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Discuss Oven and hob on same MCB and diversity. in the Electrical Forum area at ElectriciansForums.net

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Even with a single cooker you can turn everything to max and draw the rated power and so exceed the diversity calcs, it is just no sane chef would be doing that...

Only time it happens is right after I've installed a new cooker/hob, when I turn everything on full for a while to burn all the elements clean and get rid of the smoke and smell before handing over.
 

happyhippydad

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Well It looks like the consensus is my time consuming, brilliantly formed maths is correct but of absolutely no use 😃. Still I enjoyed working it out!

I've just been working on another equation for excel to work out my average yearly interest rate over the past 10 years. took about 30 mins to realise I need to use nth root in the equation. I do love maths!

Thanks for the discussion and insight to all who replied, especially @Lucien Nunes for his usual intelligent and in depth explanations.
 

David Prosser

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My thought is it should be treated as one device if they are off one common isolator. Cooking devices in diffrent rooms should not be.
 

Lucien Nunes

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HHD I know you are always keen to analyse and get to the bottom of what's going on and I wish more people would do that, rather than relying on rules of thumb and guesswork. OK, in this case I wasn't in agreement that your method was an accurate model but it prompted some discussion and comparing of theory and practice and I think that is often lacking. People do stuff on paper to pass exams, and then nail stuff to the wall, but don't make enough of a connection between them. IMO the real trick is not to get too fixated on regs, which are just the particular locally-recognised standards that we generally work to, but rather to look at the physics that makes electrical stuff work. Heating elements obey ohm's law, not BS7671!

E2A: But, next time, please don't use Q for an unknown current. Capital Q is charge, usually in coulombs. Either x (the general unknown) or I (for current, the actual quantity that was unknown in this case) would suit. Since Q=It, using Q for current makes time disappear, which could cause wider issues with the universe.

My thought is it should be treated as one device if they are off one common isolator

I can see what you are getting at, i.e. one cooking station controlled as a unit from a single point, but referring to the isolator specifically seems arbitrary as it has no effect on how the appliances are used.
 
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happyhippydad

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HHD I know you are always keen to analyse and get to the bottom of what's going on and I wish more people would do that, rather than relying on rules of thumb and guesswork. OK, in this case I wasn't in agreement that your method was an accurate model but it prompted some discussion and comparing of theory and practice and I think that is often lacking. People do stuff on paper to pass exams, and then nail stuff to the wall, but don't make enough of a connection between them. IMO the real trick is not to get too fixated on regs, which are just the particular locally-recognised standards that we generally work to, but rather to look at the physics that makes electrical stuff work. Heating elements obey ohm's law, not BS7671!

E2A: But, next time, please don't use Q for an unknown current. Capital Q is charge, usually in coulombs. Either x (the general unknown) or I (for current, the actual quantity that was unknown in this case) would suit. Since Q=It, using Q for current makes time disappear, which could cause wider issues with the universe.



I can see what you are getting at, i.e. one cooking station controlled as a unit from a single point, but referring to the isolator specifically seems arbitrary as it has no effect on how the appliances are used.
Haha... I first put an X in the equation, as you rightly say this is the standard letter used for a variable, but it looked like this.... 0.3 x X, I realise It should just be written 0.3X but I wanted (at least initially) to show the multiplication sign. 0.3 x I looked too much like 0.3 x 1, or with the multiplication sign removed 0.3I, now looking like 0.31.

I then used 'Y', which I think I should have stuck with. Q shall never be used again in such a form!😀
 

Lucien Nunes

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But Y is the symbol for admittance, the reciprocal of impedance (Y=1/Z). Many capital letters stand for quantities and should not be used generally.

Its very often possible to distinguish 0.3I from 0.31 automatically by context (0.3I has dimensions of current but 0.31 is dimensionless.) However if an explicit multiplication symbol is needed to avoid ambiguity or for visual clarity, there is a choice of the asterisk * (from ASCII-based programming) or a full stop aka period or centre dot which is the conventional algebraic symbol to use on paper. Conventions that use the centre-dot for decimal fractions theoretically use the period for multiplication and vice versa. I would understand 0.3I, 0⋅3.I, 0⋅3*I etc as equivalent. In vector algebra the two multiplication operators ⋅ and x signify different operations, but again it would be clear from context that the distinction doesn't apply here.
 

Midwest

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I've not read through thoroughly all the replies, but when I was calculating diversity for two appliances, I would use two calculations. With one free standing, it would be one calculation.

I based my rational on that the later are sometime supplied with a plug, with very simple cooking activity and the former could have multiple zones for a hob and two or three or more zones for the oven part. Much more cooking activity.

That said, I once had a Range style electrical cooker, which had 3 ovens, manufacturer required 40A supply. With all three ovens going at full pelt, never pulled more than 14A.
 

Lucien Nunes

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Ours only has two ovens but with both of those on, the grill, all four rings and the lights, it uses about half an amp.
 

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