1 or 2 dedicated 120VAC circuits for my CNC?

If I have a 200C wire that is rated at lets say 20A, would that be adequate for a 20A circuit if my temps are going to be nowhere near the 200C? Is the amp rating of the wire the same up to the 200C? Or does the amp rating go up as the temp goes up and maxes out at 200C? That sounds like a completely stupid question now that I read it, but I just want to be sure I understand it.

Wikipedia has a good explanation of ampacity.

[url] en.wikipedia.org/wiki/Ampacity [/url]

 

So I have the CNC completely wired except end stops. I forgot to order them. Will just any old limit switch work? Any recommendations? 

Ones made by Balluff are good, but be seated before checking the price!
Mechanical fully enclosed ones should do for metal mills and plasma, inductive ones also good but might need a bit of protection from debris.
Anything from Omron should do, since you are aiming for good quality.

I'm partial to NC 3-wire inductive proximity switches.  I believe the trick with these is to mount them in a way that the trigger/flag crosses the sensing volume rather than approaches.  Put another way, if you think of the proxy like a flashlight, you want something (flag) to cut the beam from the side rather than moving the flashlight towards the device you're trying to sense.

I've read they're more repeatable this way.  And you aren't going to smash the proxy if something goes wrong and tries to hit the hard stop.  And the NC circuit means if a wire breaks or something, the controller will see it as triggering the limit (fail-safe).

On the other hand, I've also used $0.25 cheapo microswitches as limits on a couple of low-budget builds.  They weren't repeatable to a 'thou, but that didn't matter much for a stepper plasma and I could run them at 24vdc for some noise immunity (at the cost of the contacts burning out sooner).

As with everything, it's a cost-performance decision.  If you have a table-mounted ATC, tool length probe, or specific fixturing you may wish to have very repeatable limits.  Otherwise, anything that gets you in the ballpark and doesn't fail frequently should be sufficient.

Thanks guys for the info. I think for now I will start with the switches and maybe upgrade to inductive proximity switches if needed down the road.

On these Omron switches, there are three connections. One says NC, another NO and the last C. How would I wire these to the Mesa 7i76?

 

Thanks