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Sometimes it might seem prudent to work a circuit hot, especially if it’s only 120V.
For example, you need to replace a receptacle on the back porch of a house, but the breaker panel is in the garage. Rather than traipse all the way through the house, open the breaker indicated in the panel directory, traipse all the way through the house, test the receptacle with your DMM, curse the idiot who filled out the panel, then traipse all the way through the house again...you just work it hot. After all, the wires stab in from the back.
What can possibly go wrong?
You might inadvertently touch something energized, like a nicked wire or the stripped end of that hot wire you bent “out of the way.”
With 120V supplied to that circuit, you could easily draw more than the 6mA that prevents you from letting go, but far less than what it takes to trip that 20A breaker. Maybe this won’t kill you before someone sees your distress and opens that breaker, but it can permanently damage nerves and other tissues.
Don’t work something hot unless there is no other choice. Most of us have gotten that 120V tingle and survived it. This has led to a tradition of violating common safety rules such as locking out the supply and wearing the appropriate PPE when working on these circuits. Ignore that tradition so you live to traipse yet again!
Source: Mark Lamendola | Mindconnection