Well, if the fuse is replaced by foil as you suggest, then you need to re-calculate the ratings. However, that is not a responsible design.
Of course if the overload is a few times 100mA, or even a few times 1000mA above the correct load, there will be very few cases where we fear for the integrity of the fixed wiring, so there is no need to disconnect that. A dangerous fault, say one that draws twice or ten times the normal load current is the sort of thing that might cause damage and fuses and MCBS are intended to be sized to detect that.
Much as the fuse does not suddenly blow at 1% over its nominal rating, neither does the cable, it just goes from being a bit warm to being a bit warmer.
Even if we could make devices that had a knife edge tripping behaviour, they would be no use to us, as they would then also need to include delays to allow switch on surges and other transients to be pass without false tripping.
Well, if the fuse is replaced by foil as you suggest, then you need to re-calculate the ratings. However, that is not a responsible design.
Of course if the overload is a few times 100mA, or even a few times 1000mA above the correct load, there will be very few cases where we fear for the integrity of the fixed wiring, so there is no need to disconnect that. A dangerous fault, say one that draws twice or ten times the normal load current is the sort of thing that might cause damage and fuses and MCBS are intended to be sized to detect that.
Much as the fuse does not suddenly blow at 1% over its nominal rating, neither does the cable, it just goes from being a bit warm to being a bit warmer.
Even if we could make devices that had a knife edge tripping behaviour, they would be no use to us, as they would then also need to include delays to allow switch on surges and other transients to be pass without false tripping.
