3.35kw combination microwave

[catdog1121]

Hey guys,

So a customer has bought some fancy 3.35kw combination microwave that comes with a prewired flex of 1.5mm, total load would therefore be 14.57A, can you use diversity on a combination microwave (cooking appliance) so 10A + 30% of remaining load meaning its 11.37A so it can be put on a 13A FCU?

Problem being that they currently have a hardwired oven (2.2kw) on a 32A cooker circuit so want to add the microwave to this circuit but obviously just using a connection plate would mean the 1.5mm cable (That cannot be replaced) would be protected by a 32A mcb which is obviously not allowed, if I can put it on a fcu then that would protect the 1.5mm cable..

 

[Lucien Nunes]

What OCP do the manufacturers stipulate?

 

[snowhead]

Combination microwaves are usually either or, not both functions at the same time.

 

[Strima]

Depending on manufacturers instructions the microwave will be fine on a 1.5mm 32 amp dedicated circuit as there's no risk of overload.

 

[catdog1121]

Depending on manufacturers instructions the microwave will be fine on a 1.5mm 32 amp dedicated circuit as there's no risk of overload.

In a fault condition is there not a risk of overload? I was always told the OCP device was there to protect the cable and that the cable needed to have a higher rating than the OCP device?
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What OCP do the manufacturers stipulate?

Everywhere I can see it says Amperage required is 16A.. But its silly because that would mean I cant used a 13A fcu to protect the cable and I cant add it on with the current oven as its on a 32A circuit breaker so the only thing I can think is a new 16A circuit.

 

[pc1966]

This may not be the same, but it claims (when you select English as the language) 3.3kW and a 13A plug:

Low-Priced Oven EB8013ED | KKT KOLBE

Order and buy the 60 cm stainless steel built-in oven with rotary spit and catalytic plates quickly and conveniently at a low price here in the online

www.kolbe.de

Either someone can't do their maths, or they are making some diversity assumptions!
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Reading the data-sheet though does not say anything like that, and just shows 3 terminals for the connection of power (nothing on cable size of MCB rating, etc).
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It says that it requires a 16A supply..

Then it is a 16A spur needed.

Or the rather dodgy option of a 16A MCB off a ring that is viewed with some derision around these parts...
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Something odd about posting time-lines here!

If you have the dedicated 32A cooker circuit you could take a 16A MCB off to save CU space and/or additional cable run.
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You could ask them what the maximum protection MCB is.

If they say it is OK to be protected by 32A then you can use that directly, though I would still use cable rated to match the supply MCB.

 

[catdog1121]

This may not be the same, but it claims (when you select English as the language) 3.3kW and a 13A plug:

Low-Priced Oven EB8013ED | KKT KOLBE

Order and buy the 60 cm stainless steel built-in oven with rotary spit and catalytic plates quickly and conveniently at a low price here in the online

www.kolbe.de

Either someone can't do their maths, or they are making some diversity assumptions!

Its a
Neff C1AMG84N0B

Both here: https://www.howdens.com/-/media/how...8973/clh_asset_levelb_110593/ass_25405064.pdf

and:

Neff C1AMG84N0B N50 Compact Oven With Microwave - STAINLESS STEEL - Appliance City

We love this stunning compact oven with microwave from Neff, it will look amazing in your kitchen. With retractable dials and touch controls, the C1AMG84N0B has a sleek and stylish finish. It has five cooking functions, including the pizza function for perfect bases and toppings and Hot Air for...

www.appliancecity.co.uk

It says that it requires a 16A supply..

If it were the only cooking appliance I would just downrate the 32A to 16A but because there is also an Oven and sods law the consumer unit is in one corner of the house and the appliance is in the other corner. I think looking at the installation manual its clearly for the european market but is also being sold here.
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The microwave has a fan oven so If the fan gets jammed up it could start pulling more load (Not sure it would make all the difference) which means it would not necessarily be a fixed load like an element so I think the cable needs protection. I think given everything points towards a 16A supply required it would be safest to put it on its own 16A circuit. I guess I may lose the job to someone else that will just put it into a dual fixed appliance plate or something but hey least I wont lose sleep worrying it might catch on fire.

 

[catdog1121]

This may not be the same, but it claims (when you select English as the language) 3.3kW and a 13A plug:

Low-Priced Oven EB8013ED | KKT KOLBE

Order and buy the 60 cm stainless steel built-in oven with rotary spit and catalytic plates quickly and conveniently at a low price here in the online

www.kolbe.de

Either someone can't do their maths, or they are making some diversity assumptions!
[automerge]1601150726[/automerge]
Reading the data-sheet though does not say anything like that, and just shows 3 terminals for the connection of power (nothing on cable size of MCB rating, etc).
[automerge]1601151186[/automerge]

Then it is a 16A spur needed.

Or the rather dodgy option of a 16A MCB off a ring that is viewed with some derision around these parts...
[automerge]1601151376[/automerge]
Something odd about posting time-lines here!

If you have the dedicated 32A cooker circuit you could take a 16A MCB off to save CU space and/or additional cable run.

Do you mean take the 6mm cable and put it into another small consumer unit and have 2x 16A cicuits? Making the 32A circuit a submain? The issue is the 6mm cable goes into an isolator and it would look silly having a small CU basically sat on the worksurface (no real way to pull cable back without damaging tiling etc.)

They have plenty of room in the consumer unit and I suggested SWA round the house at a very low level so can be almost hidden by the gravel going round the edge of the house but I think its the cost. (Even though they are happy to spend £650 on a fancy combi microwave thing).

Cant come off the ring as its over 2kw should be on dedicated circuit.

My main point was wondering if I could use diversity to put a 13A FCU which in theory I can but if the manufacturer specifies a 16A supply then I guess thats out the window.

 

[Lucien Nunes]

If the fan gets jammed up it could start pulling more load (Not sure it would make all the difference)

If the fan starts taking one extra amp it will overheat much more dramatically than the cable. These things are usually impedance protected and/or have a thermal fuse.

it would look silly having a small CU basically sat on the worksurface

But you don't need a CU, just an MCB in a skinny DIN rail enclosure, possibly also doubling as the outlet for the flex, allied with a DP switch to isolate.

Diversity relies on the randomisation that occurs when the usage of different loads is unrelated, such as multiple rings on a cooker. In this case, if the design allows you to switch on 3.4kW of load to achieve a certain cooking function, it's a 3.4kW load.

 

[Wilko]

wondering if I could use diversity to put a 13A FCU which in theory I can but if the manufacturer specifies a 16A supply then I guess thats out the window.

Hi - yes, my read of the Neff instructions is that 16A connection is required, so no 13A fcu. Sorry.

 

[pc1966]

Do you mean take the 6mm cable and put it into another small consumer unit and have 2x 16A cicuits? Making the 32A circuit a submain? The issue is the 6mm cable goes into an isolator and it would look silly having a small CU basically sat on the worksurface (no real way to pull cable back without damaging tiling etc.)

Essentially yes, but as Lucian has just said, I was thinking of just a small DIN enclosure for the microwave. Could even be hidden in a cupboard adjacent to the oven itself if the accessible isolation switch is already there.

So if you have a 32A feed & isolator already in, you can keep the 32A available for any other oven (at least as far as diversity allows) but tap off after the isolation switch a 16A MCB just to feed the microwave.

Probably there are smaller / neater options, but something like this:

2 Module Surface Mounting Plastic Enclosure with Fitted DIN Rail and Side Opening Grey Tinted Access Window

Snap closing tinted door

www.cef.co.uk

Or even this:

1 or 2 Module IP40 Open Front Enclosure with Moulded DIN Rail

Without window

www.cef.co.uk

They have plenty of room in the consumer unit and I suggested SWA round the house at a very low level so can be almost hidden by the gravel going round the edge of the house but I think its the cost. (Even though they are happy to spend £650 on a fancy combi microwave thing).

Yes, such is the way of folk

 

[telectrix]

In a fault condition is there not a risk of overload? I was always told the OCP device was there to protect the cable and that the cable needed to have a higher rating than the OCP device?

normally, yes, but the oven is what is known as a fixed load. i.e. it can't overload the cable by drawing more than it's rated current, xcept in the case of a fault (short circuit), where the MCB will trip.

 

[catdog1121]

In a fault condition is there not a risk of overload? I was always told the OCP device was there to protect the cable and that the cable needed to have a higher rating than the OCP device?

normally, yes, but the oven is what is known as a fixed load. i.e. it can't overload the cable by drawing more than it's rated current, xcept in the case of a fault (short circuit), where the MCB will trip.

It does have a motor for the fan and microwave and god knows what other fancy things, if the motor for example gets clogged up it would create more resistance and pull more load. I agree its very unlikely but there is still a chance a fault could create a load in excess of the cable but not trip the mcb. I know the cable is short and would likely in that very rare event be fine, if it were an oven which is just an element and maybe a small fan then yes I would agree but I am not convinced about this thing, the manufacturer says it needs a 16A circuit so I think its best to follow that.

 

[telectrix]

It does have a motor for the fan and microwave and god knows what other fancy things, if the motor for example gets clogged up it would create more resistance and pull more load. I agree its very unlikely but there is still a chance a fault could create a load in excess of the cable but not trip the mcb. I know the cable is short and would likely in that very rare event be fine, if it were an oven which is just an element and maybe a small fan then yes I would agree but I am not convinced about this thing, the manufacturer says it needs a 16A circuit so I think its best to follow that.

give it it's own dedicated circuit. 2.5mm cable on a 16A MCB. bombproof.

View: https://www.youtube.com/watch?v=haX0ACElUQc

 

[Strima]

In a fault condition is there not a risk of overload? I was always told the OCP device was there to protect the cable and that the cable needed to have a higher rating than the OCP device?

The unit is a fixed load, or can draw a maximum load, so there's no risk of overload, under fault conditions that would be overcurrent and the protective device should operate.

 

[telectrix]

under fault conditions, i.e. short circuit L-N or L-E, you'll get several hundred amps. a 32A Type B breaker need approx.160A to trip within specified limits. this activates the magnetic part of the MCB. the thermalpart reacts to overcurrent, not necessarily of such high magnitude. e.g. trips according to the time/current curves in appendix, #3.

 

[catdog1121]

The unit is a fixed load, or can draw a maximum load, so there's no risk of overload, under fault conditions that would be overcurrent and the protective device should operate.

I asked the man the myth the ledgend John Ward, his reply is this...

433.3.1 allows omitting a protective device for overload, if the characteristics of the load make an overload situation unlikely. A fixed appliance with only heating elements can't overload, as the total load is just the total of the various elements. However that can't be used for other devices, a microwave would not be permitted as there are various faults that could occur which would result in an overload.
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under fault conditions, i.e. short circuit L-N or L-E, you'll get several hundred amps. a 32A Type B breaker need approx.160A to trip within specified limits. this activates the magnetic part of the MCB. the thermalpart reacts to overcurrent, not necessarily of such high magnitude. e.g. trips according to the time/current curves in appendix, #3.

Yep totally agree but its not the short circuit fault I am trying to protect against, its overload, if it were an Oven then it would be a fixed load with only element so could not create an overload current however a microwave can have a fault that can cause an overload.

 

[catdog1121]

Essentially yes, but as Lucian has just said, I was thinking of just a small DIN enclosure for the microwave. Could even be hidden in a cupboard adjacent to the oven itself if the accessible isolation switch is already there.

So if you have a 32A feed & isolator already in, you can keep the 32A available for any other oven (at least as far as diversity allows) but tap off after the isolation switch a 16A MCB just to feed the microwave.

Probably there are smaller / neater options, but something like this:

2 Module Surface Mounting Plastic Enclosure with Fitted DIN Rail and Side Opening Grey Tinted Access Window

Snap closing tinted door

www.cef.co.uk

Or even this:

1 or 2 Module IP40 Open Front Enclosure with Moulded DIN Rail

Without window

www.cef.co.uk

Yes, such is the way of folk

Thanks yeah a din enclosure splitting to two 16a circuits I think is viable although I would probably think it should be a metal enclosure. I am thinking extend from cooker back plate (change to a blank plate) to a 2 way metal din enclosure, loop line into two 16A mcbs. Then take 2 cables to two cooker plates, one for oven one for microwave oven..

 

[telectrix]

OK< so go with post#14 then.