Quick check please guys

[oharaf]

Cooker circuit maximum demand of appliances is 6200W

6200/230 = 27A so 32A MCB & 6mm T&E

Cable run is approx 10m so VD = 7.3/1000 x 32 x 10 = 2.34v = 1%

cheers

 

[Spark123]

You use your design current for the VD, so is (7.3 x 27 x 10)/1000 = 1.97v

 

[oharaf]

Sorry

 

[FingRinal]

You've forgotton about applying diversity to your cooker circuit - From Table 1A OSG, current demand to be assumed is 15.1A (without socket-outlet) therefore if clipped direct, you could get away with 1mm on a B16 for up to 16m (OSG Chap.7).

 

[ban-all-sheds]

Would that be a sensible design?

 

[FingRinal]

Why are you accusing the IEE of not being sensible?

 

[GaryMo]

Because no sane person on earth would install a 1.0/1.0mm twin and earth cable to supply a 6.2kW cooker on a B16 MCB.

 

[FingRinal]

Why not? Can you base an answer on engineering? If you came across it on a PIR, for example, what would you do? And what would you do if the person ordering the PIR took the issue further? Why do you think Table 1A is insane?

 

[GaryMo]

Would you install a 6.2kW cooker on a 1.0/1.0 t&e?

Would anybody else consider installing a 6.2kW cooker on a 1.0/1.0 t&e?

I'll start the ball rolling.....I wouldn't.
I personally don't like to use diversity for cooking appliances unless I have no choice and even then I wouldn't dream of running it so tight. I just couldn't see Christmas running smoothly with your chosen cooker installation.

 

[Chri5]

FR while I did hold some empathy towards your ability to metaphorically throw the odd cat in amongst the pigeons I'm starting to doubt your sanity.

While I have no doubt you vision and expertise allows to to conclude the response you proffered, it's duffy duck.

Diversity, well hey yes it's valid but lets not get carried away with everything you read and your personal digestion, understanding and comprehension of the tables.

As a designer of a circuit you have to make the call and certify it. Tell me you would happily do that for a 4 bed house with 4 occupants and feeding requirements that warrant heavy 3 hours a day use of all 4 hob rings and an oven.

For ease of answer please work to the assumption that the cooker is an all in one unit.

LOL


I hope you understand that even if your just attempting to be contrary, you should appreciate (and consider) the 'eyes' that will read this thread .

Just maybe some silly sod will accept your theory and wire as you suggest.

Stop and read your posts and if you really feel the need to post and suggest something that is outside all installers conventions have the sense to qualify your post fully.

 

[FingRinal]

So, you can't give a sound engineering argument.

If you had said that you'd clamped a great number of cookers during the period when every element was switched on and noted how long it took for the current to 'settle', you would have a practical answer. One that might suprise you given the 'actual' running spec. of cables.

But the OSG App. 8 Cooker Circuits is quite explicit in its advice as is Table 1A. Would it be appropriate to 'assume' that the IEE have considered this point suficiently to include it in their 17th Edition OSG when they have removed other information?

Whatever your personal feelings are regarding diversity, I bet you actually apply diversity in all manner of your daily jobs - ring finals, socket radials, lighting circuits, CU installations etc. I also bet that you run plenty of shower circuits 'tight'.

Diversity is a tried and tested design practice. Without it, for example, overseas telephone calls would cost an awful lot more. It allows considerable savings in both materials and costs.

Why wouldn't Christmas run smoothly with a correctly designed and correctly installed installation? Are you suggesting that the socket circuits and lighting circuits would fail too, as they would be pushed a lot hotter at Christmas time?

 

[conny]

For what its worth here is my 2p worth.

As an armature winder with past experience of domestic installs, (yes many years ago I admit but still fairly relevant as far as I am concerned), I would never dream of using 1.0mm for a cooker circuit or any circuit that had heating elements in it. For crying out loud a ring circuit has to use at least 2.5mm!! and who says there are going to be any heavy duty appliances connected to it?

If I am installing a motor I don't use a cable that is rated for the FLC of the motor I use a higher rated cable to allow for any fault that may develop or any operator error. (i.e. someone running a motor continously by over-riding any safety devices/thermal cutouts when the motor is only rated for short duration operation). Don't tell me it doesn't happen because it does! Have you ever seen the consequnces and devastation an over heated cable can cause because of the resulting fire?

Come into the real world man and stop seeing the OSG and BS7671as the gospel that must be adhered to to the letter.
Yes, in an ideal world maybe their calculations would suffice but we do NOT live in an ideal world where everything is hunky-dory and nothing goes wrong.

For your sake and the safety of your clients please err on the side of caution and use some common sense. Would you let a plumber use 8mm bore piping for your central heating if he said it would cope because he didn't think you would have all your radiators on at once?

 

[oharaf]

Stuff it lets go for a bit of nice lighting flex instead!!!!!!!!!!!!

WHat is being demonstrated here is the difference between what 'calculations' can tell you you could do and then applying good old common sense!!!

The so called 'mathematics' is really a 'statistical' process which we all know is bull poo most of the time

I should know I have spent the last 12 years teaching the urchins in school how to cook the figures (that is the school leaders not the kids)

Still it tickled me and got a rise out of others

It is 6mm and nothing less tomorrow

 

[trey]

I think you've highlighted the difference in perception of risk. A potentially 6.2kw device on 1mm2 sounds crazy - despite the fact that it will only spike to full power and settle before cable will overheat (the point of diversity) whereas a shower running at the limit of the cable for 30 mins is seen as fine.

Just as a point though, assuming the cable is sheathed, 1mm2 will only take 15.0A not 15.1A. So the house will catch fire and explode

As for you looking for a grounded engineering solution. Let's assume you apply diversity and get 15.1A. You have to assume that is the typical load during the period the device is used. Now a cooker will be on for 30mins to 3 hours. Now calculate the rise in temperature of the conductor for 30mins to 3 hours. You'll see that the current capacity of the cable soon falls out of spec.

 

[conny]

Oh go on!
Play the game man!!

Use 1.0mm, over-ride the thermostats for each element, turn all rings, grill and oven full on and see how long it takes for the fireworks to start!!

Gwon, gwon, you know you want to!!