Locking out power: Locking out power prevents the machine from harming the user while the machine is being worked on. Dangerous voltages and the potential for the machine to move will exist if the machine is powered up while it is being serviced.
NEVER WORK ON OR INSIDE A MACHINE THAT IS POWERED UP OR HAS THE POTENTIAL TO BE ACCIDENTALLY POWERED UP
The regulations at your workplace may vary from standard regulatory requirements. When conflicting regulations are encountered, follow your workplace regulations. If there is ANY uncertainty, contact your workplace supervisor.
Locking power out from a machine is required for any servicing. Power down the machine and the computer by the normal methods. Remove the power source from the machine and lock it out as per your workplace regulations. This may involve an actual lock on a breaker box, a nametag, or some similar methods.
Many machines have multiple sources of power (control box, spindle, etc). Be sure to find all power sources and lock all of them out prior to any service.