Induction hobb possible fault or not!

[greeny]

I was trying to reduce/monitor our use of electricity using an eon monitor, clamp meter type, by switching our household devices on and off.
When the induction hobb was off at its touch controls, I decided to switch it off also at the Cooker Control Unit, (its own unique isolator on the wall).
The cooker switched splashed with a considerable spark,,,,,why/how could this be if the hobb appeard to be off with no indication of anything on the units glass.
Could this be an inductive build up of energy, like that of capacitors.
I have repeated the switching off and it splashes every time!
I have always left the cooker control swich on in the past and never swiched it off untill now, perhaps I will just go back to doing that, I have never had any indication of a fault before
Any ideas please

 

[telectrix]

with the hob off. turn off all other MCBs. check if it's pulling any current. you could have a dodgy isolator. ( loose connection or a conductor very close to the earthed back box, shorting out when you operate the switch)