Oven Wiring

[Maurice TaylorParticipant @mauricetaylor82093]

Hi, Vic

Could you please tell us, what power is stated on the rating plate on the oven.

Thank you

Maurice

[Maurice TaylorParticipant @mauricetaylor82093]

Hi Dave ,

I don’t think anybody said anything about a cooker, only an oven was mentioned.

Regarding 20 amp mcb surely is there to protect the cable,it won’t protect a 1.25mm

flex.

There should be a fuse in the wall mounted connector unit to protect the 1.25mm flex.

Maurice

 

[VicParticipant @vic]

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.

Bill

I think I’ve mentioned twice now that this is the original NEFF cable that came with the oven.

Maurice, the rating plate says 3.45kW.

 

[Maurice Taylor]

On Maurice Taylor Said:

Hi Dave ,

I don’t think anybody said anything about a cooker, only an oven was mentioned.

Regarding 20 amp mcb surely is there to protect the cable,it won’t protect a 1.25mm

flex.

There should be a fuse in the wall mounted connector unit to protect the 1.25mm flex.

Maurice

 

Where I come from ‘cooker’ and ‘oven’ are synonymous.   Beside the point though, because my 10kW cooker is just an example of something different having to be done to connect any appliance drawing over 13A.   Immersion heaters,  power showers, ovens, cookers, air-con, and workshop equipment like a big welders etc.

The usual arrangement for big boys is a separately fused spur, and I think Vic’s 20A MCB is fine for the spur itself and the oven cable we suspect is on the thin side.   (It’s not on the thin side if insulated with Silicone Rubber!)

And don’t forget the thin connection is to an appliance, often fused internally.  Another set of rules…

In Vic’s spur, not connected to the ring, there is no need for a fuse in the wall-box, just as there is no need for 13A sockets to be individually protected with fuses.

There are situations where wall-boxes are fused.  My gas central heating system, consuming a few amps maximum, is spurred off the ring main, not the consumer unit.  As the spur is hard wired, with no fused plug, the ring is protected from an appliance fault by the spur connecting via a fused terminal box, imitating a plug!  Covers many requirements, but I suggest not “good enough” for connecting any appliance consistently consuming 3kW or so.

Another exception is trailing socket extenders, fused in the extender itself and the plug.

Sorry Maurice, but this stuff gets complicated.   I’m happy up until the regulations apply, then I send for an electrician!

Dave

 

[Vic]

On Vic Said:

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.

Bill

I think I’ve mentioned twice now that this is the original NEFF cable that came with the oven.

Maurice, the rating plate says 3.45kW.

 

Yes I know, you’ve even shown photos of it, but somehow the message isn’t getting across.

If it’s on a single radial back to the distribution board, the relevant MCB should probably reflect the oven’s load;
e.g. 20A is likely too high to protect the cable/oven.
If it’s fed off a spur from a ring main with a 20A MCB, then it likely should have a fused spur outlet to protect the flexi.
N.B. I’m not up to speed with the current regs, as this house was up and running when we moved in.

My previous house had a single oven on a radial back to the fuse board with a dedicated fuse.
The flexi was about 1.5mm, as was the twin and earth feeding the connection box.
Obviously that precluded me from replacing the large single oven with a pair of smaller ones, as the combined load would be too high for the 1.5mm twin & earth.

Bill

[Vic]

On Vic Said:

[…]

Maurice, the rating plate says 3.45kW.

 

…and at the risk of putting my foot in it again; that’s presumably why

1. the appliance connector is rated at 16A
2. the flex is supplied with bare ends, not a 13A plug

[myself … I only ever queried the csa of the wires]

MichaelG.

[duncan webster 1Participant @duncanwebster1]

My 3 kW kettle has a 1 sqmm cable, supplied by Russel Hobbs. It doesn’t get hot, or even warm.

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW. If it had an integral electric hob I’d call it an electric cooker, not an oven. Perhaps it’s a regional dialect thing

There appears to be a world of difference between what is required for cables buried in trunking under plaster and those hanging in free air, no doubt due to heat insulation

[duncan webster 1]

On duncan webster 1 Said:

 

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW. If it had an integral electric hob I’d call it an electric cooker, not an oven. Perhaps it’s a regional dialect thing.

Thank you. As in the title of my original post, it’s just an oven. If it was a double oven or combined oven and hob (commonly called a cooker) I would have put it in the thread title.

Edit: As expected, when I put the word Cooker into Google it displays nothing but cookers. No pictures of an oven on its own at all.

[duncan webster 1]

On duncan webster 1 Said:

My 3 kW kettle has a 1 sqmm cable, supplied by Russel Hobbs. It doesn’t get hot, or even warm.

Hi Duncan, are you sure it’s 1.0mmsq cable and 3kW element ?

Emgee

[duncan webster 1Participant @duncanwebster1]

The plate on the kettle says 3 kW, and 1 sqmm is moulded into the cable. I must admit I was surprised.

[Vic]

On Vic Said:

On duncan webster 1 Said:

 

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW. If it had an integral electric hob I’d call it an electric cooker, not an oven. Perhaps it’s a regional dialect thing.

Thank you. As in the title of my original post, it’s just an oven. If it was a double oven or combined oven and hob (commonly called a cooker) I would have put it in the thread title.

Edit: As expected, when I put the word Cooker into Google it displays nothing but cookers. No pictures of an oven on its own at all.

On duncan webster 1 Said:

My 3 kW kettle has a 1 sqmm cable, supplied by Russel Hobbs. It doesn’t get hot, or even warm.

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW.

There appears to be a world of difference between what is required for cables buried in trunking under plaster and those hanging in free air, no doubt due to heat insulation

My Dualit kettle has the same cable according to the words moulded into the sheath.

There are plenty of ovens these days that are supplied with moulded 13A plugs which you can cut off when connecting to a proper oven switch.

The heating effect comes in with volt drop, which comes from both length as well as sqmm. and time.

The 10A rating for Emgee’s cable will be for the nominal length of 100M which will have a much greater volt drop that 1/2M of kettle cable.

As Vic has stated he does not have the ability to pick and choose his cable size as the propriety moulded plug prevents this.

[EmgeeParticipant @emgee]

The 10A rating for Emgee’s cable will be for the nominal length of 100M which will have a much greater volt drop that 1/2M of kettle cable.

Hi Duncan

That is the quoted maximum current for any length of the quoted type of cable, it’s the Volt drop that will be affected by cable length and is quoted as mv/amp/metre

Emgee

 

 

[Michael GilliganParticipant @michaelgilligan61133]

This must be my ‘find of the day’ … a 65 page list of applicable standards:

https://assets.publishing.service.gov.uk/media/649bf3c1f90109000c818938/ds-0085-23-low-voltage-equipment-notice.pdf

🙂

MichaelG.

.

[Dave Halford]

On Dave Halford Said:

On Vic Said:

On duncan webster 1 Said:

 

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW. If it had an integral electric hob I’d call it an electric cooker, not an oven. Perhaps it’s a regional dialect thing.

Thank you. As in the title of my original post, it’s just an oven. If it was a double oven or combined oven and hob (commonly called a cooker) I would have put it in the thread title.

Edit: As expected, when I put the word Cooker into Google it displays nothing but cookers. No pictures of an oven on its own at all.

On duncan webster 1 Said:

My 3 kW kettle has a 1 sqmm cable, supplied by Russel Hobbs. It doesn’t get hot, or even warm.

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW.

There appears to be a world of difference between what is required for cables buried in trunking under plaster and those hanging in free air, no doubt due to heat insulation

…
The heating effect comes in with volt drop, which comes from both length as well as sqmm. and time.

The 10A rating for Emgee’s cable will be for the nominal length of 100M which will have a much greater volt drop that 1/2M of kettle cable.

As Vic has stated he does not have the ability to pick and choose his cable size as the propriety moulded plug prevents this.

The idea that current ratings are length related is new to me: is there a reference?

Heating is entirely due to current, Watts = Amps Squared * resistance.  Thus a 3A cable is rated for 3A whatever its length.

This might explain the confusion.  If a 13A cable from an extender drum is run 30 metres to a garden shed and used to power a 3kW fan-heater,  the voltage at the heater will drop and it will draw less than 12.5A.    The voltage drop in the shed is caused by the cable’s ohmic resistance, which converts the resistance dropped energy into heat spread evenly along the entire length of cable.   Though it wastes energy the temperature of the air-cooled cable won’t rise beyond design limit because it has a large cooling surface area.    Conversely, if the cable is rewound on to the drum and used to power the same heater 2 metres away from  a power point, then the same cable could overheat.  It’s because heat is trapped inside the drum, and each turn of cable insulates heat trying to escape from it’s neighbours.  Short cables are much less likely to be heat insulated than long ones, where the user has opportunity to coil and box it.

Voltage drop due to cable length is often reduced by increasing cable diameter, but it’s also possible to increase the line voltage with transformers.   The transformer method is much preferred in power distribution systems because it saves millions of tons of Copper, but no such savings in a garden-shed installation!

Vic would be extremely ill-advised to mess with the cable supplied with his oven on the basis of our posts:

• We don’t know his cable is too thin!   It’s all supposition.
• The diameter/current guidelines being quoted are for PVC insulated cables.  If Vic’s cable is insulated with silicone rubber, it can run significantly hotter on thinner wire.   Silicone rubber may be necessary to manage thermal heat leaking from the oven into the wiring, in which case substituting PVC insulated wire of any size would be dangerous.
• Too many misunderstandings exhibited!

I think Vic is fixed.  He has the right type of spur and junction box, both protected by a correctly sized MCB.   The only fault in the original installation was the live terminal coming loose and allowing sparking.   The MCB didn’t blow because the current drawn by the oven was within limit.   Spark heat did the damage, not excess current.   Cable size played no part in this drama, and this type of fault is not prevented by fuses, current breakers or RCDs.

Dave

 

[duncan webster 1Participant @duncanwebster1]

I never mentioned length.

[SillyOldDuffer]

On SillyOldDuffer Said:

On Dave Halford Said:

On Vic Said:

On duncan webster 1 Said:

 

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW. If it had an integral electric hob I’d call it an electric cooker, not an oven. Perhaps it’s a regional dialect thing.

Thank you. As in the title of my original post, it’s just an oven. If it was a double oven or combined oven and hob (commonly called a cooker) I would have put it in the thread title.

Edit: As expected, when I put the word Cooker into Google it displays nothing but cookers. No pictures of an oven on its own at all.

On duncan webster 1 Said:

My 3 kW kettle has a 1 sqmm cable, supplied by Russel Hobbs. It doesn’t get hot, or even warm.

My normal size domestic oven (just an oven, no hob) is rated at less than 3 kW.

There appears to be a world of difference between what is required for cables buried in trunking under plaster and those hanging in free air, no doubt due to heat insulation

…
The heating effect comes in with volt drop, which comes from both length as well as sqmm. and time.

The 10A rating for Emgee’s cable will be for the nominal length of 100M which will have a much greater volt drop that 1/2M of kettle cable.

As Vic has stated he does not have the ability to pick and choose his cable size as the propriety moulded plug prevents this.

The idea that current ratings are length related is new to me: is there a reference?

Heating is entirely due to current, Watts = Amps Squared * resistance.  Thus a 3A cable is rated for 3A whatever its length.

This might explain the confusion.  If a 13A cable from an extender drum is run 30 metres to a garden shed and used to power a 3kW fan-heater,  the voltage at the heater will drop and it will draw less than 12.5A.    The voltage drop in the shed is caused by the cable’s ohmic resistance, which converts the resistance dropped energy into heat spread evenly along the entire length of cable.   Though it wastes energy the temperature of the air-cooled cable won’t rise beyond design limit because it has a large cooling surface area.    Conversely, if the cable is rewound on to the drum and used to power the same heater 2 metres away from  a power point, then the same cable could overheat.  It’s because heat is trapped inside the drum, and each turn of cable insulates heat trying to escape from it’s neighbours.  Short cables are much less likely to be heat insulated than long ones, where the user has opportunity to coil and box it.

Voltage drop due to cable length is often reduced by increasing cable diameter, but it’s also possible to increase the line voltage with transformers.   The transformer method is much preferred in power distribution systems because it saves millions of tons of Copper, but no such savings in a garden-shed installation!

Vic would be extremely ill-advised to mess with the cable supplied with his oven on the basis of our posts:

• We don’t know his cable is too thin!   It’s all supposition.
• The diameter/current guidelines being quoted are for PVC insulated cables.  If Vic’s cable is insulated with silicone rubber, it can run significantly hotter on thinner wire.   Silicone rubber may be necessary to manage thermal heat leaking from the oven into the wiring, in which case substituting PVC insulated wire of any size would be dangerous.
• Too many misunderstandings exhibited!

I think Vic is fixed.  He has the right type of spur and junction box, both protected by a correctly sized MCB.   The only fault in the original installation was the live terminal coming loose and allowing sparking.   The MCB didn’t blow because the current drawn by the oven was within limit.   Spark heat did the damage, not excess current.   Cable size played no part in this drama, and this type of fault is not prevented by fuses, current breakers or RCDs.

Dave

 

Thanks Dave. I should get the cable soon and I’ll make sure the terminals are tight.

The Crabtree cable outlet is quite interesting (to me) in that when you turn the screw it pulls a metal plate upwards trapping the cable against a similar plate. I’ve seen something similar but where I believe the plate I was pushed down by the screw.

[EmgeeParticipant @emgee]

Dave

Not all points made in your last post are are 100% correct but further discussion will only become boring to other members.

If your assumption is correct about damage being caused by arcing then that reinforces the decision by the IEE to require an Arc Fault Detection Device is fitted for 32A socket circuits in high rise buildings, homes for the elderly, houses of multiple occupation and purpose built student accommodation.
Usually AFAIK the device is fitted to protect all final circuits in the consumer unit although that is not required by BS7061, but Vic’s oven circuit would be included because of the 13A integral socket.

AFDD’s are protective devices installed in consumer units to provide protection from arc faults. They use microprocessor technology to analyse the waveform of the electricity being used to detect any unusual signatures which would signify an arc on the circuit.

Emgee

[duncan webster 1]

On duncan webster 1 Said:

I never mentioned length.

Duncan didn’t.  I bungled trimming the quoting content, losing Dave Halford’s statement:  The 10A rating for Emgee’s cable will be for the nominal length of 100M which will have a much greater volt drop that 1/2M of kettle cable.   My bold.

The current rating of a cable being related to ‘a nominal length of 100M‘ is new to me, and I suspect it’s a misunderstanding.

Dave

 

 

[duncan webster 1Participant @duncanwebster1]

Just to digress a bit, I once worked on a job which had a high voltage high frequency induction heating coil. It had a habit of arcing across the ptfe insulation, so the boffins decided we should have 2 brass balls (think golf ball size) a measured distance apart so that if it wanted to arc, it would do between the balls. These were in an enclosure with a light detector, so if it arced the control system would shut down the current. We’d got the balls in place, but not the detector when they decided to have a run. Sure enough we got the arc between the balls, but it didn’t shut off. It vaporised the balls, and the smoke drifted down the rig hall before one of these clever chaps noticed and hit the Estop.

[Author]

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