diversity

[ezekiel]

if installing a oven and seperate hob can you apply diversity to them as one cooking item

4.3kw oven and 5.8kw hob can these be run in one circuit from 40a mcb in 6mm to ccu then feeds to oven/ hob

hob says wiring to be 2.5 from hob unsure on how this can be (confused)

 

[ericmark]

Except for an induction hob I see no reason not to apply diversity.
At 18.7A and 25A likely they would run on 32A MCB.
6mm cable does not have a single rating looking at Table 4D5 the current could be as low as 23.5A although more likely 34A and also the cable must be protected so although 2.5mm is big enough to take the 18.7A to the oven it will need a fuse or MCB.
The problem is getting one which looks right. A board able to take 20A MCB or fuse tend to be on large size

There are some flush mount units the local whole sale outlet may help.
But since work in a Kitchen comes under Part P and councils charge £100+ I would think you are better off getting a registered electrician.

 

[ezekiel]

yeah understand partp and me not doing work but trying to understand the circuit, can you confirm is this right:

4.3 and 5.8 kw with diversity = approx 20amps
40a mcb in cu to ccu in 6mm, from there in 6mm to dual outlet plate
one 6mm feed direct to oven
one 6mm feed to some type of unit fused down to 20a, then 2.5 to hob (which states it needs 2.5mm)
the hob is 1 metre away from the top of oven.

i have learned to design one circuit correctly , but this oven/hob thing has thrown me and cant get my head round it.

 

[ericmark]

yeah understand partp and me not doing work but trying to understand the circuit, can you confirm is this right:

4.3 and 5.8 kw with diversity = approx 20amps

Already told you that's 43.7A i.e. 18.7A + 25A

40a mcb in cu to ccu in 6mm, from there in 6mm to dual outlet plate
one 6mm feed direct to oven

Unlikely you can have 40A on 6mm cable

one 6mm feed to some type of unit fused down to 20a, then 2.5 to hob (which states it needs 2.5mm)
the hob is 1 metre away from the top of oven.

i have learned to design one circuit correctly , but this oven/hob thing has thrown me and cant get my head round it.

Fused connection units only go to 13A so this oven will need a special.
Normal would be to take new supply from consumer unit.

 

[bongos]

if installing a oven and seperate hob can you apply diversity to them as one cooking item

I've often wondered this. If applying diversity to oven and hob separately then I make it to be around 12.6A for the oven and 14.5A for the hob. Total of the hob and oven with diversity is ~27.1A

If diversity is applied to the oven and hob power combined then you come out with a total with diversity as ~20.2A

Which method is the correct way of calculating diversity?

 

[ericmark]

if installing a oven and seperate hob can you apply diversity to them as one cooking item

I've often wondered this. If applying diversity to oven and hob separately then I make it to be around 12.6A for the oven and 14.5A for the hob. Total of the hob and oven with diversity is ~27.1A

If diversity is applied to the oven and hob power combined then you come out with a total with diversity as ~20.2A

Which method is the correct way of calculating diversity?

Diversity shown in books is only a guide. If for example you are required to use lights at all times you can't have diversity however if they are on PIR control and very unlikely more than half are used at any one time you can increase diversity.
In the end if you get it wrong the MCB will open as long as correct MCB is used.

With ovens and hotplates once hot the simmerstat or thermostat will be switching the devices off and on and you are unlikely to use more than 60% of total so likely a 32A MCB will not have a problem supplying the pair.

However this is not true where induction hobs are used because as it switches off one ring it re-routes extra power to other rings so no diversity can be used with induction hobs.

However with a single oven the power is below 13A so a standard fused connection unit to supply oven is no problem but once more than 13A is used finding a neat unit to limit the current becomes a problem as one has moved into the commercial size and it would normally have a commercial size protection unit.

As a result to avoid fitting a kitchen consumer unit they are normally fed with there own supply.

 

[ezekiel]

thats excellent info you obviously knowledgeable and so to continue:

now read in hob instructions no diversity allowed on appliance, which must be wired in 2.5

as the mcb is 40a and cable is 6mm (def i checked today) then this circuit is no good for the hob as 2.5 is rated too low for mcb

i calculate hob needs 25a so a 32a mcb on 6mm sounds about right although i would still need to get from 6mm cable down to 2.5 somehow, so unless im missing the point or you can just join the 2.5 to 6mm in the ccu or got a unsual rated hob?

 

[ericmark]

Cable rating depends on the temperature it can run at and the medium it runs through so a 6mm cable clipped direct able to run at 90 deg C can carry 58 amps with ambient at 20 deg C.
However a 6mm cable Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface) rated at 70 deg C would have a maximum of 23.5 amp.
With 2.5mm cable we would have 33 amp or 13.5 amp with same conditions.
So with a 25A MCB you could easy run XLPE (Cross-Linked Polyethylene) or LSZH (Low Smoke Zero Halogen) cable from switch to hob.
On the first post I gave you link to table showing what the cables can take. There is a little more than shown in that table but close enough and it does seem strange to stipulate 2.5mm cable on a hob?
Since you need Part P to work in a kitchen if you are able to wire hob why not run an extra cable from consumer unit it will all come within the same LABC inspection and of course you don't want it to fail so why mess around?