Holy hell there is some terrible/inaccurate information in this thread… with no assistance on how to actually apply these products.

First and foremost a breaker is NOT a replacement for a fuse. It never was and never will be. Where a breaker could fail, a fuse would not.

Breakers are thermal devices, and with a dead short, there is a chance the breaker could weld itself closed (aka ON) rending it useless, and with a worst case scenario electrical FIRE. The fuse in turn would be your last line of defense.

Application:

• Breakers are used to manage temporary overload conditions.
• Fuses are used to protect the mains cabling from fire / short circuit.

To answer your question OP. Breakers are sized to protect the LOAD, not the wire. Buy reputable products from companies who publish datasheets regarding their trip curves. Not all are the same, and the application will determine what to use.

Here is a blow delay curve for a breaker and fuse. The trip is NOT instant, and it’s a time vs current relationship.




Fuses on the other hand need to be sized to protect the wire, and also to make sure it can cover the short current interrupt rating. I always use HRC (High Rupturing Capacity) fuses on my battery mains from REPUTABLE brands like Bussman Cooper, MEGA or other. No import garbage.

The operating voltage of the system also matters in both these examples. Failure to do so may result in arcing which would in turn not stop current flow and result in fire. Its a low concern in 12v system, but still worth mentioning.

Consult the manufacturers spec sheet and you need to calculate you actual loads you are trying to protect. Arbitrarily sizing this stuff because some guy on the forum says it's good is how you burn your rig down.

This is a decent video to watch if you want a little more info:
YouTube

Circuit breakers generally are not used in an OEM automotive application. Other than aftermarket lighting where it serves more as an on/off switch.