Hob

[Mark1796]

I have just swapped an induction hob. Old one was 7kw new one is 7.35kw. Wire is 2x6mm+2.5mm twin & earth. Hob is on same floor as fuse box and about 5m away as the crow flys. No clue what cable is running through. 

Problem is hob is on dedicated circuit protected by 16amp mcb. As maths predicts if you put all 4 hobs on it trips the switch. Old hob occasionally tripped circuit breaker. Considering swapping mcb out for a 32A one. 

 

[Andy™]

redesign the circuit for the load and replace MCB as required, do your testing & paperwork and youre done...

 

[Spoon]

As Andy says, do all calcs and design accordingly.

Why do you want to change the breaker size for something bigger if you don't know what cable is installed?

 

[Sharpend]

In layman’s terms: 

you can not just change breaker for a larger size without knowing the cable capacity. If cable capacity is smaller than the breaker you put in the cable will give way before the breaker trips, potentially resulting in a fire. 
 

so unless you are able to ascertain the size of existing cable then generally a bad idea. 
hence the importance of understanding design. 

 

[Ardet R]

You would need to be able to make some assessment of the installation method for your 6mm² twin and earth cable.

If the cable is entirely surrounded by insulation for a distance then you would be limited to 20A, though most other methods would allow a 32A breaker.

Without this information you could be causing a later problem if the cable overheats.

Ensuring the cable that reaches the cooker switch is the same physical cable that leaves the consumer unit would be a good start.

Having the circuit on 16A makes you think why is it on 16A?, there may well be a good reason (although it may be just chance/incompetence/convenience) if you can find out the original reason then this may help clarify things.

 

[Mark1796]

Thanks, folks! not sure why a fully qualified electrician would put a 7kw appliance on a 16A breaker in the first place. System was fully certified and van had right markings. GCSE pyhisics suggests that's not wise. Might have to track him down. 

Having said that It is not often we want 4 rings going full blast so it has only tripped a couple of times in past 4 years. Also time frame when it is pulling max current would be short < 10 mins. 

Cable runs through ceiling void of kitchen so is likely to have some insulation for part of its run at least. 

 

[NozSpark]

7kw is near enough to 16A after taking diversity into account..... without knowing the installers reasoning I wouldn't be able to call them out on it though

 

[Murdoch]

My guess is that there was a spare 16A mcb in the board ....