Hob + Oven connection

[adamr7747]

Hi All,

I'm planning on changing my existing free-standing cooker for a 7.2kW induction hob and a 3kW integrated oven (not bought yet, but I'm trying to do some forward-planning). The existing cooker has a 6mm T&E cable running to a dual outlet plate. There is then a CCU and a run of 8m (1.5m in metal conduit under plaster and 6.5m in ceiling void) of 10mm T&E to the CU, with a 32A MCB (& an RCD covering a number of circuits).

So, that gives (with 0 diversity and ignoring volt drop) a max current of 42.5A which is fine for the 10mm cable & would mean a change of the MCB to 45A.

Basically, I'm wondering about what to do "downstream" of the outlet plate, as I'm assuming the flexes on the appliances will be less than 10mm. If the oven has 2.5mm then the 45A MCB would be overrated for the max current the flex can take but of course the oven will never draw nearly that much. However, I assume that the possibility of a fault with the oven and/or cable means that I need to fit an FCU after the outlet plate.

Fine so far, but is it actually possible to fit 10mm cores into the supply side of an FCU and, if not, where am I going wrong?

Thanks for any advice/pointers,
Adam

 

[echoes]

Well the normal advice would be to connect the oven and the hob to the dual cooker outlet, respecting the calculations for diversity.

It is also frequently advised to 'fuse down' using an FCU for appliances 3kW and less, so given that the oven is rated at 3kW, an FCU could be placed between the outlet and the oven flex. 2.5 mm² would suffice.

However, the installation instructions state: Fuse: min: 15A max: 20A.

You can't get a 15A fuse in an FCU, so in order to comply with the instructions, this oven needs its own circuit from a consumer unit.

The instructions also list a 'fuse' as an example of an all-pole isolation device

"The electrical installation is to be set
up so that the appliance can be isolated
from the mains with a minimum
3mm all-pole contact separation.
Suitable separation devices include
e.g. cut-outs, fuses (screw fuses are
to be taken out of the holder), RCD’s
and contactors."

 

[adamr7747]

Well the normal advice would be to connect the oven and the hob to the dual cooker outlet, respecting the calculations for diversity.

Do you mean just wire both appliances direct into the outlet regardless of flex size?

It is also frequently advised to 'fuse down' using an FCU for appliances 3kW and less, so given that the oven is rated at 3kW, an FCU could be placed between the outlet and the oven flex. 2.5 mm² would suffice.

And in this case run the 2.5mm² from the outlet plate to the FCU, on the logic that the FCU prevents a current over 13A running down the cable (except in a hard-to-imagine situation where the short length of cable between the outlet and the FCU is damaged & shorts)?

However, the installation instructions state: Fuse: min: 15A max: 20A.

You can't get a 15A fuse in an FCU, so in order to comply with the instructions, this oven needs its own circuit from a consumer unit.

Gah.

And now I've found another thread here about this exact cooker, with Electrolux saying they're reviewing the manual text. This was in 2007.

Thanks,
Adam

 

[ericmark]

I would warn against touch controls with an induction hob. The hobs are very quick acting and with ours which has knobs if a pan starts to boil over turning off the power with the knob will stop it boiling over as quick as lifting the pan off the heating area.

However my mother had one with touch controls and by time one had touched all the bits to turn down the heat it had boiled over. Touch controls may look good and seem like an easy clean option but with knobs it does not boil over in first place so does not need cleaning.

 

[echoes]

Belated....

Do you mean just wire both appliances direct into the outlet regardless of flex size?

Yes. The appliances are fixed so overload protection for each may be omitted. You MUST ensure that fault protection is adequate though, and the supply to the dual plate MUST be overload-protected. If in doubt, use an FCU.

And in this case run the 2.5mm² from the outlet plate to the FCU, on the logic that the FCU prevents a current over 13A running down the cable (except in a hard-to-imagine situation where the short length of cable between the outlet and the FCU is damaged & shorts)?

Yes. And if it does short, the device in the CU will operate and disconnect the supply.

And now I've found another thread here about this exact cooker, with Electrolux saying they're reviewing the manual text. This was in 2007.

Thanks,
Adam

There seem to be many examples of silly oven instruction manuals. Often this is due to them being written for the European market where 16A radials are common.

If the oven is rated at 3kW, then an unswitched fcu (13 A) next to the outlet plate would be fine.