installing sparky insists installation is safe and correct, 3 others under rate the cable

[Flanders]

So the 40 amp breaker will protect your cable so there is no chance of you overloading the cable as the breaker will trip out if you do this, but i do agree the correct size cable as not been installed as per the design and of course what you have paid , as handy sparkes suggest it may be worth doing some load test to see what the true current draw of the hob is and you may find out that it runs at less than 40 amps . Having said all that i still think you are within your rights to have the cable replaced with a 10mm as that was what was specified or at the very least have some money back

 

[Wilko]

How can you have electrical work done by a junior that could be unsafe and a cert promised by a supervisor that hasn't supervised. Is there a loophole here?

Likely the company has appointed the supervisor to that role and they are then responsible for the work. You could confirm this with ELECSA, who I guess is their registration body for Part P purposes?

 

[arnold123]

Thank you Flanders 4th expert to think/state cable is under rated. The owner is the supervisor and yes they notify ELECSA. I think installer had best intentions and knew what to do re 10mm quote but is now trying to cover himself as things have gone wrong rather than hands up after all there is a lot of money riding on it...

 

[Midwest]

Interesting thread.

I've looked at the Neff web site for maximum connected load, and as ever they (like other manufacturers) are as useful as a chocolate fire grate, unless you want to know how to cook a quiche.

I see from some of the retailers of this hob (as others have said), suggesting a connected load of 10800 watts. With diversity, (OP the diversity formula has worked pretty well up till now), that's suggests to me a total current of just over 21amp (assuming no socket outlet in cooker control), have I got that figure correct, members?

OP, reading Neff's glossy brochure on their kitchen appliances, specifically induction hobs, it praises the attributes of it's product;

'Induction hobs are extremely energy efficient, saving you money on your electricity bills. Only the base of the pan heats up, so only the precise amount of energy you need is ever used'.

If diversity was not applied, then the calculation for 10800 watts, would be something like 47amps (even too much for your 10mm perhaps). If you had an electric shower (where diversity cannot be applied), how would you feel about one of your siblings taking a shower for two hours (the time it takes me to cook a cordon bleu meal for her indoors )? Now this hob is very unlikely to be 'extremely energy efficient' pulling 10800 watts, for two hours, would it.

Whilst I'm no manufacturer of induction hobs, I suspect if you turned on every hob to max, each would cyclic on and off very often and very quickly, therefore unlikely to draw full connected load of 10800 watts.

I would suggest, to put your mind at rest, and take up the offer of having the hob monitored with a clamp meter. Either that, or you go through the pain of having your new flooring ripped and the subsequent mess, to installed a replacement cable, that's probably unnecessary.

Just my opinion. That's about 4 - 4 now

 

[arnold123]

End of day I just want a safe installation that I can be confident of......which passes LABC, from my limited knowledge gleaned off forums and speaking to sparks, diversity is a dark art.
It cannot be applied to a shower in your own words which is a single appliance but could be applied to a hob, single appliance. Hmmmm!
Or can it.. fair enough for an appliance that has multi function ie range or old type cooker, oven, grill, hob. I have the pink paperwork for the hob and it's 10100w. It varies from curry's , JL, marks electrical website but it is 10100w.

The whole part P self certify , in my opinion, is questionable - re my experience. I didn't buy it for energy efficiency, I purchased it because it was easy to clean.

I disagree that 10mm installed in my situation taking de rating into the calcs would not be enough.

 

[Dcf]

These hobs work slightly differently than a normal hob
where a normal hob switches on and off via a stat quite quickly when it is near temperature ,induction hobs usually switch themselves up/ down in stages of 100-200 watt reaching a max of roughly 2 to 2.5 kw a zone.
2 zones in boost normally take up the whole rating of the hob i.e. 40A and using the power of 4 zones but will be on for so little time on full chat that i wouldn't bother
most i come across are in the range of 7-8 kw these days ,so to seems to me that neff have added up all the zones and come up with 10kw .kinda 2+2 =5 in a way
My advice to the Op would get something like an owl meter and measure the thing starting 1 zone at a time and then add other zones
my bet is that it never gets above 5kw in normal everyday operation.

 

[Midwest]

End of day I just want a safe installation that I can be confident of......which passes LABC, from my limited knowledge gleaned off forums and speaking to sparks, diversity is a dark art.
It cannot be applied to a shower in your own words which is a single appliance but could be applied to a hob, single appliance. Hmmmm!
Or can it.. fair enough for an appliance that has multi function ie range or old type cooker, oven, grill, hob. I have the pink paperwork for the hob and it's 10100w. It varies from curry's , JL, marks electrical website but it is 10100w.

The whole part P self certify , in my opinion, is questionable - re my experience. I didn't buy it for energy efficiency, I purchased it because it was easy to clean.

I disagree that 10mm installed in my situation taking de rating into the calcs would not be enough.

You might think its a dark art, but its an acknowledge way of 'determination of the maximum demands for an installation and includes the current demand to be assumed for commonly used equipment'. It's been used for decades, and some believe that it is too conservative for modern day efficient appliances. It is referred to appendix A in the 'On Site Guide', delivered by the IET, not a document produced by some back street body or Sunday periodical.

An electric shower, is an instantaneous type, and 100% f.l. is applied to the first device in an installation (OSG). Your hob is designed to operate differently.

Part P has nothing to do with the application of diversity, mentioned in reg 311 of BS7671. If you bought your hob because it was easy to clean, why pay over £1000 for something, that most pay a lot less for something similar, the cleaning is endemic of the design of such products.

I can understand your frustration over not getting something you asked for, but you've asked for advice on this forum, and on others, it would appear. Just because we are not telling you what you want to hear, doesn't mean it is incorrect advice.

My pilferer range cooker, has a manufacturers supply flex, no bigger than the one that supplies my standard lamp. It hasn't melted yet.

 

[HandySparks]

End of day I just want a safe installation...

In which case, like I said, get the maximum current measured. Then you'll have a real verified figure to work with.

For your info, we have a four ring induction hob, and the current consumption of the whole house didn't exceed 35A at any time during December.

 

[Flanders]

Thank you Flanders 4th expert to think/state cable is under rated. The owner is the supervisor and yes they notify ELECSA. I think installer had best intentions and knew what to do re 10mm quote but is now trying to cover himself as things have gone wrong rather than hands up after all there is a lot of money riding on it...

Just to be clear I am not stating the cable is under ratted at it should take 46 amps with the method of installation ( Referance method D) and you have a 40 amp MCB protecting it , I'm just saying you paid for a 10mm cable and got a 6mm so the company installing it has saved money and so should pass the saving onto you just a quick google and you can get 6mm for about £2.50 a meter and 10mm for about £4.50 a meter , The thing is, it may course a lot of disruption chopping out the wall and floor to the replace the cable which as others have said may or may not be required subject to a load test , this is why I suggested coming to a financial compromise if it turns out that the maximum demand does not exceed 40 amps

 

[Midwest]

One assumes the cable in question is 6242y cable, twin & earth. I've looked through the installation methods, and find no' 72 which suggests installation method D. The only tables referring to IM D, are for armoured cables. I suspect you would use Table 4B3 to apply a rating factor?

One assumes the cable is installed within the ceiling void (installation method B) at some point, within the property? Referring to Table 4D5, there is no IMB, we refer then to Table 4D2A, which gives a ccc for 6mm cable (2c) of 38amp? Or is that incorrect? There may be other de-rating factors.