No. Fuse size should be directly related to current draw. So should wire size. You don't base them on each other, you base them both on current draw.

That being said, I have a somewhat different approach for determining fuse size. It's rare that you'll be drawing enough current to blow the fuse on both amps. In your case, that's a 30 and 60 amp fuse. The chances of you ever drawing 90 amps is rare. The jensen amp is just pushing high frequency drivers (or so I assume), and their power consumption tends to stay low.

My general rule of thumb is to use 1 fuse size over whatever size fuse is on the sub amp. So in your case, that would be an 80 amp fuse. In this particular situation you're only talking about a 10 amp difference, but this rule of thumb works well most of the time.

It's always good to err on the size of a fuse that's too small. if you blow a couple of them, then move up to the next size (Never exceed the combined total of your amp fuses, i.e. 90 amps in your case).

With wire, you want just the opposite. You want to err on the side of too big. Wire that's too small will not only limit the performance of your equipment, it can become a safety issue.

 

So, let's say he wanted to use 1/0AWG power cable. You still would recommend a 90 amp fuse?----- You see what I'm saying? There is no point. You would be doing the same job as the amps internal fuse. You are suppose to be protecting the wire from melting and starting a fire..... therefore, you mise well put the biggest fuse the WIRE can handle safely. If his amps DID start drawing too much current, they would blow the internal fuse...... as it should.

 

Personally i would still use the smallest fuse that you can without blowing, it is just added protection if there should be a short. If there is a short and you have a 300A fuse it may not blow right away and could start a fire... i run 1/0 wire and run a 150A fuse at my battery for safety sake.

 

I guess you can never be too safe!

 

I run a fuse to protect against a chafed wire causing a direct short to ground. You will NEVER melt a wire that is of adequate gauge for the application. That is NOT what the fuse is there for. The fuse is there to protect against a direct short, so it is extremely stupid to run a fuse that's too big. You want to cause minimal current to be allowed to short to ground before that fuse blows, which is why you should always run the smallest fuse possible.

 

The rule of thumb is to add the values of the fuses in your amps. The sum is the value you should use under the hood. It has nothing to do with the size of your wire.

 

Ok, but don't exceed the max. current value of the wire size you are using!

 

Of course.