2 Ovens on Cooker Circuit

[JohnW2]

But do they state fuse (opd) requirement in all cases?

I obviously cannot speak for 'all' cases, but in some cases they certainly do.

Don't ovens/hobs which are supplied without a flex merely state the required supply? The opd will then depend on the cable. Ovens/hobs supplied with a flex will state the fuse size which will apply to both the supply needed and flex rating.

We've been over this ground many times before. Some manufacturers appear to specify OPD ratings as a means of protecting the innards of their machines (becasue they can't be bothered to install internal protection), even if that sometimes means that one has to use a lower-rated OPD than would be needed to adequately protect the cable. Unfortuately, BS761 plays into their hands, by giving theoretical 'teeth' to their MIs.

Kind Regards, John

 

[EFLImpudence]

I obviously cannot speak for 'all' cases, but in some cases they certainly do.

Merely translated by someone with no electrical knowledge ?

We've been over this ground many times before.

Yes.

Some manufacturers appear to specify OPD ratings as a means of protecting the innards of their machines (becasue they can't be bothered to install internal protection),

Extractor fans, yes, although the fuse demanded is many times higher than it could be but ovens?

Is there any difference in the innards of a built-in single oven and a similar oven which is part of a cooker.

even if that sometimes means that one has to use a lower-rated OPD than would be needed to adequately protect the cable. Unfortuately, BS761 plays into their hands, by giving theoretical 'teeth' to their MIs.

It does, but we don't have a suitable 16A opd so is it unacceptable to work it out ourselves?.

 

[JohnW2]

Is there any difference in the innards of a built-in single oven and a similar oven which is part of a cooker.

Who knows?! Indeed, it's even possible that the oven part of a cooker has internal protection.

even if that sometimes means that one has to use a lower-rated OPD than would be needed to adequately protect the cable. Unfortuately, BS761 plays into their hands, by giving theoretical 'teeth' to their MIs.

It does, but we don't have a suitable 16A opd so is it unacceptable to work it out ourselves?.

If the MI demands a low OPD rating (lower than would be necessary to protect the external supply cable) in order to provide protection for some puny-sized conductors within the oven, then I don't see that any calculations you did (assuming you knew the CSA of those puny conductors) would result in a different answer from that in the MIs - do you?

Kind Regards, John

 

[mfarrow]

An 800KMF with appropriate fuse and gland(s) would probably be the most practicable solution to the bulk issue an MCB creates.

 

[JohnW2]

An 800KMF with appropriate fuse and gland(s) would probably be the most practicable solution to the bulk issue an MCB creates.

Yes, that thought occurred to me, provided one can get low-enough rated fuses (one probably can). However, I can't see how one could use glands with a 800KMF - what was your plan? I think one might have to just use 'external' cable restraint (clips/cleats).

Kind Regards, John

 

[EFLImpudence]

But do they state fuse (opd) requirement in all cases?

I obviously cannot speak for 'all' cases, but in some cases they certainly do.

Not doubting you but have you an example?
I am having trouble finding oven specifications which even state the current.

If the MI demands a low OPD rating (lower than would be necessary to protect the external supply cable) in order to provide protection for some puny-sized conductors within the oven, then I don't see that any calculations you did (assuming you knew the CSA of those puny conductors) would result in a different answer from that in the MIs - do you?

Well, I'm not so sure.

We do not have 16A fuses therefore we cannot comply with the MIs without major work - unlike in Europe.

I am aware of your view on opd rating and the belief that it should somehow protect appliances as well as the cable but -
is it reasonable to expect major rewiring or contorted circuits incorporating additional CUs in kitchens before someone may use a bog-standard oven which, under the regulations for omission of overcurrent protection, could be fitted to the existing circuit.

 

[JohnW2]

Not doubting you but have you an example?

Not off the top of my head, but I'll see what I can find.

I am aware of your view on opd rating and the belief that it should somehow protect appliances as well as the cable but - is it reasonable to expect major rewiring or contorted circuits incorporating additional CUs in kitchens before someone may use a bog-standard oven which, under the regulations for omission of overcurrent protection, could be fitted to the existing circuit.

It's not really my belief that OPDs should necessarily be used for that purpose, but I do recognise that, in the absence of adequate internal protection in appliances/equipment, it's not such a bad idea to provide some protection externally.

However, that's not really the point. As I said, it's BS7671 that has caused all this. Most electricians believe that OPDs should be used only to protect cables (fixed or otherwise) up to the point at which they enter appliances/equipment, and that's a very reasonable/defensible viewpoint. However, BS7671 effectively gives manufacturers the power to over-ride that by requiring OPDs to be rated so as to fulfill functions beyond protection of those cables. There are certainly some senses/areas in which it is totally appropriate for BS7671 to require compliance with manufacturers instructions, but to have given the manufacturers a totally 'blank cheque' is, IMO, more than a little unwise.

Kind Regards, John

 

[mfarrow]

When I say gland, I refer to a curved rectangular box which is sold separately to sit over the cable entries and I believe even comes with the cheap copies. I've not seen one in the flesh so not sure how practicable it is for T&E, but would be less ghaulish than a galv adaptable box.

The MEM fuse range goes down to 15A as standard, but I believe Lawson manufacture smaller sizes.

 

[JohnW2]

When I say gland, I refer to a curved rectangular box which is sold separately to sit over the cable entries and I believe even comes with the cheap copies.

Ah, I'm not familiar with them. I have several KMF800s in my installation and none came with any such 'add-ons', and I hadn't seen or heard of them. I suspect that they may detract to some extent from the small overall size of the KMF800, which is its main attraction.[/quote]

The MEM fuse range goes down to 15A as standard, but I believe Lawson manufacture smaller sizes.

Thanks. As I said, I suspected that would be the case.

Kind Regards, John

 

[ban-all-sheds]

An 800KMF with appropriate fuse and gland(s) would probably be the most practicable solution to the bulk issue an MCB creates.

Is that going to be any smaller than a 2-module enclosure (don't think you can get 1-module ones)?

 

[ban-all-sheds]

An 800KMF with appropriate fuse and gland(s) would probably be the most practicable solution to the bulk issue an MCB creates.

Is that going to be any smaller than a 2-module enclosure (don't think you can get 1-module ones)?

..would be less ghaulish than a galv adaptable box

One can buy boxes which are not made of galvanised steel.

 

[JohnW2]

An 800KMF with appropriate fuse and gland(s) would probably be the most practicable solution to the bulk issue an MCB creates.

Is that going to be any smaller than a 2-module enclosure (don't think you can get 1-module ones)?

Depth-wise (which would probably be the main issue behind a cooker), it almost certainly would be smaller - unless, as I said, you could find a shallow enclosure in which you could mount an MCB 'sideways'.

Kind Regards, John

 

[flameport]

Many of these ovens which state 16A fuse are needed do not require 16A at all. The actual rating is often far less, and the easiest method is to get a list of replacement elements for the oven and see what rating they are. Typically 2.5kW

For those which have multiple heating elements, it is almost always the case that only one element can be selected at a time (e.g grill or oven), or the combined total of the elements which can be used simultaneously is still far less than 16A.

 

[ban-all-sheds]

Depth-wise (which would probably be the main issue behind a cooker), it almost certainly would be smaller - unless, as I said, you could find a shallow enclosure in which you could mount an MCB 'sideways'.

Kind Regards, John

If by "sideways" you mean with the MCB not facing you - i.e. with the DIN rail it's on at right angles to the plane of the wall, (the MCB could still be vertical) then I think a 2-module enclosure would be shallower than a KMF 800.

 

[ban-all-sheds]

When I say gland, I refer to a curved rectangular box which is sold separately to sit over the cable entries and I believe even comes with the cheap copies.

Ah, I'm not familiar with them. I have several KMF800s in my installation and none came with any such 'add-ons', and I hadn't seen or heard of them. I suspect that they may detract to some extent from the small overall size of the KMF800, which is its main attraction.