The 16amp question but different

[Eddy0987654321]

I realise this question have been asked before but I still have found no definitive answer.
Unusually this is a New house build.
Kitchen ring final circuit using 20 amp dp switches to isolate the white goods (including F/freezer etc and d socket) on a 32amp CB.
All wiring 2.5mm.
Appliance: Oven (mircrowave combi) 3.65kW 16amp.

Qu. It is within regs to have it connected unfused to the dp switch on the radial 2.5mm cable.

Further information.
This is one of two ovens placed vertically with the lower oven (identical load of 3.65kw) on a separate 6mm radial.
Also with a induction hob (5.2kW) with a separate 6mm radial.

I don’t think it is, and have been in conversation with the electrician who won’t provide a cct diagram, but I have a photo of the installation to B boxes.
He reassures me that the cabling is ‘adequate’ and the 32amp MCB is okay.

But surely, unlike say a F Freezer which protected by its fuse, this oven is not and in theory the 2.5mm radial could be overloaded, although unlikely unless the load changes.

Is there any specific reg. this is in violation of, that I could quote, or is it just poor practice, bending the regs?

 

[EFLImpudence]

Kitchen ring final circuit using 20 amp dp switches to isolate the white goods (including F/freezer etc and d socket) on a 32amp CB.
All wiring 2.5mm.
Appliance: Oven (mircrowave combi) 3.65kW 16amp.

Qu. It is within regs to have it connected unfused to the dp switch on the radial 2.5mm cable.

You might be able to argue that it would be within the requlations using the omission of overload protection regulations but it would not be done, and as you go on to explain what you have, there is no point doing it.

Further information.
This is one of two ovens placed vertically with the lower oven (identical load of 3.65kw) on a separate 6mm radial.
Also with a induction hob (5.2kW) with a separate 6mm radial.

You can connect all the cooking appliances to the 6mm² radial and that would be perfectly acceptable.
A 32A 'cooker' circuit is good for 15kW (possibly more) of appliances because of 'diversity' which means that because of the cycling on and off of the appliances, the full load will never be on at the same time.

I don’t think it is, and have been in conversation with the electrician who won’t provide a cct diagram, but I have a photo of the installation to B boxes.
He reassures me that the cabling is ‘adequate’ and the 32amp MCB is okay.

He is correct.

But surely, unlike say a F Freezer which protected by its fuse, this oven is not and in theory the 2.5mm radial could be overloaded, although unlikely unless the load changes.

Ovens cannot overload the spur circuit, but with other things on the ring, that could overload the ring.

Is there any specific reg. this is in violation of, that I could quote, or is it just poor practice, bending the regs?

It is just not necessary.

 

[EFLImpudence]

Having reread, it appears you have TWO 6mm² radials. Is that correct?

If so, why are you even asking about putting one of the ovens on the ring circuit?

 

[Eddy0987654321]

Having reread, it appears you have TWO 6mm² radials. Is that correct?

If so, why are you even asking about putting one of the ovens on the ring circuit?

For clarity, this is a new build.
I was given a site visit and took photos.
From this this there were chalk wall markings. 'oven' looks to be a 6mm radial and 'Hob' (induction) an additional 6mm radial.

My interest was tweaked when I saw 'm/w' on one of the 2.5 cables from the 20amp grid switch back box.
Initially I thought the electrician thought it was a standard built in microwave oven BUT this is a 16amp 3,65kW combination oven with the same element and load of the matching single oven.

He confirmed he is aware of this.

So its unused and on the 2.5mm ring final protected by a 32amp MCB.

Simply, you think this is okay?

Thank you for taking the time to reply.......I just like fused spurs my self, these grid switches seem like a trend at the moment. Not that a 13amp FS would be appropriate for the oven in question.

 

[EFLImpudence]

My interest was tweaked when I saw 'm/w' on one of the 2.5 cables from the 20amp grid switch back box.
Initially I thought the electrician thought it was a standard built in microwave oven BUT this is a 16amp 3,65kW combination oven with the same element and load of the matching single oven.
He confirmed he is aware of this.
So its unused and on the 2.5mm ring final protected by a 32amp MCB.

Simply, you think this is okay?

Technically it might be as far as the oven is concerned but, as I said, it might result in the ring - not the spur - being overloaded so not compliant.
As there is no need to do it, I would say it is poor design which is against the regulations.

I just like fused spurs my self, these grid switches seem like a trend at the moment. Not that a 13amp FS would be appropriate for the oven in question.

There is no point having Fused Connector Units for the spurs to appliances; there is a fuse in the plug - except the oven - which protects the spur cable.
You might as well just use 20A switches - if that is what you want.
They are just a trend - or fashion - and are not required regulation-wise.

 

[Eddy0987654321]

He is an image.
The chalk ident 'M/W' is for thee combi oven 3.65kW.

Hmm, can see how to load an image from a file on PC, any help?

Thanks for the replies again EFL.

 

[EFLImpudence]

Just copy and paste (or drag) pictures.

 

[Eddy0987654321]

To the right are the b boxes for the hob and oven.
To the left the b boxes for spur from oven radial and M/W from ring final.
These are exactly the same loads.

 

[Eddy0987654321]

Well, the compromise is that he is going to put the second oven on another 6mm radial from the oven switch. Is this a better solution?
Its still not a 16amp device on a 16amp protection but the radial is well in spec. even if both ovens are on.
Didn't realise you (domestic) could ring the NICEIC for advice, they were not happy with the original installation.

 

[EFLImpudence]

All 6mm² cable (oversized actually) - Simples.

I don't really know why anyone would think of anything else.

 

[Eddy0987654321]

Agreed, but he's keeping the 2.5mm socket* and putting an isolating switch in the grid for it (unused but maybe in the future) but running an additional cable from the switch for the second oven and adding a connection point behind the oven.
*The plaster board is now over the wiring and it's being done as 2nd fix.
Anyway I took on the might of the large building company a won! lol.

His excuse was odd, essentially 'yes now I know its an 16 amp oven, we aren't told the model numbers and spec (yea?) we will do this, if you are okay with it, but it would have been alright anyway'
He tried to explain the full load on an oven is rarely maintained etc. I get this, but new builds should be right imo, its a clean drawing board for a start.

For what I'm paying, I'd expect gold conductors not copper and you barely get copper on the central heating anymore!

Thank for the help on this.

 

[sparkwright]

Only just started to read all the comments on this post, so forgive me if I don't understand some things, or get things wrong.

Are you certain the microwave was on the ring circuit, and that another separate radial circuit had been run to the grid switch?

Were they intending fitting a fused outlet or 13 amp socket behind or adjacent the microwave, in conjunction with the 20 amp dp switch?

Personally I wouldn't connect a 16 amp microwave (even with diversity) to a ring circuit, especially in a new building, but that's just me.

 

[Eddy0987654321]

His excuse was that he thought the combi-Microwave was initially just a Microwave oven. But oddly he was going to let the installation remain when the item was correctly identified as a 16amp 3.65kW device.

His reasoning being it would rarely draw (if ever) the full load on the spec plate.
I’m not quite sure if they were going to add a plug or use a connector plate.

I haven’t ‘named and shamed’ the builders in question but it does raise the issue of quality/safety governance. They apparently don’t create the wiring drawing of the installed cct, only the generic layout, before the customer selects optional extras such as this additional combi oven.

 

[JohnW2]

... Personally I wouldn't connect a 16 amp microwave (even with diversity) to a ring circuit, especially in a new building, but that's just me.

His excuse was that he thought the combi-Microwave was initially just a Microwave oven. But oddly he was going to let the installation remain when the item was correctly identified as a 16amp 3.65kW device. .... His reasoning being it would rarely draw (if ever) the full load on the spec plate. .... I’m not quite sure if they were going to add a plug or use a connector plate.

I'm a little surprised that, until sparkwright mentioned it, there had not been more discussion about 'diversity' - which is the official name for the "reasoning" presented by the electrician.

Applying the standard/accepted concept of diversity to a 3.65kW cooking appliance, such an appliance can be considered as representing a load of no more than about 11.6A - which is why such appliances (like the one I have) often come with a 13A plug attached.

Some, like sparkwright, may feel that such is not 'ideal', but I would not say that there's anything fundamentally wrong with the design. The average current drawn over appreciable periods of time by a tumble dryer is probably greater than that drawn by a combi-microwave, yer many/most dryers are connected via 13a plugs, most commonly to ring circuits.

Kind Regards, John

 

[Eddy0987654321]

I'm a little surprised that, until sparkwright mentioned it, there had not been more discussion about 'diversity' - which is the official name for the "reasoning" presented by the electrician.

Applying the standard/accepted concept of diversity to a 3.65kW cooking appliance, such an appliance can be considered as representing a load of no more than about 11.6A - which is why such appliances (like the one I have) often come with a 13A plug attached.

Some, like sparkwright, may feel that such is not 'ideal', but I would not say that there's anything fundamentally wrong with the design. The average current drawn over appreciable periods of time by a tumble dryer is probably greater than that drawn by a combi-microwave, yer many/most dryers are connected via 13a plugs, most commonly to ring circuits.

Kind Regards, John