I have the Cerwin Vega 52amp, using 8gauge power and ground. Both ran back to the battery. The manual says 25 amp inline fuse ,but I’ve seen others using 40,50 and 60 amp. Iv had no problems using a 25 amp so why the differences in fuse ampridge.

 

Manufacturers recommendations...depending the efficiency of the amp...the "juice" the amp consumes and uses..ie... the un-technical answer...lol!

 

Regardless of what others use, ALWAYS use what your amp manufacturer recommends as max fuse and wire size for the install. This is the only thing externally protecting the amp from overload/surge/spikes/shorting from chaffed-pinched wires/ etc..
Most current amps have built in circuitry for overload protection but I can assure you that’s a 50/50 shot at helping to protect the amps circuitry “after” the external issue has occurred.

Different amps require different current loads(power) to run. This is what dictates wire size and especially the fuse size to protect the amp.

You can always oversized the wiring (not that there is an advantage to it) but NEVER oversized the recommended fuse size.

 

Moto Mike and Tesnevo are absolutely correct. Follow the manufacturers recommendations. I'm gonna take it a step farther and tell you where those specs come from. The B52 is 200 RMS X 2. That gives you 400 watts RMS. Take 400w divided by 13.8v = 28.9 can't buy a 28.9 fuse so they recommend a 25. As Tesnevo said. You always want to be on the low side. So a good rule of thumb I always use is to take total RMS and divide by 13.8. Just have to make sure the RMS is accurate.