Surge protector that has failed catastrophically is
indicated by the light. But a surge protector that fails
catastrophically was grossly undersized - failure directly
traceable to a human. Other modes of protector failure
exist. For example, a properly sized protector will
eventually degrade - the preferred mode of failure. Indicator
light would never report this failure. No earth ground means
no effective protection. That dedicated earthing wire to
central earth ground must be less than 3 meters. These
failure conditions also are not reported by that indicator
lamp.

IOW it says that light reports failure. It forgets to
mention which type of failure - or why. It forgets to mention
that the light can not report a good protector. All an
indicator can report is that the protector was grossly
undersized for the task - a failure directly traceable to
human installation failure.

Surge protectors do not operate like fuses. Fuses take so
long to open that 300 consecutive transients could pass
through a protector before that fuse even considered blowing.
The fuse is only to protect humans because a surge protector
was grossly undersized - too few joules.

The fuse keeps surge protector from burning down the house -
which is why surge protectors under a pile of papers or behind
a desk can add new dangers. Fuse would not disconnect
appliances from AC power. Just another reason why effective
protectors are located when utilities enter the building, at
the service entrance, and less than 3 meters to central earth
ground.

al wrote:
So it's pretty much like a fuse - how does it not blow if there's
a large load being driven by it (6 sockets could be powering quite
a bit) if it's delicate enough to stop (and very quickly) a surge
in power?