Visual Inspection

An open glass-bodied fuse can usually be found by visual inspection. Earlier in this course, figures 2-4 and 2-5 showed you how an open plug-type and an open glass-bodied cartridge-type fuse would look. If the fuse element is not complete, or if the element has been melted onto the glass tube, the fuse is open.

It is not always possible to tell if a fuse is open by visual inspection. Fuses with low current ratings have elements that are so small, it is sometimes not possible to know if the fuse link is complete simply by looking at it. If the fuse is not glass-bodied, it will not be possible to check the fuse visually. Also, sometimes a fuse will look good, but will, in fact, be open. Therefore, while it is sometimes possible to know if a fuse is open by visual inspection, it is not possible to be sure a fuse is good just by looking at it.