New oven with plug

[ban-all-sheds]

My problem is, my current setup and oven came with no plug and wired straight into a junction box to a separate cooker switch on the wall, and is on a different wiring system with its own fuse.

Dear JohnW2, there's a clue in there somewhere, to the op do what taylortwocities said, and ignore the rest of the nonsense.

There is also an electric hob connected to the switch, and its not from memory connected into the junction box.

So this is the wall switch, I could've sworn that there was a fuse slot on the front.

I'll need to check the fuse rating in the FCU when I get home.

It is no criticism of the OP to want to make sure that there actually is an accessory which can be replaced with a socket, nor can people be criticised for seeking clarification.

You really are not very good at this, are you.

 

[ban-all-sheds]

Is it possible that the part of your brain that interprets visual verbal representations has become totally bewildered and confused by the digitally generated pointless waffle that spews out of your finger tips.

What is possible is that you are utterly incompetent at doing this.

 

[EFLImpudence]

In the UK, if a maker mandates a 13A fused supply that immediately raises the question of why is he doing that,

I would think it because he has supplied the smallest flex possible for the load and knows the arrangements in the UK.

and how the hell can he sell his appliance in geographies where a 13A fused supply cannot be provided.

Then he will 'mandate' a 16A OPD as he knows that is what they have in those places.

But in geographies where socket circuits are 16A, mandating a maximum 16A circuit will create no problems and will prompt no questions.

Unlike the ones who do that but do not alter their instructions for the UK leading to the numerous questions on here about these appliance being alright on a 13A plug.

I have never seen a manufacturer's instruction mention the omission of overload possibilities.

No, I mean that if a maker can assure that his appliance will be plugged into a circuit with a 16A OPD, and not hard wired into one with a 50A, it may give him scope to cut corners on how he engineers and protects the internals of it.

Mmmm. I'm trying to think of how that would be done.

I wasn't. When I wrote "But if the maker really has designed the internals on the assumption of a maximum 16A protective device, what can you do?" I was talking about the internals of the appliance.

If we are still talking about an oven then it will be designed with the smallest wires acceptable for the load to each element and the likely heat.

In any case, apart from protection of the supplied flex, I am sure the OPD size will be based on the minimum required for the appliance to function correctly.
Hence the difference in instructions that call for an actual or minimum fuse rating.

 

[ban-all-sheds]

I would think it because he has supplied the smallest flex possible for the load and knows the arrangements in the UK.


Then he will 'mandate' a 16A OPD as he knows that is what they have in those places.

How can he mandate two different device ratings for the same equipment?

Mmmm. I'm trying to think of how that would be done.

Mmmm. I'm trying to think if there are any cable sizes which get adequate fault protection from a B16 but not a B50.

Hence the difference in instructions that call for an actual or minimum fuse rating.

Instructions which call for a minimum 13A, or 16A, would be satisfied by a 10kA one.

 

[EFLImpudence]

How can he mandate two different device ratings for the same equipment?

Because that's what is usual in the different areas. It was you who introduced the word mandate.

Mmmm. I'm trying to think if there are any cable sizes which get adequate fault protection from a B16 but not a B50.

Then there should be internal fusing
or the wires will be their own fuses.

Instructions which call for a minimum 13A, or 16A, would be satisfied by a 10kA one.

Exactly.

As is often mentioned, what happens when the oven has a hob attached?

 

[ban-all-sheds]

Because that's what is usual in the different areas. It was you who introduced the word mandate.

It is not possible for the same item to need different maxima in different areas, unless the areas enjoy different laws of physics.

Then there should be internal fusing

Should be, yes.

But what if there isn't?

As is often mentioned, what happens when the oven has a hob attached?

You're missing the point.

This whole mini-topic started when I asked "But if the maker really has designed the internals on the assumption of a maximum 16A protective device, what can you do?".

I'm not defending such a practice, just observing that it is technically possible (I think) for an appliance to be made which relies on an external OPD for internal fault protection, and for the rating of that device in those circumstances to be no more than 16A.

 

[JohnW2]

I'm not defending such a practice, just observing that it is technically possible (I think) for an appliance to be made which relies on an external OPD for internal fault protection, and for the rating of that device in those circumstances to be no more than 16A.

Opinions obviously differ since, whilst you say that you think that would be technically possible, when you first mentioned this, my response was essentially the opposite - i.e. that I found it difficult to see how that could be possible ...

If the manufacturer had somehow determined that there would be a significant additional safety problem with the oven if the external protection were >16A, then I would agree. ... However, as has been said before, I do find it difficult to see how that could be the case. Quite apart from the fact that it's hard to think of even remotely likely scenarios in which an oven could create a significant overload (even a jammed small fan probably wouldn't), even a B16 would allow 30A+ to flow through the fault for a few minutes, and that would probably be enough to 'fry' whatever was involved, so I don't think it would be significantly worse with a higher-rated OPD.

I wonder which of us is right?

Kind Regards, John

 

[EFLImpudence]

It is not possible for the same item to need different maxima in different areas, unless the areas enjoy different laws of physics.

Of course it is. That's what's available -
but you are using different words to confuse the matter.
It won't be stated that the appliance needs <whatever>; it will be: Fuse rating - 13A or 16A

Should be, yes. But what if there isn't?

Then the manufacturer has decided it's not necessary.

You're missing the point.

This whole mini-topic started when I asked "But if the maker really has designed the internals on the assumption of a maximum 16A protective device, what can you do?".

I can't think how that would be - in an oven.
Conversely to what you wrote; that includes a 1A protective device.
I think you are using terms which are not actually used - or are used in error.

I'm not defending such a practice, just observing that it is technically possible (I think) for an appliance to be made which relies on an external OPD for internal fault protection, and for the rating of that device in those circumstances to be no more than 16A.

An appliance, perhaps, not an oven.

I'm still struggling with what that actually means.
Wouldn't it have to mean that the appliance had wiring too small to cope with the loads?

 

[ban-all-sheds]

However, as has been said before, I do find it difficult to see how that could be the case. Quite apart from the fact that it's hard to think of even remotely likely scenarios in which an oven could create a significant overload (even a jammed small fan probably wouldn't), even a B16 would allow 30A+ to flow through the fault for a few minutes, and that would probably be enough to 'fry' whatever was involved, so I don't think it would be significantly worse with a higher-rated OPD.

30+A will go through a B50 for ever.

The current at which a B16 fast trips could be passed by a B50 for over 10 minutes, so if a low-but-not-near-zero impedance fault could arise then you've got the potential for some serious overheating to occur.

IHNI how feasible such a fault is, but a 3kW element with a fault 15-20% of the way along will draw a current which a B16 would break "immediately" but a B50 would tolerate for several minutes, probably for long enough for insulation to catch fire, conductors to melt etc, which would not be a good thing.

As I said, I am in no way defending the practice of making an appliance without its own internal protection, but I don't see how we can be certain that there is no way that one would ever be made, nor that if there was one a B16 would provide fault protection but a B50 would allow a fire to start. People blithely assume that an oven cannot create an overload, but that means they are assuming that the electronics which prevent multiple elements coming on at the same time cannot fail.

Why do I have to keep pointing out that what's happened here is that you said

The question of whether the oven, rather than its cable, needs 13A protection is a matter often discussed here (including recently) - and I think that the consensus is that, if it really needs such protection (which is probably doubtful), it would/should be provided internally within the oven.​

and I then asked what are you gonna do if it does need such protection, and it hasn't been provided internally because the maker judges that the circuit OPD, or plug fuse, will do the job perfectly well? IMO one thing you can't do is to assume that you can safely connect it directly to a cooker circuit with no fusing down.

 

[EFLImpudence]

The current at which a B16 fast trips could be passed by a B50 for over 10 minutes, so if a low-but-not-near-zero impedance fault could arise then you've got the potential for some serious overheating to occur.

But it is an oven; does that matter?

IHNI how feasible such a fault is, but a 3kW element with a fault 15-20% of the way along will draw a current which a B16 would break "immediately" but a B50 would tolerate for several minutes, probably for long enough for insulation to catch fire, conductors to melt etc, which would not be a good thing.

But if it has a 3kW element, presumably that will not be the only element so the external protection would have to be greater than 13A anyway.
It's more likely, if it has a 13A fuse in the plug, that two 6A elements are all that could be on together.
Also, I don't think that's possible with an element. A fault a 20% of the way along will mean a current five times the intended. If the element were able to sustain this without arcing/melting then it would not work very well at its design current.
How can a loose element wire maintain continuos contact to create these faults?

As I said, I am in no way defending the practice of making an appliance without its own internal protection, but I don't see how we can be certain that there is no way that one would ever be made,

Well, if it is made then we don't need to worry, do we? You are postulating faults where there is no internal protection.
Has anyone ever seen an oven with internal protection?

nor that if there was one a B16 would provide fault protection but a B50 would allow a fire to start.

I suppose that is a fair point but I repeat the point about ovens with hobs attached. Are they different than those without?

People blithely assume that an oven cannot create an overload, but that means they are assuming that the electronics which prevent multiple elements coming on at the same time cannot fail.

Ok, but a three element oven presumably could only draw 18A at the most.

Why do I have to keep pointing out that what's happened here is that you said

The question of whether the oven, rather than its cable, needs 13A protection is a matter often discussed here (including recently) - and I think that the consensus is that, if it really needs such protection (which is probably doubtful), it would/should be provided internally within the oven.​

and I then asked what are you gonna do if it does need such protection, and it hasn't been provided internally because the maker judges that the circuit OPD, or plug fuse, will do the job perfectly well? IMO one thing you can't do is to assume that you can safely connect it directly to a cooker circuit with no fusing down.

Apart from the fact that the same thing could be part of a cooker.

 

[JohnW2]

30+A will go through a B50 for ever.

Indeed. Theoretically 56.5A should.

The current at which a B16 fast trips could be passed by a B50 for over 10 minutes, so if a low-but-not-near-zero impedance fault could arise then you've got the potential for some serious overheating to occur.

Indeed.

IHNI how feasible such a fault is, but a 3kW element with a fault 15-20% of the way along will draw a current which a B16 would break "immediately" but a B50 would tolerate for several minutes, probably for long enough for insulation to catch fire, conductors to melt etc, which would not be a good thing.

[I presume you mean a fault to earth at 15-20% from the neutral end.] As you may recall, when I first heard people (particularly EFLI) arguing that a load like an oven was "not likely" to produce an overload [hence its cables not required to have any overload protection, per 433.3.1(ii)], I used to use the very argument you have just produced, but I eventually decided that they/he were right in saying that such an overload was "not likely" (which is all that reg requires). In fact, once I started thinking, I came to the conclusion that, despite not being totally impossible, it was incredibly unlikely (hence certainly "not likely") that such a fault would result in a sustained high overload current, since I think it could probably only happen if not only did the fault arise, but with the L side of the broken element then rapidly getting welded to the earthed casing.

If one comes to this conclusion that an overload is "not likely", such that BS 7671 would not require any overload protection of the supply cable, then it is hard to see why anything within the oven actually needs overload protection, either.

If the manufacture of an oven were to 'require' ('mandate', in the language you have recently been using) anything, it would seem more logical that it should be an RCD than an OPD - since it seems almost inconceivable that an L-N (rather than L-E) overload current could arise.

.... and I then asked what are you gonna do if it does need such protection, and it hasn't been provided internally because the maker judges that the circuit OPD, or plug fuse, will do the job perfectly well? IMO one thing you can't do is to assume that you can safely connect it directly to a cooker circuit with no fusing down.

As above, I think one could if one were prepared to assume (as BS 7671 is prepared to do in relation to the supply cable) that it is "not likley" that the oven can create an overload.

Kind Regards, John

 

[ban-all-sheds]

I wonder why we have fused plugs.

 

[DetlefSchmitz]

Well, if it is made then we don't need to worry, do we? You are postulating faults where there is no internal protection.
Has anyone ever seen an oven with internal protection?

Well, yes. We were in a holiday cottage when the oven element stopped working. The owner came with a handyman and replaced the oven's internal fuse.

 

[JohnW2]

I wonder why we have fused plugs.

Presumably because some, maybe most, loads connected by plugs/sockets probably are "likely" (not "not likely") to be able to create overload currents, for which the circuit's OPD might well not provide adequate protection for the appliance's cable (and, more controversially, maybe its innards).

Kind Regards, John

 

[EFLImpudence]

Well, yes. We were in a holiday cottage when the oven element stopped working. The owner came with a handyman and replaced the oven's internal fuse.

Do you know what caused it?