Question regarding providing power to kitchen island

[enginearin]

Hello all,

I am undertaking electrical installation in a new build house myself (notified to building control and will be inspected by them for sign off) and i am looking for some advice on providing power to a kitchen island.

I had installed two cable ducts within the floor slab to carry the feed to induction hob and to carry the ring circuit or fused spur onto the island for a couple of sockets. Unfortunately the wife has changed the kitchen design since and this has left me with only one available duct. To further compound the issues, the single four ring hob has now become two two ring hobs (max 16A each, 1.5mm flex cables attached).

In light of these issues i was considering running a single supply to the island (RCD protected with 40A MCB in the CU) then fitting a small CU with individual 16A MCBs for the hobs and say 6A MCB for a radial with a couple of sockets. The question i have, is whether it is acceptable to run this feed to the island in Twin and Earth (provided it meets the current carrying criteria when derating factors are applied)? It will be deeper than 50mm in the ceiling / false wall until it becomes clipped direct (on wall surface) behind kitchen units to enter the duct so i believe this (in combination with the RCD) means that armoured cable is not required.

Obviously cable CSA are getting large here... Would it be prudent to apply any level of diversity when considering cable derating factors (i cant see all four rings on the hobs going full chat continuously at the same time)

Any comments / pointers / previous experience greatly appreciated

Thanks

Tim

 

[Deleted member 26818]

Why can't you use one T&E for the hobs and either one or preferably two for the ring?

 

[enginearin]

Why can't you use one T&E for the hobs and either one or preferably two for the ring?

Thanks for the quick response

One T&E for the both hobs in parallel would mean that the 1.5mm flex's on each hob have the ability to draw 32A would it not (we would need to protect at 32A to permit full power on both hobs, but would need to protect at 16A to protect the flex... there goes my diversity question again)?

I was originally intending to pull a 6mm T&E for each of the hobs and one or two 2.5mm for the rings but I dont think that i can pull all those cables through one 40mm duct 2m long with a 90 degree bend at each end (into and out of the floor)

 

[Deleted member 26818]

One 6mm T&E for the hobs, and preferably two 2.5mm T&E for the ring.
You could problem get away with just spurring the double socket and using one 2.5mm T&E.
There's nothing preventing you from using one cooker switch for both hobs.

 

[enginearin]

One 6mm T&E for the hobs, and preferably two 2.5mm T&E for the ring.
You could problem get away with just spurring the double socket and using one 2.5mm T&E.
There's nothing preventing you from using one cooker switch for both hobs.

I'm assuming then that we ignore the potential flex overcurrent issue and consider only the installed cable up to cooker switch when considering MCB protection? That makes my life much easier.

Thanks for your help.

 

[Deleted member 26818]

Yes, though others may disagree.
I believe it unlikely that the flex would be subject to overcurrent during normal use, and that an earth fault would cause the MCB to operate before any damage to the flex would occur.

 

[davesparks]

I'm assuming then that we ignore the potential flex overcurrent issue and consider only the installed cable up to cooker switch when considering MCB protection? That makes my life much easier.

Thanks for your help.

Overload protection is not required for fixed loads which by their nature cannot become overloaded.

 

[telectrix]

if these hobs have 1.5mm flexes attached, have they also got 1363 plug tops on?

 

[hotfingers]

I think most new cookers seem to come with 1.5mm flex on now days drawing just over the 13amp mark so probably no plug top

 

[Dave OCD]

I'd run a 6mm T & E for the hobs and a single 2.5 for the socket/s from the kitchen ring via a switched FCU on the wall above the base unit where the ducting runs from -should be plenty of room in a 40mm duct for those. And I'd also have the kitchen ring on it's own circuit, makes sense when you consider the number of appliances in a modern kitchen.

 

[Dave OCD]

if these hobs have 1.5mm flexes attached, have they also got 1363 plug tops on?

Don't be ridiculous, they'd only have 1 plug top at most. :tongue3:

 

[Deleted member 26818]

Don't know how many sockets are intended to be installed in the island?
Could be that there will be only one double?

 

[telectrix]

Don't be ridiculous, they'd only have 1 plug top at most. :tongue3:

haha. a comedian.you should be on the stage. the next one leaves in an hour. :mickey: