Electronic – power cable: more strands, or bigger strands

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.

It all depends on what insulation is used. There are lots of different kinds of insulation and manufacturers make them with different thicknesses (single build, double build, triple build, etc.). Most data sheets show the results of an scrape abrasion test. In this test, a sample of the magnet wire is secured firmly in place and a needle is scraped along the surface of the magnet wire. The datasheet usually records the number of scrapes the insulation can withstand until the needle breaks through the insulation and shorts the wire.

So that spec on the data sheets will give you a good relative feel for how different magnet wire types compare to each other. But it doesn't really answer your question of how well magnet wire will work for what you are doing. Here are a couple of thoughts. I think you'd be surprised how tough a good quality magnet wire can be. A popular type in the motor industry is a heavy build MW-35. It holds up pretty well and should be able to withstand being assembled. Just try not to use any sharp/pointed tools that could scrape or puncture the insulation. Also keep in mind that for many, many magnet wire applications like motors and transformers, the magnet wire gets coated with a varnish or epoxy to give it more long term protection against rubbing, vibration, etc. That doesn't mean your application would need varnish but magnet wire is very often used that way.

I think if you pick a good quality magnet wire and are careful not to nick or scrape it during assembly, you should be okay.