cooker diversity

[dunny123]

I have to install a cooker (3.5kw) and ceramic hob in a kitchen. The hob rating is a total of 6.4 Kw (thats 4 x 1.6kw for each plate)

There is an existing supply in approx 10M of 6sq mm T&E. Currently this terminates onto a ccu with socket. Assuming I replace the ccu for one without a socket:

6.4KW + 3.5 KW = 9.9kW = 43A

The proteus/centaur CU only has MCBs available in up to 40A.

Looking at the OSG it appears I am allowed diversity for cooking appliances of 10A + 30% of rated current, so therefore my total design current could be calculated as 26.92A (Hob -10A + 5.35A) + (cooker (10A + 1.57A)

My question is have I interpreted the above correctly, and if so what should be the size of the protective device 32A allowing for diversity, or >40A for total theoretical load ?

 

[SeanT]

You're looking in the wrong place for whether this is allowable or not - is the 6mm buried in the wall or clipped direct? If the cable is ok then 40 amps should be plenty.

 

[equitum]

If the cable is buried in the plaster in some places and clipped to joist in others (not covered in thermal insulation) its reference method 1 which is 47A.

 

[dunny123]

The route for the cable from the CU is up into the loft thru plaster, along into above kitchen then down in the plaster to CCU.

 

[EdwardCurrent]

Hello,
Noticed this 10A + 30% of rated current equation on here the other day.
Isn't it 10A + 30% of the remaining rated current ?? (+5 if s/o inc).

Christmas morning must push many cookers close to overloading the mcb ??

Ed

 

[dunny123]

Looking at the curve for a 40A mcb, it wont trip at 55A for over 10,000 seconds!

 

[EdwardCurrent]

Sorry Dunny,

I see that you did the calc using the remaining A etc..

Ed

 

[dunny123]

Thannks EdwardCurrent. Does that mean my calcs are OK? What should the MCB be ?

 

[EdwardCurrent]

Hello Dunny,

I would fit a 30A mcb to protect the cable. As you say your design current will be @6200W. (@27A).(Fitting a larger mcb will probably mean your cable size will need to be 'upped', (no need in your case ).).

Hope this helps.

Ed