I have come into a decent supply of 24 awg / 6 conductor shielded cable. My steppers are 3amp/ph. Can I get away with using this? It has always been my understanding that amp ratings on wire is very conservative so that it should be ok. Opinions?
24 gage wire is more suited for signal or control wire, not current conducting wire.
Yes, wire is conservatively rate BUT that is to prevent voltage drop while conducting current over longer runs. You can create problems to see how SMALL of a wire you can get away with, especially if you pull more than 3 amps during a fast jog or acceleration move. Then again, don't complain if you run small wire and start losing steps for no apparent reason.
Can you get "away with it"? Probably.
BUT you may be more satisfied if you used 18-3 or 18-4 or something a bit more robust to carry power to the motors.