When doing control system installations, startups and servicing its always best to assume all wires are hot, even if lockout tagout is in place, until you personally check for voltage. Using a wand or a multimeter, it can save you a from a mild shock or potentially death. Too many times I have seen control panels and cabinets with other circuits running through them to some other location and it wasn't documented anywhere. The breaker may be off and the disconnect locked out but that wire you are about to unscrew has 220V AC on it. Not only do you risk getting killed, damage to the equipment is also a possibility. I have personally seen uncapped wire bundles hanging off a test cell, a couple feet above head height that were supposedly safe. Come to find out that they were, in fact, not safe. While up on said test cell, installing the new control system door and hatch sensors, I go to drag that demoed wire & cable bundle out of my way and as I do, sparks start flying and other systems in the room start turning off. Someone in their maintenance crew that was tasked with the demo did NOT follow Rule #2: Follow proper procedures.
Another time, we were working down in South Texas at a city water booster site, upgrading the tank and pump controls. The old system was housed in a stand up cabinet 8ft tall with incoming wires from the top, sides and through the bottom. We were trying to figure out where the wires for a particular level sensor where located at so we could reconnect them. Turned out they were coming in from the top of the control cabinet and tucked away behind the back plane, could hardly see them, much less the uncapped ends. I reach back there to bring them forward and , much to my surprise, was happily greeted with a 300V welcome. Luckily, it was only minor and we finished up the job.
It all comes down to this: you are responsible for your own safety. Don't rely on someone else to properly follow procedures and protocols until you verify it yourself.
So remember, Rule #4: Operate under the assumption that all wires are live.
Check out the previously reviewed rules below!