Cooker/hob connections

[Madrab]

Hi there, i'm a newby here and just looking to confirm a few points with the wiring for a new cooker/hob from the wealth of expertise that seems to inhabit this forum. Just about to start my training for - Part p (defined scope) domestic electrical qualification

I've looked around many similar posts but none seem to match so hopefully you can advise.

Just moved into a flat and replacing kitchen, as part of that a new single oven (to be hard wired & rated at 3.2 - 3.5Kw 13-14A as per the manual), a gas hob and hood are being installed. There is an 30A protected, dedicated radial circuit, fed from a separate fused (not MCB) isolator beside the main CU in 6mm t&e. The cable runs to a 45amp DP cooker switch above the worktop that feeds a 45A CCU below. There is a switched FCU right beside the CCU that I assume is a spur from the CCU as it is isolated when the cooker switch is off.

What I need to check is -

A) The cooker manual asks for a fused DP isolation switch within the fixed wiring but I have never heard of nor can find any rated above 13A - will the existing installation be OK? Even then a 3.5kw draw should surely be covered, by my calculation, by min 15A? (3.5Kw/240V = 14.6A)
B) Is that fact that a FCU has been spurred in 2.5mm from the CCU within the regs given that it's a down stream protected spur under 3m?
C) Depending on the previous answer, the gas hob has electric ignition cable with a fixed plug - I plan to use the FCU that is spurred from the CCU with a 3A fused as per the hob specs, any issue there?
D) I have 25A heat resistant flex to feed the oven from the CCU, anyone see an issue with using that?
E) there is no additional feed that the hood could use, the sockets are separate spurs from the ring therefore could not feed from them, any issue with feeding the hood with another 3A FCU from the radial given the draw on the circuit is well within limits?

Many thanks in advance
Rob

 

[PrenticeBoyofDerry]

A) The cooker manual asks for a fused DP isolation switch within the fixed wiring but I have never heard of nor can find any rated above 13A - will the existing installation be OK? Even then a 3.5kw draw should surely be covered, by my calculation, by min 15A? (3.5Kw/240V = 14.6A)

The manual is directing you towards a 13A DP FCU, diversity willl alow this.

B) Is that fact that a FCU has been spurred in 2.5mm from the CCU within the regs given that it's a down stream protected spur under 3m?

As far as FCU being downstrem it complies, but the matter that the spur is taken form a dedicated cooker circuit, would lead me to ask what is the FCU protecting?

C) Depending on the previous answer, the gas hob has electric ignition cable with a fixed plug - I plan to use the FCU that is spurred from the CCU with a 3A fused as per the hob specs, any issue there?

That would be logical

D) I have 25A heat resistant flex to feed the oven from the CCU, anyone see an issue with using that?

What does the MI state? and what is 25A flex in real money?

E) there is no additional feed that the hood could use, the sockets are separate spurs from the ring therefore could not feed from them, any issue with feeding the hood with another 3A FCU from the radial given the draw on the circuit is well within limits?

No issues taking a spur providing it complies to the methods used on spurs from socket circuits (RFC and Rads)
You could take it from the light circuit!

 

[Madrab]

Many thanks for the reply.

The manual is directing you towards a 13A DP FCU, diversity willl alow this.

So does that mean another 13A DP FCU needs to be installed say after the main cooker switch? If the oven pulls it's maximum of >14A wont that then continually blow a 13a fuse? Also may be a bit difficult getting 6mm cable to fit?

As far as FCU being downstream it complies, but the matter that the spur is taken form a dedicated cooker circuit, would lead me to ask what is the FCU protecting?

It was protecting the old gas hob ignition but wanted to check that it was ok being a spur from the CCU before using it.

What does the MI state? and what is 25A flex in real money?

The MI states a min of H05VV-F 3coresx1.5mm2, the cable I have is white flexible Heat resistant cable @ 2.5mm2 - rated at 25A/6kw

I just wished to check the validity of taking another spur from the cooker radial for the hood, it would much be easier than running a new chase from the lighting circuit as it is some distance away.

Thanks again

 

[PrenticeBoyofDerry]

So does that mean another 13A DP FCU needs to be installed say after the main cooker switch? If the oven pulls it's maximum of >14A wont that then continually blow a 13a fuse? Also may be a bit difficult getting 6mm cable to fit?

Does not mean that you have to install 13A FCU after the CCU, could go in before it or replaced by it. You should manage to get 6.00mm in supply and load sides of this type of accessory. If you start putting other cables in could get a bit tight!
The oven is very unlikely to ever draw on full load long enough to cause the 13 Amper to blow, diversity takes you under 13Amps.

It was protecting the old gas hob ignition but wanted to check that it was ok being a spur from the CCU before using it.

The amount of power required by the ignition is not going to cause any real issues.

The MI states a min of H05VV-F 3coresx1.5mm2, the cable I have is white flexible Heat resistant cable @ 2.5mm2 - rated at 25A/6kw

That will be fine.

I just wished to check the validity of taking another spur from the cooker radial for the hood, it would much be easier than running a new chase from the lighting circuit as it is some distance away.

Ideally appliances such as cookers would be better on dedicated circuits, but you need to do a little maths and work out what the potential load of the circuit is and whether you have made provisions to satisfy the requirements.

 

[Madrab]

Thanks again Prentice.

If I understand diversity, then it's the calculation performed given the fact that it's unlikely that the max Amp draw will be reached by the appliance, though the oven has one setting (grill and top element on full at the same time) that draws 3.2KW, which is nearly 13.5 amps @ 240v or nearly 14amps @ 230v, will this still be ok for a FCU @ 13amps?

Not wishing to question too much, just wanted to be sure, apologies if I haven't grasped it correctly.

 

[Madrab]

Anyone else have a view on this diversity consideration? Appreciate Prentice's replies which have answered all of my queries, big thanks to him just getting a bit sick of pizza'a and fish suppers and want to get this oven connected

Another thought is, given the Cooker circuit was already present without the FCU do I need to have an FCU inline anyway? Given the MI asks for it I would guess so to avoid a large overload but that doesn't seems to make sense given the max draw on one of the oven's power settings, according to the MI, is around 14A and that largest FCU I can find is 13A. What would the rammifications be if it wasn't installed, depending on the answers re diversity? Would that require a drop in fuse rating at the main isolator to say 20A to avoid a massive overload before a 30A fuse blows, even though the MI asks for 30A?
Begs the question whether the book of words is correct or not, wouldn't be the first time I'd guess

Any thoughts?
Thanks again

 

[EFLImpudence]

Are you sure that the top element and grill element can be on at the same time?

As you have said 'top element' - is there a bottom one?

 

[PrenticeBoyofDerry]

What is the make and model of this oven?
Total output means everything being on at the same time. So lets have the details and consider what could be on and the possibility of any overloads.

 

[Madrab]

Thanks guys...

I have uploaded the MI rating page

As you can see the max rating is 3.2/3.5Kw and going by their specs that is almost 13.5A > 14.5A@240v or worse 14A > 15A @230v . There are 2 settings on the oven - Top/bottom element on full pulling 3.2Kw for as long as it take to reach max temp ~ 10/15mins or even more?Another setting where the grill and top element are on max - Again 3.2Kw.
Even then their own reckoning says the max draw is 3.5Kw = 14.6A (if @ 230V it would be nearly 15A!). That brings me back to a 13A FCU having fun trying to handle a minimum of 15 min on at least 13.5A, more likely a 14A or more draw without blowing or at least it would be pretty hot under the collar? Not something I would be too happy with.

 

[EFLImpudence]

Yes, you are correct.

As it is impossible to comply with the MIs just connect the oven to the CCU with 4mm² flex.

A socket or fused connection unit could also be wired to the CCU to power the hob igniter.

Edit - just noticed that an FCU is already there so all's just right.

 

[echoes]

Deleted

 

[Madrab]

Cheers for that EF

Wonder if it's worth the bother to let the supplier know that it's not practical to follow their MI?

Deleted

Deleted? Sorry, don't understand.

 

[echoes]

I wrote something that I then realized was a load of rubbish, so I deleted it.