fuses vs. circuit breakers

Contrary to popular belief, fuses and circuit breakers ("overcurrent
devices") are not designed to protect equipment (machines, radios,
TVs, final glide calculators, nor other electric or electronic
devices) from damage caused by overcurrent or short-circuit
conditions. These are safety devices which protect the wire and the
power source--and thus personnel--from damage. Fuses in commercial
applications are often sized at 300% of the load, but usually 125%
(depending upon the type of fuse). Circuit breakers are usually sized
125% but can also be 300% larger than the load. This allows the
momentary overcurrent situation which occurs at start-up in all
electrical and electronic devices.

A properly sized fuse or circuit breaker should prevent your battery
from exploding and/or your glider from catching fire if there is a
short in your radio (for example), but they WILL NOT protect your
radio itself from damage caused by the battery (or lightning, etc.).
With either fuses or circuit breakers, the electrical/electronic
device could be fried before the overcurrent device "blows."

As to whether fuses or circuit breakers are faster, there again it
depends on the type of fuse and circuit breaker. A "slow-blow" or a
"dual element" fuse will not blow as fast as a "one time" fuse, but
the one time fuse will not carry the momentary overcurrent and must be
sized considerably larger (300% of the load) to compensate. The same
are true of circuit breakers, there are fast acting and slower acting
circuit breakers and they are sized accordingly.

I have spent the last 30 years as an electrician and I have never seen
a fuse or circuit breaker save a machine. This is because if they
blow, 90% of the time the problem is with the machine. The other 10%
are things like wire or a connection that has gone bad, or operator/
service man (or pilot) error. On extremely rare occasions, the
overcurrent device blows because of an over-voltage event ("spike")
which causes the machine to short out. But even then, it is a problem
with the machine that blows the fuse or CB. This over-voltage
condition is rarely a problem in a glider with a 12 or 14 volt
battery.

So don't worry about fuses versus circuit breakers. Neither one will
save your instruments, but both will save your glider equally well.