What amp circuit required for 2 ovens and a hob

[SUNRAY]

No, you've not misunderstood anything, but I had completely missed and/or forgotten it !

People are obviously free to apply diversity separately to each appliance, and then add up the after-diversity currents, if they wish to - but such an approach will be much less 'generous' (in terms of diversity) than if one did it for the total cooking appliance load on the circuit - since if one does it separately for each appliance,one's after-diversity figures includes a "10A minimum" for each and every appliance (whereas there is only one "10A" if all appliances are considered together).

As an example,with Sunrays figures above, if both loads are on the same circuit, then applying diversity to the two together would result in an after-diversity figure of about 21.5A, not much more than half Sunray's 40.5A figures when the appliances are considered separately.

Kind Regards, John

When I did my 16th course the IEE guidance notes for tutors specified it was per appliance, and the example was for a circuit containing an oven and a hob.

The difference should have come out exactly 20A different

 

[JohnW2]

When I did my 16th course the IEE guidance notes for tutors specified it was per appliance, and the example was for a circuit containing an oven and a hob. The difference should have come out exactly 20A different

If you mean "per appliance" literally, that surely makes no sense, does it?

Would it make sense that a 4-plate hob and an oven (two 'appliances') should represent double the after-diversity load that it would represent if exactly the same hob and oven would represent if physically 'joined together' in a single'case' and called a "cooker" (one 'appliance')?

Kind Regards, John

 

[SUNRAY]

If you mean "per appliance" literally, that surely makes no sense, does it?

Would it make sense that a 4-plate hob and an oven (two 'appliances') should represent double the after-diversity load that it would represent if exactly the same hob and oven would represent if physically 'joined together' in a single'case' and called a "cooker" (one 'appliance')?

Kind Regards, John

I've never had cause to query it before. However what if it were 2 full cookers in a busy household?

The difference should have come out exactly 20A different

of course not, just realised the error

 

[JohnW2]

I've never had cause to query it before.

Fair enough. However, you surely agree that if one has, say, 4 'heating rings' (of whatever type),a grill and twoovens all fed by the same circuit, then the electrical load they represent (with or without diversity) is the same if they are all in one 'case' (i.e.a "twin-oven cooker" = "1 appliance) as it would be if they were in 7 separate cases' (= "7 appliances"), or vice versa? All that matters is that all those 'bits of load' are on the same circuit.

However what if it were 2 full cookers in a busy household?

It's unlikely that "2 full cookers" would be on the same circuit but, if they were (and the circuit were man enough) then the above still applies. After all, if I constructed a cooker with 8 'rings', 2 grills and 4 ovens, you would presumably regard it as "one appliance" and therefore apply diversity to the 'total of everything', wouldn't you?

As I wrote in my response to ebee, I don't think that 'busy household' is particularly relevant. The usual diversity calculation presumably assumes the 'worst case' - of 'everything being switched on from cold simultaneously. If the average (i.e.'after diversity') coregent drawn during the first, say, 30 mins of that is X amps, then the average (hence 'after diversity') current over modest (say 30 min) periods of time will never be greater than X amps (in fact, a bit less) no matter how long the period of use goes on - i.e.even if it is used continuously for, say, 18 hours or more.

of course not, just realised the error

Indeed, but I did not bother to 'nit pick' over that small error

Kind Regards, John

 

[SUNRAY]

I happened to click on the centre title thinking it was the current thread

This from 2009 was right in the middle of the screen:

Diversity is a grey area and is up to the designer.
I like to err on the side of caution otherwise you may get the situation of cold turkey on Xmas Day when both ovens and the hob may well be going full blast.

For domestic ovens the rule is to allow 10 amps plus 30% of the remainder. This is valid for a single appliance but was not designed for several appliances so I tend to apply 10 amps plus 30% for EACH appliance.

So for this situation you get:

Oven 1 (15A) = 10+ 1.5 = 11.5
Oven 2 (15A) = 10+ 1.5 = 11.5
Hob ( 31.3A) = 10+ 6.5 = 16.5

Total assumed load = 39.5amps

albeit similar sort of posts appear there too.

 

[JohnW2]

This from 2009 was right in the middle of the screen:

.... For domestic ovens the rule is to allow 10 amps plus 30% of the remainder. This is valid for a single appliance but was not designed for several appliances so I tend to apply 10 amps plus 30% for EACH appliance. .... So for this situation you get:
Oven 1 (15A) = 10+ 1.5 = 11.5
Oven 2 (15A) = 10+ 1.5 = 11.5
Hob ( 31.3A) = 10+ 6.5 = 16.5
.... Total assumed load = 39.5amps

Well, I strongly disagree, for reasons I have explained (i.e. it makes absolutely no sense ).

@Taylortwocities ...do you (or did you in 2009 ) really believe that (if they are all supplied by the same circuit) those three bits of cooking equipment represent a total after-diversity current of 39.5A if they exist in three different boxes/cases, but only about 25.4A if they are built into one box/case called a "dual-oven cooker"?

That would surely make absolutely no electrical sense,would it?

Kind Regards, John

 

[ebee]

If you mean "per appliance" literally, that surely makes no sense, does it?

Would it make sense that a 4-plate hob and an oven (two 'appliances') should represent double the after-diversity load that it would represent if exactly the same hob and oven would represent if physically 'joined together' in a single'case' and called a "cooker" (one 'appliance')?

Kind Regards, John

In Essence, a 4 ring hob plus a grill, plus an oven built as a traditional age old "Cooker" and seperates hob/grill/oven , then both cases should produce equal results if the wattages are the same in both cases and the likely type of usage is the same then there is no practical difference from that point of view. The end result after a diversity calculation should be the same in both instances if they are on one circuit of one appliance or of one circuit of three appliances.
The diversity allowance is just as good or bad in both of those cases.
If the modern trend over the years becomes to use bigger pans, grills and ovens to cook lashings more food simultaneously to accomodate many more people, or conversely smaller smaller smaller then we might find it appropriate to alter diversity calculations if we think that full load periods and stats cycling on/off are greatly affected by this trend.
This allowance is tried and tested over many years and seems to work well - providing that unexpected trips have not been under-reported.

 

[SUNRAY]

In Essence, a 4 ring hob plus a grill, plus an oven built as a traditional age old "Cooker" and seperates hob/grill/oven , then both cases should produce equal results if the wattages are the same in both cases and the likely type of usage is the same then there is no practical difference from that point of view. The end result after a diversity calculation should be the same in both instances if they are on one circuit of one appliance or of one circuit of three appliances.
The diversity allowance is just as good or bad in both of those cases.
If the modern trend over the years becomes to use bigger pans, grills and ovens to cook lashings more food simultaneously to accomodate many more people, or conversely smaller smaller smaller then we might find it appropriate to alter diversity calculations if we think that full load periods and stats cycling on/off are greatly affected by this trend.
This allowance is tried and tested over many years and seems to work well - providing that unexpected trips have not been under-reported.

Despite some of my comments I am essentially OK with diversity as shown in regs (see post#46).
However I would always use a cable rated for the appliance rather than the OCPD to cater for the tripping that can and does occur (albeit very rare) and future upgrading. The price difference between 4 and 6mm² really isn't worth the hassle of future works.

 

[ebee]

Must admit I have never bought any 4.0 T & E, the price diff was minimal if any and was not always easy to obtain a few years ago. In fasct 10.0 was a rarity until showers got hotter too.

 

[EFLImpudence]

Despite some of my comments I am essentially OK with diversity as shown in regs (see post#46).

Ok. That did not appear to be the case.

However I would always use a cable rated for the appliance rather than the OCPD to cater for the tripping that can and does occur (albeit very rare) and future upgrading. The price difference between 4 and 6mm² really isn't worth the hassle of future works.

That's nothing to do with diversity; just ignoring installation methods and a liking for wasting copper.

 

[SUNRAY]

Must admit I have never bought any 4.0 T & E, the price diff was minimal if any and was not always easy to obtain a few years ago. In fasct 10.0 was a rarity until showers got hotter too.

I don't think I've ever purchased 4mm² T&E and only ever 200m of 3 core flex as 100m of 6mm² is very heavy to handle as an extension lead.

 

[SUNRAY]

Ok. That did not appear to be the case.

I take it you missed that post.

That's nothing to do with diversity; just ignoring installation methods and a liking for wasting copper.

I don't believe that's the case, I would describe it as common sense based many years of experience of replacing 4mm² cable in 32A feeds where some skinflint jackarse couldn't be bothered use the one braincell in his bonce.

The fact a cable has a rating of xxA doesn't mean it's suitable for a circuit rated or running at xxA

 

[ebee]

The fact a cable has a rating of xxA doesn't mean it's suitable for a circuit rated or running at xxA

I beg to differ, unless someone has got their sums or tests wrong then it should do so with a bit of headroom as a safety factor.
The fact we often add a bit on for our own piece of mind probably helps mitigate hotspots, poor quality cable, out of limit o.p.ds and slightly loose connections, after all not every circuit is absolutely 100% perfick in every way is it?

 

[JohnW2]

In Essence, a 4 ring hob plus a grill, plus an oven built as a traditional age old "Cooker" and seperates hob/grill/oven , then both cases should produce equal results if the wattages are the same in both cases and the likely type of usage is the same then there is no practical difference from that point of view. The end result after a diversity calculation should be the same in both instances if they are on one circuit of one appliance or of one circuit of three appliances. The diversity allowance is just as good or bad in both of those cases.

Exactly my point. It makes absolutely no sense that one should regard the load represented by a number of 'cooking devices' (on the same circuit) as being different according to whether they are all in one 'box' or several boxes!

If the modern trend over the years becomes to use bigger pans, grills and ovens to cook lashings more food simultaneously to accomodate many more people, or conversely smaller smaller smaller then we might find it appropriate to alter diversity calculations if we think that full load periods and stats cycling on/off are greatly affected by this trend.

That's true - but, as I've said, I suspect that the diversity calculations are already designed to cover 'the worst case' (of absolutely 'everything' being switched on from cold simultaneously) - and nothing could be 'worse' than that 'worst case'.

This allowance is tried and tested over many years and seems to work well - providing that unexpected trips have not been under-reported.

Exactly, as I said, there is no evidence that are diversity calculations are 'broken',so they don't need 'mending'

Kind Regards, John

 

[JohnW2]

The fact a cable has a rating of xxA doesn't mean it's suitable for a circuit rated or running at xxA

Eh?? What on earth do you think a cable's "current rating" means, then ?

Kind Regards, John