The standard fuses supplied with these plugs are normally rated at the circuit capacity of the supply outlet and associated wiring. They blow when the current exceeds that of the circuit and the current rating of the plug itself and the connected wiring.
Your idea to replace these with a current reading closer to the load rating is a good idea if the plug and cord is directly attached to the appliance or fixture load. If the plug and cord is part of an "extension cord" or "outlet strip" it may be more appropriate to set the amperage reading of the fuse closer to the rating of the plug / cord / outlet strip.
For a direct attached load only a general guideline can be given for the fuse rating. Certainly the current load listed on the name plate of the device is a very good starting place. But if the load is a motor or other inductive type load the startup current surge can be much higher than the listed running current level. This needs to be taken into account for fuse selection.
A final comment is that it would always be a good idea to leave some margin between fuse rating and running current. Fuses used at their rated level or more can age and eventually fail before expected.
In my experience, it's more likely that a problem is in a connection somewhere than an outright severed wire.
Start by identifying which outlets have power or not. A simple plug-in tester is an easy way to do this (as well as identify some common ways to miswire).
Next, take the covers off (but don't remove the outlets) and use a non-contact voltage meter to check if there is any power to the wires.
I'm actually hesitant to post this picture, but I couldn't find one without an idiot holding a live outlet in their hand. Don't do this. This person is one tiny mistake away from electrocuting themselves.
Hopefully what you'll find is that power eventually comes into one but isn't connected correctly, and that it continues on from there.
Check light switches and fixtures as well.
Also worth nothing: if your non-contact tester beeps, but your plugin tester doesn't show power, this is a good indication there is a problem with the neutral.
After this, if you can't identify any power in a non-working outlet, you can check working ones. You're looking specifically for a disconnect in a wire that is feeding the rest of the circuit, so logically the ones nearest the dead circuits are most likely to be doing that.
It's also possible the connections are done using pigtails, and there can still be a bad or miswired connection so it's worth checking this too:
After you've exhausted all of this, it's time to start thinking about hidden junctions and broken wires. If you know of a hidden junction, that's not only illegal but highly likely to have a problem.
You probably will have a good idea now of which wires go where, so if you can identify power on one receptacle that is likely feeding to a broken one, then you can start trying to trace the wire through the wall (and this is when you'll start opening drywall or climbing through the attic).
Your non-contact tester (especially if you have one with a sensitivity adjustment) MAY be able to trace through the wall, but it's actually quite difficult in my experience. Likewise stud detectors often have voltage detection, and this might be able to trace the wire, but again it's just not that accurate.
One thing that might also help to identify a broken wire is to check for continuity. Turn the power off, and use a multimeter in continuity (Ω) mode. Test between receptacles: neutral to neutral, ground to ground and hot to hot. If you get continuity on one or two of them, it will at least tell you that there is a partial connection and you're looking for a bad connection or broken wire. Tip: use an extension cord plugged in to one receptacle to test two that are farther apart than your multimeter leads.
Since in your case you said it was working and there were no changes that should cause it to stop, I'm not sure this will really provide you any useful information, but thought it's worth putting out there.
Best Answer
1500 W/ 230 V = 6.5 A
800 W / 230 V = 3.5 A
Now, a fused circuit should normally be loaded to 80% capacity. So on a dedicated circuit, you would need an 8 A or 4.5 A fuse.
But, usually circuits feed more than one outlet. So you need to find out what else is being fed by the same fuse. Most devices will have a sticker declaring the draw. Add up the amps, add in your pump, and stay withing the 80% capacity limit. If you go over, add another breaker/fuse and make it a dedicated circuit. If amps aren't posted, W/230 will give you the current draw.