Avoiding Fire, power cables and fuses

Ok I have a couple questions regarding power cables and fuses.  I am getting ready to add 2nd amp.  Looked at the wire charts on power and ground section and have a few questions.  I have a usx2050 50 x 2 rms  and will be adding a phoneix gold R2:52 250 rms bridged.  The chart indictes total rms wattage and distance for the power and ground.  I know I will be ok with 8 guage grounds but the power I'm a little confused.  Do I use the total bridged rms for the us acuostic amp which is 160 rms for a total of 410 rms or do I use 100 watt rms (50 x 2).  Also I currently have a 30 amp fuse after the battery.  What do I need to bump that up to.  I currently have 8 guage power and grounds.  Power is running about 8' to 10'.  grounds are about 1'

Also on my distribution block what size fuses do I need to use for both amps?

I'd go with the 4awg and a 150 amp fuse.

Maximum amperage draw is indicated by the value of the fuses in the amplifiers as supplied by the manufacturer.  Fusing will allow amperage to flow up to the point of the fuse rating.  Add the fuses up;  does their total amp rating exceed the maximum amperage for an 8 gauge wire?  (...refer to the chart...you see it tells you that 100 amps is the maximum amperage capacity for 8 ga. wire...)

If your amplifiers' max draw (fuses) is less than that, then 8 gauge is proper to use for the main power wire.  It must never be larger than the ground wire(s).  The amplifiers will accept 8 gauge wire as well, so use the same gauge to run to each amp.  So, all wiring (power and ground) will be 8 gauge.

The fuse on the main power wire must not be greater than 100 amps (again, the chart.)  But it can be less than that, for reasons of cost, type of fuse available, etc.  It should be greater than the sum total of the amplifier's fuses (but doesn't have to be, depending on the ohm loads you are giving the amps.  Higher impedance loads like 4 ohms will result in less amperage draw.)

The fuses in the distro block are, there again, only there to fuse the wire, not the amplifiers.  Using 8 gauge wire out of the distro, you will follow the same advice as I told you about the main power wire.  That is, fuse no higher than the wire's capacity but equal to or higher than the connecting amplifier's fuse rating.

Ok so if I'm understanding this here is what I do.

usx 2050 has 20 A fuse, Phoenix gold r252 has 20 amp fuse (40 A total)  Power cable of 8 guage is appropriate.

ground cables of 8 guage are also approrpiate.  I need a 40 amp fuse after the battery.  I would need two 20 amp fuses in the distribution block.

Is that correct?

Fuses upstream of amps should be chosen based on the wire size.  Wire size should be chosen based on amplifier size.  You may use any size fuse you want as long as it is at least as large as the fuses in the amps (so it won't blow during normal operation) and not larger than the wire can sustain (so it WILL blow if there is a problem and protect the wire.)