Unknown Near-Death Experience

Or Why I'm buying a non-contact voltage tester

So the new house has a Mother In Law setup- basically a full apartment in the basement.  That means we have two hookups for electric dryers, and two washing machine hookups. I went to hook the dryer up downstairs and saw that it had an old 3-wire outlet.  Not a newer one like you can buy at any hardware store but an OLD one.  Upstairs was a more modern 3-wire outlet.  I'm not doing laundry in the kitchen so I figured I'd take the plug from upstairs and put it in the basement.  No big deal.
Turn off both breakers labeled "dryer."  Unscrew the face plate. Pull the outlet out of the wall.  Unscrew the wires in the receptacle. Take it to the basement, do the same.  Screw the wires into the newer receptacle.  Fix the outlet in place. Attach the face plate. Turn on the breaker for the downstairs dryer leaving the upstairs one switched off because there are exposed wires until I put a different plug in place. Plug in the dryer and...

I did all this and the dryer worked!  WOOO!

A few hours later, the water heater is only putting out warm water.  This is a 6 month old water heater so I'm a bit bewildered.  I Google up some ideas and settle on the symptoms pointing to a bad thermostat.  Home Depot has a repair kit that has two elements and both thermostats for my water heater for 32 bucks.  SWEET.  I buy that, kill the water heater breaker and put in the two new thermostats. Turn the breaker marked "Water Heater" on and wait half an hour.  Water is still cold.  Not just lukewarm but COLD.  wtf.

Commence spidey sense...

I go back to the breaker box and turn off both labeled Dryer and the one labeled Water Heater.  I turn on the water heater breaker and go back to the water heater.  No sound, no nothing.  The dryer won't turn on.  I turn that breaker back off and turn on the first one labeled dryer.  The dryer won't turn on but now there's a faint humming from the water heater if my ear is right against it.  I go back and turn it off.  I turn on the second dryer breaker and the dryer turns on.  I turn on both dryer ones and give it half an hour.  Hot water comes out.

Conclusions:
1- The breaker box is mis-labeled.
2- The water heater is on one labeled dryer.
3- The upstairs dryer outlet is on the one for the water heater.
Most exciting...
4- When I turned off both dryer breakers and went upstairs and pulled apart the 240-volt 30-amp outlet, I was futzing around with LIVE FREAKING WIRES.  WTF?!?!?!

Thankfully I'm a little paranoid and my gun training was in play.  Rule number 1 of firearm handling?  "Every gun is always loaded.  Treat it as such."  Every wire is always hot.  Treat it as such.  I did that and I'm quite glad.  Best case, I could have tripped the breaker and arc welded my screwdriver to the outlet.  Worst case, I could be dead and my house could have burned down before I made a payment on it.

So I'm getting one of these right friggin now.

Our next adventure revolves around a riding mower and my overwhelming hatred of mine.