Advice re appliance sockets required

[EFLImpudence]

no greater and no less.

I disagree. Greater is irrelevant.

Diversity applied to all the appliances is 25A.

Excluding an integral socket at the switch -
With 32A MCB the diversity would be 10A + 44% (53% of FL).
Were the OP to fit a 40A MCB then the diversity would be 10A + 60% (66%).
I think that perfectly satisfactory.

 

[Astra99]

Nobody has voiced any concern at the increasing number of appliances coming into this country which are designed for continental Europe with (supposedly) 16A plugs. Sooner or later the "powers that be" will have to allow the use of Schuko French style (to ensure polarisation) sockets on 16A radials specifically for this.

I would also elicit opinion on the following. Compare the pin size of the Schuko plug rated at 16A with the old 15A (or even 5A) BS546 plug; or our much loved but often maligned BS1363 plug. It looks like the Schuko wouldn't carry 5A let alone 16!! Anyone care to comment?

PS I am familiar with the Schuko plugs and sockets, and I would be hard-pressed to get a 6mm cable in the socket! Our BS1363 sockets will accept a single 6mm with ease!

 

[Astra99]

One thing I did forget in my previous post was to compare the pin size of the 16A IEC 60309 plug with the BS546 15A. No prizes for guessing which is the larger!

 

[EFLImpudence]

One thing I forgot to ask (not a trick question - I genuinely want to know your opinion) ... do you feel it is appropriate to use a diversity calculation to argue that a 3,600W cooking appliance can be connected with a 13A plug/socket (or 13A FCU)?

That would depend on the configuration.

Were the load two elements of 1,800W which came on and off together then obviously not - 15A on or off.

However, there may be three elements 1,200W each (for ease), two oven and one or two for grill, which cannot be all on together so the maximum load would be 10A on or off.
You may say, then, why specify 16A but this is what they have in Europe so may not relate to the actual usage.

I feel you are going to retort that that is your point and if it is 15A and you have two therefore diversity may not work but if on a 32A or 40A circuit it would be satisfactory.
Then there is the hob, of course, but then the likelihood of ALL being on at the same time becomes less likely; the more elements there are the better diversity works.
Were this one unit with the same loading do you think it less likely that all will be on together - not just switched on but actually drawing current.


Oven and cooker manufacturers do seem reluctant lately to furnish the values and operating modes of their products.

 

[EFLImpudence]

Also -

How much does the load reduce when the elements heat up?

 

[JohnW2]

One thing I forgot to ask (not a trick question - I genuinely want to know your opinion) ... do you feel it is appropriate to use a diversity calculation to argue that a 3,600W cooking appliance can be connected with a 13A plug/socket (or 13A FCU)?

That would depend on the configuration. ... Were the load two elements of 1,800W which came on and off together then obviously not - 15A on or off.

Actually, I'm not sure that even that is 'obvious'. As I understand it, the concept of diversity applies 'over time' as well as 'over space' (different elements etc.). In other words, if there is a 3,600W load which is either 'on' or 'off', but one knows that, on average, the thermostat will cycle it on/off with a duty cycle of, say, 50% or less, then, that actually represents an average load (over a reasonable time period) of 7.5A or less. However, having said that, I don't think that either of us would probably put a 13A plug on such a thing.

However, there may be three elements 1,200W each (for ease), two oven and one or two for grill, which cannot be all on together so the maximum load would be 10A on or off.

Sure, but that's not really 'diversity', at least not in the statistical sense - you're talking about an appliance which cannot draw more than 10A - so a 13A plug would obviously be fine.

Oven and cooker manufacturers do seem reluctant lately to furnish the values and operating modes of their products.

Indeed - and I suppose some would argue that means that only the manufacturers can actually specify what 'supply' the appliance actually needs.

Kind Regards, John

 

[JohnW2]

Also - How much does the load reduce when the elements heat up?

Yep, that's another factor - but difficult to quantify when one doesn't know what temperature each of the elements is going to be at.

Kind Regards, John

 

[ruddyr1]

Ok thanks for all the diversity guff. Basically if I interpret that into English Im stuffed without rewiring and adding extra circuits.

Ok easier question anyone know of a good manufacturer of stuff I can plug in

Cheers

 

[Risteard]

If one has, say, 6 elements spread across three appliances, I would suspect that it is, in practice, statistically more likely that more will be 'on' simultaneously than if one had 6 elements in one appliance.

If all were being used how often do you envisage that all 6 would be heating simultaneously, and how long for?

They cycle on and off which is part of the point with diversity.

do you feel it is appropriate to use a diversity calculation to argue that a 3,600W cooking appliance can be connected with a 13A plug/socket (or 13A FCU)?

Leaving aside diversity for the time being, cooking appliances often quote their total connected load, which is not the same thing as the total possible load, given that even where elements can not be energised simultaneously the manufacturers often add these together in order to achieve a more impressive figure. So a "3.6kW load" may actually have a maximum draw of 1.5kW for example.

 

[JohnW2]

Ok thanks for all the diversity guff. Basically if I interpret that into English Im stuffed without rewiring and adding extra circuits.

Not necessarily. As you will have seen, I've been arguing both sides of the 'diversity guff' business, and at least some of the electricians here would take the view that, by application of diversity, you could run all three of your appliances off one circuit.

That's why I said, early on, that your best bet would be to get an electrician to appraise the situation - since (s)he may feel that you don't need many, if any, additional circuits.

Kind Regards, John

 

[ekmdgrf]

How much does the load reduce when the elements heat up?

Good question. Are you thinking what I'm thinking? Use a pilot light to keep the elements warm?

 

[JohnW2]

If one has, say, 6 elements spread across three appliances, I would suspect that it is, in practice, statistically more likely that more will be 'on' simultaneously than if one had 6 elements in one appliance.

If all were being used how often do you envisage that all 6 would be heating simultaneously, and how long for? ... They cycle on and off which is part of the point with diversity.

Sure, that is 'part of diversity', but not all of it. As I've been saying, the reason for having multiple appliances, and the way in which they are to be used, is another factor in the statistical melting pot.

The point is perhaps clearer in extreme cases. Consider a kitchen shared by three people/households, with three cookers side-by-side (one for each of them), likely to be used at roughly the same time. Application of standard diversity calculations to each of the three cookers, separately, is fine - the result of those calculations being the postulated 'average' load presented by each appliance over a period of usage time. However, in that situation, I'm not sure that it is reasonable to lump all three cookers together and calculate a (lower total) after-diversity load. Put in more formal statistical terms, the legitimacy of averaging across all three cookers essentially relies on an assumption that the times that the three cookers are used are statistically 'independent' of one another. If all three users tend to cook at roughly the same time, that assumption of independence is invalid.

The reality, of course, that the 'safety margins' built into things such as the cable current-carrying-capacities of cables we work with are such that there will rarely be problems, at least as far as cables are concerned. I'm certainly not concerned about the cables. However, I'm perhaps a bit less comfortable with the prospect of the short-term 'overloading' of MCBs that can can result from 'generous' application of diversity (e.g. theoretically anything up to 80A or so, even if very briefly, through a 32A MCB).

Leaving aside diversity for the time being, cooking appliances often quote their total connected load, which is not the same thing as the total possible load, given that even where elements can not be energised simultaneously the manufacturers often add these together in order to achieve a more impressive figure. So a "3.6kW load" may actually have a maximum draw of 1.5kW for example.

Sure, the information provided by manufacturers can be confusing and misleading - and I certainly agree that, in terms of electrical common sense, all aspects of design should be on the basis of the actual maximum possible current draw. However, as has been discussed, at least until next year, those electricians who feel constrained (by employers, insurers or scheme operators) to work strictly to the word of BS7671 are presumably stuck with having to follow "Manufacturer's Instructions" to the letter, even if those 'letters' are daft and/or inappropriate.

Kind Regards, John

 

[JohnW2]

Also - How much does the load reduce when the elements heat up?

To give you some illustrative figures ....

If we consider ambient temp to be 20°C, then at 250°C the resistance would have increased (hence current decreased), relative to ambient, by a factor of about 1.9 (very substantial) if the element were made out of copper. However, if (which I would think would be far more likely) the element were made out of Nichrome, the change would only be a factor of about 1.09, which is not all that much.

Kind Regards, John

 

[ruddyr1]

Can you just bear with me for a couple of years whilst I go do a course.

I was hoping this forum was for DIY questions. I wouldnt vote for UKIP but Ive had about as much diversity as I can take.



Question 2, if I stand in a bucket of water and stick my fingers in the plug socket will it hurt?

But thanks all the same.

And no all the appliances will not be on at the same time, chances are there would be one oven and two hob induction rings on or the hob and the microwave combi as Im only cooking for me and the wife.

I cant ever envisage all being on at once. Which makes me think...why am i buying them?

 

[JohnW2]

Can you just bear with me for a couple of years whilst I go do a course. I was hoping this forum was for DIY questions. I wouldnt vote for UKIP but Ive had about as much diversity as I can take.

As I implied in what I recently wrote to you, the problem is that it's not really a DIY question - since, as you will have seen, even electricians will argue about the answer. As I said, if you get an electrician to assess the situation, it's quite possible that (s)he will decide that it's OK for you to run all three appliances off one circuit (hence no new circuits would be required) - but that's not really a decision that a DIYer could make.

Kind Regards, John