1 or 2 dedicated 120VAC circuits for my CNC?

• The conductors between the distribution block and branch circuit breakers can be sized to match that branch circuit.
• Make sure your distribution block assembly ( blocks & jumpers) can handle the max system amps.
• According to NEC/NFPA70 (2017), assuming there's no conductor length ampacity reduction
  • your 3A & 10A branch circuits both could use 18awg
  • Your 20A branch can use 14
  • The feeder from the main CB to the distribution block can be 12awg, as can the line-in (unless you're using SJOOW from the wall)
  • There's no harm in increasing conductor size over the minimum in the tables - only your wallet hurts and the wires are harder to work with.  i.e. - If you're wiring up a bunch of 16awg, and need some 18awg in a few little branches... consider using the 16awg instead so you're not buying/stocking a huge assortment of sizes.
• Based on the above - and after review of wire lengths & so forth - I'd personally run 12awg everywhere and 18awg on the two smaller branch circuits.  Two wire sizes cuts down on the hidden work (multiple ferrule sizes, connectors, label sizes, etc.).
• Badger Wire has a chart that goes up to 250c insulation for specialty wires, but I'm not sure of their sources as they're about 5% higher than NEC/NFPA70.

Thanks for the info. I did notice that the ratings on Badgers chart are slightly more than the ratings I found for some of my wire. I kinda wonder if the difference has to do with the ambient temperature that each manufacturer uses as their base? I am not real sure what ambient temperature to use? Badger uses 40C.

I actually started with kind of the same plan to use 12awg and 18awg for most but then I started running into issues with the 12awg not fitting into some terminals. And based on my research of the wire I was using it seemed like 18awg was not big enough. But I didn't really find any concrete numbers that I felt confident in. So I ordered some 14awg to kind of fill the gap.

How much does strand count affect amperage rating? Or does it?
Also how does voltage affect the amp rating?

Thanks

For your purposes, strand count and voltage don't affect ampacity.

I'm sure they do, in fact, affect ampacity somehow - an EE can chime in here - but for what you're doing it's a non-issue.

What you (we) care about is insulation rating, gauge (cross-section), length, fill factor, and conductor count (for multi-conductor cables).

And yea, it sucks when a component's terminals are just a bit too small for the gauge you've installed.  Cramming the wire in is tempting but not the right move.

Great! Thanks!

In researching some of the 18AWG wire I bought I came across these answers (by people) to the question about amp ratings for the 18-22AWG wire. It is crazy how drastically different they all are. They obviously all got the ratings from different charts/calculators. 

 

I have also tried a bunch of calculators and they all seem different as well. Most of them spit out a super low amp rating. And then a few spit out super high ratings. Here are two different calculators. The first shows really low amp rating and the second shows really high rating. Note that they are not comparing similar size wire. But look at the gauge wire compared to the amp ratings. 

 

 

It seems almost impossible to find accurate data.

Yep.

That's why I go by NEC and then treat everything smaller than 18awg as signal wires.

The responses below with crazy high amps are for 200c... and I don't want anything in my cabinet at that temp even if the wire can handle it.

And 1.5a for 20awg?  Maybe for aluminum conductor insulated with dog turds.