Ovens, plugs, kitchen rings and diversity

[JohnW2]

I thought it was the use of a plug which you were challenging?

Well, that was the subject of the thread but as usual we have wandered.

Although it was admittedly the language in which I phrased my OP, the 'plug' is really a red herring. What the discussion is really about is whether it is acceptable to invoke diversity to allow a ~20A oven to be on a circuit protected by a 13A OPD (and, potentially, wired with cable with a CCC of 13A, if you could find it!). You think not (because it does not contain more than one 'independently cycling elements') - so I presume you would say the same if there were no plug, but, rather a dedicated hard-wired circuit with a hypothetical 13A MCB - is that the case?

Kind Regards, John

 

[JohnW2]

Indeed - but, of course, the one type of kitchen load they did not consider is the one we are discussing - namely cooking appliances.

I know - I posted that extract from Wiring Matters to show the use of the concept of diversity over time.

Yes, I realised that, but was just thinking that, in terms of demonstrating the working of diversity over time to EFLI, it would have been even better if it had included cooking load(s)!

Kind Regards, John

 

[EFLImpudence]

What the discussion is really about is whether it is acceptable to invoke diversity to allow a ~20A oven to be on a circuit protected by a 13A OPD (and, potentially, wired with cable with a CCC of 13A, if you could find it!).

Yes, it was not the actual plug I was against but that it has a 13A fuse.

You think not (because it does not contain more than one 'independently cycling elements') - so I presume you would say the same if there were no plug, but, rather a dedicated hard-wired circuit with a hypothetical 13A MCB - is that the case?

Well, yes - as above - but it would seem I must concede.

Having said that, diversity, be it for cookers, lighting circuits or whole installations only ever considers multiple loads and the premise that they are not all on/used at the same time; nowhere, apart from the quotes from Bas , does anywhere mention the time factor or rather how to allow for this.

As for the original question, I still cannot see it is right that the design current for a single 20A load can be 13A (10A + 30%) OR 13.8A (20 / 1.45 for MCBs).

 

[ban-all-sheds]

I presume the conventional time is per cycle period of the appliance or could it be a total of the cycled periods?

Cyclic loads aren't quite the same - my suggestion that a "short time" might be "conventional time" was based on an inference.

An inference which further reading has shown might be flaky. It may not be correct to regard anything less than a long time as a short time.

Again we can only draw inferences from the guidance for cyclic loads. 6.2.3 of Paul Cook's Commentary has a table of times in minutes for different cable sizes (csa & core count). Those times are the ones at which it becomes not worth calculating the thermally equivalent load, for it will not yield a lower cable size.

I will scan and post the table and associated explanation, but not right now, but to pick an example, the time quoted for a 2-core 2.5mm² cable is 15 minutes. So if your Imax ≤ In ≤ Iz has produced a 2.5mm² cable and the duration of Imax in a cycle is more than 15 minutes it won't be worth looking at a thermally equivalent load to see if you can drop the cable size. Under 15 minutes and it might be.

So maybe "short time" is 15 minutes for that cable. Getting back to your shower, if we assume it's an overloaded 6mm² cable the time is 18 minutes.

I would be unsure how to calculate the figures.

I think there are details of that too in Commentary.

 

[ban-all-sheds]

Why have we got this 230/240v nonsense again?
2.34 Kw relates to 240v. Nobody has a 230v supply, it is 240v (measure it). At 240v each will consume 9.75A, 19.5 for two of them. After diversity 13.15A so too much for a 13A plug.

Winston - will you STFU - NOBODY wants to see you demonstrating yet again that you are so stupid that you do not understand the concept of using a nominal voltage in calculations. We have got the message - we all know you are stupid. Now go away.

 

[ban-all-sheds]

That bit of 533.2.1 relates to 'cyclic loads' - do showers actually qualify as that?

Only insofar as any load can be considered cyclic if it has a regular cycle.

 

[ban-all-sheds]

Yes, I realised that, but was just thinking that, in terms of demonstrating the working of diversity over time to EFLI, it would have been even better if it had included cooking load(s)!

It's got a toaster

 

[JohnW2]

Yes, it was not the actual plug I was against but that it has a 13A fuse.

You think not (because it does not contain more than one 'independently cycling elements') - so I presume you would say the same if there were no plug, but, rather a dedicated hard-wired circuit with a hypothetical 13A MCB - is that the case?

Well, yes - as above - but it would seem I must concede.

No-one, and certainly not me, wants you to concede unless you are actually convinced, and it sounds as if you aren't! As I've tried to explain, I'm not convinced by my (different) view, either, since I don't know what we are most concerned about - average current over time, proportion of time with current >In of the OPD, a combination of the two, or what.

Having said that, diversity, be it for cookers, lighting circuits or whole installations only ever considers multiple loads and the premise that they are not all on/used at the same time; nowhere, apart from the quotes from Bas , does anywhere mention the time factor or rather how to allow for this.

Again, it depends upon what one's criteria are. IF one is interested in average current over time, then "multiple loads which are not all on at the same time" is no different from 'one load which is not on all the time'. On the other hand, if one were interested in the proportion of time with current >In of the OPD, that would, indeed, usually be greater with the single load than with multiple 'independent' loads. As I've said, I don't know which of these is the more relevant to a diversity calculation.

As for the original question, I still cannot see it is right that the design current for a single 20A load can be 13A (10A + 30%) ...

In case it's not obvious, I can sympathise with your view - but I think it's probably more quantitative than conceptual. What if it were two, independently cycling, 10A loads? If the on/off duty cycle were the same for those two loads (and the same as the duty cycle for the single load), the average total current over time would be the same as with a single 20A load, and the main difference would be that the proportion of time for which current was >In with the single 20A load would be double the proportion with the 2 x 10A loads. ... so it might be, for example, that total current was >In for 40% of time for the single load and 20% of the time for the two loads - but would that, in your mind, necessarily make the difference between 'unacceptable' and 'OK'?

Kind Regards, John

 

[winston1]

[quote="ban-all-sheds";p="3183662"
Winston - will you STFU - NOBODY wants to see you demonstrating yet again that you are so stupid that you do not understand the concept of using a nominal voltage in calculations. We have got the message - we all know you are stupid. Now go away.[/quote]

NO I am NOT stupid. The people that are stupid are those that use a so called nominal voltage that has never existed in calculations. The oven manufacturers use 240V because that is what it is. Using a lower figure results in a lower current figure which appears OK when in fact the actual current is out of spec. Dangerous or not?

 

[ban-all-sheds]

Winston - you are stupid.

You are an idiot.

You are an ignoramus.

You are an imbecile.

You are tedious beyond belief.

And you still can't scrape up enough thinking power to use the Quote button properly.

 

[JohnW2]

So if your Imax ≤ In ≤ Iz has produced a 2.5mm² cable and ...

I'm a bit confused. Assuming that I correctly understand what you mean by Imax, are we not discussing/considering situations in which Imax > In? If Imax ≤ In, then there is surely no need to think about diversity or any other 'adjustment'?

Kind Regards, John

 

[winston1]

Winston - you are stupid.

You are an idiot.

You are an ignoramus.

You are an imbecile.

You are tedious beyond belief.

And you still can't scrape up enough thinking power to use the Quote button properly.

There is no need for such rudeness. On some forums you would be banned for it.
The people that are stupid are those that dreamed up the idea of a nominal voltage that does not exist and those sparks who follow like sheep and use a non existent voltage in calculations.

 

[ban-all-sheds]

I'm a bit confused. Assuming that I correctly understand what you mean by Imax, are we not discussing/considering situations in which Imax > In?

Initially one uses Imax as Ib.

If it looks like it might be profitable, one can do calculations based on the duration of Imax vs Imin to see if an Ib < Imax can be arrived at.

 

[ban-all-sheds]

There is no need for such rudeness.

First of all it is not rudeness - it is an accurate assessment of you. I accept that you might be upset by it - people like you often find that the truth hurts.

Secondly there is every need for such an assessment.

The people that are stupid are those that dreamed up the idea of a nominal voltage that does not exist and those sparks who follow like sheep and use a non existent voltage in calculations.

And there you go again - still thinking that there are people here who don't realise what an uncomprehending lump of uselessness you are, and that therefore you need to show us once more.

 

[JohnW2]

Initially one uses Imax as Ib. ... If it looks like it might be profitable, one can do calculations based on the duration of Imax vs Imin to see if an Ib < Imax can be arrived at.

OK - but Imin hasn't got much to do with it, has it? In the sort of situations we've been discussing, it will usually be zero!!

If one tried to apply this to the sort of multiple cyclic load (e.g. hob) cooker situations that EFLI has been talking about, this could get very complicated, because one wouldn't simply have a dichotomy of Imin and Imax. Rather, there would be several different total currents, each with different (and probably unknown!) durations, two or more of which may well be above In.

Kind Regards, John