How to safely connect a 27A electric hob to 45A cooker circu

[willy614]

Firstlty, may i assure you i have genuinely spent hours over the last 2-3 days searching this site, and google etc to answer my question - i post advice (in my subject area) on another forum and it annoys me when people are too lazy too look - i have seen some similar advice but nothing which matches. Because of this i am hoping someone in the future will benefit from the replies here for their potential searches.

I am helping my mum with some updates to her house and am updating the kitchen units. I am replacing an old stand alone cooker for a built in single oven and seperate hob (yes i know there are lots of matches on this site for this, please bear with me).

The oven says it should be hardwired so i am planning a 13A switched FCU (the cooker is 2.4kW which i make as just over 10A) for that. I was going to change a double socket for a dual box (advice on another post here!!) to fit an FCU and single socket however could i simply fit a new FCU off the CCU?

The hob is 6.5kw which i make just over 28A (although with diversity applied considering the chances of having all 4 rings on max at the same time, this will mostly be less). I was intending to connect this to the old CCU but this is 45A which seems to much.

The fusebox is the old type with push in slots/plugs containing fusewire therefore i think she may have to have this replaced anyway, which may solve the problem as the dedicated cooker circuit can be adjusted here but in the mean time or if not, is there a way i can safely connect it?

As far as i'm aware there aren't 30A/32A FCUs so is there a way i can protect this?

Thank you in advance for the help (and for the other help i have reguarly received on here in the past - particuarly the advice on how to sort out the wires when i removed a rose to fit a new modern light bar and didn't mark the wires leading to trips- DOH! - one quick search on here and a few mins with a multimeter later and i was sorted )

 

[1john]

Replace the fuse with a 30A/32A mcb

 

[sherlockholmes]

I often see 'diversity' come up on here, what does it mean exactly in the electrical context?

 

[1john]

It is applied to installations to work out the maximum demand, for instance, if you added up ecery socket outlet in a house and assumed they would all be at 13A then you would need a pretty hefty service fuse and would need one circuit per socket.

 

[flameport]

I was intending to connect this to the old CCU but this is 45A which seems to much.

Too much for what?
The fuse is there to protect the cable. Therefore if using 6mm cable for the hob, where is the problem?

The neatest solution is to fix a double backbox behind the oven, and fit a cooker outlet plate on one side for the hob and a 13A FCU on the other side for the oven.

 

[sherlockholmes]

It is applied to installations to work out the maximum demand, for instance, if you added up ecery socket outlet in a house and assumed they would all be at 13A then you would need a pretty hefty service fuse and would need one circuit per socket.

So you design circuits to run at x percent of maximum, on the understanding that if it were 100% the circuit would have tripped, but it almost certainly never will be? That makes sense, thank you. Is x a fixed value or a case by case thing? Rule of thumb or detailed calculation?

 

[1john]

It doesn't work exactly as I described, what I described was just to get an idea of diversity. each type of circuit has a different percentage of diversity applied to it.

Breifly, and off the top of my head it is -

Lighting - 66% of the total current demand

Power - 100% of first circuit + 40% of all of all other circuits

Cooker - first 10A + 30% of the full load of the appliance over 10A + 5A if there is a socket outlet on the control unit.

instantaneous heater - no diversity permittedHope this makes sense.