Oven connection using existing cable

[dannydc]

Hi

I'm in the process of installing an Ikea kitchen at my mum's. I've extended the ring-main around the kitchen and everything is chased in nicely, ready for a joiner to do the worktops at the weekend.

The oven is <13A but doesn't come with a plug, but it would be good to have the option of a more powerful oven in the future without too much hassle (it would never be anything over 20A).

Behind where the oven will be there's an old FCU and cable for an immersion heater that no longer exists. It's multi-core cable - either 4 or 6mm² and the other end of the cable terminates next to the fuse box.

I want to re-use that cable as it runs through the dining room end of the kitchen so running a new cable would be a big job. I know it's a job for a sparky, so my question is:
Does the oven need an accssible FCU?
Or can the existing back box be used with a cooker connection plate and the oven connected directly to that?
If I need to chase out a hole for a back-box for an FCU that is accessible (rather than behin the oven), can it be fixed to the wall inside a cupboard?

thanks!
Danny

 

[PrenticeBoyofDerry]

I've extended the ring-main around the kitchen.

Follow the safe zones and RCD protected I hope!

The oven is <13A but doesn't come with a plug, but it would be good to have the option of a more powerful oven in the future without too much hassle (it would never be anything over 20A).

Okay

Behind where the oven will be there's an old FCU and cable for an immersion heater that no longer exists. It's multi-core cable - either 4 or 6mm² and the other end of the cable terminates next to the fuse box.

Multi core do you mean stranded or is it flex? How have come to the assumption that it is 4mm or 6mm?

I want to re-use that cable as it runs through the dining room end of the kitchen so running a new cable would be a big job. I know it's a job for a sparky

Do you know this cable is suitable for continued service?

so my question is:
Does the oven need an accssible FCU?

Yes, these accessories should be accessible for maintenance, inspection and testing

Or can the existing back box be used with a cooker connection plate and the oven connected directly to that?

Very likely but
What do the manufactures instruction say?

If I need to chase out a hole for a back-box for an FCU that is accessible (rather than behin the oven), can it be fixed to the wall inside a cupboard?

Yes but an FCU behind an oven would be considered accessible, if the oven can be removed to access it.

 

[ban-all-sheds]

Accessing it might be a frequent occurrence with a 4.6kW oven connected to it.

 

[dannydc]

I've extended the ring-main around the kitchen.

Follow the safe zones and RCD protected I hope!

The cables are surface clipped behind the units apart from the chased-in verticals to the sockets.

Behind where the oven will be there's an old FCU and cable for an immersion heater that no longer exists. It's multi-core cable - either 4 or 6mm² and the other end of the cable terminates next to the fuse box.

Multi core do you mean stranded or is it flex? How have come to the assumption that it is 4mm or 6mm?

It's stranded and sizing is from visual only. Is there a way to test the cable? I did a basic continuity test on it which was fine.

I want to re-use that cable as it runs through the dining room end of the kitchen so running a new cable would be a big job. I know it's a job for a sparky

Do you know this cable is suitable for continued service?

I presume that a sparky can test it(?)

so my question is:
Does the oven need an accssible FCU?

Yes, these accessories should be accessible for maintenance, inspection and testing

Or can the existing back box be used with a cooker connection plate and the oven connected directly to that?

Very likely but
What do the manufactures instruction say?

The manual says 2.5mm², either Three core butyl insulated from a 13A spur box or socket, or an "Oven Control Circuit" with PVC twin and earth and a 15/20A fuse.
http://www.manualslib.com/manual/600763/Zanussi-Zob35301bk.html?page=17#manual

If I need to chase out a hole for a back-box for an FCU that is accessible (rather than behin the oven), can it be fixed to the wall inside a cupboard?

Yes but an FCU behind an oven would be considered accessible, if the oven can be removed to access it.

So *asuming the existing immersion heater cable is ok fine*, we could use an oven protection circuit (which I presume is the same as a cooker outlet plate?) on the existing back-box behind the oven as the oven will be removeable and so is considered accessible - is that correct?

That way we wouldn't need to install a visible FCU which would require chasing out.

 

[dannydc]

Accessing it might be a frequent occurrence with a 4.6kW oven connected to it.

Accessing what? The cooker connection plate?

Assuming the cable is 2.5mm² (I'll check it if I can find out how to!), then it should be good for 20A and my understanding is that a 20A cooker connection plate is common so I'm not sure what would cause a problem that would need accessing (tripped fuse?)

 

[ban-all-sheds]

Accessing what? The cooker connection plate?

The FCU with its 13A fuse.

 

[dannydc]

Accessing what? The cooker connection plate?

The FCU with its 13A fuse.

I see. Is a 20A cooker connection plate ok? It'd be a dedicated circut from the fuse box with a 30mA breaker.

 

[PrenticeBoyofDerry]

The cables are surface clipped behind the units apart from the chased-in verticals to the sockets.

That is okay, what about RCD?

It's stranded and sizing is from visual only. Is there a way to test the cable? I did a basic continuity test on it which was fine.

If you know the overall length of the cable it would be possible to calculate the CSA of it. But would need somewhere near accurate measurements of each conductor and accurate readings on each conductor.

I presume that a sparky can test it(?)

One could, a visual of the cable, plus you need r1,r2 and rn contiuity and an insulation resistance test, would do this.

The manual says 2.5mm², either Three core butyl insulated from a 13A spur box or socket, or an "Oven Control Circuit" with PVC twin and earth and a 15/20A fuse.
http://www.manualslib.com/manual/600763/Zanussi-Zob35301bk.html?page=17#manual

Okay.

So *asuming the existing immersion heater cable is ok fine*, we could use an oven protection circuit (which I presume is the same as a cooker outlet plate?) on the existing back-box behind the oven as the oven will be removeable and so is considered accessible - is that correct?

I don't know what you mean by oven protection circuit, but you can put an outlet plate on the backbox and connect directly.
I would suspect the immersion circuit was only ever designed for 15A demand. So very likely to be 2.5mm or imperial version depending on age.

That way we wouldn't need to install a visible FCU which would require chasing out.

Does this circuit have another means of isolation, other than at the CU/Fuse board. It is not requirement to have one, but a recommendation.

 

[dannydc]

The cables are surface clipped behind the units apart from the chased-in verticals to the sockets.

That is okay, what about RCD?

The only RCD is the consumer unit/fusebox (30mA) - I haven't added any other RCD devices. Is that correct?

That way we wouldn't need to install a visible FCU which would require chasing out.

Does this circuit have another means of isolation, other than at the CU/Fuse board. It is not requirement to have one, but a recommendation.

It doesn't - the consumer unit is around 3m away in the pantry, but because the other end isn't terminated into the consumer unit yet, adding an accessible isolator there will be easy. Putting one next to the oven would be a bigger job as it'll need breaking out.

 

[ban-all-sheds]

http://www.manualslib.com/manual/600763/Zanussi-Zob35301bk.html?page=17#manual

I'll use one of these, then, shall I?

Just what is the field of ignorance of the people who write these manuals? Is it electrical? Is it the English language?



Anyway - rant over...

sizing is from visual only

You need to measure it properly. It would be unusual to use 4mm² for an immersion heater, let alone 6mm².

Is a 20A cooker connection plate ok?

Didn't know they did them that small.

Can't see the advantage in not using a normal one.

 

[PrenticeBoyofDerry]

The only RCD is the consumer unit/fusebox (30mA) - I haven't added any other RCD devices. Is that correct?

If it protects the circuits you have installed sockets on and buried cable, yes.

It doesn't - the consumer unit is around 3m away in the pantry, but because the other end isn't terminated into the consumer unit yet, adding an accessible isolator there will be easy. Putting one next to the oven would be a bigger job as it'll need breaking out.

It is handy to have a local means of double pole isolation, but as the cooker circuit will be use for the oven only, it will be okay to use the circuit breaker as an isolation point, although it is likely to be only single pole.

 

[dannydc]

Thanks for the invaluable help guys

 

[JohnW2]

Accessing it might be a frequent occurrence with a 4.6kW oven connected to it.

I suppose that depends upon your view of diversity. Even if the 4.6kW relates to 230V (which it very probably doesn't), that would only be (just!) 13A (at 230V) after-diversity.

Kind Regards, John

 

[ban-all-sheds]

I was going to say that my view of diversity has nothing to do with the fusing current for a BS 1362. But that would have been when I was thinking that was 1.5In, not 1.9....