What does “amperage” mean when I try to use a cable (wire)? Is it the number of machines that can be connected like the channel of Ae2? Or is it the relationship between the EU and voltage, like Ohm’s law?

It sends 2 packets, each of which is 256 EU/t. Added together it drives a machine at 512 EU/t. But the Cable Ratings should not be confused with the actual value, which is determined by the machine emitting power.