Fuses duty

[BundyRoy]

I used to think the main job of a fuse is to protect against a short but I'm starting to think it is to protect from a constant overload. My reasoning is that if there is a short than this creates a massive current in an instant and regardless of the fuse size it is likely to blow straight away to prevent further damage. Whereas a fault that causes a largish current draw will eventually melt cables/start fire unless the fuse blows.

Is this theory sound or am I off track. I know it protects from both but is the fuse size less important for a short.

 

[David_AVD]

The fuse is there to protect the cable following it against short term large overloads and long term lesser overloads.

You should always use the smallest value fuse that will work without blowing for the given load.

 

[AAH]

And the wire should always be rated to carry a higher current than the rating of the fuse.

 

[BundyRoy]

I know fuses are always on the positive side and I figure there must be a reason for this. Why can't they be on the negative cable? Doesn't the same current flow through both.

 

[AAH]

It's just convention to fuse the positive. In some applications both the negative and positive are fused if there's any potential for contact or fusing to other voltage rails.

 

[David_AVD]

Also, if you fused the negative wire in a system that has the negatives commoned for data transfer, when the fuse blew the power would simply go via the signal wire or where ever it could leading to even more issues.