OSG pg 160.Cooker circuits in household and similiar premises. 8.4

[entech]

Hi all with respect to the above ref from the 17th OSG.

Could someone explain how "a 30 or 32 A circuit is usually appropiate for household or similiar cookers of rating up to 15kW".

is the key in the words " rating of 15kW" , in that its not a 15kW load??

using i=p/v amps would be around 65 amps!!

 

[Spudnik]

Diversity is your friend.

 

[not clever]

1500/230 = 65A

Deduct 10amp = 55A (you add the 10amp back on later)
30% of 55 = 16.5A

16.6 + 10 = 26.5A

Add another 5amp if a socket is on the ccu

Diversity is a wonderful thing, now back to me beers.

But I always put in a dedicated circuit for cooker/oven/hob

 

[entech]

Cheers for reply Jason.

I thought diversity is used when you are determing design current for the entire installation ??

this is where i am getting a little confused as surely a oven of 15kW rating in full use would
keep tripping the protective device of 30 or 32A.

 

[Spudnik]

Its very unlikely that the oven will ever pull FL.

This is why diversity can be applied.

 

[entech]

I have been looking on the net trying to find how the rating of a cooker is achieved but cannot find much info.

I presumed that if an oven was rated at say 15kW then surely thats what can be demanded.

Its doing my nut in now........ )

 

[Spudnik]

Well, yes and no.

The max rating will rarely be achieved as this will often include other functions which will not be able to be used all at the same time for eg, grill.

 

[not clever]

Get the manufacturers part number for the cooker & look on their websites or look in the spec pages of the user manuals or look at the spec plate fitted to the rear or just inside the oven door of the cookers.

I presumed that if an oven was rated at say 15kW then surely thats what can be demanded.

DIVERSITY ......... even if everything was on at the same time the stats would be cutting in & out so not all items would be a full demand at the same time.

 

[Des 56]

I would have thought the rating could only be achieved if all elements are cold,the individual controls, all on max, and the control switch swinging them all into action in one go, and that maximum only for a very brief period

 

[entech]

I would have thought the rating could only be achieved if all elements are cold,the individual controls, all on max, and the control switch swinging them all into action in one go, and that maximum only for a very brief period

so the protective device would trip in this instance.

sod's law says that if it can happen it will, or was it murphys law???..... or finagles law???? )

 

[Graeme Harrold]

Even if all of the elements are on, the circuit will be overloaded, but this will only be for short periods. Have a look at the time curves for a 32A device and with 55A flowing it will take in the region of 500 seconds to trip.

 

[Des 56]

so the protective device would trip in this instance.

sod's law says that if it can happen it will, or was it murphys law???..... or finagles law???? )

Probably wouldn't trip the 32 amp mcb for about 20 mins at full whack, and that max level wouldn't be sustained for long enough

Sorry Graeme didn't see your reply and I seem to have said simillar

 

[entech]

Even if all of the elements are on, the circuit will be overloaded, but this will only be for short periods. Have a look at the time curves for a 32A device and with 55A flowing it will take in the region of 500 seconds to trip.

Would the cable withstand such current flow for such a period of time??

 

[martysparky]

Well we are dawning on the time when most cookers will be used to there most (cooking christmas dinners).

 

[entech]

Thanks for the replies guys.

With further reading I understand that diversity it to be used when calculating the overall demand for an entire installation and not used for working out cable sizes for individual circuits.

The load used by a domestic home as seen by the supplier would be lower than the sum of all appliances in the installation added together as all the appliances would not be in use at the same time. Diversity is used for this purpose.

 

[lamb]

Would the cable withstand such current flow for such a period of time??

Yes, the cable would take roughly one hour at full load current to come up to maxiumum operating temperature (70 deg for PVC).

 

[Graeme Harrold]

Thanks for the replies guys.

With further reading I understand that diversity it to be used when calculating the overall demand for an entire installation and not used for working out cable sizes for individual circuits.

The load used by a domestic home as seen by the supplier would be lower than the sum of all appliances in the installation added together as all the appliances would not be in use at the same time. Diversity is used for this purpose.

Diversity can be applied to individual circuits. Is that not where this thread started..............

 

[entech]

Diversity can be applied to individual circuits. Is that not where this thread started..............

Yes diversity is applied for individual circuits when working out max demand as per bs7671.

 

[Sav]

Sorry to put a spanner in the works, but:
1500 /230 = 6.52 amps not 65amps !!

Am i missing something here ??
Sav

 

[Graeme Harrold]

Sorry to put a spanner in the works, but:
1500 /230 = 6.52 amps not 65amps !!

Am i missing something here ??
Sav

Sav, Yes a ZERO it was 15Kw = 15 x 1000 = 15000w not 1.5Kw

And for entech, diversity can be used to reduce cable sizes on individual circuits if you want