Fuses are very imprecise devices. A 10A fuse won't really protect you from an overload of 20A. It could take an hour to blow or not blow at all. Both the 10A and 20A fuse will protect you from 1000A short circuits.
This sounded surprising and so I picked the first fuse I could find on RS and looked at its datasheet [1].
The characteristic curve shows that the 10A fuse is expected to blow after about 4s at 20A. Of course there's sample-to-sample variation and different ambient conditions etc, but how do those four seconds become "an hour to blow or not blow at all"?
My bedside lamp has a 1mm (or thinner) wire. If it faulted out and drew 10a the RCD won’t blow, but the wire will melt. Not immediately, but after a while.
The 3A fuse will melt long before the wire though.
aix1|2 days ago
The characteristic curve shows that the 10A fuse is expected to blow after about 4s at 20A. Of course there's sample-to-sample variation and different ambient conditions etc, but how do those four seconds become "an hour to blow or not blow at all"?
[1] https://docs.rs-online.com/bc0e/0900766b81585c97.pdf
ssl-3|2 days ago
Dave Jones of EEVBlog fame did some experiments with this several years ago: https://www.youtube.com/watch?v=WG11rVcMOnY
(I'm not arguing for or against any concept here; I'm just presenting some non-datasheet data.)
hdgvhicv|2 days ago
My bedside lamp has a 1mm (or thinner) wire. If it faulted out and drew 10a the RCD won’t blow, but the wire will melt. Not immediately, but after a while.
The 3A fuse will melt long before the wire though.