Oven Wiring

[VicParticipant @vic]

Michael, I just counted the number of strands and measured the diameter of several of them with a caliper. I could have used a micrometer but there would have been a danger of crushing the cable giving a false reading.

[Michael GilliganParticipant @michaelgilligan61133]

Understood, Vic … it’s no big issue, I just mentioned it for the general pool of knowledge: because I believe 1.35 is the next-size-down.

[ Happy, as always, to be corrected ]

MichaelG.

[VicParticipant @vic]

Having completed the job I was impressed with the *Crabtree outlet, much better than the BG.

* I’ve always liked Crabtree stuff. Many years ago a large B&Q near to where I used to live in West London used to offer a lot of electrical products in MK, Crabtree and a budget version. The Crabtree stuff always looked the best. Some years later MK stuff started to look a bit more modern. Just as well as B&Q seem to have discontinued the other brands. I must remember to seek out Crabtree if I need any other stuff like this in future.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

2/ There is no indication the Vic’a switched outlet has an integral 13A socket.

4/ The physical current rating of a cable is directly proportional to both the amount of copper and the temperature resistance of it’s insulation. The APPROVED rating depends on the environment it is installed in (ambient temperature, number of cables, thermal insulation etc AND local regulations. A physically identical cable may have different approved rating depending on country and installation.

5/ Vic’s 1.5mm2 cable is OK for his 3.4kW / 16A load because the insulation is rated to a higher temperature and is in free air. The same applies to the 1mm kettle cable being OK for 3kW

6/ The MCB is there to protect the wiring. Ideally it shoud be a 16A “B” type to protect the flexible section but in realtity the probability of a fault of the narrow overload range that would trip a 16A MCB but not a 20A before the cable caught fire is small. Not impossible with an oven though. A short scicit between adjacent turns of a spiral wound element is not unknown.

Robert

Seems you missed Vic’s message #742216 in which he states a combined unit with a 13A outlet describes a CCU (cooker control unit), no doubt the reason why the electrician used a 20A mcb rather than a 16A.

The cable is in a void, possibly not ventilated, at the back of the oven. The oven insulation will not prevent all heating of the air within the void so the cable may well be working way above it’s rated temperature of 70deg C (pvc outer/pvc conductor insulation) see the NEFF connector data.

The Crabtree unit should last a good few years without issues.

Emgee

[Robert Atkinson 2Participant @robertatkinson2]

To be precise he said the outlet is combined with a switched 13A socket. I take this to mean next to. It is not the “classic” UK cooker isolator with a 13A socket as part of the isolator. I standby my statement that neither the damaged outlet or any of the possible replacements he showed images of had an integral socket.
I don’t know how the oven and 13A socket was wired but the consumer unit has a separate MCB labeled “kitchen sockets”. It would not be appropriate to wire a 13A socket and a fixed 3kW load to a single 16A MCB. A common kitchen item like a kettle would trip it with the oven on.

We don’t know the teperature rating of the cable. The H05VV-F 3G1.5 part of the number is the same as a common cable code but does not specify a temperature. This cable is 70 deg C https://assets-cdn.helukabel.com/suppliers/Helukabel/documents/db/HELUKABEL_M29450_EN_GB.pdf

But this with same code is 80 deg C https://procab.be/be-en/products/d/pc3g15—power-cable—h05vv-f-3g1-5—3-x-1-5-mm2—16-awg

Both say they are suitable for ovens. We can only assume thet NEFF have used a suitable cable.

Robert.

[VicParticipant @vic]

This is the switch type I have.

[EmgeeParticipant @emgee]

Hi Vic

Yes as I expected a CCU which would normally be wired in 6.0mmsq minimum and protected by a 32A mcb but your electrician reduced the mcb rating to offer some protection to the oven connecting cable and leave capacity to run a food mixer or other low current item without causing an overload if the oven is operating, or a kettle if not using the oven.

Emgee

[Vic]

On Vic Said:

This is the switch type I have.

In light of recent discussions … will you be re-labelling that switch ??

🙂

MichaelG.

[Vic]

On Vic Said:

This is the switch type I have.

Ahh, that is not what you have shown the back of previously. All those where square for a start. e.g #742058
Don’t use a kettle in the socket when the oven is on or you may get a trip.

Robert.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

On Vic Said:

This is the switch type I have.

Ahh, that is not what you have shown the back of previously. All those where square for a start. e.g #742058
Don’t use a kettle in the socket when the oven is on or you may get a trip.

Robert.

This is a game changer!   Now I don’t know what Vic is up to.

The damaged square unit shown in #742058 is a plain junction box, suitable for a 15A oven protected by a 20A MCB.

The cooker switch is a different kettle of fish, and I think it’s wrong because it misleads.

• A cooker switch in the kitchen implies to future installers that it’s OK to connect a 10kW cooker (over 40A), when the MCB and maybe the spur wiring aren’t up to that.  The rating of the wire inside the wall is now in question.   I doubt a professional electrician would fit a cooker switch to anything less than a suitably hefty spur, so Vic doing it creates a booby trap.
• Running the 15A oven and using the 13A socket at the same time exceeds the 20A MCB.   Not dangerous, but why bother?

Swapping the burnt junction box for another junction box is a repair.   Substituting a cooker switch for a junction box is a design change, requiring a re-think.   My amateur gut says don’t do it:  what do trained electricians advise?

Dave

 

[VicParticipant @vic]

The very first picture I posted was of the connection behind the oven (we don’t have a cooker) someone on here mentioned (I can’t be bothered to go back and look) if it was switched, and what type it is. I’m not sure this switch would be in a very convenient place behind the oven?

Michael, I think I’ll just leave it as we both know we don’t have a cooker. 🤣 And we know if we turn it off the control panel on the Oven (did I say we don’t have a Cooker?) goes off.

This particular switch, in fact nearly all the others we have in the house were here when we moved in. We did replace the oven not long after but both the Gas Hob (blast, maybe I shouldn’t have mentioned that) were installed by qualified Electrician/Gas fitter.

The Electrician suggested we really needed a new consumer unit and I was keen to have it replaced as well (small, old, plastic). As part of the process and wiring the oven (damn, should we have got a cooker?) NO we didn’t have space for a free standing oven and hob (sorry Cooker). He fully tested our electrics and provided a certificate.

To date, only the OvenCooker thingy has gone bang. We’ll probably never know why but can suspect or suggest, a very, very, slightly loose connection because it took maybe 10 years to melt.

[EmgeeParticipant @emgee]

Dave

Vic didn’t try to mislead anyone, if you and Robert had read and understood the messages Vic posted you would have been better informed, in particular message #742216.

The pics in his earlier posts were clearly the oven outlet connection box fitted below worktop height which is quite usual in an oven/cooker installation.

Vic hasn’t replaced the CCU, it has always been there and is no doubt wired in a suitable sized cable and originally protected by a 32A mcb.

The circuit cable type and size will be stated on the electrician’s report, after changing the consumer unit he would have tested all final circuits and recorded the results on the certificate Vic mentions.

Emgee

[VicParticipant @vic]

You can’t fit a Cooker in our kitchen, only a separate Oven and Hob, there isn’t space. The Hob is Gas, I know as I can see the flames. 😉

The Electrician checked the wiring to the replacement Oven when he fitted a new consumer unit.

[Emgee]

On Emgee Said:

Dave

Vic didn’t try to mislead anyone, if you and Robert had read and understood the messages Vic posted you would have been better informed, in particular message #742216.

The pics in his earlier posts were clearly the oven outlet connection box fitted below worktop height which is quite usual in an oven/cooker installation.

Vic hasn’t replaced the CCU, it has always been there and is no doubt wired in a suitable sized cable and originally protected by a 32A mcb.

The circuit cable type and size will be stated on the electrician’s report, after changing the consumer unit he would have tested all final circuits and recorded the results on the certificate Vic mentions.

Emgee

Thank you. 😊 That is exactly the case.

[VicParticipant @vic]

I just know I’m going to regret saying this but I’m sure the oven reached temperature quicker today than it used to?

[Michael GilliganParticipant @michaelgilligan61133]

Entirely logical, Vic

MichaelG.

[Robert Atkinson 2Participant @robertatkinson2]

OK so we don’t know what cable size is between the “cooker + 13A switched socket unit” is. Assuming it is at least 2.5mm it is protected by the 20A MCB. If it a larger size fitting two conductors into the terminals is a likey to be tight. The outlets are designed as a single item at the end of a radial circuit so are not intended to have two conductors.
If the oven is on and a 3kW kettle is plugged into the circuit the load is around 25A, more then the breaker rating. As it i a B breaker it could take a minute or two to trip.
If someone later changed the breaker to a 32A because of this, particuarly if they found 4mm cable in the consumer unit the cable between the switch unit and cable connection and the flexible cable would not have adequate protection.
As it is it is compliant and safe but I would say it is not best practice.

Robert.

[VicParticipant @vic]

When we moved into the property the existing oven I believe had a 13A plug top. The new oven selected was, according to the brochure 16A. So I elected to get an Electrician in to fit it. (I think I may have mentioned this)
Just after starting this post I started looking for more information. On some literature for NEFF Ovens it mentioned 13A but had in brackets “UK 10A”. I believe this to be a reference for a NEFF Oven fitted with a UK 13A plug. I obviously have no idea why the UK version of the Oven would be down rated to 10A.
One of the reasons for the selection of this particular NEFF Oven is that it has “Pyrolytic cleaning”. I suspect that in normal use our oven may only draw between 10 and 13 amps?  But possibly draws up to 16A when in Pyrolitic cleaning mode. This mode has been used about three or four times since we bought it.

[Robert Atkinson 2Participant @robertatkinson2]

If Fitted with a 13A plug rather than a fixed cable outlet then they may well have down rated to 10A. This is because some “13A” plugs and sockets can overheat when used at full load for a long time.

Particular combinations may be poor even though the plug or socket passes testing.

See https://engx.theiet.org/f/wiring-and-regulations/25529/bs-1363-13a-socket-continuous-max-load

Robert.

[VicParticipant @vic]

As an aside. Apparently 13A ouside sockets for *charging EV’s have an upgraded specification due to possible over heating problems.

* In spite of many non EV owners voicing concerns over range etc, many who actually drive EV’s are apparently foregoing an expensive charger and “granny charging” from a 13A socket. It apparently only adds 30 or 40 miles on an overnight charge to what’s already in the battery but this seems more than enough for many.

[EmgeeParticipant @emgee]

Robert

The unit Vic pictured is a Cooker Control Unit which will accept cables with csa up to 10mmsq, the 13A integrated socket is powered by terminal links built in.

The switched outlet connection terminals for the oven/cooker are normally the same dimensions as the incoming supply terminals.

Emgee

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