How can I disable the fuse boxes on Arkham City ? There are some (just like the one on GCPD and Justice Court) guarding some Riddler's marks. Which gadget should I use ?
If you have a straight line of sight to the fusebox, you can use the Remote Electrical Charge to shoot them and overload them.
A lot of them don't offer a straight line of sight though.
In those cases, you would use the remote-controlled Batarang, assuming you can give it an electrical charge. You'll want to look around for sparks/arcs of electricity. You'll have to throw your Batarang, get it charged by flying it through the electricity, and then guide it to the fuse box. Some of these can be pretty complex, you'll have to reverse course on the batarang sometimes, and fly through some tight areas.