Ovens, plugs, kitchen rings and diversity

[JohnW2]

We know that ('informative') Appendix 15 of the regs recommends that cooking appliances >2 kW should not be supplied from a ring final circuit. However, we also know that many ovens 'rated' right up to 3 kW come with 13A plugs fitted and are commonly plugged into a kitchen's ring final circuit.

In deciding whether this is acceptable (even if contrary to a recommendation of an informative Appendix of the regs), is it considered reasonable and permissible to invoke diversity?

In a current thread, it has been suggested that connecting a "4.68 kW" oven via a 13A plug socket is not acceptable since "at full wack it would draw over 20A". In fact, if one assumes that (as usual) the 4.68 kW is quoted at 240V then, with the usually 230V calculation, the after-diversity current would be a little under 13A.

If we were designing a dedicated circuit for this oven, it would therefore presumably be acceptable for the circuit to be (hypothetically) protected by a 13A OPD. However, accepting that such a practice would certainly not be regarded as 'ideal', what would people think about such an appliance having a 13A plug and being plugged in to a ring final circuit?

Kind Regards, John

 

[fidom]

More importantly, what would insurance companies think of such a practice?
In a kitchen with all integrated appliances it is easy to assess the maximum loading on the kitchen ring. If there is already a washing machine, a tumble dryer and a dishwasher on the ring I would be tempted to put in a dedicated circuit even for a single oven and would certainly do so for a double oven.

 

[JohnW2]

More importantly, what would insurance companies think of such a practice?

A good point, but if it could be successfully argued to be compliant with regulations, I imagine that it would be difficult for them to make an issue out of it. As I said, that are countless ovens sold with 13A plugs and (per the manufacturer's instructions) plugged into ring final circuits.

In a kitchen with all integrated appliances it is easy to assess the maximum loading on the kitchen ring. If there is already a washing machine, a tumble dryer and a dishwasher on the ring I would be tempted to put in a dedicated circuit even for a single oven and would certainly do so for a double oven.

As I said, I think that most of us would agree that to have any oven or cooker connected to a 'kitchen ring' is far from being an ideal practice, even though it is quite common.

Kind Regards, John

 

[EFLImpudence]

There is no 'yes or no' answer.

Knowledge must be employed - a limiting factor, I realise.

If the oven has, for example two 2.34kW elements (just an example) that can be on together then, obviously, diversity cannot be used.

If this is not the case and only one element at a time can be used then it may come with a 13A plug and will therefore be put on the ring.


I do feel that the 'may contain nuts' syndrome is being used in the manufacturers' instructions these days to (as with guidance documents) cover the worst case scenario.
An example is showers and RCDs. It may be wise but it is not actually the shower that requires the RCD.

 

[JohnW2]

There is no 'yes or no' answer. Knowledge must be employed - a limiting factor, I realise. ... If the oven has, for example two 2.34kW elements (just an example) that can be on together then, obviously, diversity cannot be used.

I personally don't think that is at all "obvious" - the concept of diversity relates to averaging over time as well as 'space'. In other words, it's not just a question of totting up what current all the components could be consuming simultaneously, but also takes into account the fact that, even if both are 'on' simultaneously, both will be cycling on and off by virtue of their thermostats - so that, even if both are 'on', the average power consumption over a (moderate) period of time will be a lot less than would get by totting up their 'on' currents.

If one assumes that (as usual) the 2.34 kW in your (my) example relates to 240V, then at 230V, each of them will consume about 9.34A - i.e. 18.68A for two of them. Applying the usual calculation, that amounts to an after-diversity current of about 12.6A ... which, rightly or wrongly, is regarded as the maximum average over a period of time that the appliance (the two elements) would be expected to draw. For that reason, a hypothetical dedicated circuit with a 13A OPD would presumably be regarded as fully acceptable and compliant. The question I'm posing is whether one still thinks the same way if the appliance has a 13A plug and is plugged into a ring.

An example is showers and RCDs. It may be wise but it is not actually the shower that requires the RCD.

A bit tangential to what we're discussing, but, yes, we've discussed that before. What you say is largely correct but I would suggest that even for the most rational and informed of us, it's difficult to shake off the thought that the combination of electricity, water, wet naked bodies and (quite possibly) earthed plumbing is 'crying out' for RCD protection - so I'm not sure that I blame the manufacturers in this case ... and don't forget that the regs now require (presumably for similar reasons) everything in a bathroom (even outside of zones) to be RCD protected.

Kind Regards, John

 

[EFLImpudence]

I personally don't think that is at all "obvious" - the concept of diversity relates to averaging over time as well as 'space'. In other words,

That is true but there is no 'totting up' with a load of either 4.68kW or nothing.

It's not just a question of totting up what current all the components could be consuming simultaneously, but also takes into account the fact that, even if both are 'on' simultaneously, both will be cycling on and off by virtue of their thermostats

Yes but both at the same time; this is not the same as, say, seven elements cycling independently.

- so that, even if both are 'on', the average power consumption over a (moderate) period of time will be a lot less than would get by totting up their 'on' currents.

I do not agree with calculating the fusing factor of the opd for what would be, in effect, a single load.

If one assumes that (as usual) the 2.34 kW in your (my) example relates to 240V, then at 230V, each of them will consume about 9.34A - i.e. 18.68A for two of them. Applying the usual calculation, that amounts to an after-diversity current of about 12.6A ... which, rightly or wrongly, is regarded as the maximum average over a period of time that the appliance (the two elements) would be expected to draw.

It does not matter which numbers are used. We are just using 4.68kW as an example.

For that reason, a hypothetical dedicated circuit with a 13A OPD would presumably be regarded as fully acceptable and compliant.

Not with a 4.68kW load.

The question I'm posing is whether one still thinks the same way if the appliance has a 13A plug and is plugged into a ring.

Well, if it comes with a plug then it can be plugged in.
In a small kitchen with only a couple of sockets it would not matter; in one with every appliance imaginably it could be different.

A bit tangential to what we're discussing, but, yes, we've discussed that before. What you say is largely correct but I would suggest that even for the most rational and informed of us, it's difficult to shake off the thought that the combination of electricity, water, wet naked bodies and (quite possibly) earthed plumbing is 'crying out' for RCD protection.

Precisely, but not the shower.

- so I'm not sure that I blame the manufacturers in this case ... and don't forget that the regs now require (presumably for similar reasons) everything in a bathroom (even outside of zones) to be RCD protected.

It may be a bit pedantic but they should state that a new circuit must be RCD protected.
An existing circuit and the shower itself does not but as I said it would be wise although as you are always asking "Has an RCD ever saved a life?".

 

[ban-all-sheds]

It's not just a question of totting up what current all the components could be consuming simultaneously, but also takes into account the fact that, even if both are 'on' simultaneously, both will be cycling on and off by virtue of their thermostats

Yes but both at the same time; this is not the same as, say, seven elements cycling independently.

So what do you think should be the diversity formula for an all-electric integrated cooker?

 

[JohnW2]

I personally don't think that is at all "obvious" - the concept of diversity relates to averaging over time as well as 'space'. In other words,

That is true but there is no 'totting up' with a load of either 4.68kW or nothing.

It's not just a question of totting up what current all the components could be consuming simultaneously, but also takes into account the fact that, even if both are 'on' simultaneously, both will be cycling on and off by virtue of their thermostats

Yes but both at the same time; this is not the same as, say, seven elements cycling independently.

I'm a bit lost here. What is the difference (other than the obvious!) between two elements cycling independently and seven elements cycling independently? Indeed, the (OSG) diversity formula everyone seems to use would be applicable to a single 4.68 kW element which was time-cycling, wouldn't it? Statistically speaking, the effect of time-cycling on average power consumption (over time) will be the same whether there is 1 element or 100 elements (if all elements are cycling similarly) - albeit the averaging will work better over shorter time periods with more elements.

The question I'm posing is whether one still thinks the same way if the appliance has a 13A plug and is plugged into a ring.

Well, if it comes with a plug then it can be plugged in.

Maybe I haven't been as clear as I could have been. One of the things I've been trying to ask is whether a manufacturer's decision as to whether fit a 13A plug does, or does not, take diversity into account.

- so I'm not sure that I blame the manufacturers in this case ... and don't forget that the regs now require (presumably for similar reasons) everything in a bathroom (even outside of zones) to be RCD protected.

It may be a bit pedantic but they should state that a new circuit must be RCD protected. An existing circuit and the shower itself does not.

Well, yes, the regs themselves are obviously not retrospective - but manufacturers can (and often do) 'go beyond the regs'!

...but as I said it would be wise although as you are always asking "Has an RCD ever saved a life?".

Quite so - but even I find it almost impossible to shake off the idea that, if RCDs ever save lives, the scenario of water + electricity + wet naked bodies + earthed plumbing is a situation 'crying out for an RCD'!

Kind Regards, John

 

[ekmdgrf]

That would be me posting in the wrong topic again.

 

[EFLImpudence]

So what do you think should be the diversity formula for an all-electric integrated cooker?

The standard method.

However, we are talking about an oven with two elements (total 4.68kW) which will be on and off together to which I do not think diversity should be applied.

 

[JohnW2]

The standard method .... However, we are talking about an oven with two elements (total 4.68kW) which will be on and off together to which I do not think diversity should be applied.

As I keep saying, "the standard method" of applying diversity would be applicable even if it were just a single (time-cycling) 4.68 kW element wouldn't it? If you agree with that, the diversity calculation would be at least as valid for 2 x 2.34 kW ones (in fact, a bit more valid, since it's very unlikely that the cycling of the two would be perfectly synchronised), wouldn't it?

Kind Regards, John

 

[ban-all-sheds]

The standard method.

Not according to you.

However, we are talking about an oven with two elements (total 4.68kW) which will be on and off together to which I do not think diversity should be applied.

Such an oven could easily be found in an integrated cooker.

The standard diversity method treats it the same as all the other elements in the cooker.

You do not believe that diversity should be applied to the oven part of the cooker.

So what do you think should be the diversity formula for an all-electric integrated cooker?

 

[EFLImpudence]

I'm a bit lost here. What is the difference (other than the obvious!) between two elements cycling independently

They won't be cycling independantly.
The thermostat will switch them both on and off together.

and seven elements cycling independently?

A big difference.

Indeed, the (OSG) diversity formula everyone seems to use would be applicable to a single 4.68 kW element which was time-cycling, wouldn't it?

Would it? I am saying "No".

Statistically speaking, the effect of time-cycling on average power consumption (over time) will be the same whether there is 1 element or 100 elements (if all elements are cycling similarly)

But not simultaneously which is the point.

albeit the averaging will work better over shorter time periods with more elements.

I don't think a shorter time would be better.

Maybe I haven't been as clear as I could have been. One of the things I've been trying to ask is whether a manufacturer's decision as to whether fit a 13A plug does, or does not, take diversity into account.

I don't think it would; if a plug is fitted it would only be for a 13A load (or less) and the flex will have been chosen for such, i.e. not all elements will be used together.

Well, yes, the regs themselves are obviously not retrospective - but manufacturers can (and often do) 'go beyond the regs'!

Intentionally?

Quite so - but even I find it almost impossible to shake off the idea that, if RCDs ever save lives, the scenario of water + electricity + wet naked bodies + earthed plumbing is a situation 'crying out for an RCD'!

But you have mentioned plumbing again with which I would agree - if accessible.
However, the shower itself has an all plastic exterior.

 

[EFLImpudence]

Such an oven could easily be found in an integrated cooker.

Then it won't be on a 13A fused plug - the subject of the thread.

The standard diversity method treats it the same as all the other elements in the cooker.

It treats it as part of a larger whole which it is.
Do the regulations allow applying diversity to an iron?

You do not believe that diversity should be applied to the oven part of the cooker.

You cannot apply diversity to just the oven part.

So what do you think should be the diversity formula for an all-electric integrated cooker?

As I said, the standard method.

 

[ban-all-sheds]

Let's try again.

You do not believe that diversity can be applied to an oven.

You do believe that diversity can be applied to an oven when it is in a cooker.

Those two positions are incompatible.


The standard diversity formula does not break out the oven component and treat it any differently to the other parts of the appliance. If you are not prepared to accept diversity calculations for the oven on its own then you must not, unless you want to be illogical and inconsistent, accept them for the oven when it is in an integrated cooker, and therefore you must not accept the standard diversity formula.