5.3 kw double oven on a 20 amp fuse with 2.5 cable

[egginyourface]

evening all,

I was told to run 2.5 cable from fuseboard to supply a 3.5 kw single oven. Job is done....

Now they've said theyre going to put in a 5.3kw double oven in.

Question i have is can I apply diversity to this and keep 2.5t+e or do i need to run a new 6mm,

advice would really appreciated

thanks

 

[TaffyDuck]

well on such a load then...yes....it would be up to the designer as to the right action to take here.....short of treating it as a commercial load...100% of the first load....80% of the second and 60% of remaining appliances....

Well I was taught to build in redundancy and that diversity was to do with total demand not individual circuits but I may be wrong there.. May be considered old fashioned by some but Ive lost count of the times Ive come across burnt out 2.5mm on an oven. Whatever the regs say the buck stops with the installer, hoping the client doesnt cook much is daft in my book. I have always used 4 or 6 on an oven, might be over engineered in some peoples eyes but its a better quality job

 

[WPD Lad]

The 2.5 hasn't been de rated at all, we're assuming it'll have the full ccc, if it's in a conduit I'd stick a larger cable in

 

[ample current]

full load...

So why is it 30% of the remainder and not 30% full load
it says 10A + 30% fl not remainder :dizzy2: or am i missing something????? or just being a bit dim.

 

[TaffyDuck]

So why is it 30% of the remainder and not 30% full load
it says 10A + 30% fl not remainder :dizzy2: or am i missing something????? or just being a bit dim.

OSG page 110 10amps + 30% of remainder

 

[GLENNSPARK]

diversity becomes a problem when people start adding all connected loads together and then applying diversity....doesn`t work as the overcurrent device and associated cabling will be woefully undersized/underrated.....but as has been said before....the "regs" as we see it...that is BS7671 and anything seconded to it.....OSG GN3 etc are but guidance notes after all and as such are open to question as regards issues like this.....of course it is wiser to go over rather than under in terms of protective devices and cable/s and theres the issue of futureproofing as well....but how far do you take it?....Diversity is there for us to utilise ...given the guidance laid out in BS7671....its just a case of how and where....like you wouldn`t apply diversity to such a thing as an instantainious water heater would you.....as someone who posted on this forum about 3 weeks ago was going to do.....until advised not to of course....

 

[ample current]

OSG page 110 10amps + 30% of remainder

I take it thats the green one.

 

[GLENNSPARK]

if you look it is refering to 10A +30% fl in which it means you take the full load and apply the first 10A then 30% of whats left......

 

[Gordon]

The diversity applies to a cooker incorporating oven, rings, grill and assumes that they won't all be drawing full power in one go. likelihood
is that a double oven will draw full current at some time. Better to upgrade cable accordingly.

 

[TaffyDuck]

Table A1 is concerning diversity on individual circuits and states 10amps + 30% of remainder. Table A2 is diversity of a whole system and states 10amps +30% Full load in excess of 10a

 

[GLENNSPARK]

The diversity applies to a cooker incorporating oven, rings, grill and assumes that they won't all be drawing full power in one go. likelihood
is that a double oven will draw full current at some time. Better to upgrade cable accordingly.

yet again....looking at the appliance first...or if the appliance isn`t on site at the time of design....then gathering info (make model) etc from the client and doing a bit of research on it.....find out the KW rating etc...so as to calculate/design accordingly....isn`t that the difference between installers and electricians.......

 

[TaffyDuck]

yet again....looking at the appliance first...or if the appliance isn`t on site at the time of design....then gathering info (make model) etc from the client and doing a bit of research on it.....find out the KW rating etc...so as to calculate/design accordingly....isn`t that the difference between installers and electricians.......

Couldn`t agree more, installers would go with 2.5 electricians with 6mm.

 

[GLENNSPARK]

Couldn`t agree more, installers would go with 2.5 electricians with 6mm.

no...too cut n dry for me this....electricians would go with the APPROPRIATE SIZED CABLE and associated overcurrent device at origin for the expected load.....after diversity.......

 

[TaffyDuck]

no...too cut n dry for me this....electricians would go with the APPROPRIATE SIZED CABLE and associated overcurrent device at origin for the expected load.....after diversity.......

I couldn`t disagree with you more in this particular instance. I`m not saying wire a lighting circuit in 10mm. What I am saying is for the sake of a few extra quid you have numerous advantages. The cable is under-stressed consequently it will not degrade so quickly, if the oven is used at full load the MCB wont trip, if the client upgrades the oven or redesigns the kitchen in a few years you have the redundancy in the circuit to handle it (or to add a hob in the redesign scenario) without pulling the house apart. disadvantages are that it costs a couple of quid more now (cheaper of course to going back in a years time to upgrade it).

OSG is, i concede, guidance and it specifically states that the installer can use these calculations or his own judgement at his discretion.

My discretion points me to the option of 6mm on a 32amp MCB. Yours to 2.5mm with none of the advantages stated above.

We`ll agree to disagree on this one

 

[GLENNSPARK]

I couldn`t disagree with you more in this particular instance. I`m not saying wire a lighting circuit in 10mm. What I am saying is for the sake of a few extra quid you have numerous advantages. The cable is under-stressed consequently it will not degrade so quickly, if the oven is used at full load the MCB wont trip, if the client upgrades the oven or redesigns the kitchen in a few years you have the redundancy in the circuit to handle it (or to add a hob in the redesign scenario) without pulling the house apart. disadvantages are that it costs a couple of quid more now (cheaper of course to going back in a years time to upgrade it).

OSG is, i concede, guidance and it specifically states that the installer can use these calculations or his own judgement at his discretion.

My discretion points me to the option of 6mm on a 32amp MCB. Yours to 2.5mm with none of the advantages stated above.

We`ll agree to disagree on this one

i have throughout this thread mentioned the use of diversity.....now then...where have i quoted the specific use of 2.5?....

 

[TaffyDuck]

Post 41 &42 dont start back pedaling now.