I wouls suggest that an appropiate MCB would be a better solution purely to avoid the hassle factor of replacing blown fuses. It would be likely that in the application you describe that the fault level would be low so there would probable be no advantage in using fuses
Suggestion: It depends on nature of the load. Heaters, lights, some machines are traditionally protected by fuses since the load branch circuit is not expected to fail in about 40 year period. Other loads, e.g. motors, electronics, etc. that may trip often the branch circuit, is better to protect by MCB.
For this specific application of protection of a low amperage instrumentation or control circuit, I would recommend the use of fuses for several reasons.
Fuses (used with finger-safe fuse disconnect) provides a visible disconnect for troubleshooting.
Fuses will generally coordinate better with each other at higher levels of fault current than will MCCBs with instantaneous trips.
Fuses are less expensive and are more readily available in smaller amperage ranges.
Current-limiting fuses can limit fault current and released energy if high fault current is available.
Comment: The circuit breaker application tend to have personnel inclined to reset the circuit breaker on its trip without much thinking what may have been the cause the circuit breaker trip. This can lead to the circuit breaker repeated closure to a short circuit, which substantially deteriorates the circuit breaker contacts. There are three short-circuit trips allowed by UL before it loses its label.
The fuse application experiencing a blown fuse often leads to troubleshooting first before a new fuse is inserted and circuit energized. This can be viewed as the more productive approach to corrective actions.
You don't state what kind of I/O card it is: relays, transistor, or triacs, although everyone seems to have assumed relays.
If it is a solid-state (triac / transistor), then a circuit breaker will not be fast enough to protect the silicon. Use an ultrafast fuse designed for this sort of application.
Suggestion: I agree with the previous posting. Manufacturers of encapsulated electronic power regulating circuits often protect their devices by fast fuses rather than circuit breakers.
