Home-built machine: how to make the 110 V AC electrical installation part "by the book"? (safety, "code")

The things to worry about are 1) strain relief; 2) having an appropriately rated and sized fuse or circuit breaker; 3) having a large, easily-operated, within reach of the operator, power on-off switch or other control (http://dx.com/p/ac-220-380v-waterproof-on-off-push-button-switch-167441); 4) making sure everything is properly grounded; and 5) appropriate use of conduit for fire and abrasion protection. Use a C13-style connector mounted on the side of the unit and a standard power cord if the device is portable, or conduit if nonportable. An internal AC receptacle should be enclosed in a standard metal box.

If, as you say, there is water or moisture involved with the operation of the unit then the power source (wall socket) must be equipped with a Ground Fault Circuit Interrupter (GFCI).

Generally you won't have code-compliance issues if you're not manufacturing the units for sale and if your unit looks professional (no sloppy or frayed wiring). For legal advice consult a licensed attorney.

If your unit could injure someone if not shut off immediately (e.g. if a worker's hair or clothing were to become stuck in the mechanism) consider a pull-string or other emergency shutoff mechanism. The string would be connected to a shorting plug the socket for which is wired in series with the mains.