Beast of a cooker

[brizospark]

OK I know this has already been covered but I have been asked to install a supply and isolation switch to a Rangemaster cooker which has a rating of 14kw.

This cooker has a couple of ovens and grills and induction hobs - it's a beast

My question is regarding the cable / isolation switch rating, I know there is some debate over the issue but I reckon being realistic there is no chance that the cooker will ever run at full capacity and that a 6mm cable covered by a 40a MCB (only 5m run from board no insulation under floor) and a 45a DB switch would suffice.

The other option would be a 63a MCB with 10mm cable and a 63a rotary isolator.

The house is occupied by a couple and soon to be baby.

What would you guys do in this situation?

 

[HappyHippyDad]

That won't change a thing as the elements will still be cycling on and off.

Yes, but if you switch everything on at the same time like we did, then for a short while, until the cycling/thermostat kicks in I guess it must be drawing its max current?

 

[Richard Burns]

Yes, but if you switch everything on at the same time like we did, then for a short while, until the cycling/thermostat kicks in I guess it must be drawing its max current?

Scenario:
So you have a 32A MCB for the cooker.
You switch on the oven and all rings at once, say the cooker is then taking 50A.
The 32A MCB will not trip for approximately 15 minutes at a constant current of 50A.
After less than one minute all of the rings will be up to temperature and will switch off for say 20 seconds.
(not necessarily at the same time but say within the next sixty seconds all of them will switch off for 20 seconds at some point)
So on average in that next minute 1/3 of the rings will be off and the current drawn will be on average 15 A lower so 35A.
The 32A MCB will not trip in less than 1 hour at this level.
This will repeat over each minute: all the rings come on again taking the current up to 50 A, however we are almost a temperature so they will only be on for say 15 seconds, maybe twice in that minute.
So say once the steady state is reached cycling on and off; on average, in any minute, the rings are taking half the total current so 33 A drawn.
We could, at worst case, say that half the time we are using up that 15 minutes window before the MCB trips so it would take 30 minutes to trip.

After twenty minutes the ovens reach temperature and switch off for a minute.
During that minute the total current drawn is now 13 A, the MCB has a chance to cool down extending the window of time before the MCB trips.
So say it has extended to 1.5 hours now.
Oh dinner is ready folks, switch off.
MCB never trips.

The cleaning cycles tend to take longer to run as they reach a higher temperature so could manage to reach that elusive trip time.

 

[Engineer54]

Jobs are irrelevant in this case as they are gas.
The self clean mode brings all of the oven elements on at once and takes a 45A mcb out after a while of running. the manufacturers spec has max load as 50A.

Well all i can possibly say to that is, if this is a cooker designed for domestic use, something is very wrong.
A 50A cleaning mode is just bloody ridiculous, even for many of the smaller commercial installs. Not that i've ever seen any of these high heat self clean systems work.... lol!!

 

[Richard Burns]

I do not know if this is interesting or just sad.
Working from a Rangemaster Elise 14.8kW cooker with two (2.5kW) ovens and five (3 x 1.85kW and 2 x 1.18kW) induction rings.
I have drawn some graphs using some basic assumptions (that could be entirely wrong).
Turning on both ovens and all rings at the same time, assuming one oven takes 20 mins and the other 30 mins to get to temperature and then run off for three minutes and on for three minutes, the rings will take approx 1 min for the high power rings and 1.5 minutes for the low power to get to full temperature and then run on for 20 secs and off for 20 secs, but not in sync with each other.
The MCB is assumed to be able to dissipate all the heat generated when it is taking 32A, above this the heat will increase and below this the heat will decrease (the energy loss / gain is assumed to be independent of temperature), heating of the MCB is assumed proportional to current flowing through it.



This shows that at first the heat increases but once the ovens start cycling the MCB will be able to dissipate heat faster than it gains (I could not be bothered to work out the correct formula to prevent the MCB going into negative energy:death and so would only trip in the first half hour if it was ever going to get there.
I feel this is fairly representative of a worst case, since generally the all the rings would only be on at the last 30-45 mins of oven cooking.
Admittedly replacing hot pans with cold pans (why?) during cooking would up the heating required, as would opening the oven door, however generally heating would be on for a shorter time than the time they are off as the heating is quicker than the loss of heat and I have assumed equal heating and cooling.

Just a thought, and too much time wasted, who needs bank holidays anyway!

 

[Engineer54]

You've never had to deal with Wolf cookers then. Self clean mode is ridiculous on the buggers! I've fallen fowl of them more than once now.
It's a ridiculous design on my opinion, the two I had issue with had a self clean mode which turned the whole appliance to full at once.
I don't know if it's the manufacturer giving an 'after diversity' rating in the manual or something else.

Just looked these over priced ''Wolf'' Yank ranges up, it seems the largest dual fuel range requires 40A supply connection and most of the others 28A or less. Also states in the blurb that you can only use self clean mode, on one oven at a time and you also can't use the other oven for cooking while the other oven is in self cleaning mode. So as far as i can see, the 6mm on a 32A MCB still holds even for these OTT ranges....

Why anyone, other than those with far too much money than they have sense, would even think about paying out in excess of 35,000 + pounds for a cooker is another matter altogether!! ..lol!!

 

[davesparks]

They've improved them then! They used to specify 50A on them with no mention of those rules about the self clean.
I last had dealings with one about 5 years ago so by the sounds of it they've listened to the complaints.

What you don't realise is that for your 35000 you get a one of a kind hand made (no machine could ever make anything that badly) work of art in wobbly stainless steel to make your nice homely kitchen look like a commercial kitchen!

 

[Engineer54]

They've improved them then! They used to specify 50A on them with no mention of those rules about the self clean.
I last had dealings with one about 5 years ago so by the sounds of it they've listened to the complaints.

What you don't realise is that for your 35000 you get a one of a kind hand made (no machine could ever make anything that badly) work of art in wobbly stainless steel to make your nice homely kitchen look like a commercial kitchen!

They could be gold plated for what i care, they still wouldn't get even a fraction of that 35K out of me!!
Did you see what they wanted for a an optional red or black control knob, or come to that, any of optional stuff!!

 

[davesparks]

I have never looked at the price, just the ridiculous article itself.

They are ugly, not very well made, covered in sharp edges when you try to shift them to get to the back to connect them, the list goes on!