Kitchen radial circuit on 2.5mm and 32A RCBO - Is that OK?

Hi all.  This is my 1st post here.

I'm having my kitchen rewired and am looking for a 2nd opinion that my electrician is doing it right.

He has fitted a new radial circuit for the kitchen sockets.  The cable is labelled 2 x 2.5 + 1.5mm, which I assume means 2.5mm cross sectional area for each of positive and negative and 1.5 for the earth.  The kitchen has a floor area of 9 sqm.  There is a very short run to the consumer unit.  The consumer unit was already in place and uses RCBOs (unusual for a domestic install?)  He has fitted a new 32A RCBO for this new circuit.

I've been reading up on this stuff all morning.  My understanding is that a radial circuit on 2.5mm would be better on a 20A RCBO.  I also think 20A is too low anyway.  What happens when diswasher, washing machine and kettle are all heating water at the same time?  Should I be concerned?

Also, the new oven and hob total 8.9kW.  This are supplied by the single existing 4mm cable (don't know if ring or radial circuit).  They are isolated together by 1 switch which also has a plug socket.  My understanding is that this is acceptable based on the diversity rule:

Max current for hob and cooker combined = 37A
Subtract 10A  = 27A
27 x 0.3 = 8.1A
8.1 + 10 = 18.1A
Add on 5 for socket 18.1 + 5 = 23.1A

So 4mm is fine?  Perhaps not a lot of headroom, but acceptable?  It is protected by its own 32A RCBO.

Hopefully I'm worrying about nothing, but if someone could please put my mind at rest, I'd be most grateful!

Cheers!

 

Hob is 6.6kW
Oven in 2.3kW

 

Thanks for that seneca!!

I'm not looking forward to telling him he's got to dig out all his cables on Monday morning.  They've all been cemented over.  I just hope there's no more wall chasing   Should I be getting the cement out ASAP??  Some of it may not have completely set.

What if he argues that he can change the breaker to a 20, rather than changing the cables to 4mm?   I wouldn't be happy with that, but would it be a valid argument from his point of view?

 

He chased the walls (and some floor), laid the cables (grey PVC I believe) and then cemented over the top with the intention of then getting a plasterer in to make good.  The floor will be tiled.

If the cement is acceptable (but not ideal), what if it's changed to a ring circuit instead?  That might be an easier solution.

 

Thanks for the advice Harmonic

2 x 2.5 + 1.5mm is written on the cable itself (embossed in the PVC).  The diameter of the entire cable is a little under 10mm at its widest point.

He did have metal sheaths/plates with him, but didn't use them (except maybe the floor).  I don't think he could get them into the chases that he cut.  He commented the walls are very hard (and he's not the first to say that).  Is the cementing very wrong and against regs, or is something that's acceptable when circumstances dictate, but not ideal?

Someone who gave me a quote previously mentioned diversity, although I didn't really understand it until this morning.  I'm feeling a bit disappointed that I've had to learn about all this stuff.

Thanks again!

 

The original quote states 'supply 32amp rcbo for new circuit', so will be pursuing getting this fixed so suitable for 32amps, not 20.

Not trying to pick holes in the work... but... about 5mm of the red pvc insulation of the positive 4mm cooker feed (slightly re-routed  original cable) is sitting proud of the cement used to fill the chased channel.  Should that be cause for concern, or will that be fine once skimmed over by the plasterer?

 

Again, thanks for all the valuable advice

I do think it's a radial circuit.  There is for sure a socket with a single 2.5, but haven't checked for one with 3x 2.5 cables in it.  I'll do that now.  I did consider the possibility that he may have used existing cabling for the return back to the CU, but can't see anything.  Besides, the existing cabling exists for the ring around the rest of the flat, so I think that would probably rule it out.

I'm not an electrician, but looking at it myself from a practical point of view, I do think the easiest solution would be the 2nd run back to the CU (assuming definitely radial at the moment)

Don't worry, I will try to get all this sorted amicably.  I'm not going to jump in with guns blazing!

 

Yeah, I know, photos would be useful and interesting .  I know I've not mentioned any names, but it just feels like a step too far until I've discussed it with the electrician.  Lets see how that pans out and will go from there.

There is a double socket with 3 x 2.5 cables, but 1 of the 3 goes to a fused spur(?)  (fused switch above worktop, socket below) which then goes no further.  I'm guessing that has no bearing on whether or not it's radial or ring, but happy to be corrected.

 

Have spoken to my electrician who says 2.5mm is fine because it's less than 50m (don't know if he meant cable length or floor area).

I spoke to another electrician on phone and said no way to a 32A breaker on a 2.5mm radial

In my mind, I can't see how a 32A breaker can protect a cable rated for 27A (under ideal circumstances).

Regardless of anything else though, my electrician has politely agreed to change it to a ring circuit, so I'll let it rest.  I'm just glad I spotted this before fitting my new kitchen!

A big thanks to everyone for their advice . 

Will post a final update when the electrical work has been completed.