Electrical Hob and oven dual outlet faceplate

[King84]

Hi everyone.
There is something that confuses me so I hope someone could answer.

There is an electrical Hob which is 7.8KW and electrical oven which is lets say manufacture instruction says 13A so somwhere around 2.0KWs.

If you apply diversity on Hob it comes to somwhere around 17A and I know usually you use 32A MCB with 6mm cable to make it future proof.
Now Oven as its 13A many people yet wire it in a ring but what confuses me if you wire Oven with same MCB as Hob in the dual connection cooker unit then as oven is has a design current of 13A which is less than Nomimal current of 32A MCB but Iz for the oven is 2.5mm which can take around 20A so this makes IZ less than In which should not be the case.
I know as Oven does not overload so this is fine but in a faulty condition if Oven is wired in the same connection unit as Hob as Hob is 6mm it should be ok for the Hob but Oven with 2.5mm wouldnt it burn if fault occurs?

 

[buzzlightyear]

but Oven with 2.5mm wouldnt it burn if fault occurs?

Are you talking about the cable or the stuff in the oven. If you have a heat rated cable then it would not.

 

[King84]

Are you talking about the cable or the stuff in the oven. If you have a heat rated cable then it would not.

No I am talking about the cable. I know you are meant to follow the manufactures instructions and all that but generally even if it is a heat resistant cable but inserting 2.5mm cable into the same FCU as cooker which is fed from 32A MCB makes the current carrying capacity of the cable smaller then the (In) nominal current which is 32A so in a faulty scenario wouldnt it catches fire as 6mm of hob would still be fine.

 

[buzzlightyear]

the current capacity of the cables should be fine, for both 6mm & 2.5 on the same circuit.

 

[King84]

the current capacity of the cables should be fine, for both 6mm & 2.5 on the same circuit.

Ib ≤ In ≤ Iz This is basically what I meant. If we use 2.5mm cable for oven on 32A MCB same as hob circuit Iz for the oven would become smaller then In which should be actually bigger.

 

[Funky Gibbons]

If your going to work the calculation out don’t miss anything out for e.g does the cooker switch have a socket outlet if so it works out after diversity at 17.82amps without socket outlet 22.82amps the length of cable run needs to be applied this circuit would be a radial, 6mm would suffice with oven and hob connected to cooker connection unit makes sure it is RCD protected

 

[King84]

If your going to work the calculation out don’t miss anything out for e.g does the cooker switch have a socket outlet if so it works out after diversity at 17.82amps without socket outlet 22.82amps the length of cable run needs to be applied this circuit would be a radial, 6mm would suffice with oven and hob connected to cooker connection unit makes sure it is RCD protected

I am not worried about socket or hob as I know they are pretty good considering the situation but what confuses mean as I have seen plenty of ovens are also hardwired into the same cooker connection unit . so I was referring to oven's 2.5mm cable into 32A MCB would make the Iz smaller then In.

 

[Funky Gibbons]

The current carrying capacity of the cable (Iz) to the protective device (In) shall be smaller than or equal to.

 

[loz2754]

The 13 amp fuse in the oven plug or FCU will protect the 2.5

 

[Mike Johnson]

I think the OP is talking about taking the oven plug off and wiring the oven into dual connection cooker unit with the hob.

 

[APE37]

I think what he is getting at is omission of devices for protection against overload.
As it is a fixed load, it is reasonable to expect the 2.5 for the oven to not be overloaded (13a). But it must be protected against fault current.
So you would need to ensure that the 2.5 would take the fault current and the duration of the fault and not become damaged.
But to be honest if it came with a plug fitted by the manufacturer, I would be looking at ways to incorporate a socket fir it.

 

[Mike Johnson]

Perhaps a socket spurred off the dual connection oven unit, at least then the 2.5mm would be protected by the fuse in the plug.

 

[loz2754]

Just realised the flex is 2.5mm
Too big for a 13 amp plug.
Could use 1.5mm flex for a 13 amp oven.

 

[MrPupsi]

Spur off cooker switch with a 13a fcu and hard wire oven straight into it?

 

[Mike Johnson]

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