Oven Wiring

[noel shelleyParticipant @noelshelley55608]

For ferrules use small bore thin wall copper pipe as we use on our models ? As for undersize  wire, Look at the cost of copper,manufacturers are using the thinnest they can get away with, reduces safety but it ups the profit. The issue of lead/solder flowing when cold check out the workings of the time delay fuses developed by MI-R for SOE during WW2. Noel.

[Speedy Builder5Participant @speedybuilder5]

Perhaps I am a bit dim, but shouldn’t there have been a local fuse and isolating switch at the outlet, or is this above the work surface and what got burnt up was below the w/surface ?

[noel shelleyParticipant @noelshelley55608]

The problem was resistive heating not overload or short circuit. A fuse would have been little help and an isolator  done nothing. It could be said that the wire acted as a fuse ? Noel.

[Robert Atkinson 2Participant @robertatkinson2]

Both the crabtree and MK are superior to the BG. They both use “cage clamps” to secure the conductor unlike the single point screw of the BG / Nexus.

Under no circumstances should mains flex screw connections be “tinned” with solder. As pointed out the solder cold flows resulting in loose connections eventually.
It also has two other issues,

The copper dissolves in the solder increaing the resistanceThe thansition from soldered to unsoldered is a stress raiser and can cause fatigue failures.

Robert.

[Wink HackmanParticipant @winkhackman25989]

Speaking as a retired sparky, I’d say that the ferrules are not necessary. Tighten up the terminals firmly on the wire, without tinning it.  A month later, tighten them again – stranded wire always loosens over time. BG outlets are so-so, Crabtree are good.  MK used to be top quality but some of their stuff is variable nowadays.

[VicParticipant @vic]

In spite of this incident, I have every faith in the electrician. He seemed very thorough and didn’t rush to do anything, quite the opposite. As he quoted before the work I wasn’t paying by how long he spent on the job. He also supplied all the relevant paperwork required. I’ll be using him again at some point in the future for another couple of jobs.

[Speedy Builder5]

On Speedy Builder5 Said:

Perhaps I am a bit dim, but shouldn’t there have been a local fuse and isolating switch at the outlet, or is this above the work surface and what got burnt up was below the w/surface ?

The isolator is indeed above the oven near the worktop, it’s combined with a switched 13A outlet. The burnt out wire was behind the cooker.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Both the crabtree and MK are superior to the BG. They both use “cage clamps” to secure the conductor unlike the single point screw of the BG.

Yes, I noticed that, that’s why I bought it. It does seem to be a better design.

[EmgeeParticipant @emgee]

Vic

Does that mean you don’t need the ferrules ?
Twisting and folding back the wire to terminate will work well with clamp type terminals.

On checking the cable size by calculation using your quoted figures of 32 strands of 0.22mm diam the conductor is only 1.25mm, your final circuit supply protective device is a 20A type B mcb which means the flexible cable to the cooker does not have the required protection.

Changing the mcb for a 16A would go some way but still not provide protection to the 1.25mm flex so I am surprised the cooker manufacturer has not supplied a larger size flexible connector.

Emgee

[VicParticipant @vic]

Thanks for the offer, I’ll try it without the ferrules. My cable looks very much like this, which they say is 1.5. My cable, when twisted measured about 1.45.

[EmgeeParticipant @emgee]

Vic

The conductor size is not the diameter but the cross sectional area (csa) in mmsq of all of the strands,
so in your case 32 of 0.22mm diam using pixrsq the csa is 1.25mmsq.

Emgee

[Emgee]

On Emgee Said:

Vic

The conductor size is not the diameter but the cross sectional area (csa) in mmsq of all of the strands,
so in your case 32 of 0.22mm diam using pixrsq the csa is 1.25mmsq.

Emgee

Rather light for a nominal 16A rating, is it not ?

MichaelG.

[Dave HalfordParticipant @davehalford22513]

As it’s a NEFF he conductor sqmm will be moulded into the sheath along with the spec that the cable conforms to.

The fact that the part# includes 1.5 may point to the sqmm

Oven cable is designed to run at higher temps that plain PVC twin and earth that bleeds fluid @ over 60C.

[Michael GilliganParticipant @michaelgilligan61133]

Happy to accept your assurances, Dave

My comment was based on the measurement and calculation of two Engineers

… which probably only goes to show how difficult it is to do.

MichaelG.

[VicParticipant @vic]

This is the oven plug on the NEFF supplied cable. It is marked 16/250 which I strongly suspect is the cable rating?

[Emgee]

On Emgee Said:

Vic

The conductor size is not the diameter but the cross sectional area (csa) in mmsq of all of the strands,
so in your case 32 of 0.22mm diam using pixrsq the csa is 1.25mmsq.

Emgee

I figured it would be something like that, just giving you the approximate physical size of the cable in case it helped the calculation.

[Michael Gilligan]

On Michael Gilligan Said:

Happy to accept your assurances, Dave

My comment was based on the measurement and calculation of two Engineers

… which probably only goes to show how difficult it is to do.

MichaelG.

Nothing wrong with that Michael

Ordinary house cables are made to BS6004, you can get tri-rated cable made to BS6231 which can run up to 105C, though with all cable the safe working power limit depends on whether it is in free air, clipped to others or run in trunking, the worst case being in a loft under a foot of insulation.

[Michael GilliganParticipant @michaelgilligan61133]

Sorry, Dave … I bow to your wisdom.

I shouldn’t have made any comment.

… I always thought that 1.25 flex was for 13A, and 1.5 was needed for 16A

Every day is a school-day … and it’s not yet midnight, so I can learn something else tomorrow.

MichaelG.

[John Doe 2Participant @johndoe2]

Stranded wire with no ferrule or cage, even if twisted, can be spread out by the securing screw in the terminal, so that only, say, 1/3 or 1/2 of the strands are actually held firmly. A crimped ferrule tightly contains all the strands together, meaning that they are all in good contact with the terminal and all share the load.

It seems to be the norm now to see ferrules on power cables; both in domestic 13A plugs and house lighting, and also in the industrial Ceeform 16A, 32A and 64A connectors used for television trucks and stage lighting, amongst other things. So I suspect that regulations now insist that ferrules must be used ?

As others have said, solder can cold flow, reducing the holding force of a screwed connection – no matter how much you tighten it initially. And I really doubt that electricians come back a month later to retighten the screwed connections they have installed.

Soldering joints can also cause failure of the copper wires in vibrating or flexing environments, because the solder prevents the natural flexing of stranded copper, and this leads to cracking. Wiring loom connections on a car, (which are obviously subject to vibration), are crimped, not soldered – even the high current ones, no doubt for this reason.

 

 

 

[VicParticipant @vic]

Just to close this. I’ll be picking up a Crabtree flex outlet from Screwfix, hopefully today. Although perhaps better than a bare cable, without using the correct tool I don’t believe the round ferrules offered will have as good a contact with the cable as those used by the OEM NEFF. As a result I’ve ordered a new cable from NEFF with the properly crimped ends. A new cable is cheaper than buying a crimping tool I’ll likely never use again.

[larry phelan 1]

On larry phelan 1 Said:

Interesting subject. I too am surprised at the size of cable fitted to new ovens these days. Back in the day it was always 6 mm sq, now it is no more than 1,5 ! seems a bit strange, but any new cooker I have seen is the same, some of them even fitted with a three pin plug. Am I missing out on something ??

As usual, several possibilities, some acceptable others not.

The missing something is how deep our level of understanding of electrickery is.   Wiring a plug only needs the worker to know the wiring colour code (UK Brown, Blue, Green/Yellow stripes) and which pins are LNE.   Sizing a cable for ordinary purposes only needs the worker knowing how many amps it will carry so he can look it up in a table.   The table recommends standard sizes based on regulations.  A trained electrician is knows a great deal more, and should be able to recognise various different configurations, knowing what is and is not legal/safe, and how to install and test it.   Skill levels vary: a domestic electrician may not know much about 3-phase systems, and nothing at all about about machine controllers, VFDs, or electronics.    Although electricians all get a dose of theory, they focus mainly on practical work, and don’t need to worry about where rules, regulations and guidelines come from.   These are the province of Electrical Engineers, Regulators, and Scientists, chaps who understand numbers, and have a broad view of the art of the possible.   The art of the possible is changed by experience and by developments in the pipeline.   This is the group who decide what the rest of us should do, operating setting International and National Standards, changing the law, altering training, and introducing certifications etc.

A fundamental in electrical engineering that’s not immediately obvious to those expected to follow the rules is heat.  Electrical fires are at least as dangerous as electrocution.

Don’t know what wiring system is used in the Emerald Isle (ring or spur), but most domestic UK systems are ring wired for 13A maximum fused plugs, at 240Vac single-phase.   A 13A plug is acceptable only if the appliance consumes less than about 3.1kW, enough for a smaller than normal oven.   The fuse is rated to stop the wiring from getting too hot.  My ordinary domestic oven is rated up to 10.9kW, and all elements on at the same time, which is unlikely, would pull 45A.   New rule applies: it’s not connected to the ring main with a 13A plug; it’s hard-wired to a separate fused spur.

How thick a wire needs to be to carry a given current depends on how hot the designer is happy to let it get.   PVC insulation is OK up to about 70°C, but not wise to run domestic wiring that warm.   The enamel insulation used on magnet wire has improved significantly over time : pre-1950 motors were only good up to about 110°C, whilst modern insulation can do double that.   High temperature cabling of the type found in big electric heating systems can take up to red heat, though I’d guess 400°C is more likely.  It’s not unusual to find short lengths of wiring running very hot inside an appliance, then the appliance is connected to the mains via a short length of air-cooled thinnish wire running slightly warm in open air, but the mains supply keeps temperatures down with heavy copper wires.

Trouble is there are opportunities for abuse.   Such as the DIY enthusiast who connects a 10kW oven to the mains with a 13A plug, an arrangement that will work OK for years provided not too many elements are turned on at the same time.    Or a manufacturer who increases profit by thinning down the copper, or unwisely substitutes steel or Aluminium core.    Careless bargain hunters create a big market for counterfeit and ‘too-cheap’ electrical products.

Most likely Vic’s thin looking cable is suitable, but I had to replace it I’d use the UK size recommended for 15A.   The only way to prove Vic’s cable is completely satisfactory to measure either the voltage drop at full load, or the temperature rise over say an hour. I’d only worry if it ran at more than, say 35°C, this being because persistently heated PVC tends to harden and crack.  This assumes pessimistically that the insulation is PVC – might be Silicone Rubber, OK up to about 200°C!

Dave

 

[SillyOldDuffer]

On SillyOldDuffer Said

Most likely Vic’s thin looking cable is suitable, but I had to replace it I’d use the UK size recommended for 15A.   The only way to prove Vic’s cable is completely satisfactory to measure either the voltage drop at full load, or the temperature rise over say an hour. I’d only worry if it ran at more than, say 35°C, this being because persistently heated PVC tends to harden and crack.  This assumes pessimistically that the insulation is PVC – might be Silicone Rubber, OK up to about 200°C!

Dave

 

Surely Vic’s thin flexi cable is the one supplied by Neff, a respectable manufacturer, specifically for that oven, with their proprietary connector ready fitted at the oven end.
As far as I can make out, the issue was with the wall plate outlet overheating, as the terminals hadn’t been tightened correctly.

It’s worth checking wall connections in sockets and switches etc, as the solid copper wire does seem to relax a bit over time.  I must go round our house and check outlets at some point.
I’ve experienced it when checking wiring at my parent’s house, where each socket cover, or light switch, I removed needed the screws nipping up a bit.
Similarly where we live now, built in 1995, when I’ve delved into the wiring, each outlet needs at least checking and some need tightening.
I used to see it regularly at work as well, where almost everything was powered off 50v.
Terminations which used crimp on lugs or pins seemed to be OK, but single cartridge fuse holders, where the cables terminated directly, did relax a bit; normally these were 10mm through to 25mm cables, sometimes stranded, others flexi. I always used to terminate those ends early on, and then return just before I left the site to nip them up a bit again.
A couple of times, I had a live cable feed come out in my hand, when working on adjacent fuse holders in a rack top.
I got away with it in each case, as the kit was dual power fed, so no loss of service.

Bill

[Maurice TaylorParticipant @mauricetaylor82093]

Hi,

What is the power rating of the oven,they are usually less 3kw . If you look up cable ratings  1.25mm is suitable for up to 15amp,which is well with in 12amp that the oven could draw .

All it needs is a suitable junction box on the wall. With a 13amp fuse in it.

Please correct me if I’m wrong, I cannot see point of making things complicated.

Maurice

 

[Maurice Taylor]

On Maurice Taylor Said:

Hi,

What is the power rating of the oven,they are usually less 3kw . If you look up cable ratings  1.25mm is suitable for up to 15amp,which is well with in 12amp that the oven could draw .

All it needs is a suitable junction box on the wall. With a 13amp fuse in it.

Please correct me if I’m wrong, I cannot see point of making things complicated.

Maurice

 

Depends on what’s meant by an ‘oven’.    What might be OK for a single oven only with a gas hob, is wrong for a double oven with 4 electric hobs and an extractor fan.  As I said, my cooker is over 10kW, which is a complication requiring special attention.

Einstein said “Everything should be made as simple as possible, but no simpler”    When a problem really is complicated, it needs a proper solution.  Vic’s electrician got the right answer, except we strongly suspect the live terminal inside the junction box came loose and sparked.

‘All it needs is a suitable junction box on the wall. With a 13amp fuse in it’ is wrong’ – it’s not that easy!   The oven is rated for 15A.   Vic’s electrician met that requirement by fitting a plain junction box connected on a dedicated spur back to a 20A breaker in the consumer unit.   He didn’t connect the oven to the ring, and it doesn’t need a 13A fuse.

Dave

[Vic]

On Vic Said:

This is the oven plug on the NEFF supplied cable. It is marked 16/250 which I strongly suspect is the cable rating?

Vic, the 16/250 is the maxilmum rating of the connector and has no bearing on the cable size.

Emgee

 

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