Hob & oven circuit

[wrightsonm]

I am trying to decide what is the best / neatest way of rewiring my electric hob 6.6kW and electric oven 1kW. Oven is fitted with a 13A plug.

Current wiring is 10mm from 40A fuse, to 45A isolator switch to JB (which i cant access due to kitchen cupboard) spurred 3 ways,

1. To JB connecting hob.
2. To socket on cable
3. To surface 1g socket for fridge

New 10mm cable installed. 40A fuse will be 40A MCB + RCD.
New 45A isolator.
Fridge moved to socket circuit

And this is where i cant decide the best solution.

I have pulled the hob cable through to the isolator switch with the aim of removing all of the old JBs.

So the oven?

1. Think I cant use 2.5mm from the isolator to a socket due to no suitable fused protection for the 2.5mm cable

2. FCU for the oven spurred from the cooker isolator? Will i struggle to terminate the cables in the 45A isolator switch? Presume I'd have to run 10mm to the FCU which may not fit into the FCU? Any recommended products?

3. Continue 10mm down from cooker isolator to a splitter and wire oven & hob from that? Which product?

4.put oven on socket circuit. (Would prefer to put on cooker circuit)

5. Another option that i havent considered.

Pictures of existing wiring of which all of it is being removed or replaced.



JB to cooker. (Not sure but it might only be a 20A JB...)

Oven socket

Another JB is hidden behind back of cupboard.
3 cables are fridge socket, oven cable/ socket, to hob JB.
1 10mm cable goes up to the cooker isolator.

New chase with old cable off to the right outside of zone. I could put an FCU to the right of the 2g ba k box.

Many thanks!

 

[EFLImpudence]

Disconnect existing outgoing wiring from cooker switch and remove.

Connect 6mm² cable to cooker switch and run to Cooker Connection Unit.
https://www.tlc-direct.co.uk/Products/AA45DCOP.html

To CCU connect hob cable and a 2.5mm² cable to a socket for oven.
Surely the oven must be more than 1kW?

 

[donrkebab]

1. Think I cant use 2.5mm from the isolator to a socket due to no suitable fused protection for the 2.5mm cable

Take the 10mm to an accessible dual outlet cooker unit, one side for the hob, fit a 13a s/o beside other side of dual out let for the oven. The isolator will therefore control hob and oven.

Pictures of existing wiring of which all of it is being removed or replaced.

Therefore, I have ignored all other comments.

 

[EFLImpudence]

1. Think I cant use 2.5mm from the isolator to a socket due to no suitable fused protection for the 2.5mm cable

Yes, you can and there is.

The fuse will be in the oven plug - although, it can be argued it is not necessary.

 

[AndyPRK]

I would fit a dual back box into the wall

https://www.screwfix.com/p/appleby-galvanised-steel-dual-35mm/48234

Hob hardwired one side.
Socket on the other side for use with oven

 

[wrightsonm]

0.79kW oven
0.88kW oven + fan
1.5kW grill. (Missed that one)

If I connect 2.5mm from CCU to socket, what about the potential fault protection for the cable itself?

 

[AndyPRK]

it's best to keep the 2.5mm as short as possible. (6 inches)

 

[EFLImpudence]

If I connect 2.5mm from CCU to socket, what about the potential fault protection for the cable itself?

It will be fine.

Overload protection (not really neeeded) will be by the fuse in the plug.
Fault protection will be by the MCB.

 

[AndyPRK]

Can you just explain the rules to me how Fault protection is achieved connecting a 2.5mm cable to a 40A MCB (in a wall)
Thanks

 

[ban-all-sheds]

Basically in a fault (assuming a compliant fault loop impedance) the protective device operates before the cable has time to get damaged.

 

[JohnW2]

Can you just explain the rules to me how Fault protection is achieved connecting a 2.5mm cable to a 40A MCB (in a wall)

Fault protection (as opposed to Overload protection) has nothing directly to do with the size of the cable. One could measure the fault loop impedance (EFLI) of a circuit, and thereby determine whether the circuit's MCB was providing adequate fault protection (i.e. acceptable disconnection time in the case of a fault), without having a clue as to what size cable was involved.

Kind Regards, John

 

[wrightsonm]

So i've extracted snippets of the regulations in an effort confirm some of the suggestions above.

EFLImpudence suggestion does not meet 433.1.1(ii) and does not meet 433.1.1(iii).

2.5mm2 cable Ref Method B = 24A. * 1.45 = 34.8A. MCB = 40A

433.3 doesn't apply here. 433.2.2 does.

EFLImpudence suggestion of wiring a socket to a CCB is inline does not meet 433.2.2, would probably meet 433.2.2(i) and (<6 inches) does meet 433.2.2(ii).

EFLImpudence suggestion of wiring a socket to a CCB is would meet 433.3.1(ii)

And for fault protection:

EFLImpudence suggestion does not meet 434.2.1

Not sure if 434.3(iv) would apply here or not.

Based on these extracts, it would appear:

• 2.5mm2 spurred socket is not permissible
• 2.5mm2 socket from CCU is not permissible
• socket in 2.5mm2 from 13A FCU wired from cooker isolator switch in 2.5mm2 or from CCU in 2.5mm2 is permissible

have I missed something?

Thanks
Mark

 

[wrightsonm]

Yes, you can and there is.

The fuse will be in the oven plug - although, it can be argued it is not necessary.

I think this is not permitted by 434.2.1 but an FCU before the socket would be permitted.

 

[wrightsonm]

It will be fine.

Overload protection (not really neeeded) will be by the fuse in the plug.
Fault protection will be by the MCB.

Yes I suppose you could argue that the fuse being downstream is sufficient, and the cable being in a fixed installation is sufficiently protected, and of a short length but it would be ignoring 434.2.1 "shall be no branch circuits or socket outlets"

 

[wrightsonm]

Basically in a fault (assuming a compliant fault loop impedance) the protective device operates before the cable has time to get damaged.

Yes in a correctly designed and installed system, the fault impedance would be low enough to trip a 40A MCB. 230V/40A = 5.75ohms.
This doesn't account for an over current condition that is between 24A and 40A ish.

Or should I just assume that in future no-one would be daft enough to plug a multi-way into the socket under the counter?