a 15kW cooker/oven to be on a circuit protected by a 32A device.

The ring final circuit (not ring main!) is fine, and the protective device of 32A makes it safe as far as the loading is concerned. It is not the way I would personally design the power to a kitchen but if it was a CU change rather than new circuits, the electrician can only be expected to deal with what they are presented with the best and safest way they can.

 

[DetlefSchmitz]

The proper question here is: How do you know it is 6mm? Did you measure something or read something off the cable?

 

[PrenticeBoyofDerry]

The proper question here is: How do you know it is 6mm? Did you measure something or read something off the cable?

Or by reading the schedules of test results!

 

[bowgieman]

no measuring... just read it off the cable roll holder.

 

[roberta1000]

4mm will be fine unless the oven is some wondrous beast. Many just need 2.5.

The circuit has not been designed safely, it is as simple as that!

Yes of course.

Posting at cross-purposes here, I was simply replying to an earlier suggestion (post 2 I think) that 4mm was undersized for an oven.