US residential power distribution transformers are 240 V, with a center tap. There are sometimes 240 V plugs, when high-current appliances aren't hard wired. Usually that's clothes driers and ovens/ranges. Water heaters and central HVAC systems are usually hard wired to 240 VAC.
For everything else, where more than a KW or two is overkill, the plugs connect between the center tap and one output of the transformer, for 120 V. It gives the advantage of high power where it's needed, up to 12 KW peak or 9.6 continuous, without dangerous voltages where the power isn't needed.
Modern outlets do have all of the modern safety features, like shutters and arc or ground fault detection, but the more appropriate voltage means that when they aren't available, it's still safe. There's kind of a running joke for DIYers that everyone claims to turn the power off before rewiring outlets, but no one really does, unless it's a 240 V outlet.
The concept of not cutting the power before rewiring seems hogwild to me. I touched a 120v line I thought I had turned off and am really grateful my ass fell backwards because no one else was home
What brand of pliers were they, and did they seem to be made from recycled gum wrappers?
A trick I learned when you want to flip the breaker but don't want to go all the way back to the panel is to just stick a screwdriver into a light socket.
For everything else, where more than a KW or two is overkill, the plugs connect between the center tap and one output of the transformer, for 120 V. It gives the advantage of high power where it's needed, up to 12 KW peak or 9.6 continuous, without dangerous voltages where the power isn't needed.
Modern outlets do have all of the modern safety features, like shutters and arc or ground fault detection, but the more appropriate voltage means that when they aren't available, it's still safe. There's kind of a running joke for DIYers that everyone claims to turn the power off before rewiring outlets, but no one really does, unless it's a 240 V outlet.