As I said in the first post a lack of an rcd in any circuit this appliance (an electric oven) was connected to would result in the casing becoming live because on overload device does not always cut the supply. The fault is that one of the internal components shorts to earth when the casing of the oven heats up but not when cool. Even when it does the current does not always seem to be high enough to trip an mcb ....
Thanks for clarifying. I therefore assume you are implying that the case
is earthed, but (assuming the installation is satisfactory) that it's not a 'dead short' ('negligible impedance') that is occurring, so that the fault current is not high enough to trip and MCB (or blow a fuse), but (presumably) would trip an RCD, if present.
However, I wonder what is making you believe that the case is 'live'? If the case
IS satisfactorily earthed, and IF your installation has an earth provided by your electricity supplier {rather than your own earth rod} - do you know the answer to that?) then, even if the fault current is not high enough to trip an MCB, the earthing should limit the voltage on the oven's casing to a very low (and probably fairly 'safe') level. If you have a local earth rod (a 'TT' earthing system), then the oven's case could/would rise to a dangerous voltage, which is why it is essential to protect a TT installation with RCD(s).
... but I would guess it is high enough to kill someone, although I am no expert on what it takes to do that.
The current which flows through a person if they simultaneously touch something live and something 'earthed' is determined by the voltage of the live part (relative to earth) and the resistance of their body, not the current flowing through the fault. We work on the assumption that the risk of death increases if that current is above 30mA (0.03A), which will happen if the voltage one touches is more than about 30-50V. Unless you have a TT installation, the earthing of the case should keep the voltage well below that figure, even if the MCB does not trip.
Given that ovens are often connected to 32 or 45 Amp radial circuits & the fact that this oven has no internal overload protection I think there is a possibility that when this component shorts to earth there is a possibility of the heating of the outer casing when the component heats up it makes it become a fire risk, although I am willing to admit the risk is probably extremely low.
The case is unlikley to heat up significantly, but the wiring might. However, the circuit should be designed so that the MCB would trip before the cables became excessively hot or suffered any harm - so should prevent any fire risk. The actual short within the oven, if there is one, itself might produce local heating and present some fire risk.
Trading standards say it is not their area ... I suspect it happens often as the problem part is readily available on e-bay, which is unusual for parts unless they fail regularly. ... But to get back to my original question is there a "body" or association that issues safety certificates to manufacturers?
Is this a direct import from the Far East? If so, such items are not uncommonly 'dangerous' and Trading Standards really should be interested, particularly if it bears an 'invalid' "CE mark".
Kind Regards, John