Rangemaster Cooker, check my calculations please?

[manmikey]

Hi guys
Could some one check over my figures please and correct or advise me if I have boobed?

Range Master duel fuel cooker, total electrical load 7.5Kw, which I make about 32.2 Amps

I intend to install a radial supply with 6mm twin & earth of maximum of 8 metres length, a 45amp cooker control switch (without socket) and a 45amp terminal.

Will a 32 amp MCB be ok for this load or should i go up a size? (its that diversity bit I don't really get)

Thanks, Mike

 

[Cork]

Diversity is just to cover the fact that all the heaters or rings are unlikly to be on at the same time.
If memory serves me, for household cookers take the first 10 amps, add 30% of the remaining rated current and add 5 amps if you are putting in a socket.
That puts your plan well in field.

 

[Big_Spark]

Diversity is just to cover the fact that all the heaters or rings are unlikly to be on at the same time.
If memory serves me, for household cookers take the first 10 amps, add 30% of the remaining rated current and add 5 amps if you are putting in a socket.
That puts your plan well in field.

Yet once again Diversity is applied to a cooker...

Diversity should not be applied as there will be times when the total or majority possible load of the appliance will be used. This is yet another example of DIYers reading the Regs but not understanding it's implications in the modern world...there are parts of it that need to be rewritten yet they are not

Manmikey..The 32A MCB should be sufficient for your needs under those circumstances. Should you ever find that you trip the breaker by using all of it, then you can simply change how you use the cooker OR you can install a 40A MCB..The length of run will not be an issue for 6mm² T&E for occasional use..

 

[Cork]

Big_Spark
If you have access to the IEE on site Guide to the wiring regulations, check appendix 1 of chapter 11 which deals specifically with this question. You will see that what I posted is as the IEE recommend.
Yes there is a chance that there will be nuisance tripping, but how often is all the current drawn by a cooker? The IEE preface the tables with the statement that they are guidelines. Guess the question is Is it likely to happen and what would the end effect be? To my mind the answer is very unlikely to happen and the loss should it happen very small

 

[manmikey]

Thanks guys for your prompt help, I already have a spare 40amp MCB in the distribution board so assumming this is ok for the 32amp cooker would you say that is would more suitable or would a 32amp mcb be a wiser choice?

 

[Big_Spark]

Big_Spark
If you have access to the IEE on site Guide to the wiring regulations, check appendix 1 of chapter 11 which deals specifically with this question. You will see that what I posted is as the IEE recommend.
Yes there is a chance that there will be nuisance tripping, but how often is all the current drawn by a cooker? The IEE preface the tables with the statement that they are guidelines. Guess the question is Is it likely to happen and what would the end effect be? To my mind the answer is very unlikely to happen and the loss should it happen very small

If I have access to the Onsite Guide..Oh give me a break Cork...

Just because the IEE state one thing in the Regs does not make it so..

The Regs are a MINIMUM STANDARD TO WHICH ALL ELECTRICAL WORK SHOULD COMPLY. Therefore exceeding the regs is always a good idea when prudent and economic to do so.

It is incumbant upon any installer to consider furture use of any circuit they install, as such you MUST take into account the MAXIMUM design current for that circuit. Now diversity has a role to play, but not, in my opinion, for cooker circuits, where there is a good bet that on several occasions a year at least 80% of the full poptential load of that cooker will be drawn through the circuit. It is probable that in some homes 100% of the load may be drawn on rare occasions.

If you do not account for this....well then your not very good to be honest.

 

[JohnD]

Christmas dinner is the thing... turkey in the oven, pudding in a steamer, just put on the sprouts and the carrots... all rings cycling on and off, sooner or later they'll all be on at the same time.

 

[andy]

Big_Spark
If you have access to the IEE on site Guide to the wiring regulations, check appendix 1 of chapter 11 which deals specifically with this question. You will see that what I posted is as the IEE recommend.
Yes there is a chance that there will be nuisance tripping, but how often is all the current drawn by a cooker? The IEE preface the tables with the statement that they are guidelines. Guess the question is Is it likely to happen and what would the end effect be? To my mind the answer is very unlikely to happen and the loss should it happen very small

for cookers, i would not apply much diversity because there are a few times a year (family party/christmas etc) when the cooker could be at full load. this means it could often trip the MCB. not exactly designed properly.


manmikey - what you have proposed sounds correct and i cant see any immediate problems with it.