Advice on ensuring wiring is ok for new oven & hob...ple

[Stevethetiler]

Hi guys.

Firstly, sorry if this is a duplicated thread but I dont have much time before i need to make a decision.

Story being, My less than 12mth old single built under oven has gone kaput and the manufacturer have offered a replacement or an upgrade.

Thats the good part!

What I would like confirmation of before I agree to a new oven is wether or not my existing wiring will be sufficient for the new needs of the new oven/exisiting hob.

Currently, the oven is 2800w and the hob is gas so power for ignition only.

The existing wiring is new. I have a new Consumer unit (12mths ago) and the cooker is on its own circuit with a 40ma RCBO.

This leads to a 45a dp switch at worktop level, then goes behind the units and is currently wired in 6mm to a unswitched double socket located in an adjacent cupboard.

Both oven and hob are plugged in to this double unswitched socket with 13a and 3a plugs.

Now, the new "upgrade" oven I have been offered is rated at 3600w and I have been told it should be hardwired.

My questions being:

Is it feasible to take the double socket off the existing 6mm load from the 45a dp switch and simply add a dual CCU like this one:

http://www.alertelectrical.com/prod/1022/click-45a-easyfit-dual-appliance-outlet-plate

Im thinking it would be mounted behind the oven and the oven itself hardwired in 6mm from the oven terminals to the Dual CCU plate and the power to the gas hob ignition could be run in 2.5mm from the dual CCU to the exisiting double socket (or change it for an unswitched single) in the adjacent cupboard and simply plugged in and fused down to 3a via a 3pin plug.

Does this sound plausible or would there be anything that the professionals would do differently? - is my Breaker on the CU the appropriate size?

I am only asking as I would like to know in advance if its gonna cost alot to adjust the existing wiring to accomodate the larger powered oven?

(and yes, have read up on part P lol)

Thanks in advance for any advice.

 

[PrenticeBoyofDerry]

Do you mean you have a 40A 30mA RCBO? You would get away with a 16A 30mA, do you know what the manufacturers instruction advice regarding breaker size?
all the rest sounds good.

 

[ericmark]

I would think the supply to gas hob would need a fuse. This could be a socket and plug or fused connection unit.

The oven will also need protection the manufacture will likely stipulate the size. Could be 16A.

This would likely mean the RBCO will need changing to one matching manufacturers requirements.

But basic idea is OK and if fitted by an electrician then there would likely be no problems.

As said already the RCBO will likely be 30ma @ 40ms and have a marking like B32 which means it will trip at 32A after some time and 160A within 0.1 seconds. (B means 5 times)

So to answer the question yes it can be fitted assuming the RCBO is a 40A not 40mA.

 

[ajrobb]

Is there an issue that a 13 A socket should not be connected to a circuit rated at more than 32 A?

It may also be that the oven should not be connected to a circuit rated at more than 32 A.

From OSG: "A 30 or 32 A circuit is usually appropriate for household of similar cookers of rating up to 15 kW."

These are all separate issues but all seem to point to using a 32 A circuit breaker rather than 40 A.

 

[Stevethetiler]

Thanks for the replies firstly.

I have just double checked my consumer unit and the breaker for the oven ciruit has markings on it "B40 / 30ma" so I assume it is a 40a breaker/RCBO (its a Crabtree StarBreaker unit)

I assumed that this would be OK for my exisitng oven as they Eletrical firm that fitted the CU put that size RCBO in in the FIRST place - not me!

The wiring hasnt changed since they did the work so I presumed that I wouldnt need to "lower" the rating simply because of changing the oven - if anything, I thought it would maybe need to go up in size due to the higher rated oven being offered (3.6kw)

And yes, the current 2.6kw oven and the gas hob are both simply "plugged" into an unswitched double socket in the cupboard next to the oven. The oven has 13a plug, the gas hob, 3a.

The wiring from the CU cooker circuit is in 6mm to the 45a DP Cooker isolation switch above the worktop and then the cable used for the load from this switch to the cupboard socket is also 6mm.

In my mind, I simply thought that taking the 6mm from the double socket, putting it to the supply side of a dual cooker connection plate behind the oven would work - I thought that then it wouls simply be a matter of hardwiring the new 3.6kw oven into the plate using 6mm cable and running a spur from the second outlet on the plate to the cupboard socket for the gas hob which would still be plugged in via a 3a plug. (6mm or is 2.5mm ok for that? - its 6mm at the mo)

Is this not the case? - I will check with the manufacturer regarding breaker size but if its been running on a 40a one, does this really need to be downgraded?

Im thinknig that if it does indeed need to be changed down, then it would need to be more than 16a because the oven is 3.6kw (15a) and the hob (3a) would total a max of 18a.......is that right?

(obvioulsy safety is paramount - just trying to get my head around what needs doing so I know when my electrician looks at the job in hand)

 

[ajrobb]

I'd contact the oven manufacturers to check that your oven is suitable for connection directly to a 40 A circuit. I'm pretty sure you shouldn't have a 13 A socket on a 40 A circuit though. If you had a 32 A circuit, you should be OK to connect a 13 A socket to the switched side of the cooker control point, as you can control two cooking appliances from one switch as long as they are both in the same room and within 2 m of the switch. I would want a hidden igniter socket to have an isolator switch above the counter, the cooker switch is obvious.

 

[Stevethetiler]

I'd contact the oven manufacturers to check that your oven is suitable for connection directly to a 40 A circuit. I'm pretty sure you shouldn't have a 13 A socket on a 40 A circuit though. If you had a 32 A circuit, you should be OK to connect a 13 A socket to the switched side of the cooker control point, as you can control two cooking appliances from one switch as long as they are both in the same room and within 2 m of the switch. I would want a hidden igniter socket to have an isolator switch above the counter, the cooker switch is obvious.

I just phoned Hotpoint, she just said my spark would tell me what size breaker! - she just reiterated the rating of the oven at 3600w/3.6kw!!!

Man, if your saying I shouldnt have a socket on a 40a circuit, my electrician wired it in this way when they did the CU so I thought they new what they were doing!

Yes, the hob would simply be plugged into a socket in the adjacent cupboard and fused down at plugtop to 3a. Both oven and hob controlled by the one 45a DP cooker switch next to my oven above the worktop (fed directly from the CU in 6mm) - dont see any point in having another switch above the units just to isolate the hob.

Surely, as all power to both appliances would be coming from the 45a DP cooker switch, even if i had a switched socket to sperately isolate the hob from within the cupboard, turning the master switch off would kill the power to both anyway, wouldnt it......(both appliances are within 1m of the 45a DP switch which is 300mm to the right of the hob (above the worktop) with the oven dircetly under the hob and the socket located in the cupboard next to the oven)

 

[holmslaw]

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[Stevethetiler]

Change the 40A/30mA to a 20A/30mA rcd.

Change the twin socket to a cooker dual outlet.

Hard wire the oven into one side of the dual outlet, and on the other side fit a single 13A socket for the hob.

Job done, collect brownie points, go down pub.

Excellent news - thanks.

So, the cable for the 13a socket - 6mm or 2.5mm?

Hardwiring the oven - replace the flex with 6mm wired directly to the plate?

Change RCBO to 20a/30ma such as this: http://www.amazon.co.uk/Crabtree-Starbreaker-RCBO-61-B12030/dp/B004P4VVWI - looks like the ones on my CU....

Correct?

 

[ajrobb]

I bow to holmslaw's experience - B20 CB or RCBO. (Good for up to 10 kW of household cooking appliances should you ever want to add another oven.)

Other things you can check include the rating plate on the appliance and the installation instructions. Some Hotpoint double-oven instructions show a 4mm² cable connecting the oven, which would be OK if you want to use a 32 A CB. That is the nearest we have to a standard cooker supply, which can include a 13 A socket (kettle).

As long as the circuit does not exceed 32 A, you should be OK wiring an unfused spur to a single 13 A socket in 2.5mm² T+E.

 

[holmslaw]

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[Stevethetiler]

So, the cable for the 13a socket - 6mm or 2.5mm?

Hardwiring the oven - replace the flex with 6mm wired directly to the plate?

2.5 would be ok, but if you have 6mm use that, just for a bit of consistency. Don't replace the manufacturers flex.

Change RCBO to 20a/30ma such as this: http://www.amazon.co.uk/Crabtree-Starbreaker-RCBO-61-B12030/dp/B004P4VVWI - looks like the ones on my CU

Just confirm that it is 30mA, and you will need someone to test it.

No problem. will get my sparky to change the RCBO as I dont think its something I can do myself (they seem to be wired into the CU and not simply "unpluggable" to swap them like my old CU was.

Regarding the oven hardwiring, is it ok to just wire the supplied oven flex into the dual connection plate? - I thought it would need to be "beefed" up to 6mm also? - obviously, im no expert but would take your advice regarding this....(well, my electrician would lol)

 

[holmslaw]

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[Stevethetiler]

Once you have fitted the 20A rcbo the whole circuit is downrated to 20A, so 6mm cable is no longer required.

Replacing the oven flex could invalidate the warranty and it could be difficult to terminate a 6mm cable in to a 20A rated appliance.

Thanks.

So, basically:

1. Take exisiting 6mm feed from the double socket I have in the cupboard

2. Wire this to the supply side of the dual CC plate.

3. Wire the socket in cupboard in 6mm from one of the loads of the dual CC plate.

4. Change RCBO down to 20a/30ma and test.

5. Hardwire oven to the other side of the dual CC plate with lead provided by hotpoint.

6. Plug hob into cupboard socket for ignition.

Job done, yes?

 

[holmslaw]

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