Is this a NO-NO? - 13a socket on 40a RCBO cooker circuit?

Stevethetiler · 18 Mar 2011

So, are we saying that my current RCBO is fine as long as the oven itself is connected in 6mm (by replacing the manufacturers flex and connecting one end to the oven termnal and the other endto the empty load on the dual cooker connection plate)????

If the manufacturer flex is retained and used (being wired into the empty load of the connection plate) then I would need to downrate the RCBO in line with manufacturers accordance to protect that short run of cable from ove to connection plate. The rest being in 6mm is adequately protected by the current 40a RCBO, yes?

I presume the fact that the hob will be wired via 6mm to a 3a FCU (which I will replace tomorrow in lieu of the old unswitched double) has nothing to do with the RCBO required....allbeit, techically a spur off the cooker radial...

EFLImpudence · 18 Mar 2011

Steve.

Why don't you start again? This will be a lot tidier.

Get a dual surface mount back box (flush if space is tight).
Mount it on the right of the wall in the picture as high as the cable will allow. Then you can attach the CCU which is in the picture and also the FCU for the hob.

EFLImpudence · 18 Mar 2011

Sorry, I type too slowly.

Stevethetiler said:
So, are we saying that my current RCBO is fine as long as the oven itself is connected in 6mm (by replacing the manufacturers flex and connecting one end to the oven termnal and the other endto the empty load on the dual cooker connection plate)????

If the manufacturer flex is retained and used (being wired into the empty load of the connection plate) then I would need to downrate the RCBO in line with manufacturers accordance to protect that short run of cable from ove to connection plate. The rest being in 6mm is adequately protected by the current 40a RCBO, yes?

I would say yes - others disagree.

I presume the fact that the hob will be wired via 6mm to a 3a FCU (which I will replace tomorrow in lieu of the old unswitched double) has nothing to do with the RCBO required....allbeit, techically a spur off the cooker radial...

You don't need 6mm² for the hob, 1mm² will do
Nothing to do with RCBO as protected by its own fuse.

echoes · 18 Mar 2011

I agree with flameport. And EFLI:

You'll never install that oven satisfactorily in the UK by following the instructions to the letter.
A fly in the ointment might be if your HOB needs fusing down to 3A. The MI's may say it does, but the OSG says that you may consider the combination of oven and hob as a single appliance on a suitably rated circuit (like your 40A one) ...

...so a dual outlet plate for your existing oven + gas hob on a 40A RCBO or 20A RCBO meets the requirements of the regs per se.

If in doubt then a single cooker outlet for the oven next to a single socket or unswitched FCU for the hob does the job, and would be about as compliant with MI's for both oven and hob as you could get.

Read more: //www.diynot.com/forums/viewtopic.php?t=267476&start=15#ixzz1GzjxRUYJ

Stevethetiler · 18 Mar 2011

EFLImpudence said:
Steve.

Why don't you start again? This will be a lot tidier.

Get a dual surface mount back box (flush if space is tight).
Mount it on the right of the wall in the picture as high as the cable will allow. Then you can attach the CCU which is in the picture and also the FCU for the hob.

Do you mean one of these: //www.diynot.com/forums/viewtopic.php?p=1207350#1207350 (about half way down the page)?????

If so, I dont see the point in doing that. It is, in principal, the same as what I have done is it not? - by using one of these http://www.alertelectrical.com/prod/1022/click-45a-easyfit-dual-appliance-outlet-plate isnt it the same !!! - the only difference I can see is that the run of cable used to power the single socket right next to the single CCU plate in that pic is obvioulsy ALOT shorter (being bang next door to it)

The only difference i see (correct me if i am wrong) is that there is a longer run of cable from my CCU plate to the Single socket/3a FCU??

The pic linked above also doesnt show the cable from the cooker wired into it either!

(I should point out that space is at a premium as its a big oven, also, the plate in the pic I have mounted is actually "below" the shelf that the oven will sit on. (drawer underneath) - I thought it was quite tidy LOL

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Stevethetiler
18 Mar 2011
1

Stevethetiler · 18 Mar 2011

EFLImpudence said:
You don't need 6mm² for the hob, 1mm² will do
Nothing to do with RCBO as protected by its own fuse.

My bad typing - I meant that the supply to the FCU would be in 6mm for consistency. The hob itself would be wired into the FCU via its own flex, which i believe is indeed 1mm.

EFLImpudence · 18 Mar 2011

Yes to all - that will be alright.

The only point being that the hob and oven flexes may be a bit short and you may have to disconnect them to remove the hob or oven should the need arise. Otherwise it's fine.

Stevethetiler · 18 Mar 2011

EFLImpudence said:
Yes to all - that will be alright.

The only point being that the hob and oven flexes may be a bit short and you may have to disconnect them to remove the hob or oven should the need arise. Otherwise it's fine.

Sorry for my bad explanations - its been a long day!

So just to recap. (apart from my untidy wiring lol

) the only thing I need be concerned about is wether or not the oven is wired in using the manufacturers supplied flex.

I am assuming that if it is, I will have to change the RCBO from 40a to protect that flex. (every other cable is 6mm should be fine)

I take it we can rule out the relevance of the FCU in determining the RCBO size required as it is protected already by its own fuse.

So, If the oven gets wired using the flex - i should get the nearest size RCBO (on the higher side) to match the MI???

If, by some stretch, I can wire the oven with 6mm, I am good to go on the current 40a RCBO.

Sorry, just want to be sure.

Stevethetiler · 18 Mar 2011

Oh, and btw.....

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Stevethetiler
18 Mar 2011
1

This shows where the existing unswitched double is located. I (with your advices) change this to a FCU for the gas hob which will be wired into it on a 3a fuse.

You can just make out that I have a 45a cooker control switch to the right of the oven at worktop height. This will isolate both hob and cooker.

Hope it helps explain things a bit better!

(ignore the earth shield in the cupboard...it was just used so i could pull the original cooker flex you can see back up behind the base unit and through the hole like the hob flex is done its just a bit of a trick save fiddling about trying to get it back up there!)

EFLImpudence · 18 Mar 2011

flameport said:
Overoad protection is not required for the oven cable, as there is no way it could be overloaded (the oven is a fixed load).

Not wishing to be cantankerous but by this logic all dedicated circuits - immersions and night storage heaters, for example, could run from whatever fuse or mcb. you had to hand and the oven in question could be wired in 1.5mm² all the way from the cu. from a 40A (or higher) cpd as they cannot be overloaded.

So only rings, radials and lighting cables actually need any protection from suitably rated cpds.

The answer may technically be 'yes' but it would make a mockery of a lot of the regulations and make my next assessment interesting.

EFLImpudence · 19 Mar 2011

Stevethetiler said:
I am assuming that if it is, I will have to change the RCBO from 40a to protect that flex. (every other cable is 6mm should be fine)

I would say yes, I would not be happy with it otherwise.

I take it we can rule out the relevance of the FCU in determining the RCBO size required as it is protected already by its own fuse.

Yes.

So, If the oven gets wired using the flex - i should get the nearest size RCBO (on the higher side) to match the MI???

Not higher - but you will be able to get the correct one.

If, by some stretch, I can wire the oven with 6mm, I am good to go on the current 40a RCBO..

Yes.

Stevethetiler · 19 Mar 2011

EFLImpudence said:
Stevethetiler said:

I am assuming that if it is, I will have to change the RCBO from 40a to protect that flex. (every other cable is 6mm should be fine)

Click to expand...

I would say yes, I would not be happy with it otherwise.

I take it we can rule out the relevance of the FCU in determining the RCBO size required as it is protected already by its own fuse.

Click to expand...

Yes.

So, If the oven gets wired using the flex - i should get the nearest size RCBO (on the higher side) to match the MI???

Click to expand...

Not higher - but you will be able to get the correct one.

If, by some stretch, I can wire the oven with 6mm, I am good to go on the current 40a RCBO..

Click to expand...

Yes.

Thank you very much. I will consult the MI's and either get the correct size RCBO and have my eletrician fit it (im not messing with the CU!) - as Hotpoint are coming to install the oven, I doubt that they will remove their own flex and wire it with 6mm.....this probably would void warranty but im not sure.

If they are ok with wiring it in 6mm, them i have just saved £80!

We will see but thank you to everyone who has contributed to my questions/answers...very much appreciated!

flameport · 19 Mar 2011

EFLImpudence said:
Not wishing to be cantankerous but by this logic all dedicated circuits - immersions and night storage heaters, for example, could run from whatever fuse or mcb. you had to hand and the oven in question could be wired in 1.5mm² all the way from the cu. from a 40A (or higher) cpd as they cannot be overloaded.

For some circuits this may be possible.

However if a fault occurs close to the consumer unit, the fault current will be higher, which will require that the size of the conductors is larger.
Increasing the rating of the protective device will also increase the energy during a fault, and the specifications of the protective device will affect the calculation, all of which could result in larger conductors being required to avoid thermal damage in the event of a fault.

Other regulations still apply so things such as installation method, volt drop and so on must still be considered.

EFLImpudence · 19 Mar 2011

Just thought - my comments on the cable lengths do not really apply do they?
The oven will be connected near its base - plenty of slack - and the hob will have a gas pipe - removal quite difficult already.

EFLImpudence · 19 Mar 2011

Fair enough again - thanks.

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Is this a NO-NO? - 13a socket on 40a RCBO cooker circuit?

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