Applying diversity to Cooker unit

[Damian Petsas]

Hi there hope you can shed some light.
Ive got a cooker rated at 3.5kw
A hob at 6.4 kw

Now if i look to apply diversity to this to run a single T and E to a cooker switch the from the switch to a click double cooker connection point.


is this correct?

3.5kw =15.2 A
6.4KW = 27.8 A
TOTAL = 43 A

With diversity applied I'm looking at 10a + 30% of 43a = 22.9 a

Cable run 18 m Clipped direct therefore 6mm to cooker isolator

Any advice is greatly appreciated.

 

[telectrix]

30% of 43a



​not quite. should be 30% of 33A ( remainder after the 10A).

 

[Damian Petsas]

I thought so but in the regs it says 10a +30% of full load current therefore 30% of the 43a ?? stumped me

 

[telectrix]

where's that in the regs ( green book)?

edit. even so, 6mm on a 32A MCB , you're stilll well in. have you calculated the VD?

 

[davesparks]

I thought so but in the regs it says 10a +30% of full load current therefore 30% of the 43a ?? stumped me

No it doesn't, it doesn't say anything about it in the regs. It is in the on site guide and the wording is 'the first 10A of the rated current plus 30% of the remainder of the rated current'

 

[telectrix]

wondered why i'd not seen it in 7671.

 

[Andy78]

Diversity for cookers takes into account the cyclical nature of the loads within that particular appliance and their co-ordination with each other. Where you have two separate appliances there will be no co-ordination between these appliances so I would tend to carry out a diversity calc for each appliance and then total.
You must also reference the manufacturer's information provided in case there are any requirements for cable type and size.
Also your cable size choice does not seem to have a bearing on your calculation.

 

[Resu]

This is what mine says.

 

[Damian Petsas]

Yea vd is 4.6 v

Im reading from page 117 on yellow osg

 

[davesparks]

Diversity for cookers takes into account the cyclical nature of the loads within that particular appliance and their co-ordination with each other. Where you have two separate appliances there will be no co-ordination between these appliances so I would tend to carry out a diversity calc for each appliance and then total.
You must also reference the manufacturer's information provided in case there are any requirements for cable type and size.
Also your cable size choice does not seem to have a bearing on your calculation.

Nonsense, it works just as well across multiple appliances as a single appliance. Each element in a single appliance is individually controlled exactly the same as if they were all in seperate appliances.

I had a fish and chip van at a festival last year, the total load of cooking appliances plus some downlights and fluorescents was 15KW, I worked happily on a 32A supply. My data logger recorded a max of ~30A whilst it was fully in use.

 

[Damian Petsas]

Ha Hha I've been trying to do that lol

so "It is in the on site guide and the wording is 'the first 10A of the rated current plus 30% of the remainder of the rated current'"

i take it as 10a plays the full load not the first 10a then remaining?

 

[Damian Petsas]

So andy what would you say the correct cable size for the installation?

 

[Andy78]

This is what mine says.

Now look at table A1

 

[Resu]

That's not applying diversity though is it? (Although very similar)

 

[Damian Petsas]

K your the man andy lol my baddd!!!! ha ha

so what cable size are you stating and how would you calculate it differently
is this now correct

3.5kw =15.2 A
6.4KW = 27.8 A
TOTAL = 43 A

With diversity applied I'm looking at 10a + 30% of 33a = 19.9 a

 

[Andy78]

Nonsense, it works just as well across multiple appliances as a single appliance. Each element in a single appliance is individually controlled exactly the same as if they were all in seperate appliances.

I had a fish and chip van at a festival last year, the total load of cooking appliances plus some downlights and fluorescents was 15KW, I worked happily on a 32A supply. My data logger recorded a max of ~30A whilst it was fully in use.

I have also clamp tested cheap electric hobs that allow near the stated full load current to be drawn. Not a very common occurrence I will admit, but I'll stick to what I said.

 

[Damian Petsas]

Andy is that correct now then??

 

[Andy78]

Andy is that correct now then??

My point was that your cable size did not seem to have been selected as a result of your calculation, not the calculation itself.

 

[Damian Petsas]

Well minimum cable size would be 4 mm but i uprated to 6 mm to play safe.

 

[Resu]

Now look at table A1

Table A1 is current demand to be assumed?

Table A2 is for diversity, no?

 

[Damian Petsas]

What are your thoughts Dave?

 

[Damian Petsas]

what would you say then Resu??

 

[Resu]

what would you say then Resu??

Baring in mind I am technically still a trainee...

Minimum cable size would actually be 2.5mm although you wouldn't find a circuit breaker to suit! Common sense says 6mm though, seeing as you are running a new circuit in anyway. This would future proof too (to a certain degree).

 

[Damian Petsas]

Well trainee or not i appreciate your input and best of luck buddy

 

[Resu]

Remember to add 5A if switch has a socket on it too!

 

[Damian Petsas]

Cheers bud but no switch as in h level cupboard

 

[Dave OCD]

In a new kitchen scenario with plenty of sockets I never use a cooker isolator with a socket, I don't think 5 amps is a very realistic assumption although something like a 'fast boil' 3kW kettle would admittedly only be on for short periods, I just think it's better to keep the cooker circuit purely for the cooker.

 

[telectrix]

Baring in mind I am technically still a trainee...

Minimum cable size would actually be 2.5mm although you wouldn't find a circuit breaker to suit! Common sense says 6mm though, seeing as you are running a new circuit in anyway. This would future proof too (to a certain degree).

2.5mm on a 25A MCB? then Ib<In<Iz, so circuit complies.

 

[Resu]

2.5mm on a 25A MCB? then Ib<In<Iz, so circuit complies.

Not sure they're so commonly available anymore though?