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

[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.