Steve,
A 5 or 10 amp circuit breaker would be fine, as most stereos come with inline fuses sized for that particular stereo.

And remember that the circuit breaker is designed/sized to the wire, not the components, in this case a stereo. If you're hooking the power wires from the stereo directly to the breaker, you want to be sure those wires are matched to that breaker. Either that, or the inline fuse, should be very close to the circuit breaker.

I've installed several car stereos on my boats over the years and many come with what looks to be #20 or #22 wire, which may melt before it pops a 5 or 10 amp breaker. So the inline fuse is right at the breaker.

There is a chart somewhere on the forum (and elsewhere) that has the amp ratings of various wire sizes; can't recall where it is at the moment, maybe someone else remembers.?

A chart to select wire size based on current can be found here:

[url]http://www.c36ia.com/files/12V%20wire%20size%20selector_0.jpg[/url]

Another way is to go to C375 Owner's Encyclopedia then to section: Electrical - 12V DC. Then click on "12V wire size selector.jpg" attachement.

I don't believe you have to be a Member to get the file.

The only devices on my 'accessories' circuit breaker were the fans, so I used that existing breaker when I added my stereo. I ran wiring to the stereo that would handle the maximim current the breaker would allow (forget now what gauge) and left the inline fuse near the stereo unit.

The only minor drawback is that the stereo turns on whenever power is applied to the accessories circuit. If I just want to run the fans and not waste the power that the stereo uses just to be powered up, I simply use the 'off' button on the stereo.