Electronic – What does A x B mean when referring to wire strand count

Over 18 inches you would drop about 0.675 volts with 18 gauge wire. 12 gauge would drop about 0.1 volts. You would need to use 6 or 7 gauge to handle 30 A over an extended period.

If you are not using continuous current, but pulses, you could get away with using a smaller gauge wire. However an undersized wire would heat up significantly in just a few seconds. Unless you are sending pulses of less then 1 sec, you will need a large diameter wire.

AS for the insulation, it depends on how the wire is being used and how it is routed. 30 A is a lot of current. If some one can come in contact with it, you need heavy insulation for safety. Especially if it flexes. If it is total enclosed in a non conductive housing, you could use thinner insulation.

This sort of wire is sometimes known as 'Magnet Wire' or similar names because it is frequently used for making inductors or motor coils. You can generally find it in many different wire gauges, usually coated with either enamel or polyurethane insulation.

This is one example that I have used before. It's 38AWG coated wire which is quite easy to remove the coating from with heat (you can also get it in different colours). There are many other options around.

You have to be careful though to check the current spec for this sort of wire. Given how small the diameter is, they are only usually rated for ~100mA or so at the most for the narrowest wire. Just make sure you're not going to be drawing more than its rated current to avoid heating (which could destroy the insulation if too extreme) or melting.