[Kato's 8]

Hello all!
I think I know the answer to my question but I just need confirmation that I understand correctly. Here is the scenereo: From a 10 amp switch cicuit breaker a line is run to a distribution post behind panel. This is Vans set up and in this case this scb and line is for the radios for this example. From that post my radio needs a 5amp inline fuse. I also will run a xpdr requiring a 3 amp inline fuse to same post. Question is, what happens if I attach a third line, say a 12v aux port and use 2 amp inline fuse. Is that going to be ok?
If I happen to plug in something that draws greater than 2 amps, will that just blow the 2amp inline fuse or will that trip the 10amp switch cb as well since all 3 circuits exceed 10 amps?
Thanks for input. Im trying to keep simple and as close to vans simplified plan though adding extras sem to complicate this greatly. Plus I confuse easily in this department.
Thanks again!!

 

[fatherson]

If I understand your circuit description correctly (three smaller fuses, each in parallel to each other, and each in series with one single larger switched breaker), then the switched breaker will not necessarily trip just because one of the small fuses blows. It would only do so if there were sufficient total current (in your case, 10A, summed from all three smaller fused lines) for a sufficiently long time to fault the breaker. Also, remember that the small fuse you are worried about taking out your other circuits probably won't be blowing at the exact time the other circuits are at their maximum draw. However, if the single little fuse blows because the line it was protecting was momentarily drawing a lot more current than its rating (say 8A, while the other two are drawing a couple amps a piece), then sure, you might see a bit of a thermal race-condition where the 10A breaker trips as well. Not very likely though, and you would be able to reset the breaker if that edge case were to happen.

--
Stephen

 

[Kato's 8]

Thanks for your input Stephen. It was was helpful.

 

[krw5927]

Circuit protective devices (fuses, breakers, fusible linke, etc) are there to protect the WIRE, not the device at the end of the wire. One way to skin the cat would be to size all wires downstream of the 10A switch-breaker to carry at least 10A each. Then you could forget about all the extra in-line fuses which certainly add complexity and confusion in maintenance/troubleshooting.

 

[dlloyd3]

Mine is done in a similar fashion using the Tyco W31 switch circuit breakers from Van's. From the breaker to a ATO/ATC fuse block from Steinair, a fuse for an SL30, another for the audio panel, another for the transponder.
Yes, the breaker or fuse is there to protect the wiring first. Garmin does call out something smaller than 10A and I would rather be ignorant and prudent than sorry.

 

[longranger]

Circuit protective devices (fuses, breakers, fusible linke, etc) are there to protect the WIRE, not the device at the end of the wire. One way to skin the cat would be to size all wires downstream of the 10A switch-breaker to carry at least 10A each. Then you could forget about all the extra in-line fuses which certainly add complexity and confusion in maintenance/troubleshooting.

Besides wire protection, another function of fuses and breakers is fault isolation. If you go with just one circuit protector for three items, make sure you don't mind losing all three items when any one of them faults.