220v. 230v, 240v, 250v?

[John-SJW]

I saw an oven that was rated at 3,100 watts. Now most would say that cannot be fitted on final ring circuit as rule of thumb. But:
3,100 watts draws amps of:
14.09 amps @ 220v
13.47 amps @ 230v
12.91 amps @ 240v
12.4 amps @ 250v

If the installation is 240v or 250v then it safely inside the 13 amp of a final ring circuit.

The question is, and the regs aficionados can help here, what is the voltage that should be used to assess, as maybe the voltage will vary in an installation over the years.

 

[LastManOnline]

This is a double-edged sword because of the loss of diversity. Yes the total load capacity is greater, but there is less flexibility about where the loads may be connected. With 20A circuits it is not nearly so much of a limitation as with 16A. It might take four or more of the latter to do the work of one 32A, if nuisance tripping and persistent non-trip overloads are to be avoided due to unfavourable distribution of load.

There is a really easy and practical answer to this. Take a look at the average 3 bedroomed home in ROI, France, Germany, and compare with UK. Appliance use is virtually identical. In ROI, two radials are required in the kitchen. Guess how often I get calls about mcb, s tripping??
The above fears are in practice non-existent

The above was another economic argument in favour of retaining local OCPD in the IEC60906 retrofit scenario.

I do remember similar fears in the noughties being expressed in the UK about the introduction of rcd, s. Their was a quite vocal "anti-rcd brigade" who proclaimed their own "project fear" message about the inevitability of nuisance tripping that would be caused by the rcd, s. They omitted to look at countries where these same devices had been in use for many years

 

[Lucien Nunes]

In ROI, two radials are required in the kitchen

In UK, one 32A circuit will do more than a kitchen. I'm not saying that's advisable for reasons of redundancy, but that's a separate consideration. OTOH I did manage to trip a 16A MCB in Germany with two electric heaters that I thought I had plugged into separate circuits but were actually on the same circuit. As I mentioned, there is a noticeable increase in flexibility of the 20A circuits compared to 16A.

In a previous occupation I used to go around venues plugging lots of 3kW loads into 13A sockets. What works in a domestic kitchen won't necessarily suffice in that situation, but any kind of standard plug and socket needs to be suitable for whatever wiring configurations are applicable to both.

 

[John-SJW]

Firstly, your objective analysis is as always...very refreshing. My view of the "achilles heel" is a simple one. Get rid of it. It can be done easily and inexpensively

Replace the kitchen ring (plus other rings) with 2 x20amp radials.

The immediate benefits are...


1) an extra 2kw capacity compared to the 32 amp ring

2) two circuits protecting kitchen rather than one

3) a maintenance free plugtop (fuses no longer necessary)
..... issues re heat dissapation sorted
..... Issues regarding wrong size fuse inserted sorted.
...... safety issues due to shorting out fuse sorted

4) electrical testing simplified (radials versus rings)

Why get rid of a safety asset. Madness to do so.

 

[John-SJW]

Regardless of the relative merits or disadvantages, I don't think that getting rid of the BS1363 plug is a great suggestion.

The people of Ireland might be open to this suggestion, but there'd be revolt on the streets of GB.

There are lots of ring circuits in Ireland. Maybe they want deaths and fires by reducing protection.

 

[static zap]

There are lots of ring circuits in Ireland. Maybe they want deaths and fires by reducing protection.

Maybe we need to shame more appliances .
In the 1980-90s it was VCRs that the fire-brigade usually blamed.

I wonder how many fake Iphone chargers are in untidy kitchens
with paper , polythene nearby.
or in bedrooms hidden by bedding. Smoke detectors may save lives,
but at what cost for connected convenience. !

 

[LastManOnline]

There are lots of ring circuits in Ireland. Maybe they want deaths and fires by reducing protection.

With respect John. It would be appreciated if you concentrate on electrically analysing the questions being raised rather than making throwaway / unfounded comments.

 

[John-SJW]

With respect John. It would be appreciated if you concentrate on electrically analysing the questions being raised rather than making throwaway / unfounded comments.

If you take the fuse out of the plug when on a ring, you will get fires, as an essential safety point has been removed. The farsighted men in 1942 who thought of the fuse in plug, and then regulated for it, were brilliant. We have the best. Why change what does not need changing.

 

[LastManOnline]

In summary, I do not think it was the intention of Bosch to imply that a 3.7kW load may be supplied via a 13A plug,

Got an update from Bosch this morning stating that it's hob will "not draw more than 3.7kw when being used".So this would imply a current of 15.5 amp in the UK and 16 amp in ROI on its 13 amp plugtop when the hob is on full load.

The figures don't look great. We are on the wrong side of the plugtop rating. However, (going to stick my neck out here a little). I would have no concern about installing one of these in my own home as my current Induction hob (which by coincidence only ever has 2 rings on at any one time) is constantly cycling in and out and in reality the average load is under 13 amps (probably a, few amps under after initial startup).

Would I install one in someone else's home?. Unlikely unless there is a separate circuit. This particular appliance seems to fall between a rock and a hard place according to our regs. Can't see an inspector being pleased to see it being plugged in.

Bosch I think we're more than a little careless in the way they wrote their instruction Manuel.
Secondly, it was clear to me that the "service personnel" (who were very pleasant to deal with) were struggling a little in answering technical questions. Not their fault.

 

[John-SJW]

Got an update from Bosch this morning stating that it's hob will "not draw more than 3.7kw when being used".

So, what is it set to, if it is settable, as it has a 13A fuse?
Is this a continuous 3.7kW, or a spike?
Something tells me they do not know enough about their own product.

Out of interest, my Smeg induction hob states 7.2 kW. It can be wired 3 or single phase. I assume the 7.2kW is for 3-phase connection. I put on an amp clamp, then put all rings on full with pans full of cold water, on the P setting. It was drawing only 21.46 amps at 247v, which is about 5.3 kW, way below the max of 7.2 kW they state.

 

[LastManOnline]

So, what is it set to, if it is settable, as it has a 13A fuse?

As mentioned in earlier posts. A 13 amp fuse will take 15 amps for a significant period

Out of interest, my Smeg induction hob states 7.2 kW. It can be wired 3 or single phase. I assume the 7.2kW is for 3-phase.

No. 7.2kw is also suitable for single phase. They have 3 phase on the continent in domestic dwellings and that's why the hobs are configured to be connected both ways

put on an amp clamp, then put all rings on full with pans full of cold water, on the P setting. It was drawing only 21.46 amps at 247v, which is about 5.3 kW, way below the max of 7.2 kW they state.

You are probably getting an average as the rings cycle in and out of full power

 

[John-SJW]

As mentioned in earlier posts. A 13 amp fuse will take 15 amps for a significant period

No. 7.2kw is also suitable for single phase. They have 3 phase on the continent in domestic dwellings and that's why the hobs are configured to be connected both ways

You are probably getting an average as the rings cycle in and out of full power

I know it can. I forget how long. Any offers from the group? I recall a 13A fuse blows at about 17A after about an hour. So for intermittent use that is fine, not for a continuous load like a space heater.


I put the large pans of cold water on each ring, then all on the highest P setting, then observed the clamp meter. No switching in and out at that point as all rings were on full belt.

 

[John-SJW]

Look at at a plug. It always says 13A, 250V. That is 3.2 kW.

 

[timhoward]

I know it can. I forget how long. Any offers from the group? I recall a 13A fuse blows at about 17A after about an hour.

If this graph is true a BS1362 13 amp fuse won't blow at all until over 20 amps and at least 2 hours.

 

[Julie.]

The characteristic curve isn't quite right or the markings are wrong, the characteristic must become asymptotic at a value no greater than 19.5A for a 13A fuse, or it wouldn't comply with the 1.5 rule going back to the 14th for close protection, and they are the same fuses now.

It could take up to 4 hours to operate of course.

 

[timhoward]

The characteristic curve isn't quite right or the markings are wrong, the characteristic must become asymptotic at a value no greater than 19.5A for a 13A fuse, or it wouldn't comply with the 1.5 rule going back to the 14th for close protection, and they are the same fuses now.

It could take up to 4 hours to operate of course.

Thanks Julie. I've never found a good graph for this question...