cooker diversity

[Peter Woodford]

Guys,

bit confused on diversity can you help me out don't have regs book with me at mo

9000w cooker fitting 10mm cable so

9000/230 = 39.13 amps

how do i do diversity cooker has just a normal 45amp d.p switch what size mcb do i fit

cheers

 

[Guest123]

Applying diversity to a cooker is as follows.

Take the full load, 39.13A.

Take the first 10A of this, add 30% of the remaining current i.e 30% x 29.13 = 8.73A

Total load after diversity = 10A + 8.73A = 18.73A.

Also if the control unit has a socket outlet incorporated then you add an additional 5A.

 

[Davey101]

Lenny, do you (and others on here) always use diversity on a cooker, or do you er on the side of caution (ie you go up a cable/mcb size)? Only asking, as I often wonder what happens at christmas, when you've got a hob full of pans, and the oven going full blast trying to defrost the turkey! I guess if you didnt always apply diversity, cooker installs would be a bit more expensive with a 10mm.
Has anyone here ever installed a cooker circuit, applying diversity correctly, and run into trouble?

Just curious, as its always something I've wondered about.

Also, presumably you could just fit a 45 amp mcb (or more likely a 40), as the cable* and switch are rated for it?

* Presumably, may have to do a cable calc.

 

[sparks1234]

MMM I went to look at a house this week and the owner had bought a 13.8 Kwatt cooker which equates to about 60 amps...scary.
Once diversity is applied then you come back down to about 28 amps I think from memory.
It dont seem right does it

 

[electro]

Hi Peter

Why would you use diversity to size the MCB on a cooker circuit. Fit a 10mm cable subject to I meths and protect with a 40amp type b MCB.I would only be concerned with diversity when looking at the MD for the installation.

Regards

 

[electricAl]

But it is right to apply diversity - cos these things are designed NOT to draw their rated individual currents simultaneously, as in, the oven & the hob will simply not be able to be maxed out at the same time.
And the hobs cycle all the time - as soon as the reach the dialled temp, the thermostat switches them off, and on, and off...
The manufacturers KNOW this and thats why they suggest the CSAs that they do.

But if you want to do it your own way, nothing to say you can`t.

But a wise man once said, don`t bother buying a calculator if all you`ll use it for is hammering


p.s and whilst we should always design circuits correctly (if we know how, that is) a general rule of thumb for overloads is 1.45 With the exception of BS3036 fuses, all compliant protective devices are assured to trip in the required time at no more than x1.45 their In. The powers at be have made allowance for this when calculating the ccc of each of the cables listed in BRB

 

[electro]

Hi ElectricAl

So what would you install for the above installation?

Regards

 

[Guest123]

By applying diversity to that little fella, if there is a socket outlet included, I come out at 30A.

Bit of a difference eh.

 

[electricAl]

Lenny! how could you even consider that



Personally i`d put it in with 16mm...



on a 30/32A breaker

 

[electro]

Hi Lenny

What would you install?

Regards

 

[Guest123]

Lenny! how could you even consider that

I wouldn't....was just showing the difference before and after is all.


Personally I think I' have to use 16mm on a 40A MCB and a 50A isolation switch.

 

[electricAl]

Good tip, oh guru

 

[electro]

[FONT=Times New Roman, serif]Hi Lenny, Al[/FONT]


[FONT=Times New Roman, serif]I'm confused how have you gone from using diversity on the sizing and then using 16mm² how have you come to this size?[/FONT]


[FONT=Times New Roman, serif]Regards[/FONT]

 

[Guest123]

[FONT=Times New Roman, serif]Hi Lenny, Al[/FONT]


[FONT=Times New Roman, serif]I'm confused how have you gone from using diversity on the sizing and then using 16mm² how have you come to this size?[/FONT]


[FONT=Times New Roman, serif]Regards[/FONT]

By not using diversity. I must admit I will always cater for worst case scenario and go for the cable that meets the manufacturers rating, nothing worse than looking a fool when you have to tell someone on xmas day sorry but you cant use 2 rings of your cooker.

Protection wise I will usually look at diversity on that and go lower knowing that I have the back up if I need it as I installed a big enough cable.

 

[electricAl]

Sorry Electro. We (or at least I) were/was just mocking our/we`re selves. The cooker question has been done quite a bit this week.

Back to your point....

As said, even with a outlet attached, when diversity`s applied the Ib (design current is genuinely and fairly assessed to be no greater than 24 amps.

So, as our In (rating of protective device) = or > than Ib the next common size would be Lenny`s 30A breaker (he should really have said 32A but he still thinks 3036s are new )

So Iz must be equal to or greater than In, so we`re looking for a cable (lets assume T&E is appropriate) so a 4mm would be ok in theory if a short, perfect run. As you must always check for VD you might even find the roughly...hmm...32 metres allowable for 4mm is too short.
But realistically, the run may not be wonderful old clipped direct C, so any factor applicable might well force you upto 6mm (very likely)
In the most onerous conditions, 10mm may well be needed - even if only to get you to sleep at night

Or if your running thru a foundy

But, seriously, if you apply the rules allowable you WILL come out with an appropriate cable size - and not an over engineered snake due to fear of the unknown.

Hope that does clarify it a little for you. If you want to know a little more on the subject of design etc - then i can recommend various references mate

& sorry for being silly before

 

[Guest123]

the next common size would be Lenny`s 30A breaker (he should really have said 32A but he still thinks 3036s are new )

I was referring to the Ib not In.

Cant beat a good old 3036 mind.

 

[electro]

[FONT=Times New Roman, serif]ElectricAl what would you use? Tony Blair was easier to get a answer out of LOL...........[/FONT]

 

[electricAl]

Is that a serious question?
If i could tell you which cable to use for what, i could answer all the other people that ask me - and i can`t - so won`t.

I`ve tried to encourage you toward understanding that you can`t competently design a cct without all the relevant info. Anyone who can is a much better designer than me, or an idiot.

I gave you my answer - consider all the factors and use the next Iz rated cable up. I think thats quite within the capabilities of the average spark - it certainly should be.

Otherwise, stick a 16mm in on an 80A

Tony Blair indeed

 

[electro]

Hi electricAl

You have completely missed the point and tried to over engineer a situation that does not need to be over engineered. The secret behind design is knowing when to apply it and when you don't have to. Don't concentrate to much on volt drop in domestic, look more at the installation methods and loading. ElectricAl we will make a designer out of you yet.

Regards

 

[electricAl]

I`ll look forward to that mate. Thanks for answering my question