There are two types, momentary and push-to-lock, the momentary are used with a E-stop relay, where the relay uses a latching contact, this circuit requires a start PB, however, (the latching contact is across the start PB).
Probabally a google of stop/start circuits will come up for further info.
Sometimes the over travel limits are placed in series with the latching contact, this enables the OT limits to be over-ridden by the start button, to enable jog off the limit.
AL.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.