3.4KW oven

[opps]

Hi all

My mum's stoopidly expensive Siemen's microwave combi oven failed in the early days of covid..

My generous sister spent just shy of £2000 for a replacement (different model number but the same . She also paid £100 for fitting.

The fitter refused to wire in the machine to the existing switched fused spur (13 amps). He (correctly) explained that because the oven is 3.4Kw a 13 amp fuse is under rated.

I spoke to my sister and tried to explain to her that the previous electrician had signed it off and that the principle of diversity applied. The fitter insisted the new oven have its own that . I also explained that the fuse exists to protect the integrity of the cables, meaning that if it ever draws more than 13 amps, the worst thing that will happen is that the fuse will blow.

I plan to go there tomorrow and try to lift the 40Kg oven in to the housing at shoulder height and wire it in to the fused spur that never blew over the previous 9 years.

Is there any reason why I shouldn't?

 

[winston1]

No. Make sure you get the £100 back.

 

[opps]

No. Make sure you get the £100 back.

Thanks. Much appreciated.

The oven is still sitting in the box on the floor. I will suggest that my sister asks for a partial refund- they disconnected and took away the old oven.

 

[opps]

The fitter kept insisting that the device needed a 16 amp fuse. When my sister mentioned "diversity" her retorted that he isn't an electrician and has to do as he he told (by his boss)- as an aside- if someone fits a fixed device (oven/etc), do they need to sign it off?

 

[flameport]

The fitter kept insisting that the device needed a 16 amp fuse

Some might, most do not. Plenty of instructions state 16A as they are intended for use in other countries where 16A circuits are common.
Also not helpful that most now don't actually state what the load current is, only how much energy in kWh is used on a standard test cycle.

that he isn't an electrician and has to do as he he told

Painting by numbers for the electrical industry.
At the very least, they should test the FCU/outlet or whatever to ensure it's suitable for use, and confirm what fuse/circuit breaker or whatever is installed.

 

[Adam_151]

Personally, I would not, the diversiy guidelines are intended for use across a whole cooker, rather than just the oven, which presumably can take 3.4kw on a regular repeat basis when both cooking cavities are in use together, although probably not for very long, its not like a cooker where there are enough separate load it'll always average under the diversified load. I would have no problem in assigning diversity to the cirucit when sizing a kitchen submain for example.

We have to be wary of long duration small overloads that don't operate the protetcive device, and I've changed enough fused spurs that were carrying less than 13A that I'd not delibriatly connect a load in excess of 13A to one, especially one in a void in behind a oven where its not likely to experience much passive cooling.

 

[Taylortwocities]

At full whack, your 3.4KW appliance will pull just short of 15amps.

Question: how long will it take a 13amp BS1362 fuse to blow if presented with a load of 15amps?
Answer: NEVER!!!

Crack on, it will be fine, even when cooking the turkey for Christmas!

 

[RandomGrinch]

We haven't asked/been told what is on the rest of that circuit.
It may be a dedicated oven circuit which just happens to have an FCU?
Or, if it's on the kitchen ring, you may want to keep the washing machine and tumble drier off, until the turkeys done!

...and I would want to use a slightly chunkier flex than 1.25mm2

 

[bernardgreen]

Question: how long will it take a 13amp BS1362 fuse to blow if presented with a load of 15amps?
Answer: NEVER!!!

That is true.

However the heating of the fuse and the plug need to be considered.

The cold resistance of a BS1362 fuse rated as 13 Amp is 0.0075 Ohms and the calculated heat produced in the cold fuse at 16 Amps is 1.9 Watt.

The resistance of the fuse will increase as the temperature of the fuse wire increases and this means that the amount of heat produced will be more than 1.9 Watts.

This may result in damage to plug and/or socket when 16 Amps is flowing for prolonged periods of time.

 

[Taylortwocities]

We haven't asked/been told what is on the rest of that circuit.
It may be a dedicated oven circuit which just happens to have an FCU?
Or, if it's on the kitchen ring, you may want to keep the washing machine and tumble drier off, until the turkeys done!

...and I would want to use a slightly chunkier flex than 1.25mm2

No need to worry
He has already told us that the old combi had the same load spec as the new one. So I think the load profile has been well proven.

 

[RandomGrinch]

However the heating of the fuse and the plug need to be considered.

The fitter refused to wire in the machine to the existing switched fused spur (13 amps).

So no plugs and sockets, but a switch and a fuse holder - probably something still worth checking on every now and then?

 

[sparkwright]

Personally, I would not, the diversiy guidelines are intended for use across a whole cooker, rather than just the oven, which presumably can take 3.4kw on a regular repeat basis when both cooking cavities are in use together, although probably not for very long, its not like a cooker where there are enough separate load it'll always average under the diversified load. I would have no problem in assigning diversity to the cirucit when sizing a kitchen submain for example.

We have to be wary of long duration small overloads that don't operate the protetcive device, and I've changed enough fused spurs that were carrying less than 13A that I'd not delibriatly connect a load in excess of 13A to one, especially one in a void in behind a oven where its not likely to experience much passive cooling.

I think I know what you're saying - another toasted FCU.

Are you saying diversity should really only come to play for ovens over 16 amp or so?

 

[Taylortwocities]

I think I know what you're saying - another toasted FCU.

Are you saying diversity should really only come to play for ovens over 16 amp or so?

Quite.

 

[danechip]

Did this oven come fitted with a 13A plug? I would hope not. Yes, 13A fuse is definitely under rated. It certainly wouldn't blow though, but I certainly wouldn't risk any 13A plug, socket or FCU. Too many cheap Chinese tat imports. I would go with a cooker switch avoiding any fusing if it's a dedicated cooker supply and maybe downgrade to 16A in the CU. (If not already). If it's good enough for the Germans, it will be fine here.

#Achtung!!

 

[flameport]

the oven is 3.4Kw

Is that the actual power when it's in use, or the total of the various heating components added together?