My question came up when a friend of mine asked if I could change out his Federal Pacific breaker box to a newer, safer one. My background is in industrial controls and I don't normally deal with power at the service level. I only have about two years experience so as I am now trying to learn more on my own, I'm finding a lot of things that don't add up.
I started by doing some research to see what it would take to change out a breaker panel in a house without turning off the service power. It seems to me that it would not be any different getting shocked by one of the mains than it would be to get shocked by the 120V at an outlet. Each incoming line is 120V to ground (the same as the power at a receptacle) and my body's resistance to ground would be roughly the same. And according to Ohm's Law, the current that would go through my body would be the same. I don't understand the difference.
Now obviously I don't plan on attempting this if the risk is actually as serious as i've read, and I do realize that even very low voltages can kill you if the current is high enough (would normally have to break through the skin and into the blood stream where resistance is very low), but the question still remains. Am I missing something? I've read that if you touch either incoming service line that you will most certainly die. Is that just to scare people that don't know enough about what they're doing into hiring someone?
Lastly, I would like to point out that I work on a regular basis around 480V / 240V and am quite frankly, scared of being shocked, and I take every precaution available (which normally entails shutting off the power at its source) before working around any live circuits. I also understand that even 120V can definately be deadly, even at a receptacle. I only used that as an example because I know people will often change them without killing power.
I'd like to leave this topic as purely hypothetical. Simply an example to learn from.
Thanks.