For Electrical Safety, Lock and Tag the Breaker Panel
Just because you threw the switch, it doesn’t mean it’s off!
Electrical shock can cause serious injury and even death. So when working with electricity, the only way to prevent shock is to make sure the power is off. In this video from the Fine Homebuilding archives, Sacramento, California electrical contractor Cliff Popejoy demonstrates a few procedures that, when followed, will guarantee your safety and the safety of those you work with.
Note: As an added measure of safety, you should always test a circuit with an electrical tester before touching any wiring.
From Fine Homebuilding #168