What are the risks of having a 9000watt induction hob on a 32 amp fuse at the breaker?

[katrina]

We've had a new kitchen installation and a new 9000watt induction hob fitted. The manufacturers recommendation is a 40 amp power supply, however the electrician (contracted through the kitchen supplier) had incorrectly fit a 32 amp fuse at the board. He knows this is the case , as does the retailer. (He calimed he assumed it was a 7500 watt hob despite the power draw being clearly visible on the appliance. Mistakes do happen though, I get it) We had new 6mm wiring installed and the hob is on its own circuit, its also less than 2 meters from the fuse board. . We are being told the hob is perfectly safe to use despite buying it to use at capacity, as a four ring hob wasn't meeting our needs. They have suggested sending an electrician to swap out the fuse for a 40, however do not want to replace the hob despite the fact installing it on the incorrect power supply voids any warranty. It's also worth noting the electrician knew he'd put a 32 amp fuse at the board and still submitted test sheets claiming its on 40. We have refused to allow them to simply swap the fuse until they agree a resolution we are satisfied with in writing. We have asked for an inspector to check the work, as its left us feeling uneasy. I'm looking for any independent advice I can before I just blindly allow a simple swap as if it's a non issue. I feel we are being dismissed, and the situation being downplayed, but I've read there absolutely can be bigger problems than just a tripped switch at the board. Granted I'm not an electrician hence my asking for any advice I can get. Can anyone give me a better understanding of the risks please? as I simply can't take them at their word it is 100% safe to use.
Thank you in advance for any and all assistance

 

[brianmoooore]

9000W = 39.1A. After applying standard diversity, we arrive at 18.7A.
You say that you intend to use the hob to its capacity, so maybe the standard diversity should be modified a bit, but even then, the chances of more than 32A being drawn for any significant time is minimal, so the chances of a 32A MCB ever nuisance tripping is also minimal.
If the 32A MCB was replaced with a 40A one, this would be contrary to the regs, and should result in an unsatisfactory EICR, except in the unlikely scenario that the 6mm2 T&E is entirely surface mounted.

 

[katrina]

9000W = 39.1A. After applying standard diversity, we arrive at 18.7A.
You say that you intend to use the hob to its capacity, so maybe the standard diversity should be modified a bit, but even then, the chances of more than 32A being drawn for any significant time is minimal, so the chances of a 32A MCB ever nuisance tripping is also minimal.
If the 32A MCB was replaced with a 40A one, this would be contrary to the regs, and should result in an unsatisfactory EICR, except in the unlikely scenario that the 6mm2 T&E is entirely surface mounted.

 

[DefyG]

still submitted test sheets claiming its on 40

The test sheet should also have an installation reference (Reference Method). That should determine what the current (Amps) cable is capable of safely supplying.
Unless the Ref Method is 'C' - surface clipped as Brianmoooore has said, its CCC (Current Carrying Capacity) would be less than the hobs total load.

The risk? in the unlikely event that the 32A mcb is exceeded, it will 'trip' to prevent any damage to the cable.
I say unlikely as even though the hob will draw 39.1A if fully operational, each ring will be thermostatically controlled so unlikely they will all be on together! and knowing the limitation of loading all at once, stagger them slightly.
I'm not sure I get your drift about the warranty issue if on a lower rated circuit breaker than recommended! I could understand if it was on a higher rated circuit though?
I wouldn't have any concerns about using it and maybe the occasional trip! but yes 100%

 

[oscar21]

According to the charts a 32A MCB will never trip with a 39A load, or if it does it should be enough time to boil some lentils. The chances of that breaker tripping are zip in reality.

 

[Avo Mk8]

The characteristics graph I was looking at (if I've read it correctly!) shows that for long term overload (eg over an hour) the breaker must trip by 1.45 times overload (which is 46A), and must not trip with 1.13 times overload (which is 36A)
As you say, suggesting the breaker will probably not trip.

But I don't believe the hob could consume full power for that long a period anyway.
If you put six big saucepans full of 8L of cold water and turned them all on, they would all be boiling in 30 minutes, so by that point the power consumption would drop!