Fuse sizing advice requested

[Binxie]

I'm installing a circuit off my battery bank to run two plugs: a standard 12v plug and a plug with two USB ports. I'll have a fuse box between the batteries and the plugs. Three questions:

1a. What size fuse do you recommend for the 12v plug? I'm thinking 15 A, which is what my van's fuse panels use for its 12 volt plugs.

1b. What size fuse do you recommend for the plug with two USB ports? It's the bottom one in the picture. Looking at the back, you can see that both USB plugs are on one circuit. I was thinking about a 10 A fuse in case I'm running two devices, as most USB plugs seem to have a 5 A fuse.

2. I'm going to put a resettable fuse/breaker between the batteries and the fuse box. What size do you recommend? Should I meet the total of my fuses installed in the fuse box? Say, if I did go with a 10 A and 15A fuse, then get a 25 A resettable? Or should I go higher or lower?

Thanks!

 

[SternWake]

Fuses protect the wire. Fuse size should be determined by the wire size used to power the outlets, unless the outlet's instructions say to use a specific fuse size.

You can put a 2 amp fuse on 14 awg wire, but you can't put a 40 amp fuse on 20 awg wire and have it properly protect the wire.

SO what size wire are you using? Look up ampacity charts for different wire gauges

 

[Binxie]

Fuses protect the wire.  Fuse size should be determined by the wire size used to power the outlets, unless the outlet's instructions say to use a specific fuse size.

Thanks for clearing up my basic misunderstanding! Somehow, I got the idea that fuses protected the gadgets. I have such wire guage/amp capacity charts and can take it from here.


:blush: