Suppose you lock out the controls to a motor. Will this protect you from inadvertent operation of the motor so that you can safely disconnect the leads?
Theoretically, the answer is yes. You can look at the drawing and see this motor won’t run if there’s no power to its control circuit. The problem here is you’re relying on a single safety point. It is also theoretically possible that someone could remove your lock or something else could happen to permit power to be supplied to those terminals.
You need to ask not, “What’s the minimum to do to remove power at those terminals?” but, “What can I do to ensure there won’t be power at those terminals?” So in this case, you would want to also lock out the local disconnect. You may even want to lock out the branch circuit overcurrent device if doing so won’t adversely affect operations.
Physical locks on the controls are unlikely to be bypassed or removed, but this additional layer of protection (locking out the disconnect) is there in case they are. Relying on a single point becomes even riskier when it’s done in software; there’s no physical lock.
