Range Cooker Connection Refusal.

davezawadi (David Stone): 
 

I cannot agree with you above Graham, although the “paying for 2 MCBs” comment might suit the manufacturer to make £1 more profit is possible. 

Profit isn't the issue. To retain the profit, the cost would simply be passed to the consumer in any case. It would be at least £5.00 extra to the consumer. 
 

Looking at the technical points, this appliance has a rating (the maximum possible draw) of 11.75kW. this is a consumption of 51A at 230V. There can be no reason why this should not be the final circuit rating, although it will probably never be reached due to diversity. If I fit a 40A breaker it will probably never trip, but even so, it is directed as a maximum by the instructions. These may have been written to minimise the chance of a fault damaging the appliance wiring, but at either 40 or 50A, this is unlikely unless it is the power to the clock. In any case, if there is an Earth fault that does damage something other than the fault, does it matter? 

I suggest not, except to the manufacturer who hopes to limit guarantee costs. I expect that an additional £1 for an MCB would be cheap insurance.

Diversity … but perhaps, as I said, cultural differences across the EU?

There are some assumptions here though … including any application of diversity the manufacturer may have taken into account. Perhaps more relevant is that, whilst you are looking at faults of negligible impedance, a manufacturer of an appliance with concentric heating elements will (from experience) be also looking at certain resistive faults with those elements, perhaps based on experience of previous claims. Concentric heating elements is one area I'm personally not comfy with the “fault of negligible impedance”, and it's one reason I prefer appliances with those elements to be RCD protected. 

Is that why shower manufacturers recommended it before it was required in Section 701 of BS 7671 (from 2008)? I strongly suspect it was.

It is worth noticing that most appliances contain some kind of CPD, be it a fuse or whatever. Even wall warts tend to have a thermal switch or fuse, although made down to a very low cost. The size of the appliance terminals is a weak excuse, any competent electrician will easily cope with this, by using crimp tags or the methods given above.

Huge assumption, that's also false. My oven, which can be “hardwired” has no internal OCPD, although there are probably devices on the PCB that would “pop” in a fault. My cooker hood also has no internal fuse of any description. The motor [has to have] a thermal cutout because of stalling, but a fault on the lighting circuit, or earth fault in the motor, will rely on the upstream fuse (in the FCU in my case). A 13 A fuse in the FCU destroys the PCB with the switches when the filament lamp shorts out … these things happen when you're working away, the 3 A fuse blows, someone changes it for a 13 A from a new plug, because they don't know where your storage box is with the fuses in (even though it was right next to the toolbox), switches the thing back on and BANG !!!

And to mention wall-warts. They don't even have to comply with plugs and sockets (safety) regulations, never mind the poor quality etc. - I'm surprised you mention those in the same vein as larger appliances. One of the product standards used for wall warts doesn't even limit the “SELV” voltage in single-fault conditions (the standard doesn't even recognise “SELV”), so you could, in theory, have a 5 V wall-wart that pops up to 50 V AC or 120 V DC in a fault (and on occasion, more !). OOPS.
 

edit : I will add one extra point. It is often difficult to add another circuit to many modern properties because of the construction, typically concrete floors both up and down. Mostly it should not be necessary, and it is simply needlessly expensive.

So the house was not built to take into account reasonable changes that might occur in its life? We know how poor some new builds are. Is that the appliance manufacturer's problem? If it's a must to use  such building materials, cables can be run in suitable containment or ducting. It's not that hard to design in to be honest … who's skimping now?

I am glad that you too have noticed how poor the instructions often are.

I also said I understood why they are either “lacking” or have “odd” advice … having been involved in the industry with manufacturers, maintainers, as well as install / new build etc. … there's more than one side to every story.

davezawadi (David Stone): 
 

I cannot agree with you above Graham, although the “paying for 2 MCBs” comment might suit the manufacturer to make £1 more profit is possible. 

Profit isn't the issue. To retain the profit, the cost would simply be passed to the consumer in any case. It would be at least £5.00 extra to the consumer. 
 

Looking at the technical points, this appliance has a rating (the maximum possible draw) of 11.75kW. this is a consumption of 51A at 230V. There can be no reason why this should not be the final circuit rating, although it will probably never be reached due to diversity. If I fit a 40A breaker it will probably never trip, but even so, it is directed as a maximum by the instructions. These may have been written to minimise the chance of a fault damaging the appliance wiring, but at either 40 or 50A, this is unlikely unless it is the power to the clock. In any case, if there is an Earth fault that does damage something other than the fault, does it matter? 

I suggest not, except to the manufacturer who hopes to limit guarantee costs. I expect that an additional £1 for an MCB would be cheap insurance.

Diversity … but perhaps, as I said, cultural differences across the EU?

There are some assumptions here though … including any application of diversity the manufacturer may have taken into account. Perhaps more relevant is that, whilst you are looking at faults of negligible impedance, a manufacturer of an appliance with concentric heating elements will (from experience) be also looking at certain resistive faults with those elements, perhaps based on experience of previous claims. Concentric heating elements is one area I'm personally not comfy with the “fault of negligible impedance”, and it's one reason I prefer appliances with those elements to be RCD protected. 

Is that why shower manufacturers recommended it before it was required in Section 701 of BS 7671 (from 2008)? I strongly suspect it was.

It is worth noticing that most appliances contain some kind of CPD, be it a fuse or whatever. Even wall warts tend to have a thermal switch or fuse, although made down to a very low cost. The size of the appliance terminals is a weak excuse, any competent electrician will easily cope with this, by using crimp tags or the methods given above.

Huge assumption, that's also false. My oven, which can be “hardwired” has no internal OCPD, although there are probably devices on the PCB that would “pop” in a fault. My cooker hood also has no internal fuse of any description. The motor [has to have] a thermal cutout because of stalling, but a fault on the lighting circuit, or earth fault in the motor, will rely on the upstream fuse (in the FCU in my case). A 13 A fuse in the FCU destroys the PCB with the switches when the filament lamp shorts out … these things happen when you're working away, the 3 A fuse blows, someone changes it for a 13 A from a new plug, because they don't know where your storage box is with the fuses in (even though it was right next to the toolbox), switches the thing back on and BANG !!!

And to mention wall-warts. They don't even have to comply with plugs and sockets (safety) regulations, never mind the poor quality etc. - I'm surprised you mention those in the same vein as larger appliances. One of the product standards used for wall warts doesn't even limit the “SELV” voltage in single-fault conditions (the standard doesn't even recognise “SELV”), so you could, in theory, have a 5 V wall-wart that pops up to 50 V AC or 120 V DC in a fault (and on occasion, more !). OOPS.
 

edit : I will add one extra point. It is often difficult to add another circuit to many modern properties because of the construction, typically concrete floors both up and down. Mostly it should not be necessary, and it is simply needlessly expensive.

So the house was not built to take into account reasonable changes that might occur in its life? We know how poor some new builds are. Is that the appliance manufacturer's problem? If it's a must to use  such building materials, cables can be run in suitable containment or ducting. It's not that hard to design in to be honest … who's skimping now?

I am glad that you too have noticed how poor the instructions often are.

I also said I understood why they are either “lacking” or have “odd” advice … having been involved in the industry with manufacturers, maintainers, as well as install / new build etc. … there's more than one side to every story.