Cable rating & route

[scottmeister71]

I have a double oven rated at 5kw and a ceramic hob at 5.8kw. I intended to run a 6mm cable from a 32A MCB to a CCU. From this CCU a 6mm cable to the oven. Then a 6mm cable from the oven, along the wall behind the base units (just below worktop) to another CCU in an adjacent cupboard to the hob (about 5 metres away) then a 6mm cable from this CCU to the hob.

Is this acceptable on the following counts:

1. The cable size
2. The breaker size
3. The cable route (under worktops)

Your help is gratefully received, as always. Great forum!

 

[pdcelec]

1. 10.8kW/230 = 46.96A so NO

2. NO as above

3. NO cable to be installed to BS 7671

 

[andy]

1. 10.8kW/230 = 46.96A so NO

2. NO as above

3. NO cable to be installed to BS 7671

forgetting diversity there?

 

[scottmeister71]

1. 10.8kW/230 = 46.96A so NO

2. NO as above

3. NO cable to be installed to BS 7671

forgetting diversity there?

Taking diversity into consideration, (after all I'm certainly not Jamie Oliver so am unlikely to draw anything like capacity. Can't ever remember using more than two rings on the hob for a start), what would the capacity required then be?

 

[pencil pusher]

diversity isn't really a factor as both oven and hob could well be on at same time.

cables should all be flush mounted within wall structure (preferably re-wirable)

you could get away with something along the lines of what you suggest provided you complete a ring circuit comprising 50A breaker - 32A ccu#1 - 32A ccu#2 - back to breaker. Make sure you then 'spur' off each ccu to the appliances - i.e. not on the main ring.

Are you short of spare ways on your consumer unit? You should really be taking separate radial feeds to each unit.

Stu

 

[pdcelec]

even with diversity it is 35.65A

 

[Adam_151]

Install two such circuits, one for the hob, one for the oven, use 10mm cable for one, so in future if need be, an all-in-one cooker could be fitted

 

[mapj1]

Cable route is OK as described, only if clipped direct or in surface trunking, otherwise you are stuck with permitted routes only unless you want metal conduit.
5KW is one heck of an oven - usually they are 2 or 3KW max - are you sure? Regardless- 10mm to cooker outlet anyway will allow you a 40A breaker.. Double check on oven as it sounds like it needs its own feed. What do the makers say - there reccomended cable sizes are often less than simple addition bacause they know the grill and oven elements cant be on together, or whatever it is....

 

[towman]

He did say it was a double oven - so 5kW is not that big! Is it just me or do these ovens seem to be getting bigger and having a bigger draw now. They used to be one and a half ovens really , but now they seem to be turning into "real " double ovens?!

 

[scottmeister71]

So, just to be clear, if I have a chance of running two seperate radials, what size breaker for each and what size cable for each. I don't want to do more than required because I will never use a full freestanding cooker for example (no offence to anyone who has one)

 

[Spark123]

diversity isn't really a factor as both oven and hob could well be on at same time.

cables should all be flush mounted within wall structure (preferably re-wirable)

you could get away with something along the lines of what you suggest provided you complete a ring circuit comprising 50A breaker - 32A ccu#1 - 32A ccu#2 - back to breaker. Make sure you then 'spur' off each ccu to the appliances - i.e. not on the main ring.

Are you short of spare ways on your consumer unit? You should really be taking separate radial feeds to each unit.

Stu

I thought the regs only allow a 30/32A final ring circuit.

 

[ban-all-sheds]

433-02-04 permits the use of 2.5mm² cable with 30/32A protective devices in ring finals serving BS 1363 accessories.

It does not explicitly permit anything else, but neither does it forbid it.

For other ring finals I guess a designer who knew what he was doing could use the old 0.67Iz rule. Or would 473-01-08 apply?

I'm not convinced that pencil-pusher's design of a 6mm² ring on a 50A breaker is a good one, or an allowable one, but depending on installation method I don't think it's unsafe. But two radials would be better, or a single 10mm² radial if you can get 2 x 10mm² conductors into the first CCU...

 

[pdcelec]

I have seen 45 Amp three phase ring mains in some industrial launderettes and the senior engineer I deal with says that there is nothing wrong with them.