Fuse Size for 0 AWG and 4 AWG?

If you only have one amp on the power wire and that amp is fused at 70A you only need a 70A fuse in the 0awg wire.

A 70A fuse is the safest size fuse for the application, but anything between 70 and 350A will protect the WIRE.  The important thing to remember here is that fuses have delays in them, and the higher the fuse rating the longer it will take to blow, which could theoretically damage electronics in your car from the "crowbar" effect before the fuse actually blows.  Depending on the capacity of your battery it could take several seconds for a 350A fuse to blow when shorted directly to ground!

I guess what I'm trying to say is If you're only worried about only protecting the wire go with a 350A fuse, but if you want to protect the car, too, don't go any bigger then actually have to (70A).  You can always get a larger fuse down the road if needed.

I've never heard of 0 gauge called "hot" gauge but I have heard it called "aught" gauge.  It's much more common to refer to wire actually bigger then 0 gague as aught - such as 2 aught and 4 aught.  Wire larger then 4 aught is usually referred to in mills (like 500 mils)

http://en.wikipedia.org/wiki/American_wire_gauge - look under pronunctiation toward the bottom.