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.

 

[Flanders]

I looked at it like this the cable runs behind plaster then in the ducting in the ground, then got mixed up and used table 4d4a , i also did not consider the cable in the cieling and then if there insulation in the cieling we could be looking at method 100 or 101 table 4d5 so the ccc could be as low as 27 amps so in summery if the cable does not run in the ceiling then the ccc will be 46 amps x correct factor from table 4b3 (worst case 0.96)so max ccc 44.16 amps or if it does run in ceiling then max ccc is 38 amps ,

 

[Wilko]

Not seeing it, my internet guess is 57 for the wall (C) and the conduit in the floor being 60 (B), so 46A and 38A from table 4D2A
With 2 circuits in the floor conduit there is another derating factor. But I would ignore, as its low current load to hood fan (say 100W) and won't materially impact the heat load on the hob cable.

 

[David M]

So summing up based on the situation:-

Is the cable underrated?

In my opinion based on the posted details, I doubt it, but I would use a clamp meter then test and monitor it for clarification. (assuming the installation method is fine)

Is the installation safe to use?

Provided it has conformed with the regs after inspection and test and the circuit breaker is the correct size for the circuit, then yes perfectly fine.

Is the client within their rights to insist on replacement and /or compensation?

Provided it was a written agreement that the 10mm cable was to be installed, then the client is well within their rights to have the cable reinstalled at the stipulated size. Though in this scenario I would personally make sure the cable that has been installed will be ok. I would then probably ask to be compensated rather than have the whole disruption of a new cable installed, with some sort of guarantee.

 

[davesparks]

as 2 men pulled like hell to get the 6mm in alongside another cable that powers an extractor.

Well that sounds somewhat dodgy to me,

 

[westward10]

Wish someone would produce some 8.0 cable so the debates don't occur, joking aside I would personally never protect a 6.0 pvc/pvc cable with a 40A device and rely on fine lines like installation methods and pulling the kitchen blind down should the sun shine too bright on the wall. The spec said 10.0 and I wouldn't budge from this fact.

 

[HandySparks]

... I would personally never protect a 6.0 pvc/pvc cable with a 40A device and rely on fine lines like installation methods ...

With a rating of 47A clipped direct, I would regard 17½% above the required capacity as more than adequate for 6mm² on a 40A MCB, if not in trunking or insulation. I would say that this particularly applies in the case of a domestic cooker or shower, where the cable won't be subject to full load for long periods of time.

If this was, say, an immersion heater or storage heater, which could take full power for hours at a time, then I would tend to be generous with cable size.

 

[Midwest]

As this cable would appear to be installed in a domestic property, one assumes is going to be run in the ceiling void (more than 500mm) at some point, typical of most domestic installations.

There is not an installation method for this in Table 4A2 (as far as I can see?). However, the grown ups at the IET refer to this scenario in 'Wiring Matters 28 Autumn 2008';

page 12, Cables installed in a ceiling - This is similar to installation method A.

I've read other suggestions it was installation method B, but I suppose you have to allow for non movement of air, and heating pipes etc. So ccc for 6mm, would be 32amp or 38amp respectively.

Whatever, that hob is not going to draw that sort of current, so as someone suggested early 32amp MCB on 6mm cable will be fine.

Bet the OP's having a right little chuckle at all this chit chat

 

[mattg4321]

Well that sounds somewhat dodgy to me,

I agree. This worries me far more than a 10.8kw hob on a 6mm2 cable.

The amount of times I come across people who have been advised their current 6mm2 cable isn't big enough for their shiny new cooking appliance is baffling. Why oh why do people insist on totally ignoring the decades proven and totally unambiguios diversity calculation?

I connected at least 3 circa 14kw cookers last year to existing 6mm2 supplies last year (with 32A MCB) and guess what none have ever tripped out to my knowledge. Further to that I'm struggling to recall a single instance of a customer calling me and saying "my cooker circuit trips out when I'm doing my sunday roast".

OP stop worrying about the cable size and the 'electricians' who advised you the cable is too small, make a mental note not to use them again. I will say however, that I agree if you were quoted 10mm, then that should've been installed.