Re: How to Determine Fuse Size?
It can be complicated or it can be simple. Fuses and circuit breakers have profiles. Depending on the application, you may want something that breaks quickly (virtually instantaneously) or something that breaks slower. Motors can have a large and long in rush to their loading so a breaker that can handle 200% of the rating for 30secs+ is not unusual. Some breakers can handle 150% their rating for 1hr before tripping. Something like an AC ground-fault circuit interrupter (GFCI) you want to trip yesterday.<br /><br />In general, for most DC applications you go 1-½ times the load. Equipment with a 10-amp load gets a 15-amp fuse. The idea being the equipments load will be 10-amps max until something goes wrong. In that case the load is much greater than 150% and the fuse fries before the equipment does. If fused at the equipments load rating, i.e. 10-amp load with a 10-amp fuse, you get to change fuses frequently for a problem that doesnt exist.<br /><br />Bilge pumps, being motors, are going to have a higher current draw on startup so they may have a fuse recommendation of 200% or 300% of the working load. But then again, they may not. Definitely check the manufacturers fuse recommendation and follow it.<br /><br />To know what fuses you need, you have to go thru every piece of fused equipment and determine its max load rating. Probably the best thing to do is for you to research the loads for your electronics/electrical stuff online, and then you can also get the manufacturers fuse size recommendation.
