The fuse exists to protect the equipment. It should be no larger than what is sensibly required to ensure it doesn't fail prematurely.
A too-high rated fuse may not blow in a fault condition leading to a worse failure (e.g. fire) and possibly increasing the danger to the operator.
The fuse protects the user indirectly. We're not expecting the user to be saved from electrocution because the current through their body trips the fuse, but we are expecting that the fault (say the live wire becoming detached and brushing against the case, or the transformer shorting a turn, etc) will cause the fuse to break.
post 12 is nonsense. And post 14 merely indicates the maximum fuse you should probably use in those case, not the actual fuse you should use.
And while we've sidled up to the notion of the current rating of a cable, the appropriate wire gauge to use for a 10A power cable will vary under many conditions (and these will be specified in the various electrical standards). A long run (certainly for fixed wiring) will be rated to allow no more than a certain voltage drop. For appliance cords and the like, worst case heating is more likely to be the factor. The current that the wire itself can safely carry is likely to be significantly higher.
Dave's last point makes complete sense.
House fuses protect the house wiring. The wiring is known to be rated for (say) 15A total current and the circuit breakers rated at 16A (I just checked).
The fuse in my oscilloscope is 1A. It is there to protect the scope. I would not rely on the 1A circuit breaker in the house. A fault could easily draw more than 1A, but less than 15A. This could cause significant damage. Even though the power cable might be rated for 7.5A or 10A, I'm not going to use a 7.5A or 10A fuse, because that's not what I want to protect. Whilst I wouldn't use a fuse rated higher than the cord's rating, I would certainly use one rated lower. If there's a fault, it might take out some parts of the power supply, but hopefully the fuse blows before a fire starts.
I'm primarily concerned with my safety first. So at each stage I will use the smallest breaker or fuse consistent with the normal (peak) current.
A too-high rated fuse may not blow in a fault condition leading to a worse failure (e.g. fire) and possibly increasing the danger to the operator.
The fuse protects the user indirectly. We're not expecting the user to be saved from electrocution because the current through their body trips the fuse, but we are expecting that the fault (say the live wire becoming detached and brushing against the case, or the transformer shorting a turn, etc) will cause the fuse to break.
post 12 is nonsense. And post 14 merely indicates the maximum fuse you should probably use in those case, not the actual fuse you should use.
And while we've sidled up to the notion of the current rating of a cable, the appropriate wire gauge to use for a 10A power cable will vary under many conditions (and these will be specified in the various electrical standards). A long run (certainly for fixed wiring) will be rated to allow no more than a certain voltage drop. For appliance cords and the like, worst case heating is more likely to be the factor. The current that the wire itself can safely carry is likely to be significantly higher.
Dave's last point makes complete sense.
House fuses protect the house wiring. The wiring is known to be rated for (say) 15A total current and the circuit breakers rated at 16A (I just checked).
The fuse in my oscilloscope is 1A. It is there to protect the scope. I would not rely on the 1A circuit breaker in the house. A fault could easily draw more than 1A, but less than 15A. This could cause significant damage. Even though the power cable might be rated for 7.5A or 10A, I'm not going to use a 7.5A or 10A fuse, because that's not what I want to protect. Whilst I wouldn't use a fuse rated higher than the cord's rating, I would certainly use one rated lower. If there's a fault, it might take out some parts of the power supply, but hopefully the fuse blows before a fire starts.
I'm primarily concerned with my safety first. So at each stage I will use the smallest breaker or fuse consistent with the normal (peak) current.
