What's doubly fun are multiwire branch circuits. Basically, instead of splitting the 240 V into 120 V at the breaker box, you take a 240 V branch circuit and s

What's doubly fun are multiwire branch circuits. Basically, instead of splitting the 240 V into 120 V at the breaker box, you take a 240 V branch circuit and split it into two somewhere down the line. This has two advantages: first, you need fewer wires going all the way to the breaker box; second, resistive loads on opposite legs of the circuit cancel each other out on the neutral, so you can (in theory) run 30 A worth of stuff off a single run of 14-gauge 4-wire Romex (= cheaper). Anyways, where the fun comes in, is if for some reason the neutral gets disconnected before the branch split. You now are effectively running the appliances on one branch in series with those on the other. Depending on the particular appliances involved, this means you could see up to 240 V on one leg of the circuit. This is, of course, very bad.