Four electrical jobs in a kitchen - am I right?

[quattroal]

This is my first post on DIYnot so I'll start with a big thank you to everyone who's posted and answered here over the years - you've been invaluable.

I'm in the process of a kitchen renovation, which will include me doing four electrical jobs. I *think* I know what I need to do but I'd be grateful if you could check my homework before I go any further.

1) I'm replacing an electric range cooker with a separate hob and two ovens. The maximum load of the old range was 16,485W while the three new appliances combined are 13,650W so, as I never had any issues before, I'm planning on sticking with the current 4mm circuit wiring and 32A fuse in the consumer unit. However, the specs for the two ovens note the need for 16A fuses so my plan is to add a second consumer unit after the oven switch and then connect the two ovens to two 16A MCUs and the hob to a 32A one (given it's 7,350W by itself). The diagram below explains the plan. This might be overkill but is it OK? The second consumer unit will be hidden in a cupboard so I'll keep the oven switch on the wall so I can quickly and easily isolate the appliances if needed.

2) There is already a spur off the sockets ring terminating with a connection box - I've never used it but presume a previous owner of the house had a fridge running off it. As the spur is fused, am I right in thinking I can run three sockets off it?

3) The renovation has involved removing a stud wall and, in it, I found the cable taking power to the garage - it's a separate 32A circuit running directly off the consumer unit. To reroute the cable, I'm going to have to lengthen it (there's no slack and I'd have to dismantle half the house to pull it through). Am I right in thinking I can cut it and insert a length of similar cable (it's 4mm) using connectors (eg https://www.screwfix.com/p/wago-221-series-32a-2-way-lever-connectors-100-pack/8421r) or terminal blocks (eg https://www.screwfix.com/p/hylec-32a-3-pole-terminal-block-5-pack/26896) housed in appropriate junction boxes?

4) I'll also be moving a light switch and, again, I'll need to lengthen the wiring to it. Will Wago connectors like those linked to above housed in a choc box be suitable for this too?

I'm planning on doing the work myself and then having an electrican test it at the end. Any issues with this approach, please?

Thanks in advance.

 

[Murdochcat]

This is my first post on DIYnot so I'll start with a big thank you to everyone who's posted and answered here over the years - you've been invaluable.

I'm in the process of a kitchen renovation, which will include me doing four electrical jobs. I *think* I know what I need to do but I'd be grateful if you could check my homework before I go any further.

I'm planning on doing the work myself and then having an electrican test it at the end. An

Hum. If you do plan to get a spark to “test” then find them before you do anything as the vast majority of us won’t touch this type of diy work

 

[flameport]

However, the specs for the two ovens note the need for 16A fuses

Good luck finding a 16A fuse that's appropriate for use in a domestic environment.

so my plan is to add a second consumer unit after the oven switch and then connect the two ovens to two 16A MCUs and the hob to a 32A one

None of that is required.

Connection plate at the location of each oven and the hob. Cable from the switch goes to the first one, then the second, then the third one.
Hob connected with 4mm² HO7 flex, ovens with 2.5mm² flex.

As the spur is fused, am I right in thinking I can run three sockets off it?

Yes, but it's a poor design as the total load for all of the sockets can't exceed 13A, and in a kitchen that it likely to happen quite often.

Am I right in thinking I can cut it and insert a length of similar cable

Yes, provided the cable is routed in appropriate locations and if that junction box is to be concealed, the appropriate maintenance free connectors and matching enclosure must be used.

I'll also be moving a light switch and, again, I'll need to lengthen the wiring to it.

As walls and the like have been removed it would be far better to replace the whole cable, which probably connects at the light fitting.
Also needs to be located in the appropriate zones.

 

[SUNRAY]

Connection plate at the location of each oven and the hob. Cable from the switch goes to the first one, then the second, then the third one.
Hob connected with 4mm² HO7 flex, ovens with 2.5mm² flex.

What do MI's state?
If it states 16A then 16A it must be to comply for manufacturers obligations, they can and will decline repairs if if they can demonstrate damage caused by non-compliance.

 

[flameport]

they can and will decline repairs if if they can demonstrate damage caused by non-compliance.

That will never happen.
There is no damage which could be caused by connecting the appliance to a 32A circuit instead of a 16A one.

 

[JohnW2]

What do MI's state? ... If it states 16A then 16A it must be to comply for manufacturers obligations, they can and will decline repairs if if they can demonstrate damage caused by non-compliance.

I'd love to see a half-convincing argument that damage had resulted from the OPD being >16A

 

[SUNRAY]

That will never happen.
There is no damage which could be caused by connecting the appliance to a 32A circuit instead of a 16A one.

Oh yes there is,
I have mentioned it in previous threads.

 

[SUNRAY]

I'd love to see a half-convincing argument that damage had resulted from the OPD being >16A

Mentioned in previous threads.

 

[JohnW2]

Mentioned in previous threads.

You have, but only in the context of fairly exceptional circumstances.

As Flameport (apologies - I hasn't seen his post when I posted mine!) and I have said, it's extraordinarily improbable that a piece of equipment will be damaged because its supply was protracted by a 32A OPD but would not have been damaged (or damaged as much) had it been protected by a 16A one.

Those who sell items of equipment in the UK (and also elsewhere) and ask for 165A protection probably do not understand UK electrical installations,since they are effectively saying (as the OP has concluded) that each item of equipment needs to be on its own dedicated circuit.

It's a bit like a manufacturer saying that an LED light fitting must be protected by, say, a 100 mA or 200mA fuse

 

[SUNRAY]

You have, but only in the context of fairly exceptional circumstances.

As Flameport (apologies - I hasn't seen his post when I posted mine!) and I have said, it's extraordinarily improbable that a piece of equipment will be damaged because its supply was protracted by a 32A OPD but would not have been damaged (or damaged as much) had it been protected by a 16A one.

Those who sell items of equipment in the UK (and also elsewhere) and ask for 165A protection probably do not understand UK electrical installations,since they are effectively saying (as the OP has concluded) that each item of equipment needs to be on its own dedicated circuit.

It's a bit like a manufacturer saying that an LED light fitting must be protected by, say, a 100 mA or 200mA fuse

So are you saying let's do away with over current protection in our homes?

 

[JohnW2]

So are you saying let's do away with over current protection in our homes?

That's a different question from the issue of 'warranty invalidation' which was being discussed.

However,in answer to your question,I obviously am not saying that. There should be adequate overload protection to protect all the cables involved. If it is felt that a piece of equipment is 'likely' to result in an overload (as opposed to'fault') current, then that means that the equipment's flex/whatever has to be large enough to be adequately protected by the cicuit's OPD.

If all the cables have adequate overload protection but the manufacturer feels that a greater degree of protection is required by thee equipment itself, that protection should be provided within the equipment.

 

[SUNRAY]

That's a different question from the issue of 'warranty invalidation' which was being discussed.

However,in answer to your question,I obviously am not saying that. There should be adequate overload protection to protect all the cables involved. If it is felt that a piece of equipment is 'likely' to result in an overload (as opposed to'fault') current, then that means that the equipment's flex/whatever has to be large enough to be adequately protected by the cicuit's OPD.

If all the cables have adequate overload protection but the manufacturer feels that a greater degree of protection is required by thee equipment itself, that protection should be provided within the equipment.

I'm actually trying to work out exactly what you have written here.

If I understand you correctly you appear to be suggesting that if you changed the 1.25mm² flex on a >3KW oven to 16mm² then 100A OCPD will be adequate.

 

[JohnW2]

I'm actually trying to work out exactly what you have written here.

Fair enough,although I thought what I wrote was pretty clear.

If I understand you correctly you appear to be suggesting that if you changed the 1.25mm² flex on a >3KW oven to 16mm² then 100A OCPD will be adequate.

I suspect that it would have to be 25mm² (maybe even bigger, since CCCs of flex seem to be quite low), since the requirement would be for a CCC no less than 100A but, if the 'flex' of the oven and all the fixed wiring cable of the circuit all had CCCs of at least 100A then, yes, a 100A OPD would be OK, wouldn't it? - why not ?

As I said, if the manufacturer of a piece of equipment believes that the appliance itself requires protection which may be more demanding (lower IN) than what is required to adequately protect all the wiring external to it (as per the silly hypothetical scenario you have postulated), then they should provide that protection within the equipment.

 

[SUNRAY]

Fair enough,although I thought what I wrote was pretty clear.

I suspect that it would have to be 25mm² (maybe even bigger, since CCCs of flex seem to be quite low), since the requirement would be for a CCC no less than 100A but, if the 'flex' of the oven and all the fixed wiring cable of the circuit all had CCCs of at least 100A then, yes, a 100A OPD would be OK, wouldn't it? - why not ?

As I said, if the manufacturer of a piece of equipment believes that the appliance itself requires protection which may be more demanding (lower IN) than what is required to adequately protect all the wiring external to it (as per the silly hypothetical scenario you have postulated), then they should provide that protection within the equipment.

You are wrong.
This 'thing' about requiring internal fusing does not apply to things that are designed to be permanently installed. MI's have to be considered or whatever the current term is in the big book.
If MI's state 16A OCPD then they have no obligation towards damage caused to their product by omitting that OCPD. For example if the internal wiring is overheated due to the omission.

 

[JohnW2]

You are wrong.

You are obviously welcome and entitled to that opinion.

This 'thing' about requiring internal fusing does not apply to things that are designed to be permanently installed.

Why not -and who/what said that?

MI's have to be considered or whatever the current term is in the big book.

Yes, that's what BS7671 currently says ("shall take account of")

If MI's state 16A OCPD then they have no obligation towards damage caused to their product by omitting that OCPD. ...

Agreed,but only IF they could reasonably argue that the damage really had been "caused by omitting that OCPD"

.... For example if the internal wiring is overheated due to the omission.

In reality, if a high enough overload current were flowing to damage internal wiring, then there would have been a prior fundamental faults in thee equipment itself - and in terms of common sense (and hopefully also the law) te manufacturer would "have an obligation" in relation to that primary fault, even if not also in respect to consequential damage to internal wiring secondary to the primary fault.

To return to the real world, are you really suggesting that an oven such as you mentioned can only be installed on its own dedicated 16A circuit?