Circuit Breakers vs. Fuses. (House System)

[Chaz]

Hey guys,
I'm sporting a Xantrex 4024 with eight 6 volt batteries for my house system. I was going to buy a 400 amp breaker but they are a bit on the pricey side. I have been using an ANL fuse block up till now. I have also been using 250 amp fuses. I'm thinking I might  be a little "over protected" and thinking I may step up to a 400 amp fuse as I "think" that is what I should be using. The reason being: I will blow a fuse if I have both AC's running and the shore cord loses juice. I would have thought the batteries should have just taken over but they don't get a chance. ?? ?? ??
Thoughts...............
Thanx,
Chaz

[bevans6]

This is on the DC side, right?  Fuses are probably the better way to go, relatively easy to change and not all that expensive.  4,000 watts at 24 volts (maybe you might draw your batteries down lower than that and develop higher current) is only 166 amps.  Add 50% for the surge, that's your 250 amps.  There are two schools of thought here - protect the equipment by fusing at the max draw you want it to ever see, or protect the wiring - fuse to protect the ampacity of the cable and hardware you are using.  400  seems a lot, check out what your wiring can support.

Brian

[belfert]

We went through this discussion just recently here.  Sean was pretty adamant that you want a T class fuse instead of a breaker.  The reasoning seemed to be that a T class fuse would react faster than a breaker.  Solarseller.com should have what you want if you can't find a T class fuse locally.  (Website is a bit disorganized, but the prices are pretty decent.)

I use a 225 amp DC breaker I got for free, but I guess I really should have a T class fuse.

[Sean]

The correct fuse or breaker depends on cable size.  If you use 0000 cables, Xantrex specifies a 250-amp breaker or a 400-amp fuse.  Xantrex recommends Class-T fuses, as do I.  Breakers are another issue altogether, and I can't give you a specific recommendation here without further research; suffice it to say, most are not fast-acting enough for this application.

DC protection sizing can be found on page 23 of your manual.

-Sean
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